tag:theconversation.com,2011:/uk/topics/greenland-ice-sheet-31482/articlesGreenland ice sheet – The Conversation2024-02-20T16:52:21Ztag:theconversation.com,2011:article/2237682024-02-20T16:52:21Z2024-02-20T16:52:21ZA single Antarctic heatwave or storm can noticeably raise the sea level<p>A heat wave in Greenland and a storm in Antarctica. These kinds of individual weather “events” are increasingly being supercharged by a warming climate. But despite being short-term events they can also have a much longer-term effect on the world’s largest ice sheets, and may even lead to tipping points being crossed in the polar regions.</p>
<p>We have <a href="https://www.nature.com/articles/s43017-023-00509-7.epdf?sharing_token=EJZ02zq3kFQO4XKwZVTBLdRgN0jAjWel9jnR3ZoTv0NlXBkse_V2fGVmyGVwGFcXe8LM4zjSaytnzbxkpU3vleMHbbCbjypxjcJ3p1wJddVoe1nKU4klsbQfMwCvE-m9plem7c8GygdxBfIr9KNkFEXV23v6oF28LZQkvsWpQm4%3D">just published</a> research looking at these sudden changes in the ice sheets and how they may impact what we know about sea level rise. One reason this is so important is that the global sea level is predicted to rise by anywhere between 28 cm and 100cm by the year 2100, according to <a href="https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf">the IPCC</a>. This is a huge range – 70 cm extra sea-level rise would affect many millions more people. </p>
<p>Partly this uncertainty is because we simply don’t know whether we’ll curb our emissions or continue with business as usual. But while possible social and economic changes are at least <a href="https://www.carbonbrief.org/explainer-how-shared-socioeconomic-pathways-explore-future-climate-change/">factored in</a> to the above numbers, the IPCC acknowledges its estimate does not take into account deeply uncertain ice-sheet processes. </p>
<h2>Sudden accelerations</h2>
<p>The sea is rising for two main reasons. First, the water itself is very slightly expanding as it warms, with this process responsible for <a href="https://theconversation.com/how-much-will-our-oceans-warm-and-cause-sea-levels-to-rise-this-century-weve-just-improved-our-estimate-166417">about a third</a> of the total expected sea-level rise. </p>
<p>Second, the world’s largest ice sheets in Antarctica and Greenland are melting or sliding into the sea. As the ice sheets and glaciers respond relatively slowly, the sea will also continue to rise for centuries.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/576797/original/file-20240220-30-8eophf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Large glacier in mountains meeting the ocean" src="https://images.theconversation.com/files/576797/original/file-20240220-30-8eophf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/576797/original/file-20240220-30-8eophf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/576797/original/file-20240220-30-8eophf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/576797/original/file-20240220-30-8eophf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/576797/original/file-20240220-30-8eophf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/576797/original/file-20240220-30-8eophf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/576797/original/file-20240220-30-8eophf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Elephant Foot Glacier in northern Greenland.</span>
<span class="attribution"><span class="source">Nicolaj Larsen / shutterstock</span></span>
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</figure>
<p>Scientists have long known that there is a potential for sudden accelerations in the rate at which ice is lost from Greenland and Antarctica which could cause considerably more sea-level rise: perhaps a metre or more in a century. Once started, this would be impossible to stop. </p>
<p>Although there is a lot of uncertainty over how likely this is, there is some evidence that it happened <a href="https://www.nature.com/articles/nature17145">about 130,000 years ago</a>, the last time global temperatures were anything close to the present day. We cannot discount the risk. </p>
<p>To improve predictions of rises in sea level we therefore need a clearer understanding of the Antarctic and Greenland ice sheets. In particular, we need to review if there are weather or climate changes that we can already identify that might lead to abrupt increases in the speed of mass loss.</p>
<h2>Weather can have long-term effects</h2>
<p><a href="https://www.nature.com/articles/s43017-023-00509-7.epdf?sharing_token=EJZ02zq3kFQO4XKwZVTBLdRgN0jAjWel9jnR3ZoTv0NlXBkse_V2fGVmyGVwGFcXe8LM4zjSaytnzbxkpU3vleMHbbCbjypxjcJ3p1wJddVoe1nKU4klsbQfMwCvE-m9plem7c8GygdxBfIr9KNkFEXV23v6oF28LZQkvsWpQm4%3D">Our new study</a>, involving an international team of 29 ice-sheet experts and published in the journal Nature Reviews Earth & Environment, reviews evidence gained from observational data, geological records, and computer model simulations. </p>
<p>We found several examples from the past few decades where weather “events” – a single storm, a heatwave – have led to important long-term changes. </p>
<p>The ice sheets are built from millennia of snowfall that gradually compresses and starts to flow towards the ocean. The ice sheets, like any glacier, respond to changes in the atmosphere and the ocean when the ice is in contact with sea water. </p>
<p>These changes could take place over a matter of hours or days or they may be long-term changes from months to years or thousands of years. And processes may interact with each other on different timescales, so that a glacier may gradually thin and weaken but remain stable until an abrupt short-term event pushes it over the edge and it rapidly collapses. </p>
<p>Because of these different timescales, we need to coordinate collecting and using more diverse types of data and knowledge.</p>
<p>Historically, we thought of ice sheets as slow-moving and delayed in their response to climate change. In contrast, our research found that these huge glacial ice masses respond in far quicker and more unexpected ways as the climate warms, similarly to the frequency and intensity of hurricanes and heatwaves responding to changes with the climate. </p>
<p>Ground and satellite observations show that sudden heatwaves and large storms can have long-lasting effects on ice sheets. For example a heatwave in July 2023 meant at one point <a href="https://www.carbonbrief.org/guest-post-how-the-greenland-ice-sheet-fared-in-2023/">67% of the Greenland ice sheet surface</a> was melting, compared with around 20% for average July conditions. In 2022 unusually warm rain fell on the <a href="https://www.whoi.edu/oceanus/feature/a-cold-case-filed-conger-ice-shelf-collapse/">Conger ice shelf</a> in Antarctica, causing it to disappear almost overnight.</p>
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<p>These weather-driven events have long “tails”. Ice sheets don’t follow a simple uniform response to climate warming when they melt or slide into the sea. Instead their changes are punctuated by short-term extremes. </p>
<p>For example, brief periods of melting in Greenland can melt far more ice and snow than is replaced the following winter. Or the catastrophic break-up of ice shelves along the Antarctic coast can rapidly unplug much larger amounts of ice from further inland. </p>
<p>Failing to adequately account for this short-term variability might mean we underestimate how much ice will be lost in future.</p>
<h2>What happens next</h2>
<p>Scientists must prioritise research on ice-sheet variability. This means better ice-sheet and ocean monitoring systems that can capture the effects of short but extreme weather events. </p>
<p>This will come from new satellites as well as field data. We’ll also need better computer models of how ice sheets will respond to climate change. Fortunately there are already some promising global <a href="http://imbie.org/">collaborative</a> <a href="https://climate-cryosphere.org/about-ismip6/">initiatives</a>.</p>
<p>We don’t know exactly how much the global sea level is going to rise some decades in advance, but understanding more about the ice sheets will help to refine our predictions.</p>
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<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p class="fine-print"><em><span>Edward Hanna receives funding from the UK's Natural Environment Research Council.
The research was sponsored by the World Climate Research Programme’s Climate and Cryosphere project, the International Arctic Science Committee, and the Scientific Committee on Antarctic Research, and resulted from a collaboration following an Ice Sheet Mass Balance and Sea Level expert group workshop.</span></em></p><p class="fine-print"><em><span>Ruth Mottram received funding for this work from the European Union, Horizon Europe Funding Programme for research and innovation under grant agreement Nr. 101060452 and from the Novo Nordisk Foundation for the Challenge project PRECISE (Predicting Ice Sheets on Earth), grant NNF23OC0081251.
</span></em></p>To narrow our predictions of global sea level rise, we need to know more about these sudden ‘non-linear’ changes to ice sheets.Edward Hanna, Professor of Climate Science and Meteorology, University of LincolnRuth Mottram, Climate Scientist, National Centre for Climate Research, Danish Meteorological InstituteLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2228342024-02-09T19:01:37Z2024-02-09T19:01:37ZAtlantic Ocean is headed for a tipping point − once melting glaciers shut down the Gulf Stream, we would see extreme climate change within decades, study shows<figure><img src="https://images.theconversation.com/files/573965/original/file-20240207-22-751n5r.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5607%2C3741&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Too much fresh water from Greenland's ice sheet can slow the Atlantic Ocean's circulation.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/iceberg-calving-from-eqip-glacier-on-disko-bay-royalty-free-image/534972902?phrase=melting+glaciers+greenland&adppopup=true">Paul Souders/Stone via Getty Images</a></span></figcaption></figure><p>Superstorms, abrupt climate shifts and New York City frozen in ice. That’s how the blockbuster Hollywood movie “<a href="https://www.imdb.com/title/tt0319262/">The Day After Tomorrow</a>” depicted an abrupt shutdown of the Atlantic Ocean’s circulation and the catastrophic consequences.</p>
<p>While Hollywood’s vision was over the top, the 2004 movie raised a serious question: If global warming shuts down the Atlantic Meridional Overturning Circulation, which is crucial for carrying heat from the tropics to the northern latitudes, how abrupt and severe would the climate changes be?</p>
<p>Twenty years after the movie’s release, we know a lot more about the Atlantic Ocean’s circulation. Instruments deployed in the ocean starting in 2004 <a href="http://dx.doi.org/10.1038/s41586-018-0006-5">show that the Atlantic Ocean circulation</a> has <a href="https://www.ipcc.ch/srocc/chapter/summary-for-policymakers/">observably slowed</a> over the past two decades, possibly to its <a href="https://doi.org/10.1038/s41561-021-00699-z">weakest state in almost a millennium</a>. Studies also suggest that the circulation has reached a <a href="https://doi.org/10.1126/science.abn7950">dangerous tipping point</a> in <a href="https://doi.org/10.1126/science.aaf5529">the past</a> that sent it into a precipitous, unstoppable decline, and that it <a href="https://doi.org/10.1038/s41467-023-39810-w">could hit that tipping point again</a> as the planet warms and glaciers and ice sheets melt.</p>
<p>In a new study using the latest generation of Earth’s climate models, we simulated the flow of fresh water until the ocean circulation reached that tipping point. </p>
<p>The results showed that the circulation could <a href="http://www.science.org/doi/10.1126/sciadv.adk1189">fully shut down within a century</a> of hitting the tipping point, and that it’s headed in that direction. If that happened, average temperatures would drop by several degrees in North America, parts of Asia and Europe, and people would see severe and cascading consequences around the world.</p>
<p>We also discovered a physics-based early warning signal that can alert the world when the Atlantic Ocean circulation is nearing its tipping point.</p>
<h2>The ocean’s conveyor belt</h2>
<p>Ocean currents are driven by winds, tides and water <a href="https://doi.org/10.1007/s003820050144">density differences</a>.</p>
<p>In the Atlantic Ocean circulation, the relatively warm and salty surface water near the equator flows toward Greenland. During its journey it crosses the Caribbean Sea, loops up into the Gulf of Mexico, and then flows along the U.S. East Coast before crossing the Atlantic. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/573566/original/file-20240205-17-ttiy6v.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two illustrations show how the AMOC looks today and its weaker state in the future" src="https://images.theconversation.com/files/573566/original/file-20240205-17-ttiy6v.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/573566/original/file-20240205-17-ttiy6v.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=403&fit=crop&dpr=1 600w, https://images.theconversation.com/files/573566/original/file-20240205-17-ttiy6v.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=403&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/573566/original/file-20240205-17-ttiy6v.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=403&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/573566/original/file-20240205-17-ttiy6v.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=506&fit=crop&dpr=1 754w, https://images.theconversation.com/files/573566/original/file-20240205-17-ttiy6v.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=506&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/573566/original/file-20240205-17-ttiy6v.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=506&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">How the Atlantic Ocean circulation changes as it slows.</span>
<span class="attribution"><a class="source" href="https://www.ipcc.ch/report/ar6/wg1/figures/chapter-9/faq-9-3-figure-1">IPCC 6th Assessment Report</a></span>
</figcaption>
</figure>
<p>This current, also known as the Gulf Stream, brings heat to Europe. As it flows northward and cools, the water mass becomes heavier. By the time it reaches Greenland, it starts to sink and flow southward. The sinking of water near Greenland pulls water from elsewhere in the Atlantic Ocean and the cycle repeats, like a <a href="https://doi.org/10.1002/2015RG000493">conveyor belt</a>.</p>
<p><a href="https://doi.org/10.1126/science.abn7950">Too much fresh water</a> from melting glaciers and the Greenland ice sheet can dilute the saltiness of the water, preventing it from sinking, and weaken this <a href="https://doi.org/10.1002/2015RG000493">ocean conveyor belt</a>. A <a href="https://doi.org/10.1073/pnas.97.4.1347">weaker conveyor belt</a> transports <a href="https://doi.org/10.1038/s41558-022-01380-y">less heat northward</a> and also enables less heavy water to reach Greenland, which <a href="https://doi.org/10.1073/pnas.97.4.1347">further weakens</a> the conveyor belt’s strength. Once it reaches the <a href="https://doi.org/10.1073/pnas.0705414105">tipping point</a>, it shuts down quickly.</p>
<h2>What happens to the climate at the tipping point?</h2>
<p>The existence of a tipping point was first noticed in an overly simplified model of the Atlantic Ocean circulation in the <a href="https://doi.org/10.1111/j.2153-3490.1961.tb00079.x">early 1960s</a>. Today’s more <a href="https://www.carbonbrief.org/cmip6-the-next-generation-of-climate-models-explained/">detailed climate models</a> indicate a continued <a href="https://doi.org/10.1029/2019GL086075">slowing of the conveyor belt’s strength</a> under climate change. However, an abrupt shutdown of the Atlantic Ocean circulation <a href="https://doi.org/10.1016/j.physd.2023.133984">appeared to be absent</a> in these climate models.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/p4pWafuvdrY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How the ocean conveyor belt works.</span></figcaption>
</figure>
<p>This is where our study comes in. We performed an experiment with a detailed climate model to find the tipping point for an abrupt shutdown by slowly increasing the input of fresh water. </p>
<p>We found that once it reaches the tipping point, the conveyor belt shuts down within 100 years. The heat transport toward the north is strongly reduced, leading to abrupt climate shifts.</p>
<h2>The result: Dangerous cold in the North</h2>
<p>Regions that are influenced by the Gulf Stream receive <a href="https://doi.org/10.1038/s41558-022-01380-y">substantially less heat</a> when the circulation stops. This cools the North American and European continents by a few degrees.</p>
<p>The European climate is much more influenced by the Gulf Stream than other regions. In our experiment, that meant parts of the continent changed at more than 5 degrees Fahrenheit (3 degrees Celsius) per decade – far faster than today’s global warming of about 0.36 F (0.2 C) per decade. We found that parts of Norway would experience temperature drops of more than 36 F (20 C). On the other hand, regions in the Southern Hemisphere would warm by a few degrees.</p>
<figure class="align-center ">
<img alt="Two maps show US and Europe both cooling by several degrees if the AMOC stops." src="https://images.theconversation.com/files/573569/original/file-20240205-15-mqepgl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/573569/original/file-20240205-15-mqepgl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=271&fit=crop&dpr=1 600w, https://images.theconversation.com/files/573569/original/file-20240205-15-mqepgl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=271&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/573569/original/file-20240205-15-mqepgl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=271&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/573569/original/file-20240205-15-mqepgl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=340&fit=crop&dpr=1 754w, https://images.theconversation.com/files/573569/original/file-20240205-15-mqepgl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=340&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/573569/original/file-20240205-15-mqepgl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=340&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The annual mean temperature changes after the conveyor belt stops reflect an extreme temperature drop in northern Europe in particular.</span>
<span class="attribution"><a class="source" href="http://www.science.org/doi/10.1126/sciadv.adk1189">René M. van Westen</a></span>
</figcaption>
</figure>
<p>These temperature changes develop over about 100 years. That might seem like a long time, but on typical climate time scales, it is abrupt.</p>
<p>The conveyor belt shutting down would also affect sea level and precipitation patterns, which can <a href="https://doi.org/10.1088/1748-9326/ac3955">push other ecosystems closer to their tipping points</a>. For example, the Amazon rainforest is vulnerable to <a href="https://doi.org/10.1073/pnas.2120777119">declining precipitation</a>. If its forest ecosystem turned to grassland, the transition would <a href="https://esd.copernicus.org/articles/13/1667/2022/">release carbon</a> to the atmosphere and result in the loss of a valuable carbon sink, further accelerating climate change.</p>
<p>The Atlantic circulation has <a href="https://doi.org/10.1126/science.aaf5529">slowed significantly in the distant past</a>. During <a href="https://doi.org/10.1146/annurev-marine-010816-060415">glacial periods</a> when ice sheets that covered large parts of the planet were melting, the influx of fresh water slowed the Atlantic circulation, triggering huge climate fluctuations.</p>
<h2>So, when will we see this tipping point?</h2>
<p>The big question – when will the Atlantic circulation reach a tipping point – remains unanswered. Observations don’t go back far enough to provide a clear result. While a recent study suggested that the conveyor belt is rapidly <a href="https://doi.org/10.1038/s41467-023-39810-w">approaching its tipping point</a>, possibly within a few years, these statistical analyses made several assumptions that give rise to uncertainty.</p>
<p>Instead, we were able to develop a physics-based and observable early warning signal involving the salinity transport at the southern boundary of the Atlantic Ocean. Once a threshold is reached, the tipping point is likely to follow in one to four decades.</p>
<figure class="align-center ">
<img alt="A line chart of circulation strength shows a quick drop-off after the amount of freshwater in the ocean hits a tipping point." src="https://images.theconversation.com/files/574182/original/file-20240207-28-udb2b3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/574182/original/file-20240207-28-udb2b3.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=467&fit=crop&dpr=1 600w, https://images.theconversation.com/files/574182/original/file-20240207-28-udb2b3.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=467&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/574182/original/file-20240207-28-udb2b3.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=467&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/574182/original/file-20240207-28-udb2b3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=586&fit=crop&dpr=1 754w, https://images.theconversation.com/files/574182/original/file-20240207-28-udb2b3.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=586&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/574182/original/file-20240207-28-udb2b3.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=586&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A climate model experiment shows how quickly the AMOC slows once it reaches a tipping point with a threshold of fresh water entering the ocean. How soon that will happen remains an open question.</span>
<span class="attribution"><a class="source" href="http://www.science.org/doi/10.1126/sciadv.adk1189">René M. van Westen</a></span>
</figcaption>
</figure>
<p>The climate impacts from our study underline the severity of such an abrupt conveyor belt collapse. The temperature, sea level and precipitation changes will severely affect society, and the <a href="https://doi.org/10.1029/2023GL106088">climate shifts are unstoppable</a> on human time scales.</p>
<p>It might seem counterintuitive to worry about extreme cold as the planet warms, but if the main Atlantic Ocean circulation shuts down from too much meltwater pouring in, that’s the risk ahead.</p>
<p><em>This article was updated on Feb. 11, 2024, to fix a typo: The experiment found temperatures in parts of Europe changed by more than 5 F per decade.</em></p><img src="https://counter.theconversation.com/content/222834/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>René van Westen receives funding from the European Research Council (ERC-AdG project 101055096, TAOC).</span></em></p><p class="fine-print"><em><span>Henk A. Dijkstra receives funding from the European Research Council (ERC-AdG project 101055096, TAOC, PI: Dijkstra). </span></em></p><p class="fine-print"><em><span>Michael Kliphuis does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Scientists now have a better understanding of the risks ahead and a new early warning signal to watch for.René van Westen, Postdoctoral Researcher in Climate Physics, Utrecht UniversityHenk A. Dijkstra, Professor of Physics, Utrecht UniversityMichael Kliphuis, Climate Model Specialist, Utrecht UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2159282023-10-18T16:30:09Z2023-10-18T16:30:09ZWhat will happen to the Greenland ice sheet if we miss our global warming targets<figure><img src="https://images.theconversation.com/files/554571/original/file-20231018-17-rfjr6n.JPG?ixlib=rb-1.1.0&rect=19%2C0%2C4372%2C2146&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Bryn Hubbard</span></span></figcaption></figure><p>It’s hard to overstate how crucial Greenland, and its kilometres-thick ice layer, is to climate change. If all that ice melted, the sea would rise by about seven metres – the height of a house. </p>
<p>But what happens if we fail to limit warming to 1.5°C (as looks increasingly likely)? And what happens if we do subsequently manage to rectify that “overshoot” and bring temperatures back down? A team of researchers writing in the journal <a href="https://www.nature.com/articles/s41586-023-06503-9">Nature</a> have now published a study exploring these questions.</p>
<p>In a nutshell, their work shows the worst case scenario of ice sheet collapse and consequent sea-level rise can be avoided – and even partly reversed – if we manage to reduce the global temperatures projected for after 2100. Moreover, the lower and sooner those temperatures fall, the more chance there is of minimising that ice melt and sea-level rise.</p>
<p>We already know that the Greenland ice sheet is losing more than <a href="https://essd.copernicus.org/articles/15/1597/2023/">300 billion cubic metres of ice per year</a>, currently driving global sea levels up by a little less than a millimetre per year. One major worry is that further warming could cross critical thresholds, sometimes referred to as “tipping points”. For example, as the air warms more ice will melt, lowering the elevation of the ice surface and hence exposing it to warmer air temperatures and more melting – even without continued atmospheric warming. </p>
<p>Although far more complex and nuanced in reality, it is feedback processes such as this which dictate that global warming be limited to 1.5°C above pre-industrial levels in order to avoid catastrophes, such as wholescale ice-sheet collapse.</p>
<h2>How to simulate a huge ice sheet in a computer</h2>
<p>It is critically important that we are able to predict how the Greenland ice sheet will respond to future warming. To achieve this, researchers generally use computer models of ice motion. In essence, these divide the ice sheet into tens of thousands of 3D segments and apply physical laws of ice motion to compute how each segment changes over thousands of individual time steps, factoring in things like anticipated climatic change, ice thickness, ice slope and the temperature of the ice interior and ice base.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/554577/original/file-20231018-15-tq49jv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Small tents, huge ice sheet" src="https://images.theconversation.com/files/554577/original/file-20231018-15-tq49jv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554577/original/file-20231018-15-tq49jv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=277&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554577/original/file-20231018-15-tq49jv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=277&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554577/original/file-20231018-15-tq49jv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=277&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554577/original/file-20231018-15-tq49jv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=348&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554577/original/file-20231018-15-tq49jv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=348&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554577/original/file-20231018-15-tq49jv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=348&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Research field camp on the crevassed surface of the Greenland ice sheet.</span>
<span class="attribution"><span class="source">Bryn Hubbard</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<p>However, these projections are subject to substantial uncertainties. It’s tough to know exactly how ice moves over bedrock, or what its internal temperature might be. And the climate is made up of many moving parts. Atmospheric and oceanic circulations may also change radically over the thousands or tens of thousands of years it takes for the ice sheet to settle in to a new equilibrium.</p>
<p>In the face of such challenges, a team of researchers led by Nils Bochow of the Arctic University in Norway have published their new study. They ran two independent state-of-the-art computer programs that were able to simulate how the Greenland ice sheet would respond to various possible levels of global warming, over tens of thousands of years. To mimic the effects of overshooting the critical 1.5°C threshold, they include a gradual warming trajectory to a “peak” temperature, followed by a period during which temperature stabilises to a generally lower final “convergence temperature”. </p>
<h2>Good news and bad news</h2>
<p>The results are fascinating. If temperatures peak at 2°C or so, and remain there, then the models – as expected – predict substantial ice sheet collapse after several thousands of years. </p>
<p>However, things change if warming is seriously mitigated post-2100. In those models, inertia in the ice sheet’s response – a bit like the time it takes for a ripple to settle down as it passes across a pond – means that an overshoot is at least partly reversible as long as temperatures are quickly brought back down. </p>
<p>For example, if temperature stabilises by the year 2200 at less than 1.5°C of warming, then the ice sheet should remain smaller than at present, but stable. This is the case irrespective of how far (within reason) peak temperatures overshot 1.5°C in the year 2100. In such cases the sea rise would likely be restricted to a metre or so. </p>
<p>However, such a recovery becomes impossible if it takes too long to get temperatures down or if the convergence temperature remains too high. In those scenarios, ice-sheet collapse and substantial sea-level rise become all but inevitable.</p>
<p>Perhaps the very worst can be avoided then, if we continue to work to reduce global temperatures right through this century and next. Although heartening to some degree, these projections are subject to substantial uncertainty and there is more work to do. In this regard, the authors are at pains to note that their results are not necessarily specific predictions but rather provide insight into possible pathways. </p>
<hr>
<figure class="align-right ">
<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><strong><em>Don’t have time to read about climate change as much as you’d like?</em></strong>
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<p class="fine-print"><em><span>Bryn Hubbard receives funding from the UK's Natural Environment Research Council. He is affiliated with the Centre for Glaciology at Aberystwyth University. </span></em></p>The ice will survive if temperatures are soon brought back down – new study.Bryn Hubbard, Professor of Glaciology, Aberystwyth UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2062362023-08-21T15:40:48Z2023-08-21T15:40:48ZTo predict future sea level rise, we need accurate maps of the world’s most remote fjords<figure><img src="https://images.theconversation.com/files/543613/original/file-20230821-93007-prjkm7.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4114%2C1492&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The 10km wide Petermann Fjord in northern Greenland. The author's icebreaker ship is a small dot in the middle. The cliffs on either side are a kilometre high. In the distance is the 'ice tongue' of the glacier flowing into the fjord.</span> <span class="attribution"><span class="source">Martin Jakobsson</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Understanding how glaciers interact with the ocean is akin to piecing together a colossal jigsaw puzzle. And on various icebreaker expeditions to some of the most remote fjords in northern Greenland, colleagues and I have showed that the shape of the seafloor is one of the key pieces of that puzzle.</p>
<p>To understand why the seabed is so important, we have to look at the glaciers themselves and what is causing them to retreat or even disappear. The large glaciers that meet the ocean in Greenland and Antarctica balance their mass over time largely in pace with the climate. When it snows or rains they accumulate ice, and they lose ice to melting and calving – the process where chunks of ice break off and eventually melt away into the sea. </p>
<p>But over the past few decades they are <a href="https://theconversation.com/greenland-has-lost-3-8-trillion-tonnes-of-ice-since-1992-127752">losing mass at an accelerated pace</a>, with more icebergs calving into the ocean and more ice being melted from below by relatively warm seawater. </p>
<p>Estimating how much mass will be lost is often highlighted as glaciology’s grand challenge as it constitutes a <a href="https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf">large uncertainty</a> in our predictions of future sea-level rise. To hone our predictions, it is crucial to find the areas where warmer ocean water reaches the these glaciers. </p>
<p>Most glaciers in Greenland drain into fjords in which the waters near the surface are very cold, heavily influenced by meltwater from the glaciers. Some fjords also allow in warmer water of Atlantic origin, which is saltier and therefore heavier so it enters the fjords at a greater depth.</p>
<p>The shape and depth (or “bathymetry”) of the seafloor determines whether this warmer water can reach the glaciers and cause them to melt. These fjords may have particularly complex bathymetry as they themselves were formed by glaciers which also eroded the seabed. While the inner parts can be a kilometre deep, a shallower “sill” at the entrance (formed when eroded materials accumulate or from resistant bedrock) can act as a shield against inflowing warmer water.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/543455/original/file-20230818-15-ys0939.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="diagram of fjord" src="https://images.theconversation.com/files/543455/original/file-20230818-15-ys0939.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/543455/original/file-20230818-15-ys0939.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=278&fit=crop&dpr=1 600w, https://images.theconversation.com/files/543455/original/file-20230818-15-ys0939.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=278&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/543455/original/file-20230818-15-ys0939.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=278&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/543455/original/file-20230818-15-ys0939.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=349&fit=crop&dpr=1 754w, https://images.theconversation.com/files/543455/original/file-20230818-15-ys0939.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=349&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/543455/original/file-20230818-15-ys0939.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=349&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Diagram of a fjord showing a sill that keeps out the warmer ocean water (note in Greenland the fjords are fed by glaciers not rivers).</span>
<span class="attribution"><a class="source" href="https://www.amap.no/">AMAP</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>That’s why mapping these fjords is one of the most critical steps in <a href="https://www.sciencedirect.com/science/article/pii/S2590332220305923">assessing the future</a> of the glaciers that flow into them. This is unfortunately easier said than done, since many of these glaciers flow into some of the most remote areas of the world.</p>
<h2>Ireland-sized glacier, Manhattan-sized icebergs</h2>
<p>The Petermann Glacier – the largest in the northern part of the Greenland ice sheet – drains an area of <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2012GL051634">about 74,000 square kilometres</a>, similar to the size of Ireland.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/543619/original/file-20230821-17-oouuk1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Annotated map of Greenland glaciers" src="https://images.theconversation.com/files/543619/original/file-20230821-17-oouuk1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/543619/original/file-20230821-17-oouuk1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=650&fit=crop&dpr=1 600w, https://images.theconversation.com/files/543619/original/file-20230821-17-oouuk1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=650&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/543619/original/file-20230821-17-oouuk1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=650&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/543619/original/file-20230821-17-oouuk1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=817&fit=crop&dpr=1 754w, https://images.theconversation.com/files/543619/original/file-20230821-17-oouuk1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=817&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/543619/original/file-20230821-17-oouuk1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=817&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Some of the most northerly and inaccessible fjords on earth.</span>
<span class="attribution"><span class="source">Martin Jakobsson</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Petermann is one of a few glaciers around Greenland with a floating ice tongue extending tens of kilometres from where the glacier is grounded on the seafloor. These ice tongues may <a href="https://tc.copernicus.org/articles/7/647/2013/">act as a brakes</a> on the flow of ice into the sea, slowing down mass loss. </p>
<p>In 2010, Petermann made headlines when <a href="https://earthobservatory.nasa.gov/images/45112/ice-island-calves-off-petermann-glacier">a huge chunk broke off</a> and formed an iceberg four times the size of Manhattan island. This was followed by another huge calving two years later. While calving is a natural process, these unusually large events were likely influenced by warmer waters from the Atlantic <a href="https://tos.org/oceanography/article/the-ice-shelf-of-petermann-gletscher-north-greenland-and-its-connection-to">melting the tongue from below</a>, making it thinner and more prone to break. </p>
<p>In 2015 colleagues and I <a href="https://www.nature.com/articles/s41467-018-04573-2">mapped the entire seabed of Petermann Fjord</a> for the first time. We found the entrance was still very deep: 443 metres – as deep as the Empire State Building is tall. Deep enough for that warm, heavy, salty glacier-melting Atlantic water to enter.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/543701/original/file-20230821-27-skrn6s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Ship in front of huge cliffs" src="https://images.theconversation.com/files/543701/original/file-20230821-27-skrn6s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/543701/original/file-20230821-27-skrn6s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/543701/original/file-20230821-27-skrn6s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/543701/original/file-20230821-27-skrn6s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/543701/original/file-20230821-27-skrn6s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/543701/original/file-20230821-27-skrn6s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/543701/original/file-20230821-27-skrn6s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The icebreaker Oden in Petermann Fjord. The same ship appears as a tiny dot in the image at the top of the article.</span>
<span class="attribution"><span class="source">Martin Jakobsson</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>We next wanted to compare Petermann to the Ryder Glacier to its northeast, which has been more stable since at least the 1950s. Was it kept in place by a shallow fjord entrance keeping out warmer water? </p>
<p>At the time, no ship had ever entered Sherard Osborn Fjord where Ryder Glacier drains, because the sea ice in that region is the toughest in the entire Arctic Ocean. Therefore, nothing at all was known about the seafloor. Ryder Glacier became the target for our next expedition with icebreaker Oden in 2019.</p>
<h2>Shielded from warmer water</h2>
<p>Thick ice in the narrow passage separating Ellesmere Island from Greenland made it hard to even get to Sherard Osborn Fjord. And entering the fjord was a true challenge, as large icebergs that had calved from the ice tongue floated around and occasionally blocked the entire entrance.</p>
<p>It turned out the fjord has a <a href="https://www.nature.com/articles/s43247-020-00043-0">prominent shallow sill in front of Ryder Glacier</a>. This sill shields the glacier from warmer subsurface Atlantic water, which appears to explain why it has behaved very differently compared to Petermann.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/543462/original/file-20230818-25-aktsf8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Annotated image of glacier, fjord and seabed." src="https://images.theconversation.com/files/543462/original/file-20230818-25-aktsf8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/543462/original/file-20230818-25-aktsf8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=409&fit=crop&dpr=1 600w, https://images.theconversation.com/files/543462/original/file-20230818-25-aktsf8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=409&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/543462/original/file-20230818-25-aktsf8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=409&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/543462/original/file-20230818-25-aktsf8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=514&fit=crop&dpr=1 754w, https://images.theconversation.com/files/543462/original/file-20230818-25-aktsf8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=514&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/543462/original/file-20230818-25-aktsf8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=514&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An underwater sill in front of Ryder Glacier shields it from inflowing warmer water from the Atlantic.</span>
<span class="attribution"><span class="source">Martin Jakobsson</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The bathymetry of both Petermann and Sherard Osborn fjords has now been incorporated into the <a href="https://seabed2030.org/">Seabed 2030 Project</a>, which aims to completely map the world’s ocean floor before the end of the decade. Knowing more about the seabed, and the glaciers that flow into the sea, will in turn help us to sustainably manage the ocean and, ultimately, the planet. </p>
<p>The are more completely unmapped areas in North Greenland. In 2024, we are planning another expedition with icebreaker Oden even further north to Victoria Fjord, where C.H. Ostenfeld Glacier drains. This glacier recently lost its floating ice tongue and whether or not Atlantic water makes into the fjord remains to be seen. </p>
<hr>
<figure class="align-right ">
<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
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<p class="fine-print"><em><span>Martin Jakobsson is Co-Head of Arctic and North Pacific Center at Seabed 2030, a project funded by the Nippon Foundation to map the entire global seabed.</span></em></p>Some of the world’s biggest glaciers flow into fjords in Greenland and we need to know what they’ll bump into on the seabed.Martin Jakobsson, Professor of Marine Geology and Geophysics, Stockholm UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2090182023-07-20T18:00:01Z2023-07-20T18:00:01ZWhen Greenland was green: Ancient soil from beneath a mile of ice offers warnings for the future<figure><img src="https://images.theconversation.com/files/537577/original/file-20230715-21-gwfd9c.jpg?ixlib=rb-1.1.0&rect=0%2C352%2C4733%2C3053&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Water and sediment pour off the melting margin of the Greenland ice sheet.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/qinnguata-kuussua-river-russell-glacier-greenland-royalty-free-image/604573407">Jason Edwards/Photodisc via Getty Images</a></span></figcaption></figure><p>About 400,000 years ago, large parts of Greenland were ice-free. Scrubby tundra basked in the Sun’s rays on the island’s northwest highlands. Evidence suggests that a <a href="https://www.science.org/doi/10.1126/science.1141758">forest of spruce</a> trees, buzzing with insects, covered the southern part of Greenland. Global sea level was much higher then, between 20 and 40 feet <a href="https://www.science.org/doi/10.1126/science.aaa4019">above today’s levels</a>. Around the world, land that today is home to hundreds of millions of people was under water.</p>
<p>Scientists have known for awhile that the Greenland ice sheet had mostly disappeared at some point in the <a href="https://www.nature.com/articles/nature20146">past million years</a>, but not precisely when. </p>
<p>In a new study in the <a href="http://www.science.org/doi/10.1126/science.ade4248">journal Science</a>,
we determined the date, using frozen soil <a href="https://www.campcentury.org/learning/podcasts">extracted during the Cold War</a> from beneath a nearly mile-thick section of the Greenland ice sheet. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/CYfSphNHOm8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A brief look at the evidence beneath Greenland’s ice sheet and the lessons its holds.</span></figcaption>
</figure>
<p>The timing – about 416,000 years ago, with largely ice-free conditions lasting for as much as 14,000 years – is important. At that time, Earth and its <a href="https://www.smithsonianmag.com/science-nature/how-drastic-ecological-change-led-leap-forward-behavior-weapons-and-tools-180976101/">early humans</a> were going through one of the longest interglacial periods since ice sheets first covered the high latitudes 2.5 million years ago. </p>
<p>The length, magnitude and effects of that natural warming can help us understand the Earth that modern humans are now creating for the future.</p>
<h2>A world preserved under the ice</h2>
<p>In July 1966, American scientists and U.S. Army engineers completed a six-year effort to <a href="https://blogs.egu.eu/divisions/cr/2022/01/28/camp-century-bottom-ice/">drill through the Greenland ice sheet</a>. The drilling took place at <a href="https://www.popsci.com/environment/us-army-arctic-city/">Camp Century</a>, one of the military’s most unusual bases – it was <a href="https://theconversation.com/the-us-army-tried-portable-nuclear-power-at-remote-bases-60-years-ago-it-didnt-go-well-164138">nuclear powered</a> and made up of a series of tunnels dug into the Greenland ice sheet.</p>
<p>The drill site in northwest Greenland was 138 miles from the coast and underlain <a href="https://icedrill.org/sites/default/files/Langway_2008_Early_polar_ice_cores.pdf">by 4,560 feet of ice</a>. Once they reached the bottom of the ice, the team kept drilling 12 more feet into the frozen, rocky soil below.</p>
<figure class="align-center ">
<img alt="A man in a fur-lined coat removes a long ice core about as wide as his hand" src="https://images.theconversation.com/files/537578/original/file-20230715-16554-hkfcq9.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537578/original/file-20230715-16554-hkfcq9.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=487&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537578/original/file-20230715-16554-hkfcq9.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=487&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537578/original/file-20230715-16554-hkfcq9.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=487&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537578/original/file-20230715-16554-hkfcq9.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=612&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537578/original/file-20230715-16554-hkfcq9.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=612&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537578/original/file-20230715-16554-hkfcq9.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=612&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">George Linkletter, working for the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory, examines a piece of ice core in the science trench at Camp Century. The base was shut down in 1967.</span>
<span class="attribution"><span class="source">U.S. Army Photograph</span></span>
</figcaption>
</figure>
<p>In 1969, geophysicist Willi Dansgaard’s analysis of the ice core from Camp Century revealed for the first time the details of how Earth’s climate had <a href="https://www.science.org/doi/10.1126/science.166.3903.377">changed dramatically</a> over the last 125,000 years. Extended cold glacial periods when the ice expanded quickly gave way to warm interglacial periods when the ice melted and sea level rose, flooding coastal areas around the world.</p>
<p>For nearly 30 years, scientists paid little attention to the 12 feet of frozen soil from Camp Century. One study <a href="https://www.cambridge.org/core/journals/journal-of-glaciology/article/evidence-of-the-bedrock-beneath-the-greenland-ice-sheet-near-camp-century-greenland/6F87EC12C84FAFB5BEE3E4A044B52618">analyzed the pebbles</a> to understand the bedrock beneath the ice sheet. Another suggested intriguingly that the frozen soil <a href="https://www.jstor.org/stable/40511026">preserved evidence</a> of a time warmer than today. But with no way to date the material, few people paid attention to these studies. By the 1990s, the frozen soil core had vanished.</p>
<p>Several years ago, our Danish colleagues found the lost soil buried deep in a Copenhagen freezer, and we formed an <a href="https://www.campcentury.org/home">international team</a> to analyze this unique frozen climate archive. </p>
<p>In the uppermost sample, we found perfectly preserved <a href="https://theconversation.com/ancient-leaves-preserved-under-a-mile-of-greenlands-ice-and-lost-in-a-freezer-for-years-hold-lessons-about-climate-change-157105">fossil plants</a> – proof positive that the land far below Camp Century had been ice-free some time in the past – but when?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/537531/original/file-20230714-23018-ycstss.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two microscope images show tiny plant fossils. One a moss stem and the other a sedge seed." src="https://images.theconversation.com/files/537531/original/file-20230714-23018-ycstss.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537531/original/file-20230714-23018-ycstss.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=272&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537531/original/file-20230714-23018-ycstss.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=272&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537531/original/file-20230714-23018-ycstss.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=272&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537531/original/file-20230714-23018-ycstss.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=342&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537531/original/file-20230714-23018-ycstss.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=342&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537531/original/file-20230714-23018-ycstss.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=342&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Exquisitely preserved fossils of more than 400,000-year-old moss, on the left, and a sedge seed on the right, found in the soil core from beneath the Greenland ice sheet, help tell the story of what lived there when the ice was gone.</span>
<span class="attribution"><a class="source" href="https://www.campcentury.org/press/photos">Halley Mastro/University of Vermont</a></span>
</figcaption>
</figure>
<h2>Dating ancient rock, twigs and dirt</h2>
<p>Using samples cut from the center of the sediment core and prepared and analyzed in the dark so that the material retained an accurate memory of its last exposure to sunlight, we now know that the ice sheet covering northwest Greenland – nearly a mile thick today – <a href="http://www.science.org/doi/10.1126/science.ade4248">vanished during the extended natural warm period</a> known to climate scientists as <a href="https://www.sciencedirect.com/science/article/pii/S027737912200124X">MIS 11</a>, between 424,000 and 374,000 years ago. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/537528/original/file-20230714-15-dx61m2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A composite photograph of the sediment core showing the luminescence sample used to determine when Greenland was last ice-free beneath Camp Century." src="https://images.theconversation.com/files/537528/original/file-20230714-15-dx61m2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537528/original/file-20230714-15-dx61m2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537528/original/file-20230714-15-dx61m2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537528/original/file-20230714-15-dx61m2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537528/original/file-20230714-15-dx61m2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537528/original/file-20230714-15-dx61m2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537528/original/file-20230714-15-dx61m2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The uppermost sample of the Camp Century sub-ice sediment core tells a story of vanished ice and tundra life in Greenland 416,000 years ago.</span>
<span class="attribution"><a class="source" href="https://www.campcentury.org/press/photos">Andrew Christ/University of Vermont</a></span>
</figcaption>
</figure>
<p>To determine more precisely when the ice sheet melted away, one of us, <a href="https://www.usu.edu/geo/osl/">Tammy Rittenour</a>, used a technique known as luminescence dating.</p>
<p>Over time, minerals accumulate energy as radioactive elements like uranium, thorium, and potassium decay and release radiation. The longer the sediment is buried, the more radiation accumulates as trapped electrons. </p>
<p>In the lab, specialized instruments measure tiny bits of energy, released as light from those minerals. That signal can be used to calculate how long the grains were buried, since the last exposure to sunlight would have released the trapped energy.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/TpZVa7O863A?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How optically stimulated luminescence works.</span></figcaption>
</figure>
<p><a href="https://www.uvm.edu/cosmolab/">Paul Bierman’s laboratory</a> at the University of Vermont dated the sample’s last time near the surface in a different way, using rare radioactive isotopes of aluminum and beryllium.</p>
<p>These isotopes form when cosmic rays, originating far from our solar system, slam into the rocks on Earth. Each isotope has a different half-life, meaning it decays at a different rate when buried. </p>
<p>By measuring both isotopes in the same sample, glacial geologist <a href="https://andrewjchrist.wixsite.com/website">Drew Christ</a> was able to determine that melting ice had exposed the sediment at the land surface for less than 14,000 years. </p>
<p>Ice sheet models run by <a href="https://ig.utexas.edu/staff/benjamin-keisling/">Benjamin Keisling</a>, now incorporating our new knowledge that Camp Century was ice-free 416,000 years ago, show that Greenland’s ice sheet must have shrunk significantly then. </p>
<p>At minimum, the edge of the ice retreated tens to hundreds of miles around much of the island during that period. Water from that melting ice raised global sea level at least 5 feet and perhaps as much as 20 feet compared to today.</p>
<h2>Warnings for the future</h2>
<p>The ancient frozen soil from beneath Greenland’s ice sheet warns of trouble ahead.</p>
<p>During the MIS 11 interglacial, Earth was warm and ice sheets were restricted to the high latitudes, a lot like today. <a href="https://www.sciencedirect.com/science/article/pii/S027737912200124X">Carbon dioxide levels</a> in the atmosphere remained between 265 and 280 parts per million for about 30,000 years. MIS 11 lasted longer than most interglacials because of the impact of the shape of Earth’s orbit around the sun on solar radiation reaching the Arctic. Over these 30 millennia, that level of carbon dioxide triggered enough warming to melt much of the Greenland’s ice.</p>
<p>Today, our atmosphere contains 1.5 times more carbon dioxide than it did at MIS 11, around <a href="https://keelingcurve.ucsd.edu/">420 parts per million</a>, a concentration that has risen each year. Carbon dioxide traps heat, warming the planet. Too much of it in the atmosphere raises the global temperature, as the world is seeing now.</p>
<p>Over the past decade, as greenhouse gas emissions continued to rise, humans experienced the eight warmest years on record. July 2023 saw the <a href="https://public.wmo.int/en/media/news/preliminary-data-shows-hottest-week-record-unprecedented-sea-surface-temperatures-and">hottest week on record</a>, based on preliminary data. Such heat <a href="https://theconversation.com/whats-going-on-with-the-greenland-ice-sheet-its-losing-ice-faster-than-forecast-and-now-irreversibly-committed-to-at-least-10-inches-of-sea-level-rise-185590">melts ice sheets</a>, and the loss of ice further warms the planet as dark rock soaks up sunlight that bright white ice and snow once reflected.</p>
<figure class="align-center ">
<img alt="Meltwater pours over the Greenland ice sheet in a meandering channel." src="https://images.theconversation.com/files/537579/original/file-20230715-24-4qk8ya.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537579/original/file-20230715-24-4qk8ya.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537579/original/file-20230715-24-4qk8ya.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537579/original/file-20230715-24-4qk8ya.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537579/original/file-20230715-24-4qk8ya.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537579/original/file-20230715-24-4qk8ya.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537579/original/file-20230715-24-4qk8ya.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">At midnight in July, meltwater pours over the Greenland ice sheet in a meandering channel.</span>
<span class="attribution"><span class="source">Paul Bierman</span></span>
</figcaption>
</figure>
<p>Even if everyone stopped burning fossil fuels tomorrow, carbon dioxide levels in the atmosphere would <a href="https://www.nature.com/articles/nclimate2923">remain elevated</a> for thousands to tens of thousands of years. That’s because it takes a long time for carbon dioxide to move into soils, plants, the ocean and rocks. We are creating conditions conducive to a very long period of warmth, just like MIS 11.</p>
<p>Unless people dramatically lower the concentration of carbon dioxide in the atmosphere, evidence we found of Greenland’s past suggests a largely ice-free future for the island. </p>
<p>Everything we can do to reduce carbon emissions and <a href="https://theconversation.com/the-earth-needs-multiple-methods-for-removing-co2-from-the-air-to-avert-worst-of-climate-change-121479">sequester carbon</a> that is already in the atmosphere will increase the chances that more of Greenland’s ice survives.</p>
<p>The alternative is a world that could look a lot like MIS 11 – or even more extreme: a warm Earth, shrinking ice sheets, rising sea level, and waves rolling over Miami, Mumbai, India and Venice, Italy.</p><img src="https://counter.theconversation.com/content/209018/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul Bierman receives funding from the US National Science Foundation.</span></em></p><p class="fine-print"><em><span>Tammy Rittenour receives funding from the US National Science Foundation.. </span></em></p>The soil was extracted during the Cold War from beneath one of the U.S military’s most unusual bases, then forgotten for decades.Paul Bierman, Fellow of the Gund Institute for Environment, Professor of Natural Resources and Environmental Science, University of VermontTammy Rittenour, Professor of Geosciences and Director of Luminescence Lab, Utah State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2074682023-06-29T12:17:15Z2023-06-29T12:17:15ZMeltwater is infiltrating Greenland’s ice sheet through millions of hairline cracks – destabilizing its structure<figure><img src="https://images.theconversation.com/files/534388/original/file-20230627-36062-evdjnn.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2500%2C1661&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Richard Bates and Alun Hubbard kayak a meltwater stream on Greenland's Petermann Glacier, towing an ice radar that reveals it's riddled with fractures.</span> <span class="attribution"><span class="source">Nick Cobbing.</span></span></figcaption></figure><p>I’m striding along the steep bank of a raging white-water torrent, and even though the canyon is only about the width of a highway, the river’s flow is greater than that of London’s Thames. The deafening roar and rumble of the cascading water is incredible – a humbling reminder of the raw power of nature.</p>
<p>As I round a corner, I am awestruck at a completely surreal sight: A gaping fissure has opened in the riverbed, and it is swallowing the water in a massive whirlpool, sending up huge spumes of spray. This might sound like a computer-generated scene from a blockbuster action movie – but it’s real.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/534120/original/file-20230626-19-t5ctl6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534120/original/file-20230626-19-t5ctl6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=336&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534120/original/file-20230626-19-t5ctl6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=336&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534120/original/file-20230626-19-t5ctl6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=336&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534120/original/file-20230626-19-t5ctl6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=423&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534120/original/file-20230626-19-t5ctl6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=423&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534120/original/file-20230626-19-t5ctl6.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=423&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Alun Hubbard stands beside a moulin forming in a meltwater stream on the Greenland ice sheet.</span>
<span class="attribution"><span class="source">Courtesy of Alun Hubbard</span></span>
</figcaption>
</figure>
<p>A moulin is forming right in front of me on the Greenland ice sheet. Only this really shouldn’t be happening here – current scientific understanding doesn’t accommodate this reality.</p>
<p>As a <a href="https://www.researchgate.net/profile/Alun-Hubbard">glaciologist</a>, I’ve spent 35 years investigating how meltwater affects the flow and stability of glaciers and ice sheets.</p>
<p>This gaping hole that’s opening up at the surface is merely the beginning of the meltwater’s journey through the guts of the ice sheet. As it funnels into moulins, it <a href="https://cires1.colorado.edu/science/spheres/snow-ice/images/iceMeltGraphic.jpg">bores a complex network of tunnels through the ice sheet</a> that extend many hundreds of meters down, all the way to the ice sheet bed. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/inTPFADBWt0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Scientists go into a moulin in this trailer for Into the Ice.</span></figcaption>
</figure>
<p>When it reaches the bed, the meltwater decants into the ice sheet’s subglacial drainage system – much like an urban stormwater network, though one that is constantly evolving and backing up. It carries the meltwater to the ice margins and ultimately ends up in the ocean, with major consequences for the thermodynamics and flow of the overlying ice sheet.</p>
<p>Scenes like this and <a href="https://doi.org/10.1038/s41561-023-01208-0">new research</a> into the ice sheet’s mechanics are challenging traditional thinking about what happens inside and under ice sheets, where observations are extremely challenging yet have stark implications. They suggest that Earth’s remaining ice sheets in Greenland and Antarctica are far more vulnerable to climate warming than models predict, and that the <a href="https://doi.org/10.1038/s41561-023-01208-0">ice sheets may be destabilizing from inside</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/stm1pBp0rfk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">NASA’s GRACE satellites capture Greenland’s ice loss from 2002-2021.</span></figcaption>
</figure>
<p>This is a tragedy in the making for the <a href="https://doi.org/10.1038/s41467-021-23810-9">half a billion people</a> who populate vulnerable coastal regions, since the Greenland and Antarctic ice sheets are effectively giant frozen freshwater reservoirs locking up <a href="https://nsidc.org/learn/parts-cryosphere/ice-sheets/ice-sheet-quick-facts">in excess of 65 meters</a> (over 200 feet) of equivalent global sea level rise. Since the 1990s their mass loss has been accelerating, becoming both the primary contributor to and the wild card in future sea level rise.</p>
<h2>How narrow cracks become gaping maws in ice</h2>
<p>Moulins are near-vertical conduits that capture and funnel the meltwater runoff from the ice surface each summer. There are many thousands across Greenland, and they can grow to impressive sizes because of the thickness of the ice coupled with the exceptionally high surface melt rates experienced. These gaping chasms can be as large as tennis courts at the surface, with chambers hidden in the ice beneath that could swallow cathedrals.</p>
<p>But this new moulin I’ve witnessed is really far from any crevasse fields and melt lakes, where current scientific understanding dictates that they should form.</p>
<figure class="align-center ">
<img alt="A helicopter sitting on the ice sheet looks tiny next to the gaping moulin, where a meltwater stream pours into the ice sheet." src="https://images.theconversation.com/files/534491/original/file-20230628-29982-adjj2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534491/original/file-20230628-29982-adjj2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534491/original/file-20230628-29982-adjj2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534491/original/file-20230628-29982-adjj2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534491/original/file-20230628-29982-adjj2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534491/original/file-20230628-29982-adjj2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534491/original/file-20230628-29982-adjj2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">High rates of meltwater discharge combined with a thick and gently sloping ice sheet in Western Greenland gives rise to monster holes like this moulin.</span>
<span class="attribution"><span class="source">Alun Hubbard</span></span>
</figcaption>
</figure>
<p>In a <a href="https://doi.org/10.1038/s41561-023-01208-0">new paper</a>, <a href="https://scholar.google.co.uk/citations?hl=en&user=TVrXvoEAAAAJ&view_op=list_works&sortby=pubdate">Dave Chandler</a> and I demonstrate that ice sheets are littered with millions of tiny hairline cracks that are forced open by the meltwater from the rivers and streams that intercept them.</p>
<p>Because glacier ice is so brittle at the surface, such cracks are ubiquitous across the melt zones of all glaciers, ice sheets and ice shelves. Yet because they are so tiny, they can’t be detected by satellite remote sensing.</p>
<p>Under most conditions, we find that stream-fed hydrofracture like this allows water to penetrate hundreds of meters down before freezing closed, without the crack’s necessarily penetrating to the bed to form a full-fledged moulin. But, even these partial-depth hydrofractures have considerable impact on ice sheet stability.</p>
<p>As the water pours in, it damages the ice sheet structure and releases its latent heat. The ice fabric warms and softens and, hence, flows and melts faster, just like warmed-up candle wax.</p>
<figure class="align-center ">
<img alt="Alun Hubbard using a rappelling rope lowers himself from the top of the ice sheet into a huge hold with water pouring down the sides. The hole appears to be as wide as a two-lane road." src="https://images.theconversation.com/files/534492/original/file-20230628-28043-kaqy3c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534492/original/file-20230628-28043-kaqy3c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534492/original/file-20230628-28043-kaqy3c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534492/original/file-20230628-28043-kaqy3c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534492/original/file-20230628-28043-kaqy3c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534492/original/file-20230628-28043-kaqy3c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534492/original/file-20230628-28043-kaqy3c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Alun Hubbard rappels into a moulin in October 2019, a point in the year when surface melt should have ceased but hadn’t.</span>
<span class="attribution"><span class="source">Lars Ostenfeld / Into the Ice</span></span>
</figcaption>
</figure>
<p>The stream-driven hydrofractures mechanically damage the ice and transfer heat into the guts of the ice sheet, destabilizing it from the inside. Ultimately, the internal fabric and structural integrity of ice sheets is becoming more vulnerable to climate warming.</p>
<h2>Emerging processes that speed up ice loss</h2>
<p>Over the past two decades that scientists have tracked ice sheet melt and flow in earnest, melt events have become <a href="https://www.esa.int/Applications/Observing_the_Earth/FutureEO/CryoSat/Meltwater_runoff_from_Greenland_becoming_more_erratic">more common and more intense</a> as <a href="https://climate.nasa.gov/vital-signs/global-temperature/">global temperatures rise</a> – further exacerbated by <a href="https://www.nature.com/articles/s43247-022-00498-3">Arctic warming of almost four times the global mean</a>.</p>
<p>The ice sheet is also flowing and calving icebergs much faster. It has lost about <a href="https://climate.nasa.gov/vital-signs/ice-sheets/">270 billion metric tons of ice per year</a> since 2002: over a centimeter and a half (half an inch) of global sea-level rise. Greenland is now, on average, contributing around 1 millimeter (0.04 inches) to the sea level budget annually.</p>
<p>A 2022 study found that even if atmospheric warming stopped now, <a href="https://doi.org/10.1038/s41558-022-01441-2">at least 27 centimeters – nearly 1 foot – of sea level rise</a> is inevitable because of Greenland’s imbalance with its past two decades of climate.</p>
<p>Understanding the risks ahead is crucial. However, the current generation of ice sheet models used to assess how Greenland and Antarctica will respond to warming in the future don’t account for amplification processes that are being discovered. That means the models’ sea-level rise estimates, used to inform Intergovernmental Panel on Climate Change (IPCC) reports and policymakers worldwide, are conservative and lowballing the rates of global sea rise in a warming world.</p>
<figure class="align-center ">
<img alt="Two people stand inside an ice cave with light coming from a large hole above." src="https://images.theconversation.com/files/534490/original/file-20230628-25-453mgb.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534490/original/file-20230628-25-453mgb.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=899&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534490/original/file-20230628-25-453mgb.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=899&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534490/original/file-20230628-25-453mgb.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=899&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534490/original/file-20230628-25-453mgb.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1130&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534490/original/file-20230628-25-453mgb.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1130&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534490/original/file-20230628-25-453mgb.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1130&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Daniela Barbieri and Alun Hubbard explore the contorted englacial plumbing deep inside a Greenland moulin.</span>
<span class="attribution"><span class="source">Lars Ostenfeld / Into the Ice</span></span>
</figcaption>
</figure>
<p>Our new finding is just the latest. Recent studies have shown that:</p>
<ul>
<li><p>Warming ocean currents are intruding into the <a href="https://doi.org/10.1038/s41598-019-53190-6">Antarctic</a> and <a href="https://doi.org/10.1038/ngeo316">Greenland</a> coastlines, flowing under the <a href="https://doi.org/10.1126/science.aaa0940">ice shelves</a> to undercut outlet glaciers and <a href="https://doi.org/10.5194/tc-8-1457-2014">destabilize their calving fronts</a>.</p></li>
<li><p>Increasing rainfall across the Greenland ice sheet not only depletes snow accumulation, it also <a href="https://doi.org/10.1038/ngeo2482">accelerates surface melting and ice flow</a>.</p></li>
<li><p><a href="https://doi.org/10.3389/feart.2015.00078">Algae and microbes</a>, along with <a href="https://doi.org/10.1126/sciadv.aav3738">surface snowpack melt</a>, darken the ice sheet surface, absorbing more solar radiation, which <a href="https://doi.org/10.5194/tc-14-309-2020">also accelerates ice melt</a>.</p></li>
<li><p><a href="https://doi.org/10.5194/tc-10-1147-2016">Superimposed ice slabs within the snowpack</a> are forming across the accumulation zone, forming an impermeable barrier that depletes meltwater retention and drives extraordinary runoff.</p></li>
<li><p>Water at the base of the ice sheet thaws and <a href="https://doi.org/10.1029/2010GL044397">softens the frozen bed, thereby triggering basal sliding</a> and <a href="https://doi.org/10.1002/2013GL058933">accelerating interior ice sheet flow</a> to the margins.</p></li>
</ul>
<p>In the last months, other papers also described previously unknown feedback processes underway beneath ice sheets that computer models currently can’t include. Often these processes happen at too fine a scale for models to pick up, or the model’s simplistic physics means the processes themselves can’t be captured.</p>
<p>Two such studies independently identify <a href="https://doi.org/10.1073/pnas.2220924120">enhanced submarine melting at the grounding line in Greenland</a> and <a href="https://doi.org/10.1038/s41586-022-05691-0">Antarctica</a>, where large outlet glaciers and ice streams drain into the sea and start to lift off their beds as floating ice shelves. These processes greatly accelerate ice sheet response to climate change and, in the case of Greenland, could potentially double future mass loss and its <a href="https://doi.org/10.1073/pnas.2220924120">contribution to rising sea level</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/534131/original/file-20230626-25-ynneln.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534131/original/file-20230626-25-ynneln.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=383&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534131/original/file-20230626-25-ynneln.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=383&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534131/original/file-20230626-25-ynneln.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=383&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534131/original/file-20230626-25-ynneln.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=481&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534131/original/file-20230626-25-ynneln.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=481&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534131/original/file-20230626-25-ynneln.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=481&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Greenland’s ice loss through meltwater and calving of glaciers has contributed nearly 10 centimeters (4 inches) to global sea-level rise since 1900. The chart shows sea level rise from all sources through 2018.</span>
<span class="attribution"><a class="source" href="https://climate.nasa.gov/vital-signs/sea-level/">NASA’s Goddard Space Flight Center/PO.DAAC</a></span>
</figcaption>
</figure>
<h2>Current climate models lowball the risks</h2>
<p>Along with other <a href="https://doi.org/10.1016/j.oneear.2020.11.002">applied glaciologists</a>, “<a href="https://www.pnas.org/doi/full/10.1073/pnas.1817205116">structured expert judgment</a>” and a <a href="https://doi.org/10.5194/tc-15-5705-2021">few candid modelers</a>, I contend that the current generation of ice sheet models used to inform the IPCC are not capturing the abrupt changes being observed in Greenland and Antarctica, or the risks that lie ahead.</p>
<p>Ice sheet models don’t include these emerging feedbacks and respond over millennia to strong-warming perturbations, leading to sluggish sea level forecasts that are lulling policymakers into a false sense of security. We’ve come a long way since the first IPCC reports in the early 1990s, which treated polar ice sheets as completely static entities, but we’re still short of capturing reality.</p>
<p>As a committed field scientist, I am keenly aware of how privileged I am to work in these sublime environments, where what I observe inspires and humbles. But it also fills me with foreboding for our low-lying coastal regions and what’s ahead for the <a href="https://doi.org/10.3389/fenvs.2021.751978">10% or so of the world’s population</a> that lives in them.</p><img src="https://counter.theconversation.com/content/207468/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alun Hubbard acknowledges funding from the Research Council of Norway (Centers of Excellence: CAGE & iC3), The Academy of Finland (PROFI4: Arctic Interactions) and is additionally affiliated to Oulun Yliopisto (Oulu University), Arctic Basecamp and La Venta Esplorazioni Geografiche.</span></em></p>Glaciologists are discovering new ways surface meltwater alters the internal structure of ice sheets, and raising an alarm that sea level rise could be much more abrupt than current models forecast.Alun Hubbard, Professor of Glaciology, Fulbright Scholar, University of TromsøLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2077852023-06-23T15:51:06Z2023-06-23T15:51:06ZThe melting Arctic is a crime scene. The microbes I study have long warned us of this catastrophe – but they are also driving it<p>The Arctic’s climate is warming at least four times faster than the global average, causing irrevocable changes to this vast <a href="https://news.sky.com/story/dramatic-changes-to-polar-ice-caps-revealed-on-new-map-of-arctic-and-antarctica-12898550">landscape</a> and precarious <a href="https://www.nwf.org/Educational-Resources/Wildlife-Guide/Wild-Places/Arctic#:%7E:text=The%20Arctic%20is%20a%20unique,in%20the%20summer%20to%20breed.">ecosystem</a> – from the anticipated <a href="https://earth.org/polar-bears-to-become-extinct-by-2100/">extinction of polar bears</a> to the <a href="https://www.scientificamerican.com/article/as-arctic-sea-ice-melts-killer-whales-are-moving-in/#:%7E:text=Killer%20whales%20often%20feed%20on,navigate%20through%20the%20icy%20waters.">appearance of killer whales</a> in ever-greater numbers. A new <a href="https://www.nature.com/articles/s41467-023-38511-8">study</a> suggests the Arctic Ocean could be ice-free in summer <a href="https://theconversation.com/arctic-ocean-could-be-ice-free-in-summer-by-2030s-say-scientists-this-would-have-global-damaging-and-dangerous-consequences-206974">as soon as the 2030s</a> – around a decade earlier than previously predicted.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/532508/original/file-20230618-17-lemk5e.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Map of Arctic sea ice changes" src="https://images.theconversation.com/files/532508/original/file-20230618-17-lemk5e.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/532508/original/file-20230618-17-lemk5e.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=700&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532508/original/file-20230618-17-lemk5e.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=700&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532508/original/file-20230618-17-lemk5e.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=700&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532508/original/file-20230618-17-lemk5e.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=879&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532508/original/file-20230618-17-lemk5e.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=879&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532508/original/file-20230618-17-lemk5e.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=879&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A new Arctic sea ice map compares the 30-year average with recent ten-year averages.</span>
<span class="attribution"><a class="source" href="https://www.bas.ac.uk/media-post/new-map-of-polar-regions-updated-to-reflect-ice-loss-name-changes-and-new-data/">British Antarctic Survey</a></span>
</figcaption>
</figure>
<p>But to properly understand the pace and force of what’s to come, we should instead focus on organisms too small to be seen with the naked eye. These single-celled microbes are both the watchkeepers and arch-agitators of the Arctic’s demise.</p>
<p>Scientists like me who study them have become forensic pathologists, processing crime scenes in our Arctic field sites. We don the same white anti-contamination suits, photograph each sampling site, and bag our samples for DNA analysis. In some areas, red-coloured microbes even create an effect known as “blood snow”.</p>
<p>In this complex criminal investigation, however, the invisible witnesses are also responsible for the damage being done. Microbes testify to the vulnerability of their Arctic habitats to the changes that humans have caused. But they also create powerful climate feedback loops that are doing ever-more damage both to the Arctic, and the planet as a whole.</p>
<h2>Zipping headlong into icy oblivion</h2>
<p>My first visit to the Arctic was also nearly my last. As a PhD student in my early 20s in 2006, I had set out with colleagues to sample microbes growing on a glacier in the Norwegian archipelago of <a href="https://www.theguardian.com/environment/2023/may/13/svalbard-the-arctic-islands-where-we-can-see-the-future-of-global-heating">Svalbard</a> – the planet’s northernmost year-round settlement, about 760 miles from the North Pole.</p>
<p>Our treacherous commute took us high above the glacier, traversing an icy scree slope to approach its flank before crossing a river at the ice’s margin. It was a route we had navigated recently – yet this day I mis-stepped. Time slowed as I slid towards the stream swollen with ice melt, my axe bouncing uselessly off the glassy ice. I was zipping headlong into icy oblivion.</p>
<p>In that near-death calm, two things bothered me. The water would carry me deep into the glacier, so it would be decades before my remains were returned to my family. And the ear-worm of that field season meant I would die to the theme tune to Indiana Jones.</p>
<hr>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/288776/original/file-20190820-170910-8bv1s7.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/288776/original/file-20190820-170910-8bv1s7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/288776/original/file-20190820-170910-8bv1s7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/288776/original/file-20190820-170910-8bv1s7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/288776/original/file-20190820-170910-8bv1s7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/288776/original/file-20190820-170910-8bv1s7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/288776/original/file-20190820-170910-8bv1s7.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><strong><em>This article is part of Conversation Insights</em></strong>
<br><em>The Insights team generates <a href="https://theconversation.com/uk/topics/insights-series-71218">long-form journalism</a> derived from interdisciplinary research. The team is working with academics from different backgrounds who have been engaged in projects aimed at tackling societal and scientific challenges.</em></p>
<hr>
<p>Thankfully, the scree slowed my slide – I lived and learned, quickly, that dead scientists don’t get to write up their papers. And I’m still learning about the tiny organisms that populate every habitat there: from seawater in the Arctic Ocean to ice crystals buried deep in the <a href="https://en.wikipedia.org/wiki/Greenland_ice_sheet">Greenland ice sheet</a>.</p>
<p>These micro-managers of all manner of planetary processes are acutely sensitive to the temperatures of their habitats. The slightest change above freezing can transform an Arctic landscape from a frozen waste devoid of liquid water to one where microbes get busy reproducing in nutrient-rich water, transforming themselves in ways that <a href="https://www.nature.com/articles/ismej2010108">further amplify</a> the effects of climate warming.</p>
<p>The Svalbard region is now warming seven times faster than the global average. While much of the world continues its efforts to limit global warming to 1.5°C above pre-industrial levels, in the Arctic, that battle was lost long ago.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/0VOGGdeB8eI?wmode=transparent&start=17" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Joseph Cook’s film on the microbes that inhabit the Greenland ice sheet.</span></figcaption>
</figure>
<h2>Decades ahead of us all</h2>
<p>It’s 2011, and <a href="http://www.earth.s.chiba-u.ac.jp/english/education/education02/staff16.html">Nozomu Takeuchi</a> is visiting Svalbard from Japan. It has been a difficult year back home, following the earthquake, tsunami and Fukushima nuclear incident, but Nozomu – a glacier ecologist and professor at Chiba University – is unrelenting in his quest to measure the effects of climate change. </p>
<p>Just hours after he stepped off a plane in the August midnight sun at Longyearbyen airport, we are marching up the nearest glacier. Above us, snow-capped mountain sides loom out of the swirling mist.</p>
<p>Since the 1990s, Nozomu has been collecting samples and measurements from glaciers all over the world. When we reach our goal near the snowline, he opens his rucksack to reveal a bento box full of sampling kit – stainless steel scoops, test tubes, sample bags, all arranged for efficiency. As he scurries around with practised efficiency, I think of offering help but fear I would only slow him down.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/532612/original/file-20230619-27-w8e0xr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Scientist takes a reading in snowy Arctic landscape" src="https://images.theconversation.com/files/532612/original/file-20230619-27-w8e0xr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532612/original/file-20230619-27-w8e0xr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532612/original/file-20230619-27-w8e0xr.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532612/original/file-20230619-27-w8e0xr.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532612/original/file-20230619-27-w8e0xr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532612/original/file-20230619-27-w8e0xr.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532612/original/file-20230619-27-w8e0xr.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Nozomu Takeuchi measuring the biological darkening of a Svalbard glacier in 2011.</span>
<span class="attribution"><span class="source">Arwyn Edwards</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>In truth, Nozomu is decades ahead of us all. Years ago, he made the link between the future of life and the death of ice, and these melting Svalbard glaciers are adding yet more points to his graphs.</p>
<p>Just as we apply oodles of factor 50 to protect ourselves from the Sun, so the billions of microbes sandwiched between the sky and surface of the glacier protect themselves by accumulating sunscreen-like pigments. And if enough of these pigments rest in one place under the Sun, this area of “biological darkening” absorbs the heat of the Sun much more effectively than reflective white snow and ice – so it melts faster.</p>
<p>Nozomu scoops up some of the so-called blood snow, heavily laden with algae. Under the microscope, their cells are indeed reminiscent of red blood cells. But rather than haemoglobin, these cells are laden with carotenoids – pigments also found in vegetables that <a href="https://academic.oup.com/femsec/article/94/3/fiy007/4810544?login=false">protect the algae from overheating</a>. Other patches of the glacier are verdant green, rich in algae that are busy photosynthesising light into chemical energy in this 24-hour daylight world.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/532611/original/file-20230619-29-l44kho.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Man in icy landscape holding scientific sample" src="https://images.theconversation.com/files/532611/original/file-20230619-29-l44kho.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/532611/original/file-20230619-29-l44kho.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532611/original/file-20230619-29-l44kho.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532611/original/file-20230619-29-l44kho.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532611/original/file-20230619-29-l44kho.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532611/original/file-20230619-29-l44kho.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532611/original/file-20230619-29-l44kho.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The author with a sample of ‘blood snow’, collected from a glacier surface.</span>
<span class="attribution"><span class="source">Arwyn Edwards</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Further down the glacier, the professor crushes some “dirty” ice into a bag. A different kind of algae lives here that, depending on your point-of-view, is either black, brown or purple (perhaps it depends on the tint of your sunglasses). The <a href="https://www.researchgate.net/figure/Chemical-structure-of-compound-3-purpurogallin-carboxylic-acid-6-O-b-d-glucopyranoside_fig2_51806131#:%7E:text=A%20gallotannin%20derivative%20(galloylglucopyranose%2C%20i.e.,et%20al.%2C%202012b)%20.">pigment</a> created is like the compounds that colour tea, and the algae keep it in layers like parasols above the photosynthetic factories within their cells – ensuring they have just enough sunlight to photosynthesise, but not enough to burn.</p>
<p>Open Google Earth and as you zoom in on the Arctic, you may spot the large dark stripe that scars the western margin of the <a href="https://en.wikipedia.org/wiki/Greenland_ice_sheet">Greenland ice sheet</a>. This is the “dark zone”, but it’s not caused by dark <a href="https://www.nature.com/articles/s41467-020-20627-w">dust</a> or soot. It’s alive, <a href="https://www.nature.com/articles/ismej2012107">laden with algae</a> – and it has been darkening, and growing, as Greenland warms.</p>
<p>Between 2000 and 2014, the <a href="https://www.frontiersin.org/articles/10.3389/feart.2016.00043/full">dark zone’s area grew by 14%</a>. At 279,075 km² in 2012, it was already more than twice the <a href="https://www.britannica.com/summary/England#:%7E:text=Area%3A%2050%2C301%20sq%20mi%20(130%2C278,even%20with%20the%20entire%20kingdom.).%20This%20had%20a%20powerful%20impact%20on%20the%20rate%20of%20ice%20melt%20--%20areas%20blooming%20with%20algae%20%5Bmelt%20nearly%202cm%20more%20each%20day%5D(https://www.pnas.org/doi/abs/10.1073/pnas.1918412117">size of England</a> than bare ice.</p>
<p>Next morning, I am woken by the smell of chemicals, having slept beneath a coffee table. Nozomu is busy processing his samples: bags of melting ice pinned to a clothesline by bulldog clips. They resemble bunting around the crowded room, but this is no time for celebration. The tint of each bag adds a measurement which quantifies the link between these algae, their pigments, and the death of their icy home.</p>
<h2>The case becomes urgent</h2>
<p>By the summer of 2014, glaciologists all over the world have started to listen to the warnings of pioneering ecologists such as Nozomu. The glaciers are dying even as life blossoms on their darkening surfaces. The case has become urgent.</p>
<p>I am in a helicopter, flying with colleagues to a camp in the dark zone on the Greenland ice sheet – the largest mass of glacial ice in the northern hemisphere. Covering 1.7 million km², its ice holds the equivalent of the water required to raise global sea levels by 7.7 metres.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/532620/original/file-20230619-23-shc4a3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A landscape of dark ice intertwined with blue rivers of meltwater." src="https://images.theconversation.com/files/532620/original/file-20230619-23-shc4a3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532620/original/file-20230619-23-shc4a3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532620/original/file-20230619-23-shc4a3.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532620/original/file-20230619-23-shc4a3.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532620/original/file-20230619-23-shc4a3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532620/original/file-20230619-23-shc4a3.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532620/original/file-20230619-23-shc4a3.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A highly darkened surface of the Greenland ice sheet, rich in algae and incised with rivers of meltwater.</span>
<span class="attribution"><span class="source">Arwyn Edwards</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>As we warm our climate, the rate of water flowing from this reservoir increases, with each degree Celsius added to global temperatures opening the drainage valve even wider. Feedback processes such as biological darkening have the potential to multiply the number of drainage valves that are open, hastening dramatically the rate at which sea levels rise.</p>
<p>To monitor this effect, every day <a href="https://www.gla.ac.uk/schools/ges/staff/karencameron/">Karen Cameron</a>, the leader of our camp this summer, walks to undisturbed patches of ice carrying a £100,000 backpack which contains a spectrometer to measure the darkness of the ice, capturing how it absorbs the solar energy that causes melting. The glaciologists are desperate for ground truth, and their models need data.</p>
<p>Up to this point, none of their predictions of how the Greenland ice sheet would respond to our warming climate have included biological darkening. Even if the effect were modest, it could still topple the ice sheet from a predictable, straightline response to climate warming.</p>
<p>All the time we are in Greenland, the only lifeforms we encounter are the flies that hatch from the fresh fruit and peppers in our food rations. These and the few types of glacier algae and several hundred kinds of bacteria that are biologically darkening the ice: a living scum scarring the surface of the ice sheet.</p>
<p>My work focuses on how these tiny organisms adapt to their icy habitat, but the implications of their behaviour are now of global concern. A <a href="https://screenworks.org.uk/archive/baftss-practice-research-award-2017/timeline">filmmaker</a> at the camp is weaving a thread between the ice melt in Greenland and its consequences for people living in coastal communities all over the world – from villages near my home on the <a href="https://www.theguardian.com/environment/2019/may/18/this-is-a-wake-up-call-the-villagers-who-could-be-britains-first-climate-refugees">west coast of Wales</a>, to huge metropolises like Manhattan, Amsterdam and Mumbai, and even entire low-lying island nations in the Pacific.</p>
<p>As smaller glaciers fade, and the larger ice sheets of Greenland and Antarctica start to respond with full force to our warming climate, it is these communities, capitals and countries that will bear the brunt of the flooding, inundation and erosion that comes with rising sea levels.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/532622/original/file-20230619-28-oh4l8z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two scientists inspecting an ice corer device dripping with meltwater." src="https://images.theconversation.com/files/532622/original/file-20230619-28-oh4l8z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532622/original/file-20230619-28-oh4l8z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532622/original/file-20230619-28-oh4l8z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532622/original/file-20230619-28-oh4l8z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532622/original/file-20230619-28-oh4l8z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532622/original/file-20230619-28-oh4l8z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532622/original/file-20230619-28-oh4l8z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The author (left) and Joseph Cook high on the Greenland ice sheet, meltwater dripping from their ice corer.</span>
<span class="attribution"><span class="source">Sara Penrhyn Jones</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Before heading home, our helicopter takes us on a detour, high over the ice sheet. We fly over the brown-black-purple algae to brighter, higher elevations where the palette shrinks to the blue and white of water and ice, then snow and sky. Greenland makes its own weather and, in these higher elevations, we expect the ice to be frozen all year round. When we land and begin to collect snow samples and a small ice core, however, we find we are digging into slush. The ice has started to melt up here, too. </p>
<p>We heave up our ice corer, and meltwater dribbles out from its bottom. In periods of extreme warming, much of the surface of the ice sheet can experience melting episodes, <a href="https://www.frontiersin.org/articles/10.3389/fmicb.2015.00225/full">disturbing the slumbering microbes</a> stored within the otherwise permanently frozen surface. It’s a sobering moment for us all.</p>
<p>Flying back to camp, I watch the streams become rivers and lakes as we head back over the dark zone, where melt and microbes dominate the icescape. I contemplate how much water, once locked in the ice, will become free to flow into the sea and into millions of homes by the end of the century.</p>
<h2>Popping a pingo</h2>
<p>The frozen lands of eight nations encircle the Arctic. Their soils store vast quantities of carbon: a third of the planet’s entire quantity of soil carbon resides in this frozen ground.</p>
<p>The carbon is a legacy of soils formed in past climates and preserved for millennia. However, human-induced climate change is reheating this leftover carbon, providing a luxuriant food source for microbes resident within the <a href="https://earthobservatory.nasa.gov/biome/biotundra.php">tundra</a>, which then emit it as greenhouse gases.</p>
<p>This is known as the <a href="https://en.wikipedia.org/wiki/Permafrost_carbon_cycle#:%7E:text=Carbon%20emissions%20from%20permafrost%20thaw,which%20increases%20permafrost%20thaw%20depths.">permafrost carbon</a> feedback loop. When even modest quantities of this vast carbon store reach the atmosphere, warming accelerates – resulting in faster thawing of the tundra and the release of yet more greenhouse gases.</p>
<p>Furthermore, not all greenhouse gases are equal in their impact. While carbon dioxide is relatively abundant and stable for centuries in the atmosphere, methane is less abundant and shorter-lived, but remarkably powerful as a greenhouse gas – nearly 30 times more damaging to the climate than carbon dioxide, for the same volume.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/532615/original/file-20230619-1823-ekek0j.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Scientist crouched on ice taking water samples." src="https://images.theconversation.com/files/532615/original/file-20230619-1823-ekek0j.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532615/original/file-20230619-1823-ekek0j.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=307&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532615/original/file-20230619-1823-ekek0j.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=307&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532615/original/file-20230619-1823-ekek0j.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=307&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532615/original/file-20230619-1823-ekek0j.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=386&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532615/original/file-20230619-1823-ekek0j.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=386&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532615/original/file-20230619-1823-ekek0j.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=386&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Andy Hodson sampling methane from a freshly ‘popped’ pingo.</span>
<span class="attribution"><span class="source">Arwyn Edwards</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>For more than three decades, <a href="https://www.unis.no/staff/andy-hodson/">Andy Hodson</a> has worked at the frontier where microbes, carbon and the Arctic landscape meet. In 2018, we join him on a brisk spring day in Svalbard. It’s -26°C but the snowmobile commute is thankfully brief – then we work quickly against the cold.</p>
<p>Hodson’s plan is to “pop” one of the many <a href="https://en.wikipedia.org/wiki/Pingo">pingos</a> that populate the floor of this wide open valley. Think of pingos as the acne of the Arctic: they form as permafrost compresses unfrozen wet sediments, erupting as small hills blistering the skin of the tundra.</p>
<p>The story of these microbes’ lives is complicated. They only live beyond the reach of oxygen – where oxygen is more prevalent, methane-consuming microbes thrive instead, quenching the belches of methane from below. Similarly, should mineral sources of iron or sulphide be nearby, then microbes that use them outcompete the methanogens.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/532614/original/file-20230619-15-6i78fv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A small fountain of water in an opening in the ice, amid a snowy landscape." src="https://images.theconversation.com/files/532614/original/file-20230619-15-6i78fv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/532614/original/file-20230619-15-6i78fv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532614/original/file-20230619-15-6i78fv.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532614/original/file-20230619-15-6i78fv.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532614/original/file-20230619-15-6i78fv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532614/original/file-20230619-15-6i78fv.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532614/original/file-20230619-15-6i78fv.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A popped pingo discharging supercooled water rich in methane.</span>
<span class="attribution"><span class="source">Arwyn Edwards</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>It all adds up to one of the greatest uncertainties for our civilisation: the extent and composition of greenhouse gases escaping from Arctic lands. <a href="https://www.cam.ac.uk/research/news/emissions-from-melting-permafrost-could-cost-43-trillion#:%7E:text=Increased%20greenhouse%20gas%20emissions%20from,and%20the%20University%20of%20Colorado.">Estimates of the economic impacts</a> from this permafrost carbon feedback tally in the tens of trillions of dollars to the global economy. We know it is bad news, but exactly how bad depends on the microbes in their microscopic mosaic.</p>
<p>Hodson’s field work shows that, during the Arctic winter, this pingo is probably the only source of methane in the immediate area, its chimney enabling the gas to escape from the depths of the ice before methane-consuming microbes can catch it. Annually, tens of kilograms of methane and more than a ton of carbon dioxide will escape from this pingo alone - one of <a href="https://doi.org/10.1016/j.geomorph.2023.108694">more than 10,000</a> scattered across the Arctic, in addition to its other methane-producing hotspots.</p>
<h2>A near-perfect ecosystem</h2>
<p>Arctic lands are a patchwork of permafrost carbon feedbacks, and our future depends on the uncertain fate of the microbes within. </p>
<p>While the ice melt enhances the growth of microbes in the short term, if it continues to the point of erasing habitats then the microbes will be lost with them. We recognise this danger for polar bears and walruses, but not the invisible biodiversity of the Arctic. Small does not mean insignificant though.</p>
<p>To appreciate this, we can head back to the dark zone on Greenland’s ice sheet and join <a href="https://www.rolex.org/rolex-awards/exploration/joseph-cook">Joseph Cook</a> during our summer 2014 field season. He’s lying on a mat improvised from a bath towel and a binbag wrapped in duct tape, peering into a dark, pothole-like depression in the ice. It’s a cryoconite hole, and millions of them are dotted over the edges of the ice sheet. Where pingos contribute to climate warming by emitting methane, cryoconite is a good sink of greenhouse gases, but this creates its own problems. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/532618/original/file-20230619-27-4a5amn.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Crouching scientist takes samples in the Arctic snow." src="https://images.theconversation.com/files/532618/original/file-20230619-27-4a5amn.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532618/original/file-20230619-27-4a5amn.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532618/original/file-20230619-27-4a5amn.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532618/original/file-20230619-27-4a5amn.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532618/original/file-20230619-27-4a5amn.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532618/original/file-20230619-27-4a5amn.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532618/original/file-20230619-27-4a5amn.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Joseph Cook measuring the carbon cycling activities of Greenland’s cryoconite holes.</span>
<span class="attribution"><span class="source">Arwyn Edwards</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2486.2008.01758.x">earliest estimate</a> of its ability to store carbon dioxide from the air on the ice surface of the world’s glaciers exceeded Finland’s total carbon emissions in the same year. Every cryoconite hole is a near-perfect ecosystem – with a singular flaw. Its inhabitants must melt ice to live. But the very act of melting the ice hastens the demise of their glacier habitat. </p>
<p>Despite being found in some of the harshest locations on Earth, cryoconite is home for thousands of different types of bacteria (including the all-important photosynthetic cyanobacteria), fungi, and <a href="https://microbiologysociety.org/why-microbiology-matters/what-is-microbiology/protozoa.html">protozoa</a>. Even <a href="https://www.theguardian.com/environment/2020/oct/17/tardigrade-ice-hole-arctic-greenland">tardigrades</a> thrive in cryoconite.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/532623/original/file-20230619-21-7v4otj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Microscope image of a single cryoconite granule." src="https://images.theconversation.com/files/532623/original/file-20230619-21-7v4otj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/532623/original/file-20230619-21-7v4otj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532623/original/file-20230619-21-7v4otj.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532623/original/file-20230619-21-7v4otj.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532623/original/file-20230619-21-7v4otj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532623/original/file-20230619-21-7v4otj.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532623/original/file-20230619-21-7v4otj.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Microscope image of a cryoconite granule, showing biological darkening and cyanobacteria growing through it.</span>
<span class="attribution"><span class="source">Arwyn Edwards</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Cook is professionally besotted with the perfection of this near-frozen “microscopic rainforest”. Its inhabitants are shielded and nourished at just the right depth and in the right shape for a busy ecosystem to be engineered by the interaction of sunlight with cyanobacteria, dust and ice to the benefit of all its inhabitants. The cyanobacteria use sunshine to capture carbon dioxide from the air and convert it into the slimy cement that builds each granule of cryoconite</p>
<p>However, with vast numbers of cryoconite holes dotted across the ice surface, “swarms” of these holes help <a href="https://www.frontiersin.org/articles/10.3389/feart.2015.00078/full">shape and darken the ice surface</a>. This in turn influences the melting rate, as the surface is sculpted under the sun of 24-hour daylight.</p>
<p>Writing in the scientific journal <a href="https://www.nature.com/articles/029039a0">Nature in 1883</a>, Swedish polar explorer Adolf Erik Nordenskjöld, who discovered cryoconite, thanked the organisms within cryoconite for melting away the ancient ice that once covered Norway and Sweden:</p>
<blockquote>
<p>In spite of their insignificance, [they] play a very important part in nature’s economy, from the fact that their dark colour far more readily absorbs the Sun’s heat than the bluish-white ice, and thereby they contribute to the destruction of the ice sheet, and prevent its extension. Undoubtedly we have, in no small degree, to thank these organisms for the melting away of the layer of ice which once covered the Scandinavian peninsula.</p>
</blockquote>
<h2>Taking DNA analysis to strange new places</h2>
<p>We return to Greenland in winter 2018 to explore cryoconite’s singular flaw. Cook and I are joined by Melanie Hay, then a PhD student in Arctic bioinformatics.</p>
<p>Hay and I are taking DNA analysis to strange new places to learn more about the evolution and biology of cryoconite. Powerful advances in genomics are changing our view of the microbial world, but large DNA-sequencing instruments fare best in sophisticated labs.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/532619/original/file-20230619-17-uv14gu.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Scientist sitting outside her tent with backpack, looking out at icy landscape." src="https://images.theconversation.com/files/532619/original/file-20230619-17-uv14gu.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532619/original/file-20230619-17-uv14gu.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=442&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532619/original/file-20230619-17-uv14gu.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=442&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532619/original/file-20230619-17-uv14gu.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=442&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532619/original/file-20230619-17-uv14gu.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=555&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532619/original/file-20230619-17-uv14gu.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=555&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532619/original/file-20230619-17-uv14gu.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=555&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Melanie Hay camping and sampling on the Greenland ice sheet.</span>
<span class="attribution"><span class="source">Arwyn Edwards</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Instead, we are using a stapler-sized nanopore sequencer hooked up to the USB port of a winterised laptop. Outside the tent, it is –20°C – but the DNA sequencer must run at body temperature. The only sustainable source of warmth is body heat, so I have snuggled up with the sequencer in my sleeping bag every night and in my clothes all day.</p>
<p>That evening, we are caught in a storm of hurricane force. Becoming disorientated while moving between tents would be lethal, so we crawl in a human chain through the whiteout to our sleeping tents. Hay reaches her tent but Cook’s is lost, so we squeeze into my one-person tent. Somehow I sleep soundly, while Cook is exposed to the full force of the night’s terror.</p>
<p>In the morning, we excavate Hay, whose snow-laden tent had collapsed in the night. The sequencing is complete, but storm damage to our generator means the camp is losing power, so she must work quickly. She identifies the cyanobacteria building the cryoconite – it’s a short list dominated by one species: <em>Phormidesmis priestleyi</em>.</p>
<p>This species, found in cryoconite throughout the Arctic, seems to be the ecosystem engineer of cryoconite – a microscopic beaver building a dam of dust. But the flaw is the darkness of the near-perfect cryoconite ecosystems it creates. Like the neighbouring glacier algae we met earlier, <em>Phormidesmis priestleyi</em> is biologically darkening Arctic ice, and eventually hastening the demise of the thousands of different types of organism contained in cryoconite holes.</p>
<p>And so, this work shows us ever more clearly that the <a href="https://www.nature.com/articles/s41559-020-1163-0">loss of the planet’s glaciers</a> is as much a component of the global biodiversity crisis as it is a headline impact of climate change.</p>
<h2>Last line of defence against antibiotic resistance</h2>
<p>The loss of the Arctic’s microbial biodiversity matters in other ways too. Hay and Aliyah Debbonaire are both reformed biomedical scientists seeking cures from the Arctic in the form of new antibiotics. In the summer of 2018, we are in Svalbard looking for clues.</p>
<p>The world is running out of effective antibiotics, and the Arctic’s frontiers may be our last line of defence in this antibiotic resistance crisis. Countless species of microbes have evolved to live within its harsh habitats using all the tricks in the book, including making antibiotics as chemical weapons to kill off competitors. This means they may be sources of new antibiotics.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/532631/original/file-20230619-1900-kr9gwx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Scientists (one kneeling) taking samples in the snowy Arctic landscape." src="https://images.theconversation.com/files/532631/original/file-20230619-1900-kr9gwx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532631/original/file-20230619-1900-kr9gwx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=413&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532631/original/file-20230619-1900-kr9gwx.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=413&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532631/original/file-20230619-1900-kr9gwx.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=413&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532631/original/file-20230619-1900-kr9gwx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=519&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532631/original/file-20230619-1900-kr9gwx.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=519&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532631/original/file-20230619-1900-kr9gwx.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=519&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Aliyah Debbonaire (left) and Melanie Hay sampling a cryoconite hole.</span>
<span class="attribution"><span class="source">Arwyn Edwards</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>And this is not their only application. From cheeses to eco-friendly biological washing powders, entire shopping aisles of products have been derived from cold-adapted microbes. As climate warming threatens to disrupt entire Arctic habitats, our opportunity to use, learn from, and protect this biodiversity may be lost forever.</p>
<p>As our tiny plane returns to the nearest town, Longyearbyen, we fly low over the <a href="https://theconversation.com/after-svalbard-why-safety-of-world-seed-vaults-is-crucial-to-future-food-security-79586">Svalbard Global Seed Vault</a>, which contains the fruits of more than 12,000 years of agriculture in the form of seeds from a million different varieties of crop. Nearby, a similar facility inside a disused coal mine stores essential computer programmes on microfilm – the ultimate backup for our data-addicted world.</p>
<p>Within a snowy kilometre, you can walk between the the alpha and omega of human innovation in civilisation. Both facilities have chosen the fastest-warming town on the planet as the safest place to store these treasures of humanity. Yet no such facility is dedicated to the microbial biodiversity of the Arctic, despite its critical importance to the future of the world’s biotech and medical sectors.</p>
<p>Instead, it falls to microbiologists such as Debbonaire, racing against time to identify, nurture and screen the microbes of the melting Arctic. Her painstaking work accumulates towers of Petri dishes, each a temporary refuge for a different Arctic microbe.</p>
<p>Eventually, they will be stored in <a href="https://www.dellamarca.it/en/how-does-an-ultra-low-freezer-work/">ultra-freezers</a> in laboratories scattered across the world. Such work is unglamorous to funders, so it is done piecemeal on the edges of other projects. Yet it represents our only attempt to save the microbes of the Arctic.</p>
<h2>The battle is lost</h2>
<p>Most of all, the Arctic matters because it is the fastest-warming part of the planet, and its microbes are responding first. What happens there carries implications for everyone. It is the harbinger of change for everywhere.</p>
<p>Another Arctic microbiologist could strike plangent notes regarding permafrost or sea ice, but as an ecologist of glaciers I am drawn to glacial ice.</p>
<p>Over the first fifth of this century, Earth’s glaciers have discharged some ten quadrillion (ten to the power 25) tablespoons of melt a year – and within each tablespoon, the <a href="https://www.nature.com/articles/s43247-022-00609-0">tens of thousands of bacteria and viruses</a> that were once stored within that ice.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/meltwater-is-infiltrating-greenlands-ice-sheet-through-millions-of-hairline-cracks-destabilizing-its-structure-207468">Meltwater is infiltrating Greenland’s ice sheet through millions of hairline cracks – destabilizing its structure</a>
</strong>
</em>
</p>
<hr>
<p>What’s to come is sadly predictable. Even the most modest warming scenario of 1.5°C above the pre-industrial era will lead to the extinction of at least <a href="https://www.science.org/doi/10.1126/science.abo1324">half the Earth’s 200,000 glaciers</a> by the end of the century.</p>
<p>Depending on the urgency and effectiveness of our actions as a civilisation, this century could also represent the “peak melt” in our history. Yet the battle to save many of these precious icy habitats is already lost. Instead, for scientists like me, our field work is now largely a question of documenting these “crime scenes” – so at least the knowledge of life within ice can be preserved, before it melts away forever.</p>
<hr>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/313478/original/file-20200204-41481-1n8vco4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/313478/original/file-20200204-41481-1n8vco4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=112&fit=crop&dpr=1 600w, https://images.theconversation.com/files/313478/original/file-20200204-41481-1n8vco4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=112&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/313478/original/file-20200204-41481-1n8vco4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=112&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/313478/original/file-20200204-41481-1n8vco4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=140&fit=crop&dpr=1 754w, https://images.theconversation.com/files/313478/original/file-20200204-41481-1n8vco4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=140&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/313478/original/file-20200204-41481-1n8vco4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=140&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em>For you: more from our <a href="https://theconversation.com/uk/topics/insights-series-71218?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=InsightsUK">Insights series</a>:</em></p>
<ul>
<li><p><em><a href="https://theconversation.com/prehistoric-communities-off-the-coast-of-britain-embraced-rising-seas-what-this-means-for-todays-island-nations-147879?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=InsightsUK">Prehistoric communities off the coast of Britain embraced rising seas – what this means for today’s island nations
</a></em></p></li>
<li><p><em><a href="https://theconversation.com/too-afraid-to-have-kids-how-birthstrike-for-climate-lost-control-of-its-political-message-181198?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=InsightsUK">‘Too afraid to have kids’ – how BirthStrike for Climate lost control of its political message
</a></em></p></li>
<li><p><em><a href="https://theconversation.com/climate-scientists-concept-of-net-zero-is-a-dangerous-trap-157368?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=InsightsUK">Climate scientists: concept of net zero is a dangerous trap
</a></em></p></li>
<li><p><em><a href="https://theconversation.com/noise-in-the-brain-enables-us-to-make-extraordinary-leaps-of-imagination-it-could-transform-the-power-of-computers-too-192367?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=InsightsUK">Noise in the brain enables us to make extraordinary leaps of imagination. It could transform the power of computers too
</a></em></p></li>
<li><p><em><a href="https://theconversation.com/beyond-gdp-changing-how-we-measure-progress-is-key-to-tackling-a-world-in-crisis-three-leading-experts-186488?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=InsightsUK">Beyond GDP: changing how we measure progress is key to tackling a world in crisis – three leading experts
</a></em></p></li>
</ul>
<p><em>To hear about new Insights articles, join the hundreds of thousands of people who value The Conversation’s evidence-based news. <a href="https://theconversation.com/uk/newsletters/the-daily-newsletter-2?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=InsightsUK"><strong>Subscribe to our newsletter</strong></a>.</em></p><img src="https://counter.theconversation.com/content/207785/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Arwyn Edwards receives funding from UK Research & Innovation - Natural Environment Research Council, as well as the Research Council of Norway, the Leverhulme Trust, and the Royal Geographical Society. </span></em></p>To fully understand the extent of climate-related dangers the Arctic – and our planet – is facing, we must focus on organisms too small to be seen with the naked eye.Arwyn Edwards, Reader in Biology, Department of Life Sciences, Aberystwyth UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2032772023-04-06T11:24:18Z2023-04-06T11:24:18ZNew research shows how rapidly ice sheets can retreat – and what it could mean for Antarctic melting<figure><img src="https://images.theconversation.com/files/519798/original/file-20230406-20-zctnfl.jpg?ixlib=rb-1.1.0&rect=38%2C6%2C4272%2C2833&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A glacier in Paradise Bay, Antarctica.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/glacier-paradise-bay-antarctica-2227007003">jet 67/Shutterstock</a></span></figcaption></figure><p>The <a href="https://www.bas.ac.uk/about/antarctica/geography/ice/">Antarctic Ice Sheet</a>, which covers an area greater than the US and Mexico combined, holds enough water to raise global sea level by <a href="https://www.nature.com/articles/s41561-019-0510-8">more than 57 metres if melted completely</a>. This would flood hundreds of cities worldwide. And evidence suggests it is melting fast. Satellite observations have revealed that grounded ice (ice that is in contact with the bed beneath it) in coastal areas of West Antarctica has been lost at a rate of <a href="https://www.nature.com/articles/s41561-021-00877-z">up to 30 metres per day</a> in recent years. </p>
<p>But the satellite record of ice sheet change is relatively short as there are only 50 years’ worth of observations. This limits our understanding of how ice sheets have evolved over longer periods of time, including the maximum speed at which they can retreat and the parts that are most vulnerable to melting. </p>
<p>So, we set out to investigate how ice sheets responded during a previous period of climatic warming – the last “deglaciation”. This climate shift occurred between roughly 20,000 and 11,000 years ago and spanned Earth’s transition from a glacial period, when ice sheets covered large parts of Europe and North America, to the period in which we currently live (called the <a href="https://www.ncei.noaa.gov/sites/default/files/2021-11/12%20Mid-Holocene%20Warm%20Period%20%26%20Penultimate%20Interglacial%20Period%20%26%20Early%20Eocene%20Period%20-FINAL%20OCT%202021.pdf">Holocene interglacial period</a>). </p>
<p>During the last deglaciation, rates of temperature and sea-level rise were broadly comparable to today. So, studying the changes to ice sheets in this period has allowed us to estimate how Earth’s two remaining ice sheets (Greenland and Antarctica) might respond to an even warmer climate in the future.</p>
<p>Our <a href="https://www.nature.com/articles/s41586-023-05876-1">recently published results</a> show that ice sheets are capable of retreating in bursts of up to 600 metres per day. This is much faster than has been observed so far from space.</p>
<figure class="align-center ">
<img alt="A satellite image showing blocks of ice floating in the ocean." src="https://images.theconversation.com/files/519800/original/file-20230406-26-vgkg3h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519800/original/file-20230406-26-vgkg3h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519800/original/file-20230406-26-vgkg3h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519800/original/file-20230406-26-vgkg3h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519800/original/file-20230406-26-vgkg3h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519800/original/file-20230406-26-vgkg3h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519800/original/file-20230406-26-vgkg3h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Satellite imagery reveals that Earth’s ice sheets are retreating fast.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/glacier-greenland-blocks-ice-floating-ocean-1750617149">Trismegist san/Shutterstock</a></span>
</figcaption>
</figure>
<h2>Pulses of rapid retreat</h2>
<p>Our research used <a href="https://mareano.no/en">high-resolution maps</a> of the Norwegian seafloor to identify small landforms called “corrugation ridges”. These 1–2 metre high ridges were produced when a former ice sheet retreated during the last deglaciation. </p>
<p>Tides lifted the ice sheet <a href="https://www.science.org/doi/10.1126/science.aaz3059">up and down</a>. At low tide, the ice sheet rested on the seafloor, which pushed the sediment at the edge of the ice sheet upwards into ridges. Given that there are two low tides each day off Norway, two separate ridges were produced daily. Measuring the space between these ridges enabled us to calculate the pace of the ice sheet’s retreat. </p>
<p>During the last deglaciation, the <a href="https://www.britannica.com/place/Scandinavian-Ice-Sheet">Scandinavian Ice Sheet</a> that we studied underwent pulses of extremely rapid retreat – at rates between 50 and 600 metres per day. These rates are up to 20 times faster than the highest rate of ice sheet retreat that has so far been measured in Antarctica from satellites. </p>
<p>The highest rates of ice sheet retreat occurred across the flattest areas of the ice sheet’s bed. In flat-bedded areas, only a relatively small amount of melting, of around half a metre per day, is required to instigate a pulse of rapid retreat. Ice sheets in these regions are very lightly attached to their beds and therefore require only minimal amounts of melting to become fully buoyant, which can result in almost instantaneous retreat.</p>
<p>However, rapid “buoyancy-driven” retreat such as this is probably only sustained over short periods of time – from days to months – before a change in the ice sheet bed or ice surface slope farther inland puts the brakes on retreat. This demonstrates how nonlinear, or “pulsed”, the nature of ice sheet retreat was in the past. </p>
<p>This will likely also be the case in the future.</p>
<h2>A warning from the past</h2>
<p>Our findings reveal how quickly ice sheets are capable of retreating during periods of climate warming. We suggest that pulses of very rapid retreat, from tens to hundreds of metres per day, could take place across flat-bedded parts of the Antarctic Ice Sheet even under <a href="https://tc.copernicus.org/articles/13/2633/2019/">current rates of melting</a>. </p>
<p>This has implications for the vast and potentially unstable <a href="https://thwaitesglacier.org/about/facts">Thwaites Glacier</a> of West Antarctica. Since scientists began observing ice sheet changes via satellites, Thwaites Glacier has experienced <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014GL060140">considerable retreat</a> and is now only 4km away from a flat area of its bed. Thwaites Glacier could therefore suffer pulses of rapid retreat in the near future.</p>
<p>Ice losses resulting from retreat across this flat region could accelerate the rate at which ice in the rest of the Thwaites drainage basin collapses into the ocean. The Thwaites drainage basin contains enough ice to <a href="https://thwaitesglacier.org/about/facts">raise global sea levels by approximately 65cm</a>.</p>
<figure class="align-center ">
<img alt="The Fimbul Ice Shelf in East Antarctica." src="https://images.theconversation.com/files/519513/original/file-20230405-26-wcune3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519513/original/file-20230405-26-wcune3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519513/original/file-20230405-26-wcune3.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519513/original/file-20230405-26-wcune3.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519513/original/file-20230405-26-wcune3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519513/original/file-20230405-26-wcune3.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519513/original/file-20230405-26-wcune3.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Fimbul Ice Shelf in East Antarctica.</span>
<span class="attribution"><span class="source">Christine Batchelor</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Our results shed new light on how ice sheets interact with their beds over different timescales. <a href="https://www.sciencedirect.com/science/article/pii/S092181811630491X">High rates of retreat</a> can occur over decades to centuries where the bed of an ice sheet deepens inland. But we found that ice sheets on flat regions are most vulnerable to extremely rapid retreat over much shorter timescales. </p>
<p>Together with data about the shape of ice sheet beds, incorporating this short-term mechanism of retreat into computer simulations will be critical for accurately predicting rates of ice sheet change and sea-level rise in the future.</p><img src="https://counter.theconversation.com/content/203277/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Frazer Christie receives funding from the Prince Albert II of Monaco Foundation. </span></em></p><p class="fine-print"><em><span>Christine Batchelor does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Seafloor landforms reveal that ice sheets can collapse at 600 metres per day.Christine Batchelor, Lecturer in Physical Geography, Newcastle UniversityFrazer Christie, Postdoctoral Research Associate, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1962542022-12-13T16:01:45Z2022-12-13T16:01:45ZArctic Report Card 2022: The Arctic is getting rainier and seasons are shifting, with broad disturbances for people, ecosystems and wildlife<figure><img src="https://images.theconversation.com/files/500768/original/file-20221213-10619-mim3qd.jpg?ixlib=rb-1.1.0&rect=24%2C8%2C5439%2C3628&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Rainier winters make life more difficult for Arctic wildlife and the humans who rely on them.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/reindeer-herd-in-mid-winter-norwegian-arctic-january-27th-news-photo/608180463">Scott Wallace/Getty Image</a></span></figcaption></figure><p>In the Arctic, the freedom to travel, hunt and make day-to-day decisions is profoundly tied to cold and frozen conditions for much of the year. These conditions are rapidly changing as the Arctic warms.</p>
<p>The Arctic is now seeing more rainfall when historically it would be snowing. Sea ice that once protected coastlines from erosion during fall storms is forming later. And thinner river and lake ice is making travel by snowmobile increasingly life-threatening. </p>
<p>Ship traffic in the Arctic is also increasing, bringing new risks to fragile ecosystems, and the Greenland ice sheet is continuing to send freshwater and ice into the ocean, raising global sea level</p>
<p>In the annual <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022">Arctic Report Card</a>, released Dec. 13, 2022, we brought together 144 other Arctic scientists from 11 countries to examine the current state of the Arctic system.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Some of the Arctic headlines of 2022 discussed in the Arctic Report Card.</span>
<span class="attribution"><span class="source">NOAA Climate.gov</span></span>
</figcaption>
</figure>
<h2>The Arctic is getting wetter and rainier</h2>
<p>We found that <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/993/Precipitation">Arctic precipitation is on the rise across all seasons</a>, and these seasons are shifting. </p>
<p>Much of this new precipitation is now falling as rain, sometimes during winter and traditionally frozen times of the year. This disrupts daily life for humans, wildlife and plants. </p>
<p>Roads become dangerously icy more often, and communities face greater risk of river flooding events. For Indigenous reindeer herding communities, winter rain can create an impenetrable ice layer that prevents their reindeer from accessing vegetation beneath the snow. </p>
<figure class="align-center ">
<img alt="Map shows significant increases in precipitation across the Arctic in both winter and fall." src="https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=830&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=830&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=830&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1043&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1043&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1043&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="https://www.arctic.noaa.gov/Report-Card">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>Arctic-wide, this shift toward wetter conditions can disrupt the lives of animals and plants that have evolved for dry and cold conditions, potentially altering Arctic peoples’ local foods.</p>
<p>When Fairbanks, Alaska, got 1.4 inches of freezing rain in December 2021, the moisture created an ice layer that persisted for months, bringing down trees and disrupting travel, infrastructure and the ability of some Arctic animals to forage for food. The resulting ice layer was largely <a href="https://www.ktoo.org/2022/12/06/one-third-delta-junction-bison-starve/">responsible for the deaths of a third of a bison herd</a> in interior Alaska.</p>
<p>There are multiple reasons for this increase in Arctic precipitation.</p>
<p>As sea ice rapidly declines, more open water is exposed, which feeds increased moisture into the atmosphere. The entire Arctic region has seen a more than <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/989/Sea-Ice">40% loss in summer sea ice extent</a> over the 44-year satellite record.</p>
<p>The Arctic atmosphere is also warming <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/992/Surface-Air-Temperature">more than twice as fast as the rest of the globe</a>, and this warmer air can hold more moisture. </p>
<figure class="align-center ">
<img alt="Map and time series chart show the continuing decline of the maximum extent of Arctic sea ice." src="https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=983&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=983&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=983&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1235&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1235&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1235&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="https://www.arctic.noaa.gov/Report-Card">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>Under the ground, the wetter, rainier Arctic is accelerating the <a href="https://theconversation.com/thawing-permafrost-is-roiling-the-arctic-landscape-driven-by-a-hidden-world-of-changes-beneath-the-surface-as-the-climate-warms-174157">thaw of permafrost</a>, upon which most Arctic communities and infrastructure are built. The result is crumbling buildings, sagging and cracked roads, the emergence of sinkholes and the collapse of community coastlines along rivers and ocean. </p>
<p>Wetter weather also disrupts the building of a reliable winter snowpack and safe, reliable river ice, and often challenges Indigenous communities’ efforts to <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2019/ArtMID/7916/ArticleID/850/Voices-from-the-Front-Lines-of-a-Changing-Bering-Sea">harvest and secure their food</a>.</p>
<p>When <a href="https://theconversation.com/typhoon-merbok-fueled-by-unusually-warm-pacific-ocean-pounded-alaskas-vulnerable-coastal-communities-at-a-critical-time-190898">Typhoon Merbok</a> hit in September 2022, fueled by unusually warm Pacific water, its hurricane-force winds, 50-foot waves and far-reaching storm surge damaged homes and infrastructure over 1,000 miles of Bering Sea coastline, and disrupted hunting and harvesting at a crucial time.</p>
<figure class="align-center ">
<img alt="Globe and time series chart show temperatures rising faster across the Arctic than in the rest of the world." src="https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=774&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=774&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=774&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=972&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=972&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=972&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="https://www.arctic.noaa.gov/Report-Card">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<h2>Arctic snow season is shrinking</h2>
<p>Snow plays critical roles in the Arctic, and the snow season is shrinking.</p>
<p>Snow helps to keep the Arctic cool by reflecting incoming solar radiation back to space, rather than allowing it to be absorbed by the darker snow-free ground. Its presence helps <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/1002/Lake-Ice">lake ice last longer into spring</a> and helps the land to retain moisture longer into summer, preventing overly dry conditions that are ripe for <a href="https://uaf-iarc.org/2022/12/a-future-of-more-wildfires-in-alaska/">devastating wildfires</a>.</p>
<p>Snow is also a travel platform for hunters and a habitat for many animals that rely on it for nesting and protection from predators.</p>
<p>A <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/991/Terrestrial-Snow-Cover">shrinking snow season</a> is disrupting these critical functions. For example, the June snow cover extent across the Arctic is declining at a rate of nearly 20% per decade, marking a dramatic shift in how the snow season is defined and experienced across the North. </p>
<p>Even in the depth of winter, warmer temperatures are breaking through. The far northern Alaska town of Utqiaġvik hit 40 degrees Fahrenheit (4.4 C) – <a href="https://www.washingtonpost.com/weather/2022/12/06/alaska-winter-temperature-record-utqiagvik/">8 F above freezing</a> – on Dec. 5, 2022, even though the sun does not breach the horizon from mid-November through mid-January.</p>
<figure class="align-center ">
<img alt="Map and time series chart show how June snowfall has decreased since the late 1970s." src="https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=863&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=863&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=863&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1085&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1085&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1085&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="https://www.arctic.noaa.gov/Report-Card">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>Fatal falls through thin sea, lake and river ice are <a href="https://doi.org/10.1093/pubmed/fdt081">on the rise</a> across Alaska, resulting in immediate tragedies as well as adding to the <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/1001/Consequences-of-Rapid-Environmental-Arctic-Change-for-People">cumulative human cost of climate change</a> that Arctic Indigenous peoples are now experiencing on a generational scale.</p>
<h2>Greenland ice melt means global problems</h2>
<p>The impacts of Arctic warming are not limited to the Arctic. In 2022, the <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/990/Greenland-Ice-Sheet">Greenland ice sheet lost ice for the 25th consecutive year</a>. This adds to rising seas, which escalates the danger coastal communities around the world must plan for to mitigate flooding and storm surge.</p>
<p>In early September 2022, the Greenland ice sheet experienced an <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/990/Greenland-Ice-Sheet">unprecedented late-season melt event across 36% of the ice sheet surface</a>. This was followed by another, even later melt event that same month, caused by the remnants of Hurricane Fiona moving up along eastern North America.</p>
<p>International <a href="https://omg.jpl.nasa.gov/portal/">teams of scientists</a> are dedicated to assessing the scale to which the Greenland ice sheet’s ice formation and ice loss are out of balance. They are also increasingly learning about the transformative role that warming ocean waters play.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NOAA Climate.gov</span></span>
</figcaption>
</figure>
<p>This year’s Arctic Report Card includes <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/1007/Lessons-From-Oceans-Melting-Greenland-a-NASA-Airborne-Mission">findings from the NASA Oceans Melting Greenland (OMG) mission</a> that has confirmed that warming ocean temperatures are increasing ice loss at the edges of the ice sheet.</p>
<h2>Human-caused change is reshaping the Arctic</h2>
<p>We are living in a new geological age — <a href="https://nap.nationalacademies.org/catalog/18726/the-arctic-in-the-anthropocene-emerging-research-questions">the Anthropocene</a> — in which human activity is the dominant influence on our climate and environments.</p>
<p>In the warming Arctic, this requires decision-makers to better anticipate the interplay between a changing climate and human activity. For example, satellite-based ship data since 2009 clearly show that <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/1004/Satellite-Record-of-Pan-Arctic-Maritime-Ship-Traffic">maritime ship traffic</a> has increased within all Arctic high seas and national exclusive economic zones as the region has warmed.</p>
<figure class="align-center ">
<img alt="Map shows increase in ship traffic in Arctic regions since 2009, with a nearly 50% increase in shipping around Norway and over 12% increase near Russia. Paired with a photo of a ship in sea ice." src="https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=805&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=805&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=805&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1012&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1012&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1012&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="https://www.arctic.noaa.gov/Report-Card">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>For these ecologically sensitive waters, this added ship traffic raises urgent concerns ranging from the future of Arctic trade routes to the introduction of even more human-caused stresses on Arctic peoples, ecosystems and the climate. These concerns are especially pronounced given uncertainties regarding the current geopolitical tensions between Russia and the other Arctic states over its war in Ukraine.</p>
<p>Rapid Arctic warming requires new forms of partnership and information sharing, including <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/1001/Consequences-of-Rapid-Environmental-Arctic-Change-for-People">between scientists and Indigenous knowledge-holders</a>. Cooperation and building resilience can help to reduce some risks, but global action to rein in greenhouse gas pollution is essential for the entire planet.</p><img src="https://counter.theconversation.com/content/196254/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Druckenmiller receives research funding from the National Science Foundation (NSF) and the National Oceanic and Atmospheric Administration (NOAA). </span></em></p><p class="fine-print"><em><span>Rick Thoman receives funding from NOAA/Arctic Program</span></em></p><p class="fine-print"><em><span>Twila Moon receives research funding from the National Science Foundation (NSF) and the National Oceanic and Atmospheric Administration (NOAA).</span></em></p>The annual report is also a reminder that what happens in the Arctic affects the rest of the world.Matthew L. Druckenmiller, Research Scientist, National Snow and Ice Data Center (NSIDC), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado BoulderRick Thoman, Alaska Climate Specialist, University of Alaska FairbanksTwila A. Moon, Deputy Lead Scientist, National Snow and Ice Data Center (NSIDC), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1910432022-10-06T16:30:02Z2022-10-06T16:30:02ZClimate tipping points could lock in unstoppable changes to the planet – how close are they?<figure><img src="https://images.theconversation.com/files/488489/original/file-20221006-18-h17m5t.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5850%2C2995&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Tipping points in the climate become more likely beyond 1.5°C of warming.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/world-danger-due-economic-environmental-issues-1311948422">Desdemona72/Shutterstock</a></span></figcaption></figure><p>Continued greenhouse gas emissions risk triggering climate tipping points. These are self-sustaining shifts in the climate system that would lock-in devastating changes, like sea-level rise, even if all emissions ended.</p>
<p>The first major assessment in <a href="https://www.pnas.org/doi/10.1073/pnas.0705414105">2008</a> identified nine parts of the climate system that are sensitive to tipping, including ice sheets, ocean currents and major forests. Since then, huge advances in climate modelling and a flood of new observations and records of ancient climate change have given scientists a far better picture of these tipping elements. Extra ones have also been proposed, like permafrost around the Arctic (permanently frozen ground that could unleash more carbon if thawed). </p>
<p>Estimates of the warming levels at which these elements could tip have fallen since 2008. The collapse of the west Antarctic ice sheet was once thought to be a risk when warming reached 3°C-5°C above Earth’s pre-industrial average temperature. Now it’s thought to be <a href="https://www.nature.com/articles/d41586-019-03595-0">possible at current warming levels</a>. </p>
<p>In our <a href="https://www.science.org/doi/10.1126/science.abn7950">new assessment</a> of the past 15 years of research, myself and colleagues found that we can’t rule out five tipping points being triggered right now when global warming stands at roughly 1.2°C. Four of these five become more likely as global warming exceeds 1.5°C.</p>
<p>These are sobering conclusions. Not all of <a href="https://science.altmetric.com/details/135681778/news">the news coverage</a> captured the nuance of our study, though. So here’s what our findings actually mean.</p>
<h2>Uncertain thresholds</h2>
<p>We synthesised the results of more than 200 studies to estimate warming thresholds for each tipping element. The best estimate was either one that multiple studies converged on or which a study judged to be particularly reliable reported. For example, records of when ice sheets had retreated in the past and modelling studies indicate the Greenland ice sheet is likely to collapse beyond 1.5°C. We also estimated the minimum and maximum thresholds at which collapse is possible: model estimates for Greenland range between 0.8°C and 3.0°C.</p>
<figure class="align-center ">
<img alt="A vast wall of blue and white ice with ocean in the foreground." src="https://images.theconversation.com/files/488490/original/file-20221006-14-28qmnr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/488490/original/file-20221006-14-28qmnr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/488490/original/file-20221006-14-28qmnr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/488490/original/file-20221006-14-28qmnr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/488490/original/file-20221006-14-28qmnr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/488490/original/file-20221006-14-28qmnr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/488490/original/file-20221006-14-28qmnr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Greenland’s ice sheet is showing signs of destabilising at current warming levels.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/diagonal-blue-ice-line-showing-high-793662826">David Dennis/Shutterstock</a></span>
</figcaption>
</figure>
<p>Within this range, tipping becomes more likely as warming increases. We defined tipping as possible (but not yet likely) when warming is above the minimum but below the best estimate, and likely above the best estimate. We also judged how confident we are with each estimate. For example, we are more confident in our estimates for Greenland’s ice sheet collapse than those for abrupt permafrost thaw.</p>
<p>This uncertainty means that we do not expect four climate tipping points to be triggered the first year global temperatures reach 1.5°C (which climate scientists suggest is possible in the next <a href="https://www.metoffice.gov.uk/about-us/press-office/news/weather-and-climate/2022/decadal-forecast-2022">five years</a>), or even when temperatures averaged over several years reach 1.5°C sometime in the next <a href="https://www.carbonbrief.org/analysis-when-might-the-world-exceed-1-5c-and-2c-of-global-warming/">couple of decades</a>. Instead, every fraction of a degree makes tipping more likely, but we can’t be sure exactly when tipping becomes inevitable. </p>
<p>This is especially true for the Greenland and west Antarctic ice sheets. While our assessment suggests their collapse becomes likely beyond 1.5°C, ice sheets are so massive that they change very slowly. Collapse would take thousands of years, and the processes driving it require warming to remain beyond the threshold for several decades. If warming returned below the threshold before tipping kicked in, it may be possible for ice sheets to <a href="https://www.sciencealert.com/disastrous-climate-tipping-points-could-be-reversed-if-we-act-fast">temporarily overshoot their thresholds</a> without collapsing.</p>
<p>For some other tipping points, change is likely to be more dispersed. We estimate that both tropical coral reef death and abrupt permafrost thaw are possible at the current warming level. But thresholds vary between reefs and patches of permafrost. Both are <a href="https://www.nature.com/articles/d41586-019-01313-4">already</a> <a href="https://www.theguardian.com/environment/2022/mar/18/dead-coral-found-at-great-barrier-reef-as-widespread-bleaching-event-unfolds">happening</a> in some places, but in our assessment, these changes become much more widespread at a similar time beyond 1.5°C.</p>
<p>Elsewhere, small patches of the Amazon and northern forests might tip and transition to a savannah-like state <a href="https://www.uu.nl/en/news/climate-change-tipping-points-back-to-the-drawing-table">first</a>, bypassing a more catastrophic dieback across the whole forest. Model <a href="https://egusphere.copernicus.org/preprints/2022/egusphere-2022-82/">results</a> that are yet to be published suggest that <a href="https://climatetippingpoints.info/2021/07/18/amazon-dieback-explainer/">Amazon tipping</a> might occur in several regions at varying warming levels rather than as one big event. </p>
<figure class="align-center ">
<img alt="An aerial view of burning Amazon rainforest surrounded by bare fields." src="https://images.theconversation.com/files/488493/original/file-20221006-19-9tfqka.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/488493/original/file-20221006-19-9tfqka.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=302&fit=crop&dpr=1 600w, https://images.theconversation.com/files/488493/original/file-20221006-19-9tfqka.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=302&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/488493/original/file-20221006-19-9tfqka.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=302&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/488493/original/file-20221006-19-9tfqka.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=379&fit=crop&dpr=1 754w, https://images.theconversation.com/files/488493/original/file-20221006-19-9tfqka.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=379&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/488493/original/file-20221006-19-9tfqka.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=379&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Amazon may not collapse from forest to grassland all at once.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/illegal-fire-burn-forest-trees-amazon-1924644518">Paralaxis/Shutterstock</a></span>
</figcaption>
</figure>
<p>There may also be no well-defined threshold for some tipping elements. Ancient climate records suggest ocean currents in the North Atlantic can dramatically flip from being strong, as they are now, to weak as a result of both warming and melting freshwater from Greenland disrupting circulation. <a href="https://www.sciencealert.com/a-major-ocean-current-might-be-on-the-verge-of-a-climate-change-tipping-point">Recent modelling</a> suggests that the threshold for the collapse of Atlantic circulation depends on how fast warming increases alongside other hard-to-measure factors, making it highly uncertain.</p>
<h2>Into the danger zone</h2>
<p>There are signs that some tipping points are already approaching. Degradation and drought have caused parts of the Amazon to become <a href="https://phys.org/news/2022-03-amazon-rainforest-loss-dieback.html">less resilient</a> to disturbances like fire and <a href="https://www.nature.com/articles/d41586-021-01871-6">emit more carbon</a> than they absorb. </p>
<p>The front edge of some retreating west Antarctic glaciers are <a href="https://blogs.agu.org/geospace/2019/12/04/new-study-models-impact-of-calving-on-retreat-of-thwaites-glacier/">only kilometres away</a> from the unstoppable retreat. Early warning signals in climate monitoring data (such as bigger and longer swings in how much glaciers melt each year) suggest that parts of the <a href="https://physics.aps.org/articles/v14/80">Greenland ice sheet</a> and <a href="https://www.theguardian.com/environment/2021/aug/05/climate-crisis-scientists-spot-warning-signs-of-gulf-stream-collapse">Atlantic circulation</a> are also destabilising.</p>
<p>These signals can’t tell us exactly how close we are to tipping points, only that destabilisation is underway and a tipping point may be approaching. The most we can be sure of is that every fraction of further warming will destabilise these tipping elements more and make the initiation of self-sustaining changes more likely.</p>
<p>This strengthens the case for ambitious emissions cuts in line with the Paris agreement’s aim of halting warming at 1.5°C. This would reduce the chances of triggering multiple climate tipping points – even if we can’t rule out some being reached soon.</p>
<hr>
<figure class="align-right ">
<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
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<p class="fine-print"><em><span>David Armstrong McKay is a GSI Visiting Fellow at the University of Exeter and an Associated Researcher at Stockholm Resilience Centre, and is working as a freelance research consultant and science communicator on climate tipping points with the Earth Commission (hosted by non-profit research network Future Earth and is the science component of the Global Commons Alliance, a sponsored project of Rockefeller Philanthropy Advisors, with support from Oak Foundation, MAVA, Porticus, Gordon and Betty Moore Foundation, Herlin Foundation, and the Global Environment Facility) which partially funded this study. His contribution to this study was also funded by the Earth Resilience in the Anthropocene project (European Research Council grant ERC-2016-ADG-743080) and the Leverhulme Trust (RPG-2018-046).</span></em></p>A recent paper suggested damaging climate tipping points could be closer than first thought.David Armstrong McKay, Researcher in Earth System Resilience, Stockholm UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1855902022-08-29T18:04:43Z2022-08-29T18:04:43ZWhat’s going on with the Greenland ice sheet? It’s losing ice faster than forecast and now irreversibly committed to at least 10 inches of sea level rise<figure><img src="https://images.theconversation.com/files/481620/original/file-20220829-8728-38vmqp.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1415%2C488&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A turbulent melt-river pours a million tons of water a day into a moulin, where it flows down through the ice to ultimately reach the ocean.</span> <span class="attribution"><span class="source">Ted Giffords</span></span></figcaption></figure><p>I’m standing at the edge of the Greenland ice sheet, mesmerized by a mind-blowing scene of natural destruction. A milewide section of glacier front has fractured and is collapsing into the ocean, calving an immense iceberg.</p>
<p>Seracs, giant columns of ice the height of three-story houses, are being tossed around like dice. And the previously submerged portion of this immense block of glacier ice just breached the ocean – a frothing maelstrom flinging ice cubes of several tons high into the air. The resulting tsunami inundates all in its path as it radiates from the glacier’s calving front.</p>
<p>Fortunately, I’m watching from a clifftop a couple of miles away. But even here, I can feel the <a href="https://doi.org/10.1029/2008GL036127">seismic shocks through the ground</a>.</p>
<figure class="align-center ">
<img alt="A large iceberg calves off a glacier." src="https://images.theconversation.com/files/481628/original/file-20220829-8654-38vmqp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/481628/original/file-20220829-8654-38vmqp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=344&fit=crop&dpr=1 600w, https://images.theconversation.com/files/481628/original/file-20220829-8654-38vmqp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=344&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/481628/original/file-20220829-8654-38vmqp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=344&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/481628/original/file-20220829-8654-38vmqp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=433&fit=crop&dpr=1 754w, https://images.theconversation.com/files/481628/original/file-20220829-8654-38vmqp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=433&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/481628/original/file-20220829-8654-38vmqp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=433&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A fast-flowing outlet glacier calves a ‘megaberg’ into Greenland’s Uummannaq Fjord.</span>
<span class="attribution"><span class="source">Alun Hubbard</span></span>
</figcaption>
</figure>
<p>Despite the spectacle, I’m keenly aware that this spells yet more unwelcome news for the world’s low-lying coastlines.</p>
<p>As <a href="https://cage.uit.no/employee/alun-hubbard/">a field glaciologist</a>, I’ve worked on ice sheets for more than 30 years. In that time, I have witnessed some gobsmacking changes. The past few years in particular have been unnerving for the sheer rate and magnitude of change underway. My revered textbooks taught me that ice sheets respond over millennial time scales, but that’s not what we’re seeing today.</p>
<p><a href="https://doi.org/10.1038/s41558-022-01441-2">A study published</a> Aug. 29, 2022, demonstrates – for the first time – that Greenland’s ice sheet is now so out of balance with prevailing Arctic climate that it no longer can sustain its current size. It is irreversibly committed to retreat by at least 59,000 square kilometers (22,780 square miles), an area considerably larger than Denmark, Greenland’s protectorate state.</p>
<p>Even if all the greenhouse gas emissions driving global warming ceased today, we find that Greenland’s ice loss under current temperatures will <a href="https://doi.org/10.1038/s41558-022-01441-2">raise global sea level</a> by at least 10.8 inches (27.4 centimeters). That’s more than current models forecast, and it’s a highly conservative estimate. If every year were like 2012, <a href="https://doi.org/10.5194/tc-10-1147-2016">when Greenland experienced a heat wave</a>, that irreversible commitment to sea level rise would triple. That’s an ominous portent given that these are climate conditions we have already seen, not a hypothetical future scenario.</p>
<p>Our study takes a completely new approach – it is based on observations and glaciological theory rather than sophisticated numerical models. The current generation of <a href="https://doi.org/10.5194/tc-15-5705-2021">coupled climate and ice sheet models used to forecast future sea level rise fail</a> to capture the emerging processes that we see amplifying Greenland’s ice loss.</p>
<h2>How Greenland got to this point</h2>
<p>The <a href="http://nsidc.org/greenland-today/">Greenland ice sheet</a> is a massive, frozen reservoir that resembles an inverted pudding bowl. The ice is in <a href="https://doi.org/10.1002/2013GL058933">constant flux</a>, flowing from the interior – where it is over 1.9 miles (3 kilometers) thick, cold and snowy – to its edges, where the ice melts or calves bergs.</p>
<p>In all, the ice sheet locks up enough fresh water to <a href="https://doi.org/10.1002/2017GL074954">raise global sea level</a> by 24 feet (7.4 meters).</p>
<figure>
<iframe src="https://player.vimeo.com/video/743951647" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">David Attenborough takes us on a virtuoso tour of the Greenland ice sheet.</span></figcaption>
</figure>
<p>Greenland’s <a href="https://doi.org/10.1038/307620a0">terrestrial ice has existed for about 2.6 million years and has expanded and contracted with two dozen or so “ice age” cycles</a> lasting 70,000 or 100,000 years, punctuated by around 10,000-year warm interglacials. Each glacial is driven by <a href="https://climate.nasa.gov/ask-nasa-climate/2949/why-milankovitch-orbital-cycles-cant-explain-earths-current-warming">shifts in Earth’s orbit</a> <a href="https://doi.org/10.1126%2Fscience.194.4270.1121">that modulate</a> how much solar radiation reaches the Earth’s surface. These variations are then reinforced by snow reflectivity, or albedo; atmospheric greenhouse gases; and ocean circulation that redistributes that heat around the planet.</p>
<p>We are currently enjoying an interglacial period – the Holocene. For the past 6,000 years Greenland, like the rest of the planet, has benefited from a mild and stable climate with an ice sheet in equilibrium – until recently. Since 1990, as the atmosphere and ocean have warmed under rapidly increasing greenhouse gas emissions, Greenland’s mass balance has gone into the red. Ice losses due to enhanced melt, rain, ice flow and calving now far exceed the net gain from snow accumulation.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/stm1pBp0rfk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Greenland’s ice mass loss measured by NASA’s Grace satellites.</span></figcaption>
</figure>
<h2>What does the future hold?</h2>
<p>The critical questions are, how fast is Greenland losing its ice, and what does it mean for future sea level rise?</p>
<p>Greenland’s ice loss has been <a href="https://doi.org/10.1002/2017GL074954">contributing about 0.04 inches</a> (1 millimeter) per year to <a href="https://www.ipcc.ch/srocc/chapter/chapter-4-sea-level-rise-and-implications-for-low-lying-islands-coasts-and-communities/">global sea level rise</a> over the past decade.</p>
<p><a href="https://doi.org/10.1126/science.1178176">This net loss is split between surface melt and dynamic processes</a> that accelerate outlet glacier flow and are greatly exacerbated by atmospheric and oceanic warming, respectively. Though complex in its manifestation, the concept is simple: Ice sheets don’t like warm weather or baths, and the heat is on.</p>
<figure class="align-center ">
<img alt="A large area of meltwater pools on the snowy Greenland surface and forms a river and streams." src="https://images.theconversation.com/files/481364/original/file-20220826-11967-4s6t9q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/481364/original/file-20220826-11967-4s6t9q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/481364/original/file-20220826-11967-4s6t9q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/481364/original/file-20220826-11967-4s6t9q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/481364/original/file-20220826-11967-4s6t9q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=420&fit=crop&dpr=1 754w, https://images.theconversation.com/files/481364/original/file-20220826-11967-4s6t9q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=420&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/481364/original/file-20220826-11967-4s6t9q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=420&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Meltwater lakes feed rivers that snake across the ice sheet - until they encounter a moulin.</span>
<span class="attribution"><span class="source">Alun Hubbard</span></span>
</figcaption>
</figure>
<p>What the future will bring is trickier to answer.</p>
<p>The models used by the <a href="https://www.ipcc.ch/assessment-report/ar6/">Intergovernmental Panel on Climate Change</a> predict a sea level rise contribution from Greenland of <a href="https://doi.org/10.1029/2020GL091741">around 4 inches (10 centimeters) by 2100</a>, with a worst-case scenario of 6 inches (15 centimeters). </p>
<p>But that prediction is at odds with what field <a href="https://doi.org/10.1002/2017GL074954">scientists are witnessing from the ice sheet itself</a>. </p>
<p>According to our findings, Greenland will lose <a href="https://doi.org/10.1038/s41558-022-01441-2">at least 3.3% of its ice</a>, over 100 trillion metric tons. This loss is already committed – ice that <a href="https://www.usgs.gov/special-topics/water-science-school/science/fundamentals-water-cycle">must melt and calve icebergs</a> to reestablish Greenland’s balance with prevailing climate. </p>
<p>We’re observing many emerging processes that the models don’t account for that increase the ice sheet’s vulnerability. For example:</p>
<ul>
<li><p>Increased rain is <a href="https://doi.org/10.1038/ngeo2482">accelerating surface melt and ice flow</a>.</p></li>
<li><p>Large tracts of the ice surface are undergoing <a href="https://doi.org/10.1002/2017GL075958">bio-albedo darkening</a>, which <a href="https://doi.org/10.5194/tc-14-309-2020">accelerates surface melt</a>, as well as the impact of snow <a href="https://www.carbonbrief.org/darkening-ice-speeds-up-greenland-melt-new-research-suggests/">melting and refreezing</a> at the surface. These darker surfaces absorb more solar radiation, driving yet more melt.</p></li>
</ul>
<figure class="align-center ">
<img alt="Weather stations sit atop wet snow in Greenland" src="https://images.theconversation.com/files/481370/original/file-20220826-12-ohkapl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/481370/original/file-20220826-12-ohkapl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/481370/original/file-20220826-12-ohkapl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/481370/original/file-20220826-12-ohkapl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/481370/original/file-20220826-12-ohkapl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/481370/original/file-20220826-12-ohkapl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/481370/original/file-20220826-12-ohkapl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">In August 2021, rain fell at the Greenland ice sheet summit for the first time on record. Weather stations across Greenland captured rapid ice melt.</span>
<span class="attribution"><a class="source" href="https://www.esa.int/ESA_Multimedia/Images/2022/06/Weather_station_high_on_the_Greenland_ice_sheet">European Space Agency</a></span>
</figcaption>
</figure>
<ul>
<li><p>Warm, subtropical-originating <a href="https://doi.org/10.5194/tc-8-1457-2014">ocean currents are intruding into Greenland’s fjords</a> and rapidly eroding outlet glaciers, undercutting and <a href="https://doi.org/10.1002/2015GL065806">destabilizing their calving fronts</a>.</p></li>
<li><p>Supraglacial lakes and river networks are draining into <a href="https://www.washingtonpost.com/climate-environment/2020/12/23/climate-moulins-greenland/">fractures and moulins</a>, bringing with them vast quantities of latent heat. This “<a href="https://doi.org/10.1029/2010GL044397">cryo-hydraulic warming</a>” within and at the base of the ice sheet softens and thaws the bed, thereby <a href="https://doi.org/10.1002/2013GL058933">accelerating interior ice flow</a> down to the margins.</p></li>
</ul>
<h2>The issue with models</h2>
<p>Part of the problem is that the models used for forecasting are mathematical abstractions that include only processes that are fully understood, quantifiable and deemed important.</p>
<p>Models reduce reality to a set of equations that are solved repeatedly on banks of very fast computers. Anyone into cutting-edge engineering – including me – knows the intrinsic value of models for experimentation and testing of ideas. But they are no substitute for reality and observation. It is apparent that current model forecasts of global sea level rise underestimate its actual threat over the 21st century. Developers are making constant improvements, but it’s tricky, and there’s a dawning realization that the complex models used for long-term sea level forecasting <a href="https://doi.org/10.1016/j.oneear.2020.11.002">are not fit for purpose</a>.</p>
<figure class="align-center ">
<img alt="Several brightly colored research tents dot a landscape with streams and snow on the ice sheet." src="https://images.theconversation.com/files/481605/original/file-20220829-20-7mu3w2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/481605/original/file-20220829-20-7mu3w2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/481605/original/file-20220829-20-7mu3w2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/481605/original/file-20220829-20-7mu3w2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/481605/original/file-20220829-20-7mu3w2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=419&fit=crop&dpr=1 754w, https://images.theconversation.com/files/481605/original/file-20220829-20-7mu3w2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=419&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/481605/original/file-20220829-20-7mu3w2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=419&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Author Alun Hubbard’s science camp in the melt zone of the Greenland ice sheet.</span>
<span class="attribution"><span class="source">Alun Hubbard</span></span>
</figcaption>
</figure>
<p>There are also “unknown unknowns” – those processes and feedbacks that we don’t yet realize and that models can never anticipate. They can be understood only by direct observations and literally drilling into the ice. </p>
<p>That’s why, rather than using models, we base our study on <a href="https://doi.org/10.1002/2014RG000470">proven glaciological theory</a> constrained by two decades of actual measurements from weather stations, satellites and ice geophysics.</p>
<h2>It’s not too late</h2>
<p>It’s an understatement that the societal stakes are high, and the risk is tragically real going forward. The consequences of catastrophic coastal flooding as sea level rises are still unimaginable to the majority of the billion or so people who live in low-lying coastal zones of the planet.</p>
<figure class="align-center ">
<img alt="A large sailing ship with an even larger iceberg behind it and a glacier in the distance." src="https://images.theconversation.com/files/481365/original/file-20220826-11332-ij15fr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/481365/original/file-20220826-11332-ij15fr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/481365/original/file-20220826-11332-ij15fr.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/481365/original/file-20220826-11332-ij15fr.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/481365/original/file-20220826-11332-ij15fr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/481365/original/file-20220826-11332-ij15fr.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/481365/original/file-20220826-11332-ij15fr.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A large tabular iceberg that calved off Store Glacier within Uummannaq Fjord.</span>
<span class="attribution"><span class="source">Alun Hubbard</span></span>
</figcaption>
</figure>
<p>Personally, I remain hopeful that we can get on track. I don’t believe we’ve passed any doom-laden tipping point that irreversibly floods the planet’s coastlines. Of what I understand of the ice sheet and the insight <a href="https://www.nature.com/articles/s41558-022-01441-2">our new study</a> brings, it’s not too late to act. </p>
<p>But fossil fuels and emissions must be curtailed now, because time is short and the water rises – faster than forecast.</p><img src="https://counter.theconversation.com/content/185590/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alun Hubbard is also affiliated with Oulun yliopisto - The University of Oulu, Finland, Arctic Basecamp & La Venta Explorazioni.</span></em></p>A field glaciologist explains the changes scientists are now seeing.Alun Hubbard, Professor of Glaciology, Arctic Five Chair, University of TromsøLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1847872022-06-16T12:42:27Z2022-06-16T12:42:27ZHow Iceberg Alley got its name and why it may be under threat<figure><img src="https://images.theconversation.com/files/468819/original/file-20220614-26-e9f42t.jpg?ixlib=rb-1.1.0&rect=26%2C26%2C3567%2C2338&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A large iceberg passes near Ferryland, an hour south of St. John's, Nfld., in April 2017</span> <span class="attribution"><span class="source">THE CANADIAN PRESS/Paul Daly</span></span></figcaption></figure><iframe style="width: 100%; height: 100px; border: none; position: relative; z-index: 1;" allowtransparency="" allow="clipboard-read; clipboard-write" src="https://narrations.ad-auris.com/widget/the-conversation-canada/how-iceberg-alley-got-its-name-and-why-it-may-be-under-threat" width="100%" height="400"></iframe>
<p>Iceberg Alley, the stretch of coast ranging from Labrador to Newfoundland, is the southernmost region of the northern hemisphere where one can regularly see icebergs. But hurry up! As the planet continues to warm, Iceberg Alley may soon lose its name.</p>
<p>Iceberg sightseeing is a common — and much-anticipated — activity in Newfoundland. Every spring, locals and visitors brave the region’s damp and chilly weather — it’s one of the <a href="http://doi.org/10.1007/978-3-319-45229-6_2">foggiest places on the planet</a> — to scrutinize the horizon for large white objects or embark on boat tours, hoping that luck will be on their side. </p>
<p>But with iceberg counts ranging from <a href="https://doi.org/10.20383/101.0301">zero to more than 2,000</a> per year, booking a trip in advance to see these 10,000-year-old blocks of ice can be a gamble. </p>
<h2>10,000-year-old ice</h2>
<p>Every year, <a href="https://doi.org/10.1002/2013GL059010">hundreds of billions of tonnes of ice</a>, equivalent to more than 100 million Olympic pools of water, once melted, is shed from Greenland’s glaciers into the ocean. This phenomenon is called calving. </p>
<p>The bulk of the ice calving from Greenland’s glaciers form icebergs. While about <a href="https://doi.org/10.1002/2016GL070718">10-50 per cent</a> of these icebergs melt directly in Greenland’s fjords, the majority are carried away by ocean currents.</p>
<figure class="align-right ">
<img alt="A map of the North Atlantic Ocean showing the flow of icebergs from Greenland to the coast of Newfoundland." src="https://images.theconversation.com/files/468815/original/file-20220614-21-u1jaic.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/468815/original/file-20220614-21-u1jaic.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=775&fit=crop&dpr=1 600w, https://images.theconversation.com/files/468815/original/file-20220614-21-u1jaic.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=775&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/468815/original/file-20220614-21-u1jaic.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=775&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/468815/original/file-20220614-21-u1jaic.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=974&fit=crop&dpr=1 754w, https://images.theconversation.com/files/468815/original/file-20220614-21-u1jaic.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=974&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/468815/original/file-20220614-21-u1jaic.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=974&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The icebergs that arrive in Newfoundland calve from the west coast of Greenland and follow ocean currents to the south. Data: General Bathymetric Chart of the Oceans.</span>
<span class="attribution"><a class="source" href="https://www.gebco.net/data_and_products/gridded_bathymetry_data/version_20141103/">(Frédéric Cyr)</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The Greenland ice sheet is the result of <a href="https://doi.org/10.1016/j.quascirev.2010.02.007">thousands of years of snow accumulation</a> that has reached a thickness of more than one kilometre. The pressure that comes from the enormous weight transforms the snow into ice. The same pressure pushes the glaciers — rivers of ice funnelled by numerous fjords — towards the ocean where they calve and form icebergs. </p>
<p>A subset of these icebergs, mostly originating from the west coast of Greenland, will reach Newfoundland. While these icebergs can live for as long as a decade, those reaching Newfoundland are generally <a href="https://doi.org/10.1029/2018GL077676">one to two years old</a>.</p>
<h2>Sinking of the Titanic</h2>
<p>The most famous of these icebergs is probably the one that sank the Titanic just south of the tip of the Grand Banks of Newfoundland in 1912. That year was <a href="https://theconversation.com/titanic-twist-1912-wasnt-a-bad-year-for-icebergs-after-all-25621">not an abnormal one for icebergs</a>, with 1,038 icebergs reported. Following this tragedy, in 1913, the <a href="https://www.mycg.uscg.mil/News/Article/3028040/international-ice-patrol-11-decades-of-monitoring-the-northern-atlantic-waters/">International Ice Patrol</a>, operated by the U.S. Coast Guard on behalf of several maritime nations, was created to monitor iceberg dangers for ships in the North Atlantic.</p>
<p>The International Ice Patrol’s <a href="https://nsidc.org/data/G10028">annual count of the number of icebergs that slip south of 48 degrees north</a> provides the longest and most reliable time series of icebergs in Newfoundland. In an average year, nearly <a href="https://doi.org/10.20383/101.0301">800 icebergs</a> are expected to cross the boundary, which lies just north of the Grand Banks of Newfoundland.</p>
<figure class="align-center ">
<img alt="Graphic showing the high variability in the number of observed icebergs over the past 122 years." src="https://images.theconversation.com/files/468842/original/file-20220614-8082-bt1kez.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/468842/original/file-20220614-8082-bt1kez.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=285&fit=crop&dpr=1 600w, https://images.theconversation.com/files/468842/original/file-20220614-8082-bt1kez.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=285&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/468842/original/file-20220614-8082-bt1kez.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=285&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/468842/original/file-20220614-8082-bt1kez.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=359&fit=crop&dpr=1 754w, https://images.theconversation.com/files/468842/original/file-20220614-8082-bt1kez.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=359&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/468842/original/file-20220614-8082-bt1kez.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=359&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Number of icebergs observed, 1900-2021.</span>
<span class="attribution"><span class="source">(Frédéric Cyr)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>These annual counts are extremely variable and affected by the climate of the North Atlantic. The 1980s and ‘90s were an especially cold period in the region, and more than 1,500 icebergs were observed during some of those years, with a record high of 2,202 in 1984. More recently, 1,515 icebergs were spotted in 2019, a year characterized with <a href="https://www.dfo-mpo.gc.ca/csas-sccs/Publications/ResDocs-DocRech/2021/2021_017-eng.html">colder than normal spring temperatures</a> and immediately following another cold period in the mid-2010s.</p>
<p>But these numbers decrease drastically during years characterized by milder winters and an early spring. This occurred in 2010 and 2021, where only one iceberg was observed; in 2011, which saw two icebergs; and in 2013, where 13 icebergs were recorded. Only two years, 1966 and 2006, in the 122-year time series have reported no icebergs journeying south of 48 degrees north.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/titanic-twist-1912-wasnt-a-bad-year-for-icebergs-after-all-25621">Titanic twist: 1912 wasn’t a bad year for icebergs after all</a>
</strong>
</em>
</p>
<hr>
<h2>An uncertain future</h2>
<p>With the planet warming up as a result of anthropogenic climate change, the <a href="https://doi.org/10.1038/s41586-019-1855-2">Greenland ice sheet is losing mass</a>. While this may suggest that more icebergs will calve into the ocean, it is far from guaranteed that this will lead to more sightseeing opportunities in Newfoundland. And the numbers may lie, as improvements in iceberg-detecting technology may be responsible for an <a href="https://www.navcen.uscg.gov/sites/default/files/pdf/iip/2018_Annual_Report_FINAL.pdf">apparent upward trend in counts</a>.</p>
<figure class="align-center ">
<img alt="An aerial view of a glacier with large and small chunks of ice floating in the water at its foot, with rocky slopes on either side of the narrow fjord." src="https://images.theconversation.com/files/468822/original/file-20220614-15-33xmz6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/468822/original/file-20220614-15-33xmz6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=410&fit=crop&dpr=1 600w, https://images.theconversation.com/files/468822/original/file-20220614-15-33xmz6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=410&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/468822/original/file-20220614-15-33xmz6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=410&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/468822/original/file-20220614-15-33xmz6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=515&fit=crop&dpr=1 754w, https://images.theconversation.com/files/468822/original/file-20220614-15-33xmz6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=515&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/468822/original/file-20220614-15-33xmz6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=515&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A glacier calves icebergs into a fjord off the Greenland ice sheet in southeastern Greenland in August 2017.</span>
<span class="attribution"><span class="source">(AP Photo/David Goldman)</span></span>
</figcaption>
</figure>
<p>The environmental parameters that control the number of icebergs in Newfoundland in a given year remain unclear. However, it appears that a warmer climate definitely leads to fewer or simply no icebergs at all in Newfoundland. </p>
<p>For example, when looking at the region’s three warmest years on record — 1966, 2010 and 2021 — only <a href="https://www.dfo-mpo.gc.ca/csas-sccs/Publications/ResDocs-DocRech/2022/2022_040-eng.html">zero, one and one icebergs</a> were reported. These outliers may well become the new norm as climate projections suggest with a high level of confidence that the <a href="https://www.ipcc.ch/report/ar6/wg2/">frequency and severity of extreme events</a>, such as an anomalously warm year, will increase in the future.</p>
<p>While the Newfoundland iceberg sightseeing tourism industry may well have benefited from a succession of exceptional iceberg seasons linked to a recent rebound in cold ocean conditions in the mid-2010s, its future is less certain. </p>
<p>Will the Iceberg Alley lose its name? It would be unfortunate, but it is possible. For the moment there is still time to enjoy these 10,000-year-old remnants of the past. So hurry up before it’s too late!</p><img src="https://counter.theconversation.com/content/184787/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Frédéric Cyr does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Between zero and 2,000 icebergs reach Newfoundland each spring, but the warming climate could see an end to Iceberg Alley.Frédéric Cyr, Adjunct professor, Physical Oceanography, Memorial University of NewfoundlandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1687292021-11-05T19:55:18Z2021-11-05T19:55:18ZEast Coast flooding is a reminder that sea level is rising as the climate warms – here’s why the ocean is pouring in more often<figure><img src="https://images.theconversation.com/files/430556/original/file-20211105-1798-1nq4vwo.jpg?ixlib=rb-1.1.0&rect=0%2C14%2C4752%2C3144&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">People walked down a flood sidewalk in Annapolis, Maryland, on Oct. 29, 2021.</span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/SevereWeather/7ca9566680a5453d9ed0dca4e75a06ce/photo">AP Photo/Susan Walsh</a></span></figcaption></figure><p>The U.S. East Coast has been experiencing <a href="https://www.washingtonpost.com/weather/2021/11/06/coastal-flooding-southeast-storm-charleston/">hurricane-like flooding</a> in recent days, with Georgia and the Carolinas getting the latest round. High tides are part of the problem, but there’s another risk that has been slowly creeping up: sea level rise.</p>
<p>Since 1880, average global sea levels <a href="https://www.globalchange.gov/browse/indicators/global-sea-level-rise">have risen by more than</a> 8 inches (23 centimeters), and the <a href="https://climate.nasa.gov/news/2680/new-study-finds-sea-level-rise-accelerating/">rate has been accelerating</a> with climate change.</p>
<p>Depending on how well countries reduce their greenhouse gas emissions in the coming years, scientists estimate that <a href="https://theconversation.com/ipcc-climate-report-profound-changes-are-underway-in-earths-oceans-and-ice-a-lead-author-explains-what-the-warnings-mean-165588">global sea levels could rise</a> by an additional 2 feet by the end of this century. The higher seas means when storm surges and high tides arrive, they add to an already higher water level. In some areas – including Charleston, South Carolina, where an offshore storm and high tide raised water levels <a href="https://www.washingtonpost.com/weather/2021/11/06/coastal-flooding-southeast-storm-charleston/">8.4 feet</a> on Nov. 6, 2021 – <a href="https://www.scseagrant.org/water-cities-climate-proof-the-coast/">sinking land</a> is making the impact even worse.</p>
<p>I’m a <a href="https://scholar.google.com/citations?user=p0hz6e0AAAAJ&hl=en">geoscientist who studies sea level rise</a> and the effects of climate change. Here’s a quick explanation of two main ways climate change is affecting ocean levels and their threat to the world’s coasts.</p>
<h2>Ocean thermal expansion</h2>
<p>Climate change, fueled by fossil fuel use and other human activities, is causing average global surface temperatures to rise. This is leading the ocean to absorb more heat than it did before the industrial era began. That, in turn, is causing ocean thermal expansion. </p>
<p>Thermal expansion simply means that as the ocean heats up, sea water molecules move slightly farther apart. The farther apart the molecules are, the more space they take up.</p>
<p>That expansion leads to the ocean rising higher onto land. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/430566/original/file-20211106-9522-1gq217m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Line chart showing sea level rise attributed to thermal expansion and to melting" src="https://images.theconversation.com/files/430566/original/file-20211106-9522-1gq217m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/430566/original/file-20211106-9522-1gq217m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/430566/original/file-20211106-9522-1gq217m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/430566/original/file-20211106-9522-1gq217m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/430566/original/file-20211106-9522-1gq217m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/430566/original/file-20211106-9522-1gq217m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/430566/original/file-20211106-9522-1gq217m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">How thermal expansion and melting land ice combine to create sea level rise over time. The black line is observed sea level since the start of the satellite altimeter record in 1993.</span>
<span class="attribution"><a class="source" href="https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>During the past several decades, <a href="https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level">about 40%</a> of global sea level rise was due to the effect of thermal expansion. The ocean, which covers just over two-thirds of the Earth’s surface, has been absorbing and storing <a href="https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content">more than 90%</a> of the excess heat added to the climate system due to greenhouse gas emissions. </p>
<h2>Melting land ice</h2>
<p>The other major factor in rising sea levels is that the increase in average global temperatures is melting land ice – glaciers and polar ice sheets – at a faster rate than natural systems can replace it. </p>
<p>When land ice melts, that meltwater eventually flows into the ocean, adding new quantities of water to the ocean and increasing the total ocean mass. </p>
<p>During the past several decades, about <a href="https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level">50% of global sea level rise</a> was induced by land ice melt.</p>
<p>Currently, the polar ice sheets in Greenland and Antarctica hold enough frozen waters that if they melted completely, it would raise the global sea level by up to <a href="https://nsidc.org/cryosphere/quickfacts/icesheets.html">200 feet, or 60-70 meters</a> – about the height of the Statue of Liberty.</p>
<p>Climate change is melting sea ice as well. However, because this ice already floats at the ocean’s surface and displaces a certain amount of liquid water below, this melting does not contribute to sea level rise. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/423215/original/file-20210925-46679-4tk09d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Map with colors showing increase in sea level rise worldwide." src="https://images.theconversation.com/files/423215/original/file-20210925-46679-4tk09d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/423215/original/file-20210925-46679-4tk09d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/423215/original/file-20210925-46679-4tk09d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/423215/original/file-20210925-46679-4tk09d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/423215/original/file-20210925-46679-4tk09d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/423215/original/file-20210925-46679-4tk09d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/423215/original/file-20210925-46679-4tk09d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">How average sea level rose from 1993 to 2018 across the world ocean. The rise was 6-8 inches (15-20 centimeters) in some basins.</span>
<span class="attribution"><a class="source" href="https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level">NOAA</a></span>
</figcaption>
</figure>
<p>While the <a href="http://ipcc.ch/srocc/chapter/chapter-4-sea-level-rise-and-implications-for-low-lying-islands-coasts-and-communities/">surface height of the ocean</a> is rising globally, the impact is not the same for every coastal region on Earth. The rate of rise can be several times faster in some places than others. This difference is caused by an area’s unique local conditions – such as shifts in ocean circulation and the uplift or subsidence of the land.</p>
<h2>Risk will keep rising long after emissions stabilize</h2>
<p>Nearly 4 in 10 U.S. residents live near a coastline, and millions of people are already dealing with <a href="https://oceanservice.noaa.gov/facts/sealevel.html">coastal flooding</a> during hurricanes and high tides that can damage homes, buildings and other coastal infrastructure and ecosystems. The Chesapeake Bay area was hit with flooding during high tides in late October, and the <a href="https://theconversation.com/a-20-foot-sea-wall-wont-save-miami-how-living-structures-can-help-protect-the-coast-and-keep-the-paradise-vibe-165076">Miami area now deals with high-tide flooding</a> several times a year. </p>
<p>Worldwide, researchers have estimated that sea level rise this century could cause <a href="https://www.nature.com/articles/s41598-020-67736-6">trillions of dollars in damage</a>. In some low-lying island nations, including the Maldives in the Indian Ocean and Kiribati in the Pacific Ocean, rising seas are already forcing citizens to make stark choices about building costly ocean protections that will only last so long or plan to abandon their islands.</p>
<figure class="align-center ">
<img alt="Men laying sandbags along a coastal road in Kiribati that was damaged by flooding related to sea level rise." src="https://images.theconversation.com/files/428304/original/file-20211025-15-18s2eq2.jpg?ixlib=rb-1.1.0&rect=29%2C14%2C4940%2C3308&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/428304/original/file-20211025-15-18s2eq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/428304/original/file-20211025-15-18s2eq2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/428304/original/file-20211025-15-18s2eq2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/428304/original/file-20211025-15-18s2eq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/428304/original/file-20211025-15-18s2eq2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/428304/original/file-20211025-15-18s2eq2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The people of Kiribati, a small island nation in the South Pacific Ocean, have been grappling for years with the impacts of rising seas driven by climate change, although they’ve done very little to contribute to global carbon pollution.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/damaged-roads-due-to-the-flooding-in-kirbati-tarawas-single-news-photo/495745918">Jonas Gratzer/Getty Images</a></span>
</figcaption>
</figure>
<p>Officials from countries worldwide are meeting at the <a href="https://theconversation.com/what-is-cop26-heres-how-global-climate-negotiations-work-and-whats-expected-from-the-glasgow-summit-169434">U.N. climate conference</a> with a goal of agreeing to reduce global greenhouse gas emissions enough to keep global temperatures from rising too high.</p>
<p>Even when emissions come down, sea level will keep rising for centuries because the massive ice sheets in Greenland and Antarctica will continue to melt and take a very long time to reach a new equilibrium. <a href="https://theconversation.com/ipcc-climate-report-profound-changes-are-underway-in-earths-oceans-and-ice-a-lead-author-explains-what-the-warnings-mean-165588">The latest report from the Intergovernmental Panel on Climate Change shows</a> the excess heat already in the climate system has locked in the current rates of thermal expansion and land ice melt for at least the next few decades. </p>
<p><em>This article was updated Nov. 6 with the high tide level in Charleston, S.C.</em></p><img src="https://counter.theconversation.com/content/168729/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jianjun Yin previously received funding from NSF, NOAA and NASA. </span></em></p>Climate change is making ocean levels rise in two ways. It’s a problem that will endure even after the world stabilizes and slashes greenhouse gas pollution.Jianjun Yin, Associate Professor of Geoscience, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1666772021-09-20T20:08:45Z2021-09-20T20:08:45ZScientists still don’t know how far melting in Antarctica will go – or the sea level rise it will unleash<p>The Antarctic ice sheet is the largest mass of ice in the world, holding around <a href="https://www.bas.ac.uk/about/antarctica/geography/ice/">60%</a> of the world’s fresh water. If it all melted, global average sea levels would rise by <a href="https://tc.copernicus.org/articles/7/375/2013/">58 metres</a>. But scientists are grappling with exactly how global warming will affect this great ice sheet.</p>
<p>This knowledge gap was reflected in the latest <a href="https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf">report</a> from the Intergovernmental Panel on Climate Change (IPCC). It contains projections from models in which <a href="https://www.nature.com/articles/s41586-021-03302-y">important processes</a> affecting the ice sheets, known as feedbacks and tipping points, are absent because scientific understanding is lacking.</p>
<p>Projected sea level rise will have widespread effects in Australia and around the world. But current projections of ice sheet melt are so wide that developing ways for societies to adapt will be incredibly expensive and difficult.</p>
<p>If the world is to effectively adapt to sea level rise with minimal cost, we must quickly address the uncertainty surrounding Antarctica’s melting ice sheet. This requires significant investment in scientific capacity.</p>
<h2>The great unknown</h2>
<p>Ice loss from the <a href="https://www.pnas.org/content/116/4/1095.short">Antarctic</a> and <a href="https://www.nature.com/articles/s41586-019-1855-2">Greenland</a> ice sheets was the largest contributor to sea level rise in recent decades. Even if all greenhouse gas emissions ceased today, the heat already in the ocean and atmosphere would cause substantial ice loss and a corresponding rise in sea levels. But exactly how much, and how fast, remains unclear.</p>
<p>Scientific understanding of ice sheet processes, and of the variability of the forces that affect ice sheets, is incredibly limited. This is largely because much of the ice sheets are in very remote and harsh environments, and so difficult to access.</p>
<p>This lack of information is one of the main sources of uncertainty in the models used to estimate ice mass loss. </p>
<p>At the moment, quantifying how much the Greenland and Antarctic ice sheets will contribute to sea level rise primarily involves an international scientific collaboration known as the “Ice Sheet Model Intercomparison Project for CMIP6”, or <a href="https://www.climate-cryosphere.org/mips/ismip6">ISMIP6</a>, of which we are part.</p>
<p>The project includes experts in ice sheet and climate modelling and observations. It produces computer simulations of what might happen if the polar regions melt under different <a href="https://www.sciencedirect.com/science/article/pii/S0959378016300681">climate scenarios</a>, to improve projections of sea level rise.</p>
<p>The project also investigates ice sheet–climate feedbacks. In other words, it looks at how processes in the oceans and atmosphere will affect the Antarctic and Greenland ice sheets, including whether the changes might cause them to <a href="https://www.pnas.org/content/116/30/14887">collapse</a> – leading to large and sudden increases in sea level.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/anatomy-of-a-heatwave-how-antarctica-recorded-a-20-75-c-day-last-month-134550">Anatomy of a heatwave: how Antarctica recorded a 20.75°C day last month</a>
</strong>
</em>
</p>
<hr>
<h2>Melting from below</h2>
<p>Research <a href="https://www.nature.com/articles/s41586-018-0179-y">has identified</a> so-called “basal melt” as the most significant driver of Antarctic ice loss. Basal melt refers to the melting of ice shelves from underneath, and in the case of Antarctica, interactions with the ocean are thought to be the main cause. But gathering scientific observations beneath ice shelves is a major logistical challenge, leading to a dearth of data about this phenomenon.</p>
<p>This and other constraints mean the rate of progress in ice sheet modelling has been insufficient to date, and so active ice sheet models are not included in climate models.</p>
<p>Scientists must instead make projections using the ice sheet models in isolation. This <a href="https://tc.copernicus.org/articles/14/3033/2020/">hinders</a> scientific attempts to accurately simulate the feedback between ice and climate.</p>
<p>For example, it creates much uncertainty in how the interaction between the ocean and the ice shelf will affect ice mass loss, and how the very cold, fresh meltwater will make its way back to global oceans and cause sea level rise, and potentially disrupt currents.</p>
<p>Despite the uncertainties ISMIP6 is dealing with, it has published a series of recent research including a key <a href="https://www.nature.com/articles/s41586-021-03302-y">paper</a> published in Nature in May. This found if the world met the Paris Agreement target of limiting global warming to 1.5°C this century, land ice melt would cause global sea level rise of about 13cm by 2100, in the most optimistic scenario. This is compared to a rise of 25cm under the world’s current emissions-reduction pledges.</p>
<p>The study also outlines a pessimistic, but still plausible, basal melt scenario for Antarctica in which sea levels could be <a href="https://www.nature.com/articles/s41586-021-03302-y">five times higher</a> than in the main scenarios.</p>
<p>The breadth of such findings underpinned sea level projections in the latest <a href="https://www.ipcc.ch/report/sixth-assessment-report-working-group-i/">IPCC report</a>. The Antarctic ice sheet once again represented the <a href="https://www.nature.com/articles/s41586-021-03302-y">greatest source of uncertainty</a> in these projections.</p>
<p>The below graph shows the IPCC’s latest sea level projections. The shaded area reflects the large uncertainties in models using the same basic data sets and approaches. The dotted line reflects deep uncertainty about tipping points and thresholds in ice sheet stability.</p>
<p>IPCC reports are intended to guide global policy-makers in coming years and decades. But the uncertainties about ice melt from Antarctica limit the usefulness of projections by the IPCC and others. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/this-is-the-most-sobering-report-card-yet-on-climate-change-and-earths-future-heres-what-you-need-to-know-165395">This is the most sobering report card yet on climate change and Earth's future. Here’s what you need to know</a>
</strong>
</em>
</p>
<hr>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/418587/original/file-20210831-19-1mbzr16.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/418587/original/file-20210831-19-1mbzr16.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=302&fit=crop&dpr=1 600w, https://images.theconversation.com/files/418587/original/file-20210831-19-1mbzr16.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=302&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/418587/original/file-20210831-19-1mbzr16.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=302&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/418587/original/file-20210831-19-1mbzr16.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=380&fit=crop&dpr=1 754w, https://images.theconversation.com/files/418587/original/file-20210831-19-1mbzr16.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=380&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/418587/original/file-20210831-19-1mbzr16.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=380&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The IPCC’s projections for global average sea level change in metres, relative to 1900.</span>
<span class="attribution"><span class="source">IPCC</span></span>
</figcaption>
</figure>
<h2>Dealing with uncertainty</h2>
<p>Future sea level rise poses big challenges such as human displacement, infrastructure loss, <a href="https://www.sciencedaily.com/releases/2017/01/170118082423.htm">interference with agriculture</a>, a potential influx of <a href="https://www.climate-refugees.org/spotlight/tag/Australia">climate refugees</a>, and coastal habitat degradation. </p>
<p>It’s crucial that ice sheet models are improved, tested robustly against real-world observations, then integrated into the next generation of international climate models – including those being developed in <a href="https://nci.org.au/news-events/news/nci-welcomes-access-nri-funding-announcement">Australia</a>.</p>
<p>International collaborations such as <a href="https://soos.aq/images/soos/activities/endorsement/NECKLACE-web.pdf">NECKLACE</a> and <a href="https://soos.aq/index.php?option=com_content&view=article&id=113">RISE</a> are seeking to coordinate international effort between models and observations. Significant investment across these projects is needed. </p>
<p>Sea levels will continue rising in the coming decades and centuries. Ice sheet projections must be narrowed down to ensure current and future generations can adapt safely and efficiently.</p>
<hr>
<p><em>The authors would like to acknowledge the contributions of Dr Ben Galton-Fenzi, Dr Rupert Gladstone, Dr Thomas Zwinger and David Reilly to the research from which this article draws.</em></p><img src="https://counter.theconversation.com/content/166677/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chen Zhao works under the Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, University of Tasmania. She receives grant funding from the Australian Government as part of the Antarctic Science Collaboration Initiative program (ASCI000002).</span></em></p><p class="fine-print"><em><span>Rupert Gladstone receives grant funding from the Finnish Government as part of the Coupled Ocean and Land ice Dynamics (COLD) consortium (Academy of Finland grant number 322430).</span></em></p>If the world is to adapt to sea level rise with minimal cost, we must address the uncertainty surrounding Antarctica’s melting ice sheet. This requires significant investment in scientific capacity.Chen Zhao, Research associate, University of TasmaniaRupert Gladstone, Adjunct professor, University of LaplandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1604772021-05-17T10:22:02Z2021-05-17T10:22:02ZLife in the deep freeze – the revolution that changed our view of glaciers forever<figure><img src="https://images.theconversation.com/files/399492/original/file-20210507-17-1dedwyb.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5615%2C3741&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/perito-moreno-glacier-located-los-glaciares-599713124">Saiko3p/Shutterstock</a></span></figcaption></figure><p>I’ve been fascinated by glaciers since I was 14, when geography textbooks taught me about strange rivers of ice that crept down yawning valleys like giant serpents stalking their next meal. That kernel of wonder has carried me through a career of more than 25 years. I’ve travelled to the world’s peaks and its poles to see over 20 glaciers. Yet, when I first started out as a researcher in the early 1990s, we were convinced glaciers were lifeless deserts.</p>
<p>Then in 1999, <a href="https://pubs.geoscienceworld.org/gsa/geology/article-abstract/27/2/107/207041/Widespread-bacterial-populations-at-glacier-beds?redirectedFrom=fulltext">Professor Martin Sharp and colleagues</a> discovered bacteria living beneath the Haut Glacier d’Arolla in Switzerland. It seemed that glaciers, like the soil or our stomachs, had their own community of microbes, their own microbiome. Since then, we’ve found microorganisms just about everywhere within glaciers, transforming what we thought were sterile wastelands into vibrant ecosystems. </p>
<p>So what’s all that glacier life doing? These life forms may be invisible to the naked eye, but they can control how fast glaciers melt – and may even influence the global climate.</p>
<h2>The glacier microbiome</h2>
<p>Just like people, glacier microbes modify their homes. When I first saw the melting fringes of Greenland’s vast ice sheet, it looked as if a dust storm had scattered a vast blanket of dirt on the ice. Our team later discovered the dirt included extensive mats of <a href="https://www.nature.com/articles/ismej2012107">glacier algae</a>. These microscopic plant-like organisms contain <a href="https://academic.oup.com/femsec/article/94/3/fiy025/4850643">pigments</a> to help them harvest the Sun’s rays and protect them from harsh UV radiation. By coating the melting ice surface, they darken it, ensuring the ice absorbs more sunlight which causes more of it to melt. In western Greenland, <a href="https://tc.copernicus.org/articles/14/309/2020/">more than 10%</a> of the summer ice melt is caused by algae.</p>
<figure class="align-center ">
<img alt="Bright blue glacier ice on rocky terrain." src="https://images.theconversation.com/files/399491/original/file-20210507-15-1h0xzv6.JPG?ixlib=rb-1.1.0&rect=0%2C0%2C3072%2C2304&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/399491/original/file-20210507-15-1h0xzv6.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/399491/original/file-20210507-15-1h0xzv6.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/399491/original/file-20210507-15-1h0xzv6.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/399491/original/file-20210507-15-1h0xzv6.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/399491/original/file-20210507-15-1h0xzv6.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/399491/original/file-20210507-15-1h0xzv6.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The margin of Engabreen glacier, Norway.</span>
<span class="attribution"><span class="source">Grzegorz Lis</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Again, just like us, microbes extract things from their environment to survive. The murky depths of glaciers are among the most challenging habitats for life on Earth. Microbes called <a href="https://aem.asm.org/content/80/19/6146">chemolithotrophs</a> – from the Greek meaning “eaters of rock” – survive here without light and get their energy from breaking down rock, releasing vital nutrients like iron, phosphorous and silicon to the meltwater. </p>
<p><a href="https://www.geochemicalperspectivesletters.org/article1510/">Rivers</a> and <a href="https://geochemicaltransactions.biomedcentral.com/articles/10.1186/1467-4866-9-7">icebergs</a> carry these nutrients to the ocean where they sustain the plant-like phytoplankton – the base of marine food webs which ultimately feed entire ecosystems, from microscopic animals, to fish and even whales. <a href="https://bg.copernicus.org/articles/11/2635/2014/bg-11-2635-2014.html">Models</a> and <a href="https://www.nature.com/articles/ngeo2633">satellite</a> observations show a lot of the photosynthesis in the iron-starved Southern Ocean could be sustained by rusty icebergs and meltwaters, which contain iron unlocked by glacier microbes. Recent evidence suggests something similar occurs off <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL073583">west</a> and <a href="https://www.nature.com/articles/s41598-019-53723-z">east</a> Greenland too.</p>
<figure class="align-center ">
<img alt="A microscope image depicting chains of brown rectangular cells." src="https://images.theconversation.com/files/399503/original/file-20210507-19-196z49x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/399503/original/file-20210507-19-196z49x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=452&fit=crop&dpr=1 600w, https://images.theconversation.com/files/399503/original/file-20210507-19-196z49x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=452&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/399503/original/file-20210507-19-196z49x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=452&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/399503/original/file-20210507-19-196z49x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=568&fit=crop&dpr=1 754w, https://images.theconversation.com/files/399503/original/file-20210507-19-196z49x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=568&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/399503/original/file-20210507-19-196z49x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=568&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Glacier algae from the Greenland ice sheet.</span>
<span class="attribution"><span class="source">Chris Williamson</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>But glacier bugs also produce waste, the most worrying of which is the greenhouse gas methane. When ice sheets grow, they bury <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2007GB002951">old soils and sediments</a>, all sources of carbon and the building blocks for earthly life. We think there could be thousands of billions of tonnes of <a href="https://www.nature.com/articles/nature11374">carbon buried beneath ice sheets</a> – potentially more than <a href="https://bg.copernicus.org/articles/11/6573/2014/">Arctic permafrost</a>. But who can use it in the oxygen-starved belly of an ice sheet? One type of microbe that flourishes here is <a href="https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2012.02763.x">the methanogen</a> (meaning “methane maker”), which also thrives in landfill sites and rice paddies.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/399489/original/file-20210507-15-tbe32n.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A waterfall at the edge of a glacier." src="https://images.theconversation.com/files/399489/original/file-20210507-15-tbe32n.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/399489/original/file-20210507-15-tbe32n.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=896&fit=crop&dpr=1 600w, https://images.theconversation.com/files/399489/original/file-20210507-15-tbe32n.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=896&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/399489/original/file-20210507-15-tbe32n.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=896&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/399489/original/file-20210507-15-tbe32n.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1126&fit=crop&dpr=1 754w, https://images.theconversation.com/files/399489/original/file-20210507-15-tbe32n.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1126&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/399489/original/file-20210507-15-tbe32n.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1126&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Leverett Glacier’s wild river, Greenland.</span>
<span class="attribution"><span class="source">Jemma Wadham</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Some methane produced by methanogens escapes in meltwaters flowing from the ice sheet edges. The clever thing about microbial communities, though, is that one microbe’s waste is another’s food. We humans could learn a lot from them about recycling. Some methane beneath glaciers is consumed by bacteria called methanotrophs (methane eaters) which generate energy by converting it to carbon dioxide. They have been detected in <a href="https://www.nature.com/articles/ismej201459">Greenlandic glaciers</a>, but most notably in <a href="https://www.nature.com/articles/ngeo2992?WT.feed_name=subjects_climate-sciences">Lake Whillans</a> beneath the West Antarctic Ice Sheet. Here, bacteria have years to chomp on the gas, and almost all of the methane produced in the lake is eaten – a good thing for the climate, since carbon dioxide is 80 times less potent as a greenhouse gas when measured over two decades.</p>
<p>We’re not sure this happens everywhere though. Fast-flowing rivers emerging from the Greenland Ice Sheet are <a href="https://www.nature.com/articles/s41586-018-0800-0">super-saturated with microbial methane</a> because there just isn’t enough time for the methanotrophs to get to work. Will melting glaciers release stored methane faster than these bacteria can convert it?</p>
<p>Within the thick interior of ice sheets, scientists worry that there may be vast reserves of methane. The cold and high pressure here mean that it may be trapped in its solid form, methane hydrate (or clathrate), which is stable unless the ice retreats and thins. <a href="https://science.sciencemag.org/content/356/6341/948.abstract">It happened before</a> and it could happen again.</p>
<h2>Waking the sleeping giant</h2>
<p>Despite the climate crisis, when I spend time around glaciers I’m not surprised by their continuing vitality. As I amble up to the gently sloping snout of a glacier – traversing its rubbly lunar-like fore-fields – I often feel like I’m approaching the hulk of an enormous creature. Sleeping or seemingly dormant, the evidence of its last meal is clear from the mass of tawny-coloured rocks, pebbles and boulders strewn around its edges – a tantalising record of where it once rested when the climate was cooler.</p>
<p>As I get closer, I catch the sound of the glacier’s roaring chocolate meltwaters as they explode through an ice cave, punctuated by a cascade of bangs and booms as moving ice collapses into hollow melt channels below. The winds off the ice play ominously in my ears, like the whisper of the beast, a warning: “You’re on my land now.”</p>
<figure class="align-center ">
<img alt="The author inside a giant icy chasm within a glacier." src="https://images.theconversation.com/files/399486/original/file-20210507-21-if33gy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/399486/original/file-20210507-21-if33gy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/399486/original/file-20210507-21-if33gy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/399486/original/file-20210507-21-if33gy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/399486/original/file-20210507-21-if33gy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/399486/original/file-20210507-21-if33gy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/399486/original/file-20210507-21-if33gy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Exploring a frozen melt channel of the Finsterwalderbeeen glacier in Svalbard.</span>
<span class="attribution"><span class="source">Jon Ove Hagen</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>This sense of aliveness with glaciers changes everything. Resident microbes connect these hulking frozen masses with the Earth’s carbon cycle, ecosystems and climate. How will these connections change if we take away the frigid homes of our tiny glacier dwellers? These creatures may be microscopic, but the effects of their industry span entire continents and oceans.</p>
<p>After a period of uncertainty in my own life, which involved the removal of a satsuma-sized growth in my brain, I felt compelled to tell the story of glaciers to a wider audience. My book, <a href="https://www.penguin.co.uk/books/319/319535/ice-rivers/9780241467688.html">Ice Rivers</a>, is the result. I hope the memoir raises awareness of the dramatic changes that threaten glaciers – unless we act now.</p><img src="https://counter.theconversation.com/content/160477/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jemma is Director of the Cabot Institute for the Environment at the University of Bristol, and holds an adjunct professorship at UiT, the Arctic University of Norway. She has received grant funding in the past from the Engineering and Physics Research Council UK, Natural Environment Research Council UK, the Leverhulme Trust, The Royal Society, The British Council, EU Horizon 2020 and the Research Council of Norway. She is the author of Ice Rivers (Allen Lane-Penguin Press, Jemma Wadham Ltd). </span></em></p>Glaciers aren’t sterile wastelands – they’re chock-full of microscopic life.Jemma Wadham, Professor of Glaciology, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1554642021-05-04T04:05:35Z2021-05-04T04:05:35ZClimate explained: when Antarctica melts, will gravity changes lift up land and lower sea levels?<figure><img src="https://images.theconversation.com/files/396716/original/file-20210423-21-6xipu6.jpg?ixlib=rb-1.1.0&rect=26%2C70%2C5817%2C2444&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock/Nickolya</span></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em><strong><a href="https://theconversation.com/nz/topics/climate-explained-74664">Climate Explained</a></strong> is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.</em> </p>
<p><em>If you have a question you’d like an expert to answer, please send it to <a href="mailto:climate.change@stuff.co.nz">climate.change@stuff.co.nz</a></em></p>
<hr>
<blockquote>
<p><strong>I’ve heard the gravity changes when Antarctica melts will lower the seas around New Zealand. Will that save us from sea level rise?</strong></p>
</blockquote>
<p>The gravitational changes when Antarctica melts do indeed affect sea levels all over the world — but not enough to save New Zealand from rising seas.</p>
<p>The ice ages and their effects on sea level, geology, flora and fauna were topics of intense scientific and public interest all through the 19th century. Here’s how James Croll explained the “gravity effect” of melting ice in his 1875 book <a href="https://www.google.co.nz/books/edition/Climate_and_Time_in_Their_Geological_Rel/mLYKAQAAIAAJ">Climate and Time in their Geologic Relations</a>:</p>
<blockquote>
<p>Let us now consider the effect that this condition of things would have upon the level of the sea. It would evidently tend to produce an elevation of the sea-level on the northern hemisphere in two ways. First, the addition to the sea occasioned by the melting of the ice from off the Antarctic land would tend to raise the general level of the sea. Secondly, the removal of the ice would also tend to shift the earth’s centre of gravity to the north of its present position – and as the sea must shift along with the centre, a rise of the sea on the northern hemisphere would necessarily take place.</p>
</blockquote>
<p>His back-of-the-envelope calculation suggested the effect on sea level from ice melting in Antarctica would be about a third bigger than average in the northern hemisphere and a third smaller in the south. </p>
<p>A more detailed mathematical study by <a href="https://books.google.co.nz/books?id=iqgPAAAAIAAJ">Robert Woodward</a> in 1888 has falling sea level as far as 2000km from Antarctica, but still rising by a third more than average in the north.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/ancient-antarctic-ice-melt-caused-extreme-sea-level-rise-129-000-years-ago-and-it-could-happen-again-131495">Ancient Antarctic ice melt caused extreme sea level rise 129,000 years ago – and it could happen again</a>
</strong>
</em>
</p>
<hr>
<h2>Sea-level fingerprints</h2>
<p>Woodward’s method is the basis of determining what is now called the “sea-level fingerprint” of melting ice. Two other factors also come into play. </p>
<ol>
<li><p>The elasticity of the earth’s surface means the land will bounce up when it has less ice weighing it down. This pushes water away.</p></li>
<li><p>If the ice is not at the pole, its melting shifts the south pole (the axis of rotation), redistributing water. </p></li>
</ol>
<p>Combining these effects gives the sea-level fingerprints of one metre of sea-level rise from either the West Antarctic Ice Sheet (WAIS) and Greenland (GIS), as <a href="https://www.sciencedirect.com/science/article/pii/S0277379113005039">shown here</a>:</p>
<figure class="align-center ">
<img alt="Red areas get more than the average sea level rise, blue areas get less." src="https://images.theconversation.com/files/398250/original/file-20210502-17-n7hain.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/398250/original/file-20210502-17-n7hain.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=224&fit=crop&dpr=1 600w, https://images.theconversation.com/files/398250/original/file-20210502-17-n7hain.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=224&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/398250/original/file-20210502-17-n7hain.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=224&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/398250/original/file-20210502-17-n7hain.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=281&fit=crop&dpr=1 754w, https://images.theconversation.com/files/398250/original/file-20210502-17-n7hain.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=281&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/398250/original/file-20210502-17-n7hain.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=281&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Fingerprints of sea-level change following melting of ice from West Antartica (WAIS) and Greenland (GIS) equivalent to one metre of sea-level rise on average. Red areas get up to 40% more than the average sea-level rise, blue areas get less.</span>
<span class="attribution"><span class="source">Author provided</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Woodward’s method from 1888 holds up pretty well – some locations in the northern hemisphere can get a third more than the average sea level rise. New Zealand gets a little bit below the average effect from Antarctica, and a little more than average from Greenland. Overall, New Zealand can expect slightly <a href="https://niwa.co.nz/natural-hazards/hazards/sea-levels-and-sea-level-rise">higher than average</a> sea level rise.</p>
<p><a href="https://link.springer.com/article/10.1007/s40641-015-0015-5">Combining</a> the sea-level fingerprints of all known sources of melting ice, together with other known changes of local land level such as subsidence and uplift, gives a good fit to the observed pattern of sea level rise around the world. For example, sea level has been <a href="https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level">falling</a> near West Antarctica, due to the gravity effect.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/396230/original/file-20210421-19-1rdppzg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Changes in sea level around the world, 1993-2019" src="https://images.theconversation.com/files/396230/original/file-20210421-19-1rdppzg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/396230/original/file-20210421-19-1rdppzg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/396230/original/file-20210421-19-1rdppzg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/396230/original/file-20210421-19-1rdppzg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/396230/original/file-20210421-19-1rdppzg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/396230/original/file-20210421-19-1rdppzg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/396230/original/file-20210421-19-1rdppzg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NOAA</span></span>
</figcaption>
</figure>
<h2>Sea-level rise is accelerating, but the future rate is uncertain</h2>
<p>The global average <a href="https://climate.nasa.gov/vital-signs/sea-level/">rise</a> in sea level is 110mm for 1900-1993 and 100mm for 1993–2020. The <a href="https://www.nature.com/articles/s41586-020-2591-3">recent acceleration</a> is mostly due to increased thermal expansion of the top two kilometres of the oceans (warm water is less dense and expands) and increased melting of Greenland. </p>
<p>But the <a href="https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO">Gravity Recovery and Climate Experiment</a> satellite has revealed the melting of Antarctica has <a href="https://www.pnas.org/content/pnas/116/4/1095.full.pdf">accelerated</a> by a factor of five in recent decades. Future changes in Antarctica represent a major source of uncertainty when trying to forecast sea levels.</p>
<p>Much of West Antarctica lies <a href="https://tc.copernicus.org/articles/7/375/2013/">below sea level</a> and is potentially subject to an <a href="https://en.wikipedia.org/wiki/Marine_ice_sheet_instability">instability</a> in which warming ocean water melts the ice front from below. This would cause the ice sheet to peel off the ocean floor, accelerating the flow of the glacier towards the sea.</p>
<p>In fact, this has been directly observed, both in the location of glacial “grounding lines”, some of which have <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014GL060140">retreated</a> by tens of kilometres in recent decades, and most recently by the <a href="https://schmidt.eas.gatech.edu/2019-field/firstlookunderthwaitesglacier/">Icefin</a> submersible robot which visited the grounding line of the Thwaites Glacier, 2000km east of Scott Base, and found the water temperature to be 2°C above the local freezing point.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/if-warming-exceeds-2-c-antarcticas-melting-ice-sheets-could-raise-seas-20-metres-in-coming-centuries-124484">If warming exceeds 2°C, Antarctica's melting ice sheets could raise seas 20 metres in coming centuries</a>
</strong>
</em>
</p>
<hr>
<p>The big <a href="https://www.nature.com/articles/s41558-018-0305-8">question</a> is whether this instability has been irreversibly set into motion. Some glaciologists say it <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014GL060140">has</a>, but the balance of opinion, summarised by the IPCC’s <a href="https://www.ipcc.ch/">report</a> on the cryosphere, is that:</p>
<blockquote>
<p>Observed grounding line retreat … is not definitive proof that Marine Ice Sheet Instability is underway. Whether unstable West Antarctic Ice Sheet retreat has begun or is imminent remains a critical uncertainty.</p>
</blockquote>
<p>The IPCC special report on <a href="https://www.ipcc.ch/sr15/">1.5°C</a> concluded that “these instabilities could be triggered at around 1.5°C to 2°C of global warming”.</p>
<h2>What’s in store for New Zealand</h2>
<p><a href="https://www.mfe.govt.nz/sites/default/files/media/Climate%20Change/coastal-hazards-guide-final.pdf">Predictions</a> for New Zealand range from a further 0.46 metres of sea-level rise by 2100 (under a low-emission scenario, with warming kept under 2°C) to 1.05 metres (under a high-emission scenario).</p>
<p>A continued rise in sea levels over future centuries may be inevitable — there are 66m of sea level rise locked up in ice at present — but the rate will depend on how fast we can reduce emissions. </p>
<p>A five-year, NZ$7m research project, <a href="https://www.searise.nz/">NZ SeaRise</a>, is now underway, seeking to improve predictions of sea-level rise out to 2100 and beyond and their implications for local planning.</p><img src="https://counter.theconversation.com/content/155464/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robert McLachlan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>When Antarctica’s land-based ice melts, the land bounces up slightly as the weight of the ice lifts. This affects sea levels across the world, but not enough to offset sea-level rise.Robert McLachlan, Professor in Applied Mathematics, Massey UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1502612020-11-17T16:45:45Z2020-11-17T16:45:45ZGreenland is melting: we need to worry about what’s happening on the largest island in the world<figure><img src="https://images.theconversation.com/files/369860/original/file-20201117-13-19n3zcw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Jonathan Bamber</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Greenland is the largest island in the world and on it rests the largest ice mass in the Northern Hemisphere. If all that ice melted, the sea would rise by <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL074954">more than 7 metres</a>. </p>
<p>But that’s not going to happen is it? Well not any time soon, but understanding how much of the ice sheet might melt over the coming century is a critical and urgent question that scientists are trying to tackle using sophisticated numerical models of how the ice sheet <a href="https://tc.copernicus.org/articles/14/3071/2020/">interacts with the rest of the climate system</a>. The problem is that the models aren’t that good at reproducing recent observations and are limited by our poor knowledge of the detailed topography of the subglacial terrain and fjords, which the ice flows over and in to.</p>
<p>One way around this problem is to see how the ice sheet responded to changes in climate in the past and compare that with model projections for the future for similar changes in temperature. That is exactly what colleagues and I did in a new study now published in the journal <a href="https://www.nature.com/articles/s41467-020-19580-5">Nature Communications</a>. </p>
<p>We looked at the three largest glaciers in Greenland and used historical aerial photographs combined with measurements scientists had taken directly over the years, to reconstruct how the volume of these glaciers had changed over the period 1880 to 2012. The approach is founded on the idea that the past can help inform the future, not just in science but in all aspects of life. But just like other “classes” of history, the climate and the Earth system in future won’t be a carbon copy of the past. Nonetheless, if we figure out exactly how sensitive the ice sheet has been to temperature changes over the past century, that can provide a useful guide to how it will respond over the next century. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/369795/original/file-20201117-23-1ha07y1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A man walks over grassy land with glacier in background" src="https://images.theconversation.com/files/369795/original/file-20201117-23-1ha07y1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/369795/original/file-20201117-23-1ha07y1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/369795/original/file-20201117-23-1ha07y1.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/369795/original/file-20201117-23-1ha07y1.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/369795/original/file-20201117-23-1ha07y1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/369795/original/file-20201117-23-1ha07y1.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/369795/original/file-20201117-23-1ha07y1.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Greenland’s glaciers contain around 8% of the world’s fresh water.</span>
<span class="attribution"><span class="source">Jonathan Bamber</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We found that the three largest glaciers were responsible for 8.1mm of sea level rise, about 15% of the whole ice sheet’s contribution. Over the period of our study the sea globally has risen by around 20cm, about the height of an A5 booklet, and of that, about a finger’s width is entirely thanks to ice melting from those three Greenland glaciers.</p>
<h2>Melting As Usual</h2>
<p>So what does that tell us about the future behaviour of the ice sheet? In 2013, a <a href="https://www.nature.com/articles/nature12068">modelling study</a> by Faezeh Nick and colleagues also looked at the same “big three” glaciers (Jakobshavn Isbrae in the west of the island and Helheim and Kangerlussuaq in the east) and projected how they would respond in different future climate scenarios. The most extreme of these scenarios is called <a href="https://www.carbonbrief.org/explainer-the-high-emissions-rcp8-5-global-warming-scenario">RCP8.5</a> and assumes that economic growth will continue unabated through the 21st century, resulting in a global mean warming of about 3.7˚C above today’s temperatures (about 4.8˚C above pre-industrial or since 1850). </p>
<p>This scenario has sometimes been referred to as Business As Usual (BAU) and there is an <a href="https://www.scientificamerican.com/article/the-worst-climate-scenarios-may-no-longer-be-the-most-likely/">active debate</a> among climate researchers regarding how plausible RCP8.5 is. It’s interesting to note, however, that, according to a recent study from a group of US scientists it may be the most appropriate scenario <a href="https://www.pnas.org/content/117/33/19656">up to at least 2050</a>. Because of something called <a href="https://theconversation.com/siberia-heatwave-why-the-arctic-is-warming-so-much-faster-than-the-rest-of-the-world-141455">polar amplification</a> the Arctic will likely heat up by more than double the global average, with the climate models indicating around 8.3˚C warming over Greenland in the most extreme scenario, RCP8.5. </p>
<p>Despite this dramatic and terrifying hike in temperature Faezeh’s modelling study projected that the “big three” would contribute between 9 and 15 mm to sea level rise by 2100, only slightly more than what we obtained from a 1.5˚C warming over the 20th century. How can that be? Our conclusion is that the models are at fault, even including the <a href="https://tc.copernicus.org/articles/14/3071/2020/">latest and most sophisticated available</a> which are being used to assess how the whole ice sheet will respond to the next century of climate change. These models appear to have a relatively weak link between climate change and ice melt, when <a href="https://www.nature.com/articles/s41467-020-19580-5">our results</a> suggest it is much stronger. Projections based on these models are therefore likely to under-predict how much the ice sheet will be affected. Other lines of evidence <a href="https://theconversation.com/the-arctic-hasnt-been-this-warm-for-3-million-years-and-that-foreshadows-big-changes-for-the-rest-of-the-planet-144544">support</a> this <a href="https://theconversation.com/climate-change-sea-level-rise-could-displace-millions-of-people-within-two-generations-116753">conclusion</a>. </p>
<p>What does all of that mean? If we do continue along that very scary RCP8.5 trajectory of increasing greenhouse gas emissions, the Greenland ice sheet is very likely to start melting at rates that we haven’t seen for at least 130,000 years, with dire consequences for sea level and the <a href="https://www.nature.com/articles/s41467-019-12808-z">many millions of people</a> who live in low lying coastal zones.</p><img src="https://counter.theconversation.com/content/150261/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonathan Bamber receives funding from the UK Natural Environment Research Council and the European Research Council.</span></em></p>Our new research shows the island’s largest glaciers are losing ice faster than previously thought.Jonathan Bamber, Professor of Physical Geography, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1487532020-10-26T15:18:04Z2020-10-26T15:18:04ZArctic Ocean: why winter sea ice has stalled, and what it means for the rest of the world<figure><img src="https://images.theconversation.com/files/365538/original/file-20201026-13-cl944n.jpg?ixlib=rb-1.1.0&rect=0%2C196%2C5472%2C3440&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ice floes in the Laptev Sea, Russia.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/ice-floes-arctic-sea-laptev-yakutia-504230647">Olenyok/Shutterstock</a></span></figcaption></figure><p>Arctic sea ice plays a crucial role in the Earth’s energy balance. It is covered for most of the year by snow, which is the brightest natural surface on the planet, reflecting about 80% of the solar radiation that hits it back out to space. </p>
<p>Meanwhile, the ocean it floats on is the darkest natural surface on the planet, absorbing 90% of incident solar radiation. For that reason, changes in sea ice cover have a big impact on how much sunlight the planet absorbs, and how fast it warms up.</p>
<p>Each year a thin layer of the Arctic Ocean freezes over, forming sea ice. In spring and summer this melts back again, but some of the sea ice survives through the summer and is known as multi-year ice. It’s thicker and more resilient than the sea ice that forms and melts each year, but as the Arctic climate warms – at a rate <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2019/ArtMID/7916/ArticleID/835/Surface-Air-Temperature">more than twice</a> that of the rest of the world – this multi-year ice is under threat.</p>
<p>In the last 40 years, multi-year ice has shrunk by <a href="https://nsidc.org/data/seaice_index/">about half</a>. At some time in the next few decades, scientists expect the world will see an ice-free Arctic Ocean throughout the summer, with worrying consequences for the rest of the climate system. That prospect got much closer in 2020, due in part to the exceptional summer heatwave that roiled the Russian Arctic.</p>
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Read more:
<a href="https://theconversation.com/siberia-heatwave-why-the-arctic-is-warming-so-much-faster-than-the-rest-of-the-world-141455">Siberia heatwave: why the Arctic is warming so much faster than the rest of the world</a>
</strong>
</em>
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<h2>Shutting down the sea ice factory</h2>
<p>The oceans have a large thermal capacity, which means they can store huge amounts of heat. In fact, the top metre of the oceans has about the same thermal capacity as the whole of the atmosphere. Many of us have experienced a balmy afternoon in autumn by the coast even though the air temperature inland is only a few degrees above freezing. That’s because the oceans accumulate heat slowly over the summer, releasing it equally slowly during winter.</p>
<p>So it is with the Laptev Sea, lying north of the Siberian coast. This part of the Arctic Ocean is usually a factory for new sea ice in autumn and winter as air temperatures dip below zero and surface water starts to freeze. That new ice is carried westward by persistent offshore winds in a kind of conveyor belt.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/365562/original/file-20201026-21-1112tqa.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A map of the Laptev Sea with an inset world map." src="https://images.theconversation.com/files/365562/original/file-20201026-21-1112tqa.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/365562/original/file-20201026-21-1112tqa.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=336&fit=crop&dpr=1 600w, https://images.theconversation.com/files/365562/original/file-20201026-21-1112tqa.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=336&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/365562/original/file-20201026-21-1112tqa.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=336&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/365562/original/file-20201026-21-1112tqa.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=423&fit=crop&dpr=1 754w, https://images.theconversation.com/files/365562/original/file-20201026-21-1112tqa.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=423&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/365562/original/file-20201026-21-1112tqa.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=423&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Laptev Sea lies off the coast of northern Siberia.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Laptev_Sea#/media/File:Laptev_Sea_map.png">NormanEinstein/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>This process is powered by the formation of polynyas: areas of open water surrounded by sea ice. Polynas act as engines of new sea ice production by exchanging heat with the colder atmosphere, causing the water to freeze. But if there is no sea ice to start with, the polynya cannot form and the whole process shuts down.</p>
<p>Sea ice in the Laptev Sea reached a record low in 2020, with no new ice through October, later than any previous year in the <a href="https://nsidc.org/data/seaice_index/">satellite record</a>. The exceptional summer heatwave across Siberia will have resulted in heat accumulating in the adjacent ocean, which is now delaying the regrowth of sea ice.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1316175657378799616"}"></div></p>
<p>In the 1980s, there was as much as 600,000 square kilometres of multi-year ice covering around two thirds of the Laptev Sea. In 2020, it has been ice-free for months with no multi-year ice left at all. The whole Arctic Ocean is heading for ice-free conditions in the future, defined as less than one million square kilometres of ice cover. That’s down from about 8 million square kilometres just 40 years ago. This year’s new record delay in ice formation in the Laptev Sea takes it a step closer. </p>
<p>A rapidly changing Arctic is a global cause for concern. Thawing permafrost releases methane, a greenhouse gas that is about <a href="https://www.edf.org/climate/methane-other-important-greenhouse-gas">84 times more potent</a> than CO₂ when measured over 20 years. </p>
<p>Meanwhile, the Greenland Ice Sheet, the largest ice mass in the northern hemisphere, is currently contributing more to sea levels rising than any other source, and has enough ice in it to raise global sea level by 7.4 metres. And if the machinations of a warming Arctic still seem remote, evidence suggests that even the weather across much of <a href="https://theconversation.com/arctic-breakdown-what-climate-change-in-the-far-north-means-for-the-rest-of-us-123309">the northern hemisphere</a> is heavily influenced by what happens in the rapidly changing roof of the world.</p><img src="https://counter.theconversation.com/content/148753/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonathan Bamber receives funding from the Natural Environment Research Council. </span></em></p>The Laptev Sea is one of the Arctic’s biggest nurseries of new sea ice in winter, but Siberia’s record summer heat may have halted production.Jonathan Bamber, Professor of Physical Geography, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1235542019-09-20T12:35:00Z2019-09-20T12:35:00ZWhat is the cryosphere? Hint: It’s vital to farming, fishing and skiing<figure><img src="https://images.theconversation.com/files/292490/original/file-20190914-8658-1czu2oq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Rivers of melted ice on a Western Greenland ice sheet drain into the ocean beneath the ice.</span> <span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Greenland-Melting-Ice/8056e0a0606c47e8b32f4a6a5d82738c/1/0">Photo via Caspar Haarløv/AP</a></span></figcaption></figure><p>More than 100 scientists from 30 countries released a <a href="https://www.ipcc.ch/report/srocc/">special report</a> examining climate change impacts on the oceans and a less familiar but critically important part of the Earth: the cryosphere.</p>
<p>Ice sheets, ice caps and glaciers, the floating sea ice of the polar regions, lake ice, snow on the ground, and <a href="https://nsidc.org/cryosphere/sotc/permafrost.html">permafrost</a>, permanently frozen ground in northern latitudes, all make up the cryosphere. </p>
<p>While snow and ice in our daily lives can, at times, be difficult to navigate and sometimes dangerous, people <a href="https://doi.org/10.1016/j.accre.2015.11.004">benefit greatly</a> from the cryosphere. It helps cool our planet and controls global sea level. It affects ocean currents and storm patterns around the world. The fresh water stored in snow and ice provides drinking water and irrigates crops. I am a researcher who studies snow and ice, and the fact that the Earth is beginning to lose its cryosphere as a result of global warming climate should concern all of us.</p>
<h2>Fresh water locked in massive ice sheets</h2>
<p>The Greenland and Antarctic ice sheets contain <a href="https://nsidc.org/cryosphere/quickfacts/icesheets.html">99% of the freshwater ice</a> on the planet. These ice sheets, glaciers and ice caps around the world are losing mass and are contributing to <a href="https://www.globalchange.gov/browse/indicators/global-sea-level-rise">sea level rise</a>, putting coastal regions and low-lying islands around the world at risk. </p>
<p>The Tibetan Plateau is known as the “<a href="https://medium.com/the-himalayan/preserving-tibet-the-water-tower-of-asia-f2303a65645b">water tower</a>” of Asia. The Mekong River, Yellow River, the Yangthze, Indus River and the Karnali all originate on the <a href="https://www.cfr.org/backgrounder/water-clouds-tibetan-plateau">Tibetan plateau</a> and are fed by snow and glacier melt and the water from these rivers supports hundreds of millions of people. </p>
<p>More locally, in the U.S. Mountain West, including the Cascades, Sierra Nevada and Rocky Mountains, the winter snowpack, water stored as ice and snow until spring, is the major source of water for agriculture, industry and municipal use. Like the ice sheets in the polar regions, <a href="https://www.epa.gov/climate-indicators/climate-change-indicators-snowpack">evidence</a> shows that the winter snowpack in the U.S. is shrinking. The economic impact to communities without enough cold weather and snow is numerous, whether it is a loss of winter sports such as skiing, snowmobiling and ice fishing or less water for fish or irrigation to grow food. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/292492/original/file-20190914-8701-3ekhf2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/292492/original/file-20190914-8701-3ekhf2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/292492/original/file-20190914-8701-3ekhf2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/292492/original/file-20190914-8701-3ekhf2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/292492/original/file-20190914-8701-3ekhf2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/292492/original/file-20190914-8701-3ekhf2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/292492/original/file-20190914-8701-3ekhf2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mt Rainier in the Cascade Mountain range.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/04061807986">Ted S. Warren/AP</a></span>
</figcaption>
</figure>
<p>The threats of our shrinking cryosphere involve much more than impacts to local and regional economies, however. Much of our planet’s snow and ice, located in the polar regions, is there because it is so cold. The bright white snow and ice cover functions like a mirror for the planet, reflecting back into space much of the Sun’s energy that reaches the surface. The snow and ice reinforce the cold of the polar regions and their role as our planet’s natural refrigerators. A warming Earth undermines the ability of snow and ice to moderate and stabilize the global climate. </p>
<h2>The impact of thinning ice</h2>
<p>In the Arctic, the North Polar region of Earth, much of the ocean is covered by <a href="https://nsidc.org/cryosphere/seaice/index.html">floating sea ice</a>, which forms when sea water freezes. This sea ice cover is shrinking. As the ice thins and melts, darker surfaces are exposed and absorb more of the Sun’s energy. This leads to more warming and even more melting. This cycle of heat absorption, warming and melting, known as a positive feedback, is a factor in Arctic amplification – the observation that the Arctic is warming at <a href="https://www.scientificamerican.com/article/major-report-prompts-warnings-that-the-arctic-is-unraveling1/">least twice as quickly the rate as the globe as a whole</a>. </p>
<p>The loss of the floating sea ice cover and the rapidly warming Arctic are causing a <a href="https://science.sciencemag.org/content/341/6145/519">cascade effect</a> through the Arctic food chain – from top predators like the polar bear to tiny phytoplankton that live throughout the world’s oceans. The lives of the 4 million people who live in the Arctic are being disrupted in myriad ways. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/b0giaWG5rOo?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The Greenland ice sheet releases tons of fresh water.</span></figcaption>
</figure>
<p>The ice-diminished Arctic is opening up potential shipping lanes including the northern sea route along the Russian coast and the Northwest Passage through the channels of the Canadian Arctic archipelago, all islands north of Canada except Greenland. Oil and natural gas deposits under the Arctic seafloor are becoming more accessible. The potential for economic development in the region brings with it inevitable challenges of <a href="https://en.wikipedia.org/wiki/Geopolitics_of_the_Arctic">governance and conflict</a>. </p>
<h2>The global ice budget</h2>
<p>But what is happening in the north won’t just stay there. As the Arctic warms, it may disrupt the <a href="https://www.nationalgeographic.com/environment/weather/reference/jet-stream/">jet stream</a>, the narrow band of strong west to east winds high in the atmosphere that influences weather, the tracks and intensity of storms in the middle latitudes of the Northern Hemisphere. Some scientists say that this is <a href="https://doi.org/10.1007/s10712-014-9284-0">already happening</a>. </p>
<p>And, as the Arctic’s permafrost thaws, Arctic land will release stored carbon, in the form of carbon dioxide, and methane back to the atmosphere, potentially leading to <a href="https://theconversation.com/will-the-arctic-shift-from-a-carbon-sink-to-a-carbon-source-47826">further climate warming</a>. The melting Greenland ice sheet <a href="https://advances.sciencemag.org/content/5/6/eaav9396">is contributing to sea level rise</a> in addition to melting Arctic ice caps and glaciers.</p>
<p>As our climate gets hotter, the cryosphere will continue to shrink and melt, and the impacts of losing it will likely only multiply. What we see today is just the beginning.</p>
<p>[ <em>Like what you’ve read? Want more?</em> <a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=likethis">Sign up for The Conversation’s daily newsletter</a>. ]</p><img src="https://counter.theconversation.com/content/123554/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Serreze receives funding from the National Science Foundation, NASA, and NOAA</span></em></p>Studies show that the Arctic is heating up twice as fast as the rest of the planet.Mark Serreze, Research Professor of Geography and Director, National Snow and Ice Data Center, University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1167532019-05-20T20:59:09Z2019-05-20T20:59:09ZClimate change: sea level rise could displace millions of people within two generations<figure><img src="https://images.theconversation.com/files/273866/original/file-20190510-183093-1ageusy.JPG?ixlib=rb-1.1.0&rect=0%2C0%2C3648%2C2736&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A small boat in the Illulissat Icefjord is dwarfed by the icebergs that have calved from the floating tongue of Greenland's largest glacier, Jacobshavn Isbrae</span> <span class="attribution"><span class="source">Michael Bamber</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Antarctica is further from civilisation than any other place on Earth. The Greenland ice sheet is closer to home but around one tenth the size of its southern sibling. Together, these two ice masses hold enough frozen water to raise global mean sea level by 65 metres if they were to suddenly melt. But how likely is this to happen?</p>
<p>The Antarctic ice sheet is around one and half times larger than Australia. What’s happening in one part of Antarctica may not be the same as what’s happening in another – just like the east and west coasts of the US can experience very different responses to, for example, <a href="https://www.climate.gov/news-features/blogs/enso/united-states-el-ni%C3%B1o-impacts-0">a change in the El Niño weather pattern</a>. These are periodic climate events that result in wetter conditions across the southern US, warmer conditions in the north and drier weather on the north-eastern seaboard. </p>
<p>The ice in Antarctica is nearly 5km thick in places and we have very little idea what the conditions are like at the base, even though those conditions play a key role in determining the speed with which the ice can respond to climate change, including how fast it can flow toward and into the ocean. A warm, wet base lubricates the bedrock of land beneath the ice and allows it to slide over it.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/275395/original/file-20190520-69192-1kfaj5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/275395/original/file-20190520-69192-1kfaj5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/275395/original/file-20190520-69192-1kfaj5d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/275395/original/file-20190520-69192-1kfaj5d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/275395/original/file-20190520-69192-1kfaj5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/275395/original/file-20190520-69192-1kfaj5d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/275395/original/file-20190520-69192-1kfaj5d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Though invisible from the surface, melting within the ice can speed up the process by which ice sheets slide towards the sea.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/glacier-serpimolot-bay-bear-on-northern-384912739">Gans33/Shutterstock</a></span>
</figcaption>
</figure>
<p>These issues have made it particularly difficult to produce model simulations of how ice sheets will respond to climate change in future. Models have to capture all the processes and uncertainties that we know about and those that we don’t – the “known unknowns” and the “unknown unknowns” as <a href="https://www.youtube.com/watch?v=GiPe1OiKQuk">Donald Rumsfeld once put it</a>. As a result, several recent studies suggest that previous Intergovernmental Panel on Climate Change reports may have <a href="https://science.sciencemag.org/content/354/6318/1375">underestimated how much</a> melting ice sheets will contribute to sea level in future.</p>
<h2>What the experts say</h2>
<p>Fortunately, models are not the only tools for predicting the future. <a href="https://www.nature.com/articles/nclimate1778">Structured Expert Judgement</a> is a method from a study one of us published in 2013. Experts give their judgement on a hard-to-model problem and their judgements are combined in a way that takes into account how good they are at <a href="https://www.nature.com/articles/463294a">assessing their own uncertainty</a>. This provides a rational consensus.</p>
<p>The approach has been used when the consequences of an event are potentially catastrophic, but our ability to model the system is poor. These include volcanic eruptions, earthquakes, the spread of vector-borne diseases such as malaria and even aeroplane crashes. </p>
<p><a href="https://www.nature.com/articles/nclimate1778">Since the study in 2013</a>, scientists modelling ice sheets have improved their models by trying to incorporate processes that cause positive and negative feedback. Impurities on the surface of the Greenland ice sheet cause positive feedback as they enhance melting by absorbing more of the sun’s heat. The stabilising effect of bedrock rising as the overlying ice thins, lessening the weight on the bed, is an example of negative feedback, as it slows the rate that the ice melts. </p>
<p>The record of observations of ice sheet change, primarily from satellite data, has also grown in length and quality, helping to <a href="https://iopscience.iop.org/article/10.1088/1748-9326/aac2f0/pdf">improve knowledge of the recent behaviour of the ice sheets</a>.</p>
<p>With colleagues from the UK and US, we undertook <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.1817205116">a new Structured Expert Judgement exercise</a>. With all the new research, data and knowledge, you might expect the uncertainties around how much ice sheet melting will contribute to sea level rise to have got smaller. Unfortunately, that’s not what we found. What we did find was a range of future outcomes that go from bad to worse.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/274936/original/file-20190516-69182-1oa09zo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/274936/original/file-20190516-69182-1oa09zo.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=271&fit=crop&dpr=1 600w, https://images.theconversation.com/files/274936/original/file-20190516-69182-1oa09zo.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=271&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/274936/original/file-20190516-69182-1oa09zo.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=271&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/274936/original/file-20190516-69182-1oa09zo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=340&fit=crop&dpr=1 754w, https://images.theconversation.com/files/274936/original/file-20190516-69182-1oa09zo.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=340&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/274936/original/file-20190516-69182-1oa09zo.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=340&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Reconstructed sea level for the last 2500 years. Note the marked increase in rate since about 1900 that is unprecedented over the whole time period.</span>
<span class="attribution"><a class="source" href="https://www.pnas.org/content/113/11/E1434.short">Robert Kopp/Kopp et al. (2016)</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Rising uncertainty</h2>
<p>We gathered together 22 experts in the US and UK in 2018 and combined their judgements. The results are sobering. Rather than a shrinking in the uncertainty of future ice sheet behaviour over the last six years, it has grown.</p>
<p>If the global temperature increase stays below 2°C, the experts’ best estimate of the average contribution of the ice sheets to sea level was 26cm. They concluded, however, that there is a 5% chance that the contribution could be as much as 80cm. </p>
<p>If this is combined with the two other main factors that influence sea level – glaciers melting around the world and the expansion of ocean water as it warms – then global mean sea level rise could exceed one metre by 2100. If this were to occur, many small island states would experience their current once-in-a-hundred–year <a href="https://advances.sciencemag.org/content/4/4/eaap9741">flood every other day and become effectively uninhabitable</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/275396/original/file-20190520-69195-2c9dga.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/275396/original/file-20190520-69195-2c9dga.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/275396/original/file-20190520-69195-2c9dga.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/275396/original/file-20190520-69195-2c9dga.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/275396/original/file-20190520-69195-2c9dga.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/275396/original/file-20190520-69195-2c9dga.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/275396/original/file-20190520-69195-2c9dga.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A climate refugee crisis could dwarf all previous forced migrations.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/lesbos-greece-september-30-2015-refugees-325232699?src=WxHLErac17sJTjerJLHYXA-1-7">Punghi/Shutterstock</a></span>
</figcaption>
</figure>
<p>For a climate change scenario closer to business as usual – where our current trajectory for economic growth continues and global temperatures increase by 5°C – the outlook is even more bleak. The experts’ best estimate average in this case is 51cm of sea level rise caused by melting ice sheets by 2100, but with a 5% chance that global sea level rise could exceed two metres by 2100. That has the potential to <a href="https://royalsocietypublishing.org/doi/full/10.1098/rsta.2010.0291">displace some 200m people</a>. </p>
<p>Let’s try and put this into context. The Syrian refugee crisis is estimated to have caused <a href="http://data.unhcr.org/syrianrefugees/asylum.php">about a million people to migrate to Europe</a>. This occurred over years rather than a century, giving much less time for countries to adjust. Still, sea level rise driven by migration of this size might threaten the existence of nation states and result in unimaginable stress on resources and space. There is time to change course, but not much, and the longer we delay the harder it gets, the bigger the mountain we have to climb.</p>
<hr>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=140&fit=crop&dpr=1 600w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=140&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=140&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=176&fit=crop&dpr=1 754w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=176&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=176&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/imagine-newsletter-researchers-think-of-a-world-with-climate-action-113443?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=Imagineheader1116753">Click here to subscribe to our climate action newsletter. Climate change is inevitable. Our response to it isn’t.</a></em></p><img src="https://counter.theconversation.com/content/116753/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonathan Bamber receives funding from the UK Natural Environment Research Council, The Royal Society and the European Research Council. </span></em></p><p class="fine-print"><em><span>Michael Oppenheimer receives funding from US National Science Foundation and the High Meadows Foundation. He is affiliated with the Environmental Defense Fund, Climate Central, and the Climate Science Legal Defense Fund.
</span></em></p>Sea levels could rise by two metres by 2100, sparking a refugee crisis unlike anything the world has ever seen.Jonathan Bamber, Professor of Physical Geography, University of BristolMichael Oppenheimer, Professor of Geosciences and International Affairs, Princeton UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/826752017-08-18T13:39:35Z2017-08-18T13:39:35ZGreenland: how rapid climate change on world’s largest island will affect us all<figure><img src="https://images.theconversation.com/files/182587/original/file-20170818-7937-vmrbcz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Dan Bach Kristensen / shutterstock</span></span></figcaption></figure><p>The <a href="https://www.scientificamerican.com/article/wildfire-burns-across-formerly-icy-greenland/">largest wildfire ever recorded</a> in Greenland was recently spotted close to the west coast town of Sisimiut, not far from Disko Island where I research <a href="https://arcticresearch.wordpress.com/category/blogs-from-the-field/sedigap-investigating-sediment-and-meltwater-dynamics-in-an-area-of-arctic-permafrost/">retreating glaciers</a>. The fire has captured public and scientific interest not just because its size and location came as a surprise, but also because it is yet another signpost of deep environmental change in the Arctic. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"895255754176909312"}"></div></p>
<p>Greenland is an important cog in the global climate system. The ice sheet which covers 80% of the island reflects so much of the sun’s energy back into space that it moderates temperatures through what is known as the “<a href="http://www.bbc.co.uk/education/clips/zhmb4wx">albedo effect</a>”. And since it occupies a strategic position in the North Atlantic, its meltwater tempers ocean circulation patterns. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/182595/original/file-20170818-7937-qmwhfo.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/182595/original/file-20170818-7937-qmwhfo.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/182595/original/file-20170818-7937-qmwhfo.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1022&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182595/original/file-20170818-7937-qmwhfo.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1022&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182595/original/file-20170818-7937-qmwhfo.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1022&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182595/original/file-20170818-7937-qmwhfo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1284&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182595/original/file-20170818-7937-qmwhfo.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1284&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182595/original/file-20170818-7937-qmwhfo.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1284&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Most of Greenland is covered by more than a kilometre of ice.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Greenland_ice_sheet_AMSL_thickness_map-en.svg">Eric Gaba / NGDC</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>But Greenland is especially vulnerable to climate change, as Arctic air temperatures are currently rising at <a href="http://edition.cnn.com/2016/12/14/world/arctic-report-card/index.html">twice the global average rate</a>. Environmental conditions are frequently setting new records: “the warmest”, “the wettest”, “the driest”.</p>
<p>Despite its size, the fire itself represents only a snapshot of Greenland’s fire history. It alone cannot tell us about wider Arctic climate change. </p>
<p>But when we superimpose these extraordinary events onto longer-term environmental records, we can see important trends emerging. </p>
<h2>The ice sheet is melting</h2>
<p>Between 2002 and 2016 the ice sheet lost mass at a rate of around 269 gigatonnes per year. One gigatonne is one billion tonnes. One tonne is about the weight of a walrus. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/182590/original/file-20170818-7965-1j59k7c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/182590/original/file-20170818-7965-1j59k7c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=403&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182590/original/file-20170818-7965-1j59k7c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=403&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182590/original/file-20170818-7965-1j59k7c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=403&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182590/original/file-20170818-7965-1j59k7c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=507&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182590/original/file-20170818-7965-1j59k7c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=507&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182590/original/file-20170818-7965-1j59k7c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=507&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Leave my weight out of this.</span>
<span class="attribution"><span class="source">BMJ / shutterstock</span></span>
</figcaption>
</figure>
<p>During the same period, the ice sheet also showed some unusual short-term behaviour. The 2012 melt season was especially intense – <a href="https://nsidc.org/greenland-today/2013/02/greenland-melting-2012-in-review/">97% of the ice sheet</a> experienced surface melt at some point during the year. Snow even melted at its summit, the highest point in the centre of the island where the ice is piled up <a href="http://www.esa.int/spaceinimages/Images/2014/08/Greenland_ice-sheet_height">more than 3km above sea level</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182591/original/file-20170818-7944-epr3dd.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/182591/original/file-20170818-7944-epr3dd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/182591/original/file-20170818-7944-epr3dd.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=468&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182591/original/file-20170818-7944-epr3dd.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=468&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182591/original/file-20170818-7944-epr3dd.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=468&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182591/original/file-20170818-7944-epr3dd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=588&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182591/original/file-20170818-7944-epr3dd.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=588&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182591/original/file-20170818-7944-epr3dd.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=588&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Change in total mass of the Greenland Ice Sheet (in Gt) from 2002 to 2016. Red crosses indicate the values every April.</span>
<span class="attribution"><a class="source" href="http://www.arctic.noaa.gov/Report-Card/Report-Card-2016/ArtMID/5022/ArticleID/277/Greenland-Ice-Sheet">NOAA</a></span>
</figcaption>
</figure>
<p>In April 2016 Greenland saw abnormally high temperatures and its earliest ever “<a href="http://nsidc.org/greenland-today/2016/10/2016-melt-season-in-review/">melt event</a>” (a day in which more than 10% of the ice sheet has at least 1mm of surface melt). Early melting doesn’t usher in a period of complete and catastrophic change – the ice won’t vanish overnight. But it does illustrate how profoundly and rapidly the ice sheet can respond to rising temperatures. </p>
<h2>Permafrost is thawing</h2>
<p>Despite its icy image, the margins of Greenland are actually quite boggy, complete with swarms of mosquitoes. This is the “active layer”, made up of peaty soil and sediment up to two metres thick, which temporarily thaws during the summer. The underlying permafrost, which can reach depths of 100m, remains permanently frozen. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182582/original/file-20170818-7952-1wpp4mg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/182582/original/file-20170818-7952-1wpp4mg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/182582/original/file-20170818-7952-1wpp4mg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182582/original/file-20170818-7952-1wpp4mg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182582/original/file-20170818-7952-1wpp4mg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182582/original/file-20170818-7952-1wpp4mg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182582/original/file-20170818-7952-1wpp4mg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182582/original/file-20170818-7952-1wpp4mg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Fighting off the mosquitos in boggy Greenland.</span>
<span class="attribution"><span class="source">Kathryn Adamson</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>In Greenland, like much of the Arctic, rising temperatures are thawing the permafrost. This means the active layer is growing by up to <a href="http://curis.ku.dk/ws/files/132148895/Future_permafrost_conditions_along.pdf">1.5cm per year</a>. This trend is expected to continue, seeing as under current IPCC predictions, Arctic air temperatures will rise by between <a href="http://cenperm.ku.dk/facts-about-permafrost/">2.0°C and 7.5°C</a> this century. </p>
<p>Arctic permafrost contains more than 1,500 billion tonnes of dead plants and animals (around 1,500 billion walrus equivalent) which we call “organic matter”. Right now, this stuff has been frozen for thousands of years. But when the permafrost thaws this organic matter will decay, releasing carbon and methane (another greenhouse gas) into the atmosphere.</p>
<p>If thawing continues, it’s estimated that by 2100 permafrost will <a href="http://cenperm.ku.dk/facts-about-permafrost/">emit 850-1,400 billion tonnes of CO₂ equivalent</a> (for comparison: total global emissions in 2012 was <a href="http://data.worldbank.org/indicator/EN.ATM.GHGT.KT.CE">54 billion tonnes of CO₂ equivalent</a>). All that extra methane and carbon of course has the potential to enhance global warming even further. </p>
<p>With this in mind, it is clear to see why the recent wildfire, which was burning in dried-out peat in the active layer, was especially interesting to researchers. If Greenland’s permafrost becomes increasingly degraded and dry, there is the potential for even bigger wildfires which would release vast stores of greenhouse gases into the atmosphere. </p>
<h2>Species are adapting to a changing ecosystem</h2>
<p>Major changes in the physical environment are already affecting the species that call Greenland home. Just look at polar bears, the face of Arctic climate change. Unlike other bears, polar bears spend most of their time at sea, which explains their Latin name <em>Ursus maritimus</em>. In particular they rely on sea ice as it gives them a deep-water platform from which to hunt seals.</p>
<p>However, since 1979 the extent of sea ice has decreased by around 7.4% per decade due to climate warming, and bears have had to <a href="https://link.springer.com/article/10.1007/s00300-015-1648-5">adjust their habitat use</a>. With continued temperature rise and sea ice disappearance, it’s predicted that <a href="http://rsbl.royalsocietypublishing.org/content/12/12/20160556">populations will decline by up to 30%</a> in the next few decades, taking the total number of polar bears to under 9,000.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/182592/original/file-20170818-7941-12uzylj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/182592/original/file-20170818-7941-12uzylj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182592/original/file-20170818-7941-12uzylj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182592/original/file-20170818-7941-12uzylj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182592/original/file-20170818-7941-12uzylj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182592/original/file-20170818-7941-12uzylj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182592/original/file-20170818-7941-12uzylj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Where are you, seals?</span>
<span class="attribution"><span class="source">Mario_Hoppmann / shutterstock</span></span>
</figcaption>
</figure>
<p>I have considered only a handful of the major environmental shifts in Greenland over the past few decades, but the effects of increasing temperatures are being felt in all parts of the earth system. Sometimes these are manifest as extreme events, at others as slow and insidious changes. </p>
<p>The different parts of the environmental jigsaw interact, so that changes in one part (sea ice decline, say) influence another (polar bear populations). We need to keep a close eye on the system as a whole if we are to make reliable interpretations – and meaningful plans for the future.</p><img src="https://counter.theconversation.com/content/82675/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kathryn Adamson receives funding from NERC and EU-INTERACT. She sits on the UK National Curriculum panel for OCR Geography and has collaborated with the Royal Meteorological Society, American Geophysical Union, and European Geosciences Union.</span></em></p>The ice sheet is melting and permafrost is thawing. What’s happening in Greenland will speed up climate change across the world.Kathryn Adamson, Senior Lecturer in Physical Geography, Manchester Metropolitan UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/791752017-06-26T20:07:30Z2017-06-26T20:07:30ZContributions to sea-level rise have increased by half since 1993, largely because of Greenland’s ice<figure><img src="https://images.theconversation.com/files/175478/original/file-20170625-13461-lezup7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Water mass enters the ocean from glaciers such as this along the Greenland coast.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/earthrightnow/34558983852">NASA/JPL-Caltech</a></span></figcaption></figure><p>Contributions to the rate of global sea-level rise increased by about half between 1993 and 2014, with much of the increase due to an increased contribution from Greenland’s ice, according to our new research.</p>
<p>Our study, <a href="http://dx.doi.org/10.1038/nclimate3325">published in Nature Climate Change</a>, shows that the sum of contributions increased from 2.2mm per year to 3.3mm per year. This is consistent with, although a little larger than, the observed increase in the rate of rise estimated from satellite observations. </p>
<p>Globally, the rate of sea-level rise has been increasing since the 19th century. As a result, the rate during the 20th century was <a href="https://www.nytimes.com/2016/02/23/science/sea-level-rise-global-warming-climate-change.html">significantly greater than during previous millennia</a>. The rate of rise over the past two decades has been larger still. </p>
<p>The rate is projected to increase still further during the 21st century unless human greenhouse emissions can be significantly curbed.</p>
<p>However, since 1993, when high-quality satellite data collection started, most previous studies have not reported an increase in the rate of rise, despite many results pointing towards <a href="https://www.nasa.gov/feature/goddard/warming-seas-and-melting-ice-sheets">growing contributions to sea level from the ice sheets of Greenland and Antarctica</a>. Our research was partly aimed at explaining how these apparently contradictory results fit together.</p>
<h2>Changes in the rate of rise</h2>
<p>In 2015, we completed a careful comparison of satellite and coastal measurements of sea level. This revealed a <a href="https://theconversation.com/sea-level-is-rising-fast-and-%20it-seems-to-be-speeding-up-39253">small but significant bias in the first decade of the satellite record</a> which, after its removal, resulted in a slightly lower estimate of sea-level rise at the start of the satellite record. Correcting for this bias partially resolved the apparent contradiction.</p>
<p>In our new research, we compared the satellite data from 1993 to 2014 with what we know has been contributing to sea level over the same period. These contributions come from ocean expansion due to ocean warming, the net loss of <a href="https://theconversation.com/cold-and-calculating-what-the-two-different-types-of-ice-do-to-sea-levels-59996">land-based ice from glaciers and ice sheets</a>, and changes in the amount of water stored on land.</p>
<p>Previously, after around 2003, the agreement between the sum of the observed contributions and measured sea level was very good. Before that, however, the budget didn’t quite balance.</p>
<p>Using the satellite data corrected for the small biases identified in our earlier study, we found agreement with the sum of contributions over the entire time from 1993 to 2014. Both show an increase in the rate of sea-level rise over this period.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/175479/original/file-20170625-13472-3g5tqj.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/175479/original/file-20170625-13472-3g5tqj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/175479/original/file-20170625-13472-3g5tqj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=286&fit=crop&dpr=1 600w, https://images.theconversation.com/files/175479/original/file-20170625-13472-3g5tqj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=286&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/175479/original/file-20170625-13472-3g5tqj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=286&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/175479/original/file-20170625-13472-3g5tqj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=359&fit=crop&dpr=1 754w, https://images.theconversation.com/files/175479/original/file-20170625-13472-3g5tqj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=359&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/175479/original/file-20170625-13472-3g5tqj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=359&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The total observed sea-level rise is the sum of contributions from thermal expansion of the oceans, fresh water input from glaciers and ice sheets, and changes in water storage on land.</span>
<span class="attribution"><a class="source" href="http://www.ipcc.ch/report/graphics/images/Assessment%20Reports/AR5%20-%20WG1/Chapter%2013/Fig13-01.jpg">IPCC</a></span>
</figcaption>
</figure>
<p>After accounting for year-to-year fluctuations caused by phenomena such as El Niño, our corrected satellite record indicates an increase in the rate of rise, from 2.4mm per year in 1993 to 2.9mm per year in 2014. If we used different estimates for vertical land motion to estimate the biases in the satellite record, the rates were about 0.4mm per year larger, changing from 2.8mm per year to 3.2mm per year over the same period.</p>
<h2>Is the whole the same as the sum of the parts?</h2>
<p>Our results show that the largest contribution to sea-level rise – about 1mm per year – comes from the ocean expanding as it warms. This rate of increase stayed fairly constant over the time period. </p>
<p>The second-largest contribution was from mountain glaciers, and increased slightly from 0.6mm per year to 0.9mm per year from 1993 to 2014. Similarly, the contribution from the Antarctic ice sheet increased slightly, from 0.2mm per year to 0.3mm per year.</p>
<p>Strikingly, the largest increase came from the Greenland ice sheet, as a result of both increased surface melting and increased flow of ice into the ocean. Greenland’s contribution increased from about 0.1mm per year (about 5% of the total rise in 1993) to 0.85mm per year (about 25% in 2014).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/175480/original/file-20170625-13472-16mca7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/175480/original/file-20170625-13472-16mca7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/175480/original/file-20170625-13472-16mca7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/175480/original/file-20170625-13472-16mca7i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/175480/original/file-20170625-13472-16mca7i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/175480/original/file-20170625-13472-16mca7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/175480/original/file-20170625-13472-16mca7i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/175480/original/file-20170625-13472-16mca7i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Greenland’s contribution to sea-level rise is increasing due to both increased surface melting and flow of ice into the ocean.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/nasa_ice/33806243103">NASA/John Sonntag</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The contribution from land water also increased, from 0.1mm per year to 0.25mm per year. The amount of water stored on land varies a lot from year to year, because of changes in rainfall and drought patterns, for instance. Despite this, rates of groundwater depletion grew whereas storage of water in reservoirs was relatively steady, with the net effect being an increase between 1993 and 2014.</p>
<p>So in terms of the overall picture, while the rate of ocean thermal expansion has remained steady since 1993, the contributions from glaciers and ice sheets have increased markedly, from about half of the total rise in 1993 to about 70% of the rise in 2014. This is primarily due to Greenland’s increasing contribution.</p>
<h2>What is the future of sea level?</h2>
<p>The satellite record of sea level still spans only a few decades, and ongoing observations will be needed to understand the longer-term significance of our results. Our results also highlight the importance of the continued international effort to better understand and correct for the small biases we identified in the satellite data in our earlier study.</p>
<p>Nevertheless, the satellite data are now consistent with the historical observations and also with projected increases in the rate of sea-level rise.</p>
<p>Ocean heat content <a href="http://www.nature.com/nature/journal/v453/n7198/full/nature07080.html">fell following the 1991 volcanic eruption of Mount Pinatubo</a>. The subsequent recovery (over about two decades) probably resulted in a rate of ocean thermal expansion larger than from greenhouse gases alone. Thus the underlying acceleration of thermal expansion from human-induced warming may emerge over the next decade or so. And there are potentially <a href="https://www.nature.com/nature/journal/v531/n7596/full/nature17145.html">even larger future contributions from the ice sheets of Greenland and Antarctica</a>.</p>
<p>The acceleration of sea level, now measured with greater accuracy, highlights the importance and urgency of cutting greenhouse gas emissions and formulating coastal adaptation plans. Given the increased contributions from ice sheets, and the implications for future sea-level rise, our coastal cities need to prepare for rising sea levels.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/175481/original/file-20170625-13472-189xwu9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/175481/original/file-20170625-13472-189xwu9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/175481/original/file-20170625-13472-189xwu9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/175481/original/file-20170625-13472-189xwu9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/175481/original/file-20170625-13472-189xwu9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/175481/original/file-20170625-13472-189xwu9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/175481/original/file-20170625-13472-189xwu9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/175481/original/file-20170625-13472-189xwu9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sea-level rise will have significant impacts on coastal communities and environments.</span>
<span class="attribution"><a class="source" href="http://www.scienceimage.csiro.au/image/10801">Bruce Miller/CSIRO</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure><img src="https://counter.theconversation.com/content/79175/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Church previously received funding from Australian Climate Change Research Program. </span></em></p><p class="fine-print"><em><span>Christopher Watson receives funding from the Australian Research Council and the NCRIS Integrated Marine Observing System.</span></em></p><p class="fine-print"><em><span>Matt King receives funding from Australian Research Council and Department of Environment.</span></em></p><p class="fine-print"><em><span>Xianyao Chen received funding from the National Key Basic Research Program of China and the Natural Science Foundation of China. </span></em></p><p class="fine-print"><em><span>Xuebin Zhang received funding from Pacific Climate Change Science Program (PCCSP) and follow-up Pacific-Australia Climate Change Science and Adaptation Planning program (PACCSAP) both of which were funded by the Australian Government’s International Climate Change Adaptation Initiative, and also from Australian Climate Change Science Programme (ACCSP), National Environmental Science Programme (NESP), and Centre for Southern Hemisphere Ocean Research (CSHOR).</span></em></p>Greenland’s ice is largely responsible for the accelerating pace of sea-level rise. A new analysis shows that, while Greenland accounted for just 5% of the rise in 1993, that figure rose to 25% by 2014.John Church, Chair professor, UNSW SydneyChristopher Watson, Senior Lecturer, Surveying and Spatial Sciences, School of Land and Food, University of TasmaniaMatt King, Professor, Surveying & Spatial Sciences, School of Land and Food, University of TasmaniaXianyao Chen, ProfessorXuebin Zhang, Senior research scientist, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/650212016-09-21T23:00:43Z2016-09-21T23:00:43ZScientist at work: Tracking melt water under the Greenland ice sheet<figure><img src="https://images.theconversation.com/files/138649/original/image-20160921-21720-2iudwl.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The crew of scientists prepare to put the drill stem into the Greenland ice sheet to probe water flows about a half of a mile below.</span> <span class="attribution"><span class="source">Joel Harper</span>, <span class="license">Author provided</span></span></figcaption></figure><p>During the past decade, I’ve spent nearly a year of my life living on the Greenland ice sheet to study how melt water impacts the movement of the ice. </p>
<p>What happens to the water that finds its way from the melting ice surface to the bottom of the ice sheet is a crucial question for glaciologists like me. Knowing this will help us ascertain how quickly Greenland’s ice sheet could contribute to global sea-level rise. But because doing this type of research requires studying the bottom side of a vast and thick ice sheet, my colleagues and I have developed relatively unique research techniques. </p>
<p>Our approach is to mimic the <a href="http://www.traditionalmountaineering.org/FAQ_Light_Fast.htm">alpine style</a> of mountaineering to do our polar research. That involves a small group of self-sufficient climbers who keep their loads light and depend on speed and efficiency to achieve their goals. It’s the opposite of expedition-style mountaineering, which relies on a large support crew and lots of heavy equipment to slowly advance a select few people to the summit.</p>
<p>We bring a small team of scientists who are committed to our fast and light field research style, with each person taking on multiple roles. We use mostly homemade equipment that is designed to produce novel results while being lightweight and efficient – the antithesis of “overdesigned.” The chances of scientific failure from this less conventional approach can be unnerving, but the benefits can be worth the risks. Indeed, we’ve already gained significant insights into the Greenland ice sheet’s underside.</p>
<h2>Mysterious place</h2>
<p>Our science team from the University of Montana and University of Wyoming sleeps in backpacking tents, the endless summer sunshine making shadows that rotate in circles around us. Ice-sheet camping is challenging. Your tent and sleeping pad insulate the ice as it melts, and soon your tent rises up into the relentless winds on an icy drooping pillar. Occasionally people’s tents slide off their pillars in the middle of the night. </p>
<p>But it’s not the melting on the surface that concerns us so much as what’s happening at the base of the Greenland ice sheet. Arctic warming has increased summer melting of this huge reservoir of ice, causing sea levels to rise. Before the melt water runs to the oceans, much of it finds its way to the bottom of the ice sheet. </p>
<p>The additional water can lubricate the base of the ice sheet in places where the ice can be 1,000 or more meters thick. This causes the ice to slide more quickly across the bedrock on which it sits. The result is that more ice is transported from the high center of the ice sheet, where snow accumulates, to the low elevation margins of the ice sheet, where it either calves into the sea or melts in the warmth of low elevations. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/137944/original/image-20160915-30611-po750y.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/137944/original/image-20160915-30611-po750y.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/137944/original/image-20160915-30611-po750y.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/137944/original/image-20160915-30611-po750y.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/137944/original/image-20160915-30611-po750y.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/137944/original/image-20160915-30611-po750y.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/137944/original/image-20160915-30611-po750y.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A system of pumps and heaters generates a high pressure jet of hot water that is used to melt a hole to the bottom of Greenland ice sheet.</span>
</figcaption>
</figure>
<p>One school of thought is that a feedback may be kicking in; the more water added, the faster the ice will move, and so ultimately the faster the ice will melt. </p>
<p>An alternative hypothesis is that adding more water to the bed will create large water flow pathways at the contact between the ice and bedrock. These channels are efficient at flushing the water quickly, which could limit the effects of increased melt water at the bed. In other words, by adding more water there is actually less lubrication – not more – because a drainage system develops that quickly moves the water away.</p>
<p>We know flowing water generates heat and melts open the channels in the ice. However, the enormous pressure at the base of the ice acts to squeeze the channels shut. Competing forces battle in a complicated dance. </p>
<p>We can represent these processes with equations, and simulate the opening and closing of the channels on a computer. But the meaningfulness of our results depends on whether we have properly accounted for all of the physical processes actually taking place. To test this, we need to look under the ice sheet.</p>
<p>The bottom of the ice sheet is a mysterious place we glaciologists spend a lot of time hypothesizing about. It’s not a place you can actually go and have a look around. So our team has drilled boreholes to the bed of the Greenland ice sheet to insert sensors and to conduct experiments designed to reveal the water flow and ice sliding conditions. They are essentially pinpricks that allow us to test and refine our models.</p>
<h2>Homemade heat drill</h2>
<p>Our approach to penetrating many hundreds of meters of cold ice (e.g., -18 degrees Celsius) is to run a light and nimble drilling campaign. We use alpine climbing tactics so that we can move quickly around the ice sheet to drill as many holes as we can in different places, to see if conditions vary from place to place. Our drill can be moved long distances in just a few helicopter loads, and we carry it ourselves for shorter hauls.</p>
<p>We don’t have devoted cooks or mechanics or engineers; we have a small group of faculty and carefully selected students who need to do it all. We rely on people who can fiddle with the electronics of homemade instruments while being unafraid of hard manual labor like moving fuel barrels and hooking up heavy pumps and hoses in the biting cold Greenland wind. Back in the lab, these same people must have outstanding skills to apply math and physics to data analysis and modeling. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/138346/original/image-20160919-11131-be0tol.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/138346/original/image-20160919-11131-be0tol.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/138346/original/image-20160919-11131-be0tol.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/138346/original/image-20160919-11131-be0tol.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/138346/original/image-20160919-11131-be0tol.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/138346/original/image-20160919-11131-be0tol.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/138346/original/image-20160919-11131-be0tol.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/138346/original/image-20160919-11131-be0tol.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The drill is moved long distances by helicopter, and shorter distances by hand-carrying over the ice. Our goal is to keep the drilling equipment as small and light as possible to permit easy transport.</span>
<span class="attribution"><span class="source">Joel Harper</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Our homemade drill uses hot water to melt a hole through the ice. We capture surface melt water flowing in streams, heat it to near boiling and then pump it at very high pressure through a hose to a nozzle that sprays a carefully designed jet of water. </p>
<p>Our drilling days are long, extending from morning to well into the night. When the hole is finished, that’s when our work really begins because we only have about two hours before the hole completely freezes shut again. We need to get the drill out of the hole and all experiments completed before that happens. Like astronauts who rehearse their spacewalks, we plan every step and try not to panic when something unexpected happens.</p>
<p>We conduct experiments by artificially adding slugs of water to the bed to measure how the drainage system can accommodate extra water. We send down a camera to take pictures of the bed, a suction tube to sample the sediment and homemade sensors to measure the temperature, pressure and movement of the water. We build the sensors ourselves because you just can’t buy sensors designed for the bottom of a 800-meter-deep hole through an ice sheet. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/137941/original/image-20160915-30619-1cxz58g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/137941/original/image-20160915-30619-1cxz58g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/137941/original/image-20160915-30619-1cxz58g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/137941/original/image-20160915-30619-1cxz58g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/137941/original/image-20160915-30619-1cxz58g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/137941/original/image-20160915-30619-1cxz58g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/137941/original/image-20160915-30619-1cxz58g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Joel Harper (Univ. of Montana) and Neil Humphrey (Univ. of Wyoming) operate the hot water drill.</span>
<span class="attribution"><span class="source">Joel Harper</span></span>
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<p>I’ll admit our fast, light approach to drilling comes with risks. We don’t have redundant systems and we don’t carry lots of backup parts. Our lightweight drill makes a narrow hole, and the top of hole is freezing closed as drilling advances the bottom. We’ve had scary episodes where we’ve almost lost the drill. </p>
<p>A generator fails or a gear box blows, and now the hole is freezing shut around the 700 meters of hose and drill stem. If we can’t come up with a fix within minutes, the drill is lost and the project is over. We could take much less risk by scaling up logistics and reducing our goals. But that would mean doubling the crew and the pile of equipment, and adding another zero to our budget, only to drill one or two holes a year. </p>
<p>Our light-and-nimble approach has allowed us to drill holes quickly and to move large distances. We have drilled 36 boreholes spread along 45 kilometers (28 miles) of the ice sheet’s western side. The holes are up to 850 meters deep, or about a half of a mile, and have produced multi-year records of conditions under the ice. </p>
<h2>Different physics than thought</h2>
<p>Our instruments have discovered the water pressure under the ice is higher than portrayed by computer models. The melting power of flowing water is less effective than we thought, and so the enormous pressure under the thick ice has the upper hand – the squeezing inhibits large channels from opening. </p>
<p>This does not necessarily mean the ice will move faster due to enhanced lubrication as more melt water reaches the bed. This is because we have also discovered ways the water flows in smaller channels and sheets much more quickly than we expected. Now we are retrofitting our computer models to include these physics.</p>
<p>Our ultimate goal is to improve simulations of Greenland’s future contributions to sea level. Our discoveries are not relevant to tomorrow’s sea level or even next year’s, but nailing down these processes is important for knowing what will happen over upcoming decades to centuries. Sea level rise has big societal consequences, so we will continue our nimble approach to investigating water at Greenland’s bed.</p><img src="https://counter.theconversation.com/content/65021/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joel T Harper receives funding from U.S. National Science Foundation, NASA, Swedish Nuclear Waste Management Organization (SKB). </span></em></p>A glaciologist develops a lightweight method for probing the depths of Greenland’s ice sheet to answer a crucial question: How fast is it melting?Joel T. Harper, Professor of Geosciences, University of MontanaLicensed as Creative Commons – attribution, no derivatives.