tag:theconversation.com,2011:/au/topics/ice-sheets-24915/articles
Ice sheets – The Conversation
2024-02-05T19:11:18Z
tag:theconversation.com,2011:article/222737
2024-02-05T19:11:18Z
2024-02-05T19:11:18Z
Dangerous climate tipping points will affect Australia. The risks are real and cannot be ignored
<p>In 2023, we saw a raft of news stories about climate tipping points, including the <a href="https://www.bbc.com/news/science-environment-65317469">accelerating loss</a> of <a href="https://theconversation.com/what-will-happen-to-the-greenland-ice-sheet-if-we-miss-our-global-warming-targets-215928">Greenland</a> and <a href="https://theconversation.com/antarctic-tipping-points-the-irreversible-changes-to-come-if-we-fail-to-keep-warming-below-2-207410">Antarctic</a> ice sheets, the <a href="https://www.theguardian.com/environment/2023/oct/04/south-american-monsoon-heading-towards-tipping-point-likely-to-cause-amazon-dieback">potential dieback</a> of the Amazon rainforest and the <a href="https://theconversation.com/the-atlantic-oceans-major-current-system-is-slowing-down-but-a-21st-century-collapse-is-unlikely-214647">likely weakening</a> of the Atlantic Meridional Ocean Circulation.</p>
<p>The ice sheets, Amazon rainforest and the Atlantic <a href="https://www.nature.com/articles/s41467-023-39810-w">ocean circulation</a> are among nine recognised <a href="https://www.science.org/doi/10.1126/science.abn7950">global climate tipping elements</a>. Once a tipping point is crossed, changes are often irreversible for a very long time. In many cases, additional greenhouse gases will be released into the atmosphere, further warming our planet.</p>
<p>New <a href="https://www.science.org/doi/10.1126/science.abn7950">scientific research and reviews</a> suggest at least one of Earth’s “tipping points” could be <a href="https://theconversation.com/climate-tipping-points-are-nearer-than-you-think-our-new-report-warns-of-catastrophic-risk-219243">closer than we hoped</a>. A <a href="https://global-tipping-points.org/">milestone review</a> of global tipping points was launched at last year’s COP28.</p>
<p>What will these tipping points mean for Australia? We don’t yet have a good enough understanding to fully answer this question. </p>
<p><a href="https://www.csiro.au/-/media/Environment/CSIRO_Tipping-Points-Report.pdf">Our report</a>, released overnight, includes conclusions in three categories: we need to do more research; tipping points must be part of climate projections, hazard and impact analyses; and adaptation plans must take the potential impacts into account.</p>
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Read more:
<a href="https://theconversation.com/climate-tipping-points-are-nearer-than-you-think-our-new-report-warns-of-catastrophic-risk-219243">Climate tipping points are nearer than you think – our new report warns of catastrophic risk</a>
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<h2>What are climate tipping points?</h2>
<p>Climate scientists have <a href="https://theconversation.com/what-climate-tipping-points-should-we-be-looking-out-for-27108">known for a while</a>, through paleoclimate records and other evidence, that there are “tipping elements” in the climate system. These elements can undergo an abrupt change in state, which becomes self-perpetuating and irreversible for a very long time.</p>
<p>An example is the loss of Greenland ice. Once ice is lost, climate feedbacks lead to further loss, and major ice loss becomes “committed”. It becomes unlikely the ice sheet will reform for tens of thousands of years and only if the climate cools again. </p>
<p>Triggering climate tipping points would lead to changes in addition to those commonly included in <a href="https://www.climatechangeinaustralia.gov.au/en/">climate projections</a>. These changes include a significant rise in sea level at double the rate (or even more) of usual projections, as well as extra warming, altered weather systems, climate variability and extremes. </p>
<p>Triggering one tipping point may trigger other tipping points. If that happens, the cascading impacts would push many systems outside their adaptive capacity.</p>
<p>Cutting fossil greenhouse gas emissions is the most important thing we can do to limit warming and the risk of triggering tipping points. The faster we reduce emissions, the better our chances.</p>
<p>But as the planet continues to warm, we must consider the consequences of triggering some, or several, tipping points for Australia and the resulting risks for society. We need to have the right tools for adaptation planning to consider these risks.</p>
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<img alt="Seawater floods a coastal property in Brisbane" src="https://images.theconversation.com/files/572956/original/file-20240202-21-jltl0y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/572956/original/file-20240202-21-jltl0y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/572956/original/file-20240202-21-jltl0y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/572956/original/file-20240202-21-jltl0y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/572956/original/file-20240202-21-jltl0y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/572956/original/file-20240202-21-jltl0y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/572956/original/file-20240202-21-jltl0y.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">
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<span class="caption">Adaptation planning must consider the potential impacts of tipping points, such as higher rises in sea level.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/sea-washing-over-wall-flooding-street-169034384">Silken Photography/Shutterstock</a></span>
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Read more:
<a href="https://theconversation.com/antarctic-tipping-points-the-irreversible-changes-to-come-if-we-fail-to-keep-warming-below-2-207410">Antarctic tipping points: the irreversible changes to come if we fail to keep warming below 2℃</a>
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<h2>Grappling with deep uncertainties</h2>
<p>There’s a major gap in the research literature around the implications of tipping points for the southern hemisphere and Australia. Researchers from Australian science agencies and universities came together last year to consider what global climate tipping points could mean for Australia. </p>
<p>We launched <a href="https://www.csiro.au/-/media/Environment/CSIRO_Tipping-Points-Report.pdf">our report</a> last night at the national conference of the <a href="https://www.amos.org.au/">Australian Meteorological & Oceanographic Society</a>. We identified several priority areas for the research community, risk analysts and policymakers.</p>
<p>We considered the nine global climate tipping points – and one of the most relevant regional tipping points for Australia, coral reef die-offs – as defined in a recent <a href="https://www.science.org/doi/10.1126/science.abn7950">scientific review</a>.</p>
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<img alt="" src="https://images.theconversation.com/files/572736/original/file-20240201-25-1bc4jc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/572736/original/file-20240201-25-1bc4jc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=368&fit=crop&dpr=1 600w, https://images.theconversation.com/files/572736/original/file-20240201-25-1bc4jc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=368&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/572736/original/file-20240201-25-1bc4jc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=368&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/572736/original/file-20240201-25-1bc4jc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=462&fit=crop&dpr=1 754w, https://images.theconversation.com/files/572736/original/file-20240201-25-1bc4jc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=462&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/572736/original/file-20240201-25-1bc4jc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=462&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">The nine global climate tipping points and the one most relevant regional tipping point of seven listed in Armstrong-McKay et al review (2022), and their assessed ranges of global warming where the tipping may be triggered (some other evidence or studies may differ from these ranges).</span>
<span class="attribution"><a class="source" href="https://www.science.org/doi/10.1126/science.abn7950">Adapted from: Armstrong-McKay et al. 2022</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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Read more:
<a href="https://theconversation.com/what-will-happen-to-the-greenland-ice-sheet-if-we-miss-our-global-warming-targets-215928">What will happen to the Greenland ice sheet if we miss our global warming targets</a>
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<p>For almost all tipping points, we don’t understand all the relevant processes. There are deep uncertainties about what conditions would trigger tipping points, how they would play out and their likely impacts. </p>
<p>Along with recognising the most urgent point – that deep emission cuts will limit the chances of triggering tipping points – our conclusions cover three areas.</p>
<p><strong>1. We need more research</strong></p>
<p>We need to expand research on paleoclimate records, theory and process understanding, observations, monitoring and modelling. Australia leads world-class research, including on Antarctica, the Southern Ocean, the carbon cycle, weather processes and ecosystems. It is essential we support and expand the work, bringing a southern hemisphere perspective to global efforts.</p>
<p><strong>2. Climate projections, hazard and impact analyses must include tipping points</strong> </p>
<p>Triggering some climate tipping points would have direct impacts on our coasts, ecosystems and society. In an interconnected world, other tipping points would have major indirect impacts – through climate migration, conflict, disrupted trade and more. </p>
<p>We need credible projections of what the climate looks like if tipping points are triggered. Our climate impact and risk analyses should illustrate what it really means for us. Given the limited state of knowledge, the <a href="https://link.springer.com/article/10.1007/s10584-018-2317-9">“storyline” approach</a> – linking past, current and future unfolding of events in a narrative or pathway framework – is particularly useful, informed by all the available evidence.</p>
<p><strong>3. We need to consider what it means for adaptation</strong></p>
<p>We can consider where, when and how we can act to reduce potential impacts if tipping points are triggered. Appropriate risk management accounts for likelihood, consequence and timeframe. </p>
<p>For example, planning for major coastal infrastructure with a long lifetime and low tolerance for failure could draw on the sea-level projections of “low likelihood, high impact” storylines that include the west Antarctic ice sheet collapsing. This would safeguard critical infrastructure against one worst-case risk. Of course, there is much more to adaptation than this. </p>
<p>We still have much to learn, but we cannot wait for perfect knowledge before we start planning. It’s clear the risks are real and cannot be ignored. </p>
<p>We need to focus on what we can do to avoid triggering tipping points, manage risk and build our climate resilience. There are also <a href="https://global-tipping-points.org/section4/4-0-positive-tipping-points-in-technology-economy-and-society/">positive tipping points</a> in technology, economy and society that are part of the solution. If we get it right, positive change can happen more rapidly than we might think.</p>
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Read more:
<a href="https://theconversation.com/climate-tipping-points-can-be-positive-too-our-report-sets-out-how-to-engineer-a-domino-effect-of-rapid-changes-219291">Climate 'tipping points' can be positive too – our report sets out how to engineer a domino effect of rapid changes</a>
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<img src="https://counter.theconversation.com/content/222737/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Grose receives funding from the National Environmental Science Program and the Australian Climate Service.</span></em></p><p class="fine-print"><em><span>Andy Pitman receives funding from the Australian Research Council.</span></em></p>
We don’t yet fully understand what global climate tipping points mean for Australia. But we know enough to conclude the impacts of passing one or more tipping points must now be considered.
Michael Grose, Climate Projections Scientist, CSIRO
Andy Pitman, Director of the ARC Centre of Excellence for Climate Extremes, UNSW Sydney
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/216555
2023-12-15T09:07:27Z
2023-12-15T09:07:27Z
The Sahara Desert used to be a green savannah – new research explains why
<p>Algeria’s <a href="https://whc.unesco.org/en/list/179/">Tassili N’Ajjer plateau</a> is Africa’s largest national park. Among its vast sandstone formations is perhaps the world’s largest art museum. Over 15,000 etchings and paintings are exhibited there, some as much as 11,000 years old according to scientific dating techniques, representing a unique ethnological and climatological record of the region. </p>
<p>Curiously, however, these images do not depict the arid, barren landscape that is present in the Tassili N'Ajjer today. Instead, they portray a vibrant savannah inhabited by elephants, giraffes, rhinos and hippos. This rock art is an important record of the past environmental conditions that prevailed in the Sahara, the world’s largest <a href="https://www.livescience.com/23140-sahara-desert.html">hot desert</a>. </p>
<p>These images depict a period approximately 6,000-11,000 years ago called the <a href="https://www.nature.com/scitable/knowledge/library/green-sahara-african-humid-periods-paced-by-82884405/">Green Sahara or North African Humid Period</a>. There is widespread climatological <a href="https://www.sciencedirect.com/science/article/pii/S2590332220301007#bib31">evidence</a> that during this period the Sahara supported wooded savannah ecosystems and numerous rivers and lakes in what are now Libya, Niger, Chad and Mali. </p>
<p>This greening of the Sahara didn’t happen once. Using marine and lake sediments, scientists have <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0076514">identified</a> over 230 of these greenings occurring about every 21,000 years over the past eight million years. These greening events provided vegetated corridors which influenced species’ distribution and evolution, including the out-of-Africa migrations of ancient humans.</p>
<p>These dramatic greenings would have required a large-scale reorganisation of the atmospheric system to bring rains to this hyper arid region. But most climate models haven’t been able to simulate how dramatic these events were. </p>
<p>As a team of climate modellers and anthropologists, <a href="https://www.nature.com/articles/s41467-023-41219-4">we have overcome this obstacle</a>. We developed a climate model that more accurately simulates atmospheric circulation over the Sahara and the impacts of vegetation on rainfall. </p>
<p>We identified why north Africa greened approximately every 21,000 years over the past eight million years. It was caused by changes in the Earth’s orbital <a href="https://www.britannica.com/science/precession-of-the-equinoxes">precession</a> - the slight wobbling of the planet while rotating. This moves the Northern Hemisphere closer to the sun during the summer months. </p>
<p>This caused warmer summers in the Northern Hemisphere, and warmer air is able to hold more moisture. This intensified the strength of the West African Monsoon system and shifted the African rainbelt northwards. This increased Saharan rainfall, resulting in the spread of savannah and wooded grassland across the desert from the tropics to the Mediterranean, providing a vast habitat for plants and animals. </p>
<p>Our results demonstrate the sensitivity of the Sahara Desert to changes in past climate. They explain how this sensitivity affects rainfall across north Africa. This is important for understanding the implications of present-day climate change (driven by human activities). Warmer temperatures in the future may also enhance monsoon strength, with both local and global impacts. </p>
<h2>Earth’s changing orbit</h2>
<p>The fact that the wetter periods in north Africa have recurred every 21,000 years or so is a big clue about what causes them: variations in Earth’s orbit. Due to gravitational influences from the moon and other planets in our solar system, the orbit of the Earth around the sun is not constant. It has cyclic variations on multi-thousand year timescales. These orbital cycles are termed <a href="https://climate.nasa.gov/climate_resources/211/orbital-cycles/">Milankovitch cycles</a>; they influence the amount of energy the Earth receives from the sun. </p>
<p>On 100,000-year cycles, the shape of Earth’s orbit (or <a href="https://www.britannica.com/science/eccentricity-astronomy">eccentricity</a>) shifts between circular and oval, and on 41,000 year cycles the tilt of Earth’s axis varies (termed <a href="https://www.britannica.com/science/obliquity">obliquity</a>). Eccentricity and obliquity cycles are responsible for driving the ice ages of the past 2.4 million years. </p>
<p>The third Milankovitch cycle is <a href="https://climate.nasa.gov/climate_resources/251/axial-precession-wobble/">precession</a>. This concerns Earth’s wobble on its axis, which varies on a 21,000 year timescale. The similarity between the precession cycle and the timing of the humid periods indicates that precession is their dominant driver. Precession influences seasonal contrasts, increasing them in one hemisphere and reducing them in another. During warmer Northern Hemisphere summers, a consequent increase in north African summer rainfall would have initiated a humid phase, resulting in the spread of vegetation across the region.</p>
<h2>Eccentricity and the ice sheets</h2>
<p>In our study we also identified that the humid periods did not occur during the ice ages, when large glacial ice sheets covered much of the polar regions. This is because these vast ice sheets cooled the atmosphere. The cooling countered the influence of precession and suppressed the expansion of the African monsoon system. </p>
<p>The ice ages are driven by the eccentricity cycle, which determines how circular Earth’s orbit is around the sun. So our findings show that eccentricity indirectly influences the magnitude of the humid periods via its influence on the ice sheets. This highlights, for the first time, a major connection between these distant high latitude and tropical regions.</p>
<p>The Sahara acts as a gate. It controls the dispersal of species between north and sub-Saharan Africa, and in and out of the continent. The gate was open when the Sahara was green and closed when deserts prevailed. Our results reveal the sensitivity of this gate to Earth’s orbit around the sun. They also show that high latitude ice sheets may have restricted the dispersal of species during the glacial periods of the last 800,000 years. </p>
<p>Our ability to model the African humid periods helps us understand the alternation of humid and arid phases. This had major consequences for the dispersal and evolution of species, including humans, within and out of Africa. Furthermore, it provides a tool for understanding future greening in response to climate change and its environmental impact. </p>
<p>Refined models may, in the future, be able to identify how climate warming will influence rainfall and vegetation in the Sahara region, and the wider implications for society.</p><img src="https://counter.theconversation.com/content/216555/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Edward Armstrong 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>
The Sahara Desert is green and vegetated every 21,000 years. A climate model shows why.
Edward Armstrong, Postdoctoral research fellow, University of Helsinki
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/219533
2023-12-13T17:19:17Z
2023-12-13T17:19:17Z
Antarctic study proves glacier has undergone irreversible retreat – highlighting potential for widespread ice loss
<figure><img src="https://images.theconversation.com/files/565184/original/file-20231212-19-asy8hd.JPG?ixlib=rb-1.1.0&rect=0%2C418%2C2437%2C1880&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ice on the Antarctic peninsula flowing along a channel into an ice shelf in the ocean.</span> <span class="attribution"><span class="source">Hilmar Gudmundsson</span></span></figcaption></figure><p><a href="https://www.antarcticglaciers.org/antarctica-2/west-antarctic-ice-sheet-2/pine-island-glacier/">Pine Island glacier</a> is one of the fastest flowing outlets of ice from the west <a href="https://www.pnas.org/doi/abs/10.1073/pnas.1812883116">Antarctic ice sheet</a>, draining an area three-quarters the size of the UK. In recent decades, the glacier has been retreating rapidly and losing ice, contributing more to global sea level rise than any other Antarctic glacier. </p>
<p>The speed of the glacier’s retreat and the rate that is has been losing ice has led to concerns about how stable the region is. <a href="https://tc.copernicus.org/articles/17/3761/2023/">Model results show</a> that this region of west Antarctica could collapse in the future. If it does, then it could raise global mean sea level by several metres.</p>
<p>There have been periods of rapid global sea-level rise <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2011RG000371">in the past</a> (by 1cm–2cm per year). This probably happened because glaciers were losing mass at an accelerated rate. One of the key mechanisms responsible for this is known as “<a href="https://www.antarcticglaciers.org/antarctica-2/west-antarctic-ice-sheet-2/marine-ice-sheets/">marine ice sheet instability</a>”. </p>
<p>When glaciers, like those in west Antarctica, experience a small retreat due to some change in the climate, they can continue retreating even if the change is reversed. Essentially, the glacier gets pushed beyond a tipping point, whereby it experiences rapid mass loss until it reaches a new state.</p>
<p>This kind of retreat is irreversible because the change in climate needed for the glacier to recover its original position is much greater than what initially caused it to retreat. This instability mechanism is well understood in theory, and models show it could happen in west Antarctica in the future. But until now there has been no proof that it had happened in the past.</p>
<p>In a <a href="https://www.nature.com/articles/s41558-023-01887-y">new study</a>, we found that Pine Island Glacier experienced irreversible mass loss and retreat, starting in the 1940s. Our model suggests that a temporary increase in melting under its floating ice shelf was enough to push the glacier past a tipping point.</p>
<p>This phase of accelerated retreat had finished by the 1990s. But, in a <a href="https://tc.copernicus.org/articles/15/1501/2021/">separate study</a> where we used the same model, we found that the glacier will cross future tipping points unless global warming is kept within safe limits.</p>
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<a href="https://images.theconversation.com/files/565188/original/file-20231212-29-11ree3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A glacier flowing into the ocean in west Antarctica." src="https://images.theconversation.com/files/565188/original/file-20231212-29-11ree3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/565188/original/file-20231212-29-11ree3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565188/original/file-20231212-29-11ree3.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565188/original/file-20231212-29-11ree3.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565188/original/file-20231212-29-11ree3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565188/original/file-20231212-29-11ree3.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565188/original/file-20231212-29-11ree3.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>
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<span class="caption">If it collapses, the west Antarctic ice sheet could raise global mean sea level by several metres.</span>
<span class="attribution"><span class="source">Hilmar Gudmundsson</span></span>
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<h2>What happened?</h2>
<p>Before the 1940s, Pine Island Glacier extended further than it does today. Its grounding line – the point at which glacial ice begins to float in the ocean rather than being in contact with the ground – was situated 40km further downstream on a shallow ridge on the seabed. This ridge provided a stable position for the glacier, keeping it in place, possibly for at least 5,000 to 10,000 years.</p>
<p>Recent <a href="https://www.science.org/doi/full/10.1126/science.1244341">observations</a> show that ocean conditions beneath the floating ice shelf change from year to year. Every so often, warmer waters come into contact with the floating underside of the ice, causing a lot of melting from below. In the 1940s, a climate anomaly in west Antarctica, which has been <a href="https://www.pnas.org/doi/abs/10.1073/pnas.0803627105">linked to a large El Niño event</a>, possibly triggered a temporary change in ocean conditions. </p>
<p>We found that an increase in melting due to changed ocean conditions beneath the ice shelf would have led to the thinning of its grounded ice further upstream. This caused a gap to open between the grounded glacier and seabed, allowing warmer ocean waters to flow beyond the ridge. These results are supported by <a href="https://www.nature.com/articles/nature20136">evidence</a> recovered from the sediments under the present-day ice shelf.</p>
<p>Once warmer waters circulate beneath the newly exposed ice, it triggers further melting and thinning, at an even faster rate. Our model shows that this sparked rapid retreat and accelerated ice flow over the following two to three decades, culminating with the detachment of the ice shelf from the ridge between the late 1970s and the early 1980s. The pattern and timescale of retreat shown in our model is consistent with <a href="https://www.nature.com/articles/ngeo890">observations</a> of changes in the glacier.</p>
<h2>Irreversible change</h2>
<p>After the ice shelf detached from the ridge, there was a slowdown in ice flow and a more gradual retreat. This retreat only stopped when the grounding line reached a shallow section of bedrock in the early 1990s. </p>
<p>Our analysis shows that the phase of rapid retreat between the 1940s and 1970s was irreversible. If ocean conditions cooled and there was lower melting beneath the shelf during that period, then this would have been unable to stop the ongoing mass loss. </p>
<p>These results show us that if there is a significant increase in melting at the base of a glacier’s floating ice shelf, it can retreat past a tipping point. This means that even if conditions cool down, the loss of ice mass may be irreversible.</p>
<p>The future implications of this are clear. What occurred before could happen again. If we cross future ice sheet tipping points, simply reverting back to the previous climate conditions might not be enough to fix the damage.</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>
<br><em><a href="https://theconversation.com/uk/newsletters/imagine-57?utm_source=TCUK&utm_medium=linkback&utm_campaign=Imagine&utm_content=DontHaveTimeTop">Get a weekly roundup in your inbox instead.</a> Every Wednesday, The Conversation’s environment editor writes Imagine, a short email that goes a little deeper into just one climate issue. <a href="https://theconversation.com/uk/newsletters/imagine-57?utm_source=TCUK&utm_medium=linkback&utm_campaign=Imagine&utm_content=DontHaveTimeBottom">Join the 20,000+ readers who’ve subscribed so far.</a></em></p>
<hr><img src="https://counter.theconversation.com/content/219533/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brad Reed receives funding from The Natural Environment Research Council and UK Research and Innovation.</span></em></p><p class="fine-print"><em><span>Hilmar Gudmundsson receives funding from The Natural Environment Research Council, NSF and EU Horizon 2020 programme. </span></em></p><p class="fine-print"><em><span>Mattias Green receives funding from The Natural Environment Research Coucil. </span></em></p>
Pine Island Glacier passed a tipping point decades ago, and it could do again in the future.
Brad Reed, Research Fellow in the Department of Geography and Environmental Sciences, Northumbria University, Newcastle
Hilmar Gudmundsson, Professor of Glaciology, Northumbria University, Newcastle
Mattias Green, Professor in Physical Oceanography, Bangor University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/217066
2023-11-07T19:35:06Z
2023-11-07T19:35:06Z
Luminous ‘mother-of-pearl’ clouds explain why climate models miss so much Arctic and Antarctic warming
<figure><img src="https://images.theconversation.com/files/557912/original/file-20231106-267335-z7pv6c.jpg?ixlib=rb-1.1.0&rect=68%2C8%2C5682%2C3819&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-illustration/polar-stratospheric-cloud-known-nacreous-clouds-2197976813">YanaBu, Shutterstock</a></span></figcaption></figure><p>Our planet has warmed by about <a href="https://www.ipcc.ch/report/ar6/wg1/">1.2°C since 1850</a>. But this warming is <a href="https://theconversation.com/climate-explained-why-is-the-arctic-warming-faster-than-other-parts-of-the-world-160614">not uniform</a>. Warming at the poles, especially the Arctic, has been <a href="https://www.nature.com/articles/s43247-022-00498-3">three to four times faster</a> than the rest of the globe. It’s a phenomenon known as “polar amplification”. </p>
<p>Climate models simulate this effect, but when tested against the past 40 years of warming, <a href="https://www.nature.com/articles/s43247-022-00498-3">these models fall short</a>. The situation is even worse when it comes to modelling past climates with very high levels of greenhouse gases. </p>
<p>This is a problem because these are the same models used to project into the future and forecast how the climate will change. They are likely to underestimate what will happen later this century, including risks such as ice sheet melting or permafrost thawing. </p>
<p>In our <a href="https://www.nature.com/articles/s41561-023-01298-w">new research published today in Nature Geoscience</a> we used a high-resolution model of the atmosphere that includes the stratosphere. We found a special type of cloud appears over polar regions when greenhouse gas concentrations are very high. The role of this type of cloud has been overlooked so far. This is one of the reasons why our models are too cold at the poles. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/GVCaxb_AT8w?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Polar Stratospheric Clouds over Norway (Night Lights Films - Adrien Mauduit)</span></figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/climate-explained-why-is-the-arctic-warming-faster-than-other-parts-of-the-world-160614">Climate explained: why is the Arctic warming faster than other parts of the world?</a>
</strong>
</em>
</p>
<hr>
<h2>Back to the future</h2>
<p>Looking into past climates can give us glimpses of possible futures for a range of extreme conditions. For us, this means we can use Earth’s history to find out how well our climate models perform. We can test our models by simulating episodes in the past when Earth was much warmer. The advantage of this is that we have temperature reconstructions for these episodes to evaluate the models, as opposed to the future, for which measurements are not available.</p>
<p>If we go back 50 million years or so, our planet was very hot. Carbon dioxide (CO₂) concentrations ranged between <a href="https://pubmed.ncbi.nlm.nih.gov/27111509/">900 and 1,900 parts per million (ppm)</a>, compared with 415 ppm today. Methane (CH₄) concentrations were likely also much higher. </p>
<p>Canada’s arctic archipelago was covered in <a href="https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/124/1-2/3/125757/Life-at-the-top-of-the-greenhouse-Eocene-world-A?redirectedFrom=fulltext">lush rainforests</a> inhabited by alligators, turtles, lizards and mammals. </p>
<p>For these plants and animals to survive, conditions must have been warm and ice-free year-round. Indeed, surface ocean temperatures <a href="https://cp.copernicus.org/articles/16/2381/2020/">exceeded 20°C</a> near the north pole (at about 87°N) and <a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X12003081">25°C in the Southern Ocean</a> (at about 67°S). </p>
<p>This period called the early Eocene is a perfect test bed for our models, because it was globally very warm, and the poles were even warmer, meaning it was a climate with extreme polar amplification. In addition, the Eocene is recent enough for temperature reconstructions to be available. </p>
<p>But as it turns out, the models fail again. They are much <a href="https://web.ics.purdue.edu/%7Ehuberm/Climate_Dynamics_Prediction_Laboratory/Publications/Entries/2012/11/3_Citatiion__In_Reconstructing_Earths_Deep-Time_ClimateThe_State_of_the_Art_in_2012,_Paleontological_Society_Short_Course,_November_3,_2012._The_Paleontological_Society_Papers,_Volume_18,_Linda_C._Ivany_and_Brian_T._Huber_(eds.),_pp._213262_files/HuberPSPfinalpdfcolor.pdf">too cold at high latitudes</a>. What are our models missing?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/557910/original/file-20231106-17-nm5nsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An alligator partly submerged in a lake waiting, for it’s next meal. Clouds are reflected in the still water's surface." src="https://images.theconversation.com/files/557910/original/file-20231106-17-nm5nsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/557910/original/file-20231106-17-nm5nsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=341&fit=crop&dpr=1 600w, https://images.theconversation.com/files/557910/original/file-20231106-17-nm5nsb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=341&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/557910/original/file-20231106-17-nm5nsb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=341&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/557910/original/file-20231106-17-nm5nsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=428&fit=crop&dpr=1 754w, https://images.theconversation.com/files/557910/original/file-20231106-17-nm5nsb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=428&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/557910/original/file-20231106-17-nm5nsb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=428&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Alligators, turtles, lizards and mammals lived in the Arctic about 50 million years ago, when it was much warmer than today.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/florida-alligator-sitting-lake-waiting-next-2294700385">Bradley GT, Shutterstock</a></span>
</figcaption>
</figure>
<h2>Polar stratospheric clouds</h2>
<p>In 1992 American paleoclimatologist Lisa Sloan suggested <a href="https://www.nature.com/articles/357320a0">polar stratospheric clouds</a> might have caused extreme warming at high latitudes in the past. </p>
<p>These clouds are a rare and beautiful sight today. They are also called <a href="https://glossary.ametsoc.org/wiki/Polar_stratospheric_clouds">nacreous or mother-of-pearl clouds</a> for their vivid and sometimes luminous colours. </p>
<p>They form at very high altitudes (in the stratosphere) and at very low temperatures (over the poles). In the present day climate, they appear mainly over Antarctica, but have also been observed during winter months over Scotland, Scandinavia and Alaska, at times when the stratosphere was particularly cold. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-are-the-nacreous-clouds-lighting-up-the-winter-skies-54095">Explainer: what are the 'nacreous clouds' lighting up the winter skies?</a>
</strong>
</em>
</p>
<hr>
<p>Just like greenhouse gases, they absorb infrared radiation emitted by the Earth’s surface and re-emit a portion of this energy back to the surface. This suggests polar stratospheric clouds could be one of the missing puzzle pieces. </p>
<p>They warm the surface. And their effect could be significant, especially in winter, when the sun does not rise. But they are difficult to simulate in a climate model, so most models ignore them. This omission could explain why climate models miss some of the polar warming, because they miss a process that warms the poles.</p>
<p>Three decades after Sloan’s paper, a few atmosphere models are finally complex enough to allow us to test her hypothesis. In our <a href="https://www.nature.com/articles/s41561-023-01298-w">research</a> we use one of them and find that under certain conditions, the additional warming due to these polar stratospheric clouds exceeds 7°C during the winter months. This significantly reduces the gap between climate models and temperature evidence from the early Eocene. Sloan was right. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1578684718446366720"}"></div></p>
<h2>Implications for future projections</h2>
<p>Our research explains why climate models don’t work so well for past climates when greenhouse gas levels were much higher than they are today. But what about the future? Should we be concerned?</p>
<p>There is some good news. While polar stratospheric clouds do warm the poles, they won’t be as common in the future as they were in the distant past, even if both CO₂ and CH₄ reach very high levels.</p>
<p>This is due to another difference between the Eocene and today: the position of continents and mountains, which were different back then and which also influence the formation of polar stratospheric clouds. So even if we hit early Eocene levels of CH₄ and CO₂ in the future, we would expect less polar stratospheric cloud to be formed. This suggests the standard climate models are better at predicting the future than the past. </p>
<p>It’s therefore unlikely the Arctic and Antarctica will be covered by these beautiful clouds anytime soon. But our research shows evidence from past climates can reveal processes that only become important when greenhouse gas concentrations are high. Some of these processes are not included in our models because models are tested against present day observations and other processes simply seemed more important to include. Looking into the past is a way of broadening our horizon and learning for the future.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/when-greenland-was-green-rapid-global-warming-55-million-years-ago-shows-us-what-the-future-may-hold-166342">When Greenland was green: rapid global warming 55 million years ago shows us what the future may hold</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/217066/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Katrin Meissner receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Deepashree Dutta received funding from the Australian Research Council and the Australian Government Research Training Program Scholarship. </span></em></p><p class="fine-print"><em><span>Martin Jucker receives funding from the Australian Research Council. </span></em></p>
Back when there were Arctic alligators and turtles, ‘polar stratospheric clouds’ kept their world warm. Research suggests these clouds contribute to the ‘missing warming’ in climate models.
Katrin Meissner, Professor and Director of the Climate Change Research Centre, UNSW, UNSW Sydney
Deepashree Dutta, Postdoctoral Research Associate, University of Cambridge
Martin Jucker, Lecturer in Atmospheric Dynamics, UNSW Sydney
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/209018
2023-07-20T18:00:01Z
2023-07-20T18:00:01Z
When 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 Vermont
Tammy Rittenour, Professor of Geosciences and Director of Luminescence Lab, Utah State University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/207468
2023-06-29T12:17:15Z
2023-06-29T12:17:15Z
Meltwater 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 Tromsø
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/207355
2023-06-28T15:12:36Z
2023-06-28T15:12:36Z
From raising the global sea level to crushing life on the seafloor – here’s why you should care about icebergs
<figure><img src="https://images.theconversation.com/files/534283/original/file-20230627-23-8yvpno.jpg?ixlib=rb-1.1.0&rect=26%2C13%2C4375%2C2923&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Icebergs in Disko Bay, western Greenland.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/icebergs-disco-bay-near-ilulissat-greenland-1888385068">Chris Christophersen/Shutterstock</a></span></figcaption></figure><p>Late in the evening of April 14 1912, the <a href="https://theconversation.com/titanic-twist-1912-wasnt-a-bad-year-for-icebergs-after-all-25621">RMS Titanic collided with an iceberg</a> in the north-west Atlantic. In just over two and a half hours, the Titanic sank, claiming the lives of 1,514 people.</p>
<p>The Titanic disaster is one good reason to understand icebergs better. But their significance extends far beyond posing a risk to ships and other offshore structures. Icebergs are crucial to monitor because of their profound impact on the natural world and human societies.</p>
<p>Icebergs are formed when chunks of ice break off from the front of glaciers and floating ice shelves. They exist in a range of sizes, from small formations known as “growlers” and “bergy bits” (that extend up to 5 metres above sea level), to larger icebergs aptly referred to as “giants”. </p>
<p>In 2000, one of Antarctica’s largest icebergs, <a href="https://earthobservatory.nasa.gov/images/552/iceberg-b-15-ross-ice-shelf-antarctica">called B-15</a>, had a surface area roughly the same size as Jamaica. Since then, <a href="https://earthobservatory.nasa.gov/images/92238/end-of-the-journey-for-iceberg-b-15z">B-15 has fractured</a> into a number of smaller pieces and most have melted away. </p>
<p>Icebergs that break off from an already floating ice shelf do not displace ocean water when they melt, just as melting ice cubes do not raise the liquid level in a glass. But when an ice shelf collapses, it no longer holds back inland glacial ice. This inland ice will then move faster and can rapidly release new icebergs, which displace ocean water and contribute to sea level rise. </p>
<p>In 2022, Antarctica’s <a href="https://theconversation.com/conger-ice-shelf-has-collapsed-what-you-need-to-know-according-to-experts-180077">Conger ice shelf</a> collapsed. Some of the continent’s other large <a href="https://www.antarcticglaciers.org/glaciers-and-climate/changing-antarctica/shrinking-ice-shelves/ice-shelves/">ice shelves</a> are also thought to be at risk of collapse in the future, particularly those around the unstable West Antarctic ice sheet. The collapse of the West Antarctic ice sheet alone could <a href="https://www.antarcticglaciers.org/question/ice-antarctica-melt-much-global-sea-level-rise-quickly-likely-happen/">raise the global sea level by 3.2 metres</a>. </p>
<figure class="align-center ">
<img alt="A glacier calving large chunks of ice into the ocean." src="https://images.theconversation.com/files/534292/original/file-20230627-15-c2x0zd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534292/original/file-20230627-15-c2x0zd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534292/original/file-20230627-15-c2x0zd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534292/original/file-20230627-15-c2x0zd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534292/original/file-20230627-15-c2x0zd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534292/original/file-20230627-15-c2x0zd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534292/original/file-20230627-15-c2x0zd.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 chunk of ice breaking off from a glacier in Neko Harbour, Antarctica.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/neko-harbor-glacier-calving-andvord-bay-1556725400">Steve Allen/Shutterstock</a></span>
</figcaption>
</figure>
<p>Global warming accelerates not only iceberg release, but also the rate at which icebergs melt. As icebergs melt, they release freshwater to the ocean. </p>
<p>In the northern hemisphere, a surplus of freshwater from the Greenland ice sheet in the future has the potential to weaken or even shut down the North Atlantic Conveyor “pump”, which circulates warm tropical waters northwards. If the North Atlantic Conveyor pump is significantly affected, the northern hemisphere could be plunged into <a href="https://www.tandfonline.com/doi/abs/10.1080/00167487.2005.12094137">sub-zero, glacial conditions</a>. </p>
<h2>‘Scouring’ the seabed</h2>
<p>Icebergs are often thought of as floating masses of ice. Yet their undersides regularly come into contact with the seabed, gouging out sediment on the seafloor to form “scour” marks. Some <a href="https://www.int-res.com/abstracts/meps/v186/p1-8/">15–20% of the world’s oceans</a> are affected by this phenomenon.</p>
<p><a href="https://www.sciencedirect.com/science/article/pii/S0277379116303638">Research</a> that I co-authored in 2016 on iceberg scouring in East Greenland, found that icebergs can disturb sediment up to several metres below the seabed. This disturbance poses a risk to offshore marine structures such as buried pipelines and telecommunication cables.</p>
<p>Icebergs can also crush plants and animals when they collide with the seabed. These organisms, such as seagrasses and molluscs, are important stores of carbon in polar regions. In areas of West Antarctica, referred to as <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.13523">“iceberg killing fields”</a>, iceberg scouring may recycle around 80,000 tonnes of carbon back into the atmosphere each year. </p>
<h2>Ocean fertilisers (and polluters)</h2>
<p>But it’s not all bad news. Some icebergs contain substantial amounts of iron-rich sediment, known as “dirty ice”. These icebergs <a href="https://www.nature.com/articles/s41467-019-13231-0">fertilise the ocean</a> by supplying important nutrients to marine organisms such as phytoplankton. </p>
<p>Following the passage of an iceberg, there is an increase in organism growth and levels of chlorophyll (the green pigment in plants used for photosynthesis) in the surrounding water. This can result in vibrant blooms that extract CO₂ from the atmosphere as they grow. </p>
<p><a href="https://www.nature.com/articles/ngeo2633">One study</a> on icebergs in the Southern Ocean found that these blooms can be up to ten times the length of the iceberg and can persist for more than a month. Blooms in the wake of icebergs off Antarctica have the capacity to absorb <a href="https://www.cbc.ca/news/science/icebergs-climate-change-1.3401729#:%7E:text=Ocean%20blooms%20in%20the%20wake,as%20Sweden%20or%20New%20Zealand.">up to 40 million tonnes of carbon</a> each year.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/534296/original/file-20230627-29-a5yqmx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A satellite image of a phytoplankton bloom in the Ross Sea, Southern Ocean." src="https://images.theconversation.com/files/534296/original/file-20230627-29-a5yqmx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534296/original/file-20230627-29-a5yqmx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534296/original/file-20230627-29-a5yqmx.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534296/original/file-20230627-29-a5yqmx.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534296/original/file-20230627-29-a5yqmx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534296/original/file-20230627-29-a5yqmx.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534296/original/file-20230627-29-a5yqmx.jpeg?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">January 22, 2011: a phytoplankton bloom in the Ross Sea, Southern Ocean.</span>
<span class="attribution"><a class="source" href="https://earthobservatory.nasa.gov/images/48949/bloom-in-the-ross-sea">Norman Kuring/NASA Goddard Space Flight Center</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>But icebergs hold more than just nutrients in their icy structures. Glacier ice may harbour <a href="https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-021-01106-w">ancient bacterial and viral microbes</a>, even including <a href="https://www.tandfonline.com/doi/full/10.1657/1938-4246-44.4.432">buried faecal microorganisms</a>. These microbes will eventually emerge at the glacier’s surface or in icebergs where they will enter natural ecosystems and could pose a threat to human health. </p>
<p><a href="https://journals.sagepub.com/doi/pdf/10.1177/03091333221107376">Research</a> has also identified various other contaminants within glaciers. These include soot, nuclear fallout, potentially toxic elements such as arsenic, mercury and lead, nitrogen-based contaminants such as fertilisers and animal waste, microplastics and persistent organic pollutants such as pesticides and solvents. </p>
<p>Scientists are, however, exploring the possibility of <a href="https://www.nature.com/articles/s41598-022-26952-y#:%7E:text=A%20long%2Dheld%20idea%20is,United%20Arab%20Emirates%20(UAE)">towing icebergs to water-scarce regions</a>. An iceberg holding 20 billion gallons of freshwater could potentially <a href="https://www.theguardian.com/environment/2017/may/05/could-towing-icebergs-to-hot-places-solve-the-worlds-water-shortage">meet the water needs of a million people</a> for five years – provided that the water is uncontaminated. </p>
<p>Icebergs have an impact on our oceans, atmosphere and societies. As the climate emergency intensifies and our glaciers and ice sheets continue to recede, the significance of icebergs will only grow, for better or worse.</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>Lorna Linch 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>
Icebergs don’t just pose a risk to ships – they have a profound impact on the natural world and human societies.
Lorna Linch, Principal Lecturer in Physical Geography, University of Brighton
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/203277
2023-04-06T11:24:18Z
2023-04-06T11:24:18Z
New 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 University
Frazer Christie, Postdoctoral Research Associate, University of Cambridge
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/197998
2023-01-31T06:13:03Z
2023-01-31T06:13:03Z
‘Blue marble’: how half a century of climate change has altered the face of the Earth
<p>In December 1972, Nasa’s final Apollo mission <a href="https://www.nasa.gov/mission_pages/apollo/missions/apollo17.html">(Apollo 17)</a> took the iconic <a href="https://en.wikipedia.org/wiki/The_Blue_Marble">“Blue Marble”</a> photo of the whole Earth. Many, including science fiction writer <a href="https://www.nytimes.com/2008/03/19/books/19clarke.html">Arthur C. Clarke</a>, had expected that the sight of Earth from afar would instil the belief that mankind’s future lay in space. </p>
<p>Instead, it made Earth appear more unique, and has since become an icon of the global environmental movement.</p>
<p>But that portrait is now a historical artefact. Fifty years later, on December 8 2022, Nasa took a <a href="https://epic.gsfc.nasa.gov/?date=2022-12-08">new image</a> of Earth from its <a href="https://epic.gsfc.nasa.gov/">Deep Space Climate Observatory</a> approximately 1.5 million kilometres away. The photo reveals clear changes to the face of the Earth, some of which are indicative of 50 years of climate change. </p>
<h2>Sparked environmentalism</h2>
<p>The first photos taken of Earth from space were momentous historical events. In 1966, the robotic <a href="https://nssdc.gsfc.nasa.gov/imgcat/html/object_page/lo1_h102_123.html">Lunar Orbiter 1</a> (the US’s first spacecraft to orbit the Moon) sent back some early pictures including a black-and-white image of a partly shadowed Earth. The following year, a satellite called <a href="https://www.planetary.org/space-images/earth-from-ats-3">ATS-3</a> took the first colour image of Earth.</p>
<p>Then in 1968, the crew of <a href="https://www.nasa.gov/mission_pages/apollo/missions/apollo8.html">Apollo 8</a> became the first humans to see and photograph Earth from space. They took various photos through the capsule’s windows, including the famous photo known as <a href="https://en.wikipedia.org/wiki/Earthrise">“Earthrise”</a>. </p>
<p>This photo energised the environmental movement and helped to launch the <a href="https://www.earthday.org/history/">first Earth Day</a> in 1970. Held on April 22 each year, Earth Day now involves over a billion people worldwide in activities that support environmental protection. </p>
<p>In 1972, Nasa – aware of the public value of Earth images – resolved to capture an image of the whole Earth as Apollo 17 moved away from Earth orbit. Lit by the Sun and taken at a distance of 33,000 km, the photo included the first view of Antarctica from space. The image centred on Africa rather than Europe or America, and became a photographic manifesto for global justice. </p>
<p>The Earth also provided the only visible colour in space. Dominated by blue light, water and clouds, it appeared a unique environment that displayed no signs of human activity. “We live inside a blue chamber, a bubble of air blown by ourselves,” wrote cell biologist <a href="https://archive.org/details/TheLivesOfACell/mode/2up">Lewis Thomas</a> in 1973.</p>
<p>This was also the decade in which climate scientist James Lovelock put forward the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/gaia-hypothesis">Gaia theory</a> of the Earth as a self-regulating set of combined living and non-living systems. “Earth systems science”, as it is now known, unites scientific understanding of the planet, its biosphere and its changing climate. </p>
<h2>The impact of climate change</h2>
<p>In December 2022, Nasa’s new Blue Marble photograph was compared with the original image at the University of Portsmouth’s <a href="https://www.the-whole-earth.com/">“The whole Earth: Blue Marble at 50” conference</a>. Since 1972, the planet has visibly changed.</p>
<p>The Antarctic ice sheet has visibly reduced in size, even though the main losses to the <a href="https://en.wikipedia.org/wiki/Larsen_Ice_Shelf">Larsen ice shelves</a> on the Antarctic Peninsula are not visible in this particular image. Differentiating between the permanent ice sheet and seasonal sea ice is also difficult. When the new photo was taken, sea ice was still <a href="https://climate.copernicus.eu/sea-ice">in retreat</a> from the previous winter.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/506569/original/file-20230126-22972-3mg4s2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Antarctic glacier remains of the melting Larsen A ice shelf in front of mountains." src="https://images.theconversation.com/files/506569/original/file-20230126-22972-3mg4s2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/506569/original/file-20230126-22972-3mg4s2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/506569/original/file-20230126-22972-3mg4s2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/506569/original/file-20230126-22972-3mg4s2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/506569/original/file-20230126-22972-3mg4s2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/506569/original/file-20230126-22972-3mg4s2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/506569/original/file-20230126-22972-3mg4s2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&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 Larsen A ice shelf, the losses to which are not visible in the new image.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/antarctic-glacier-remains-melting-larsen-iceshelf-3274671">Armin Rose/Shutterstock</a></span>
</figcaption>
</figure>
<p>While it can be hard to differentiate between snow and cloud in satellite images, in the original photo, some snow appears to be visible on the <a href="https://www.britannica.com/place/Zagros-Mountains">Zagros</a> and <a href="https://en.wikipedia.org/wiki/Geography_of_Iran#/media/File:Iran-geographic_map.svg">Central mountain ranges</a> in Iran (north of the Arabian Gulf). This snow has vanished entirely in the new image. However, this is again within the range of <a href="https://pubs.usgs.gov/pp/p1386g/iran.pdf">seasonal variation</a>, and <a href="https://link.springer.com/article/10.1007/s00704-014-1287-8">research</a> has failed to identify any significant long-term trend in seasonal snow cover in Iran between 1987 and 2007. </p>
<p>Most striking is the reduction in dark green vegetation in the African tropics, particularly at their northern extent. The dark shadow of <a href="https://en.wikipedia.org/wiki/Lake_Chad">Lake Chad</a> in the northern Sahara has shrunk, and forest vegetation now begins hundreds of miles further south. </p>
<p>This is consistent with evidence of desertification in north Africa’s <a href="https://theconversation.com/sahel-region-africa-72569">Sahel region</a>. <a href="https://www.sciencedirect.com/science/article/abs/pii/S0140196311003351">Research</a> found that tree density in the western Sahel declined by 18% between 1954 and 2002. And the UN Food and Agriculture Organization <a href="https://www.fao.org/3/i1757e/i1757e.pdf">estimates</a> that between 1990 and 2010, Africa lost 3–4 million hectares of forest per year, a large proportion in the Sahel. </p>
<p>Madagascar’s once-green landscape is now mainly brown. Long renowned for its ecological richness, the country is now classified a <a href="https://www.cambridge.org/core/journals/oryx/article/biodiversity-of-madagascar-one-of-the-worlds-hottest-hotspots-on-its-way-out/FDDA3F40E329166E689020CD35B42CEC">“biodiversity hotspot”</a>, a term given to a region with significant levels of biodiversity that is threatened by rapid habitat loss. </p>
<p>Many species that are found exclusively in Madagascar, including the <a href="https://small-mammals.org/2022/07/21/jumping-rat-critically-endangered/">Malagasy giant jumping rat</a>, are now at risk of extinction. The population declined by 88% between 2007 and 2019.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/david-bowie-and-the-birth-of-environmentalism-50-years-on-how-ziggy-stardust-and-the-first-un-climate-summit-changed-our-vision-of-the-future-181033">David Bowie and the birth of environmentalism: 50 years on, how Ziggy Stardust and the first UN climate summit changed our vision of the future</a>
</strong>
</em>
</p>
<hr>
<p>The original Blue Marble photo symbolised a historical turning point, from faith in unlimited progress to understanding the limitations of the planetary environment. Most satellite technology is now focused on servicing and understanding the Earth, and space exploration has confirmed just what a unique planet we inhabit.</p>
<p>The former Star Trek actor <a href="https://medium.com/starts-with-a-bang/william-shatner-cried-upon-returning-from-space-the-overview-effect-explains-why-1f3415a51815">William Shatner</a> felt this powerfully on his brief ride into space in 2021. On his return, he remarked: “I discovered that the beauty isn’t out there, it’s down here with all of us.”</p>
<p>The evidence of 50 years of environmental degradation is before our eyes. The space mission that really matters now is the mission to save Earth.</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>
<br><em><a href="https://theconversation.com/uk/newsletters/imagine-57?utm_source=TCUK&utm_medium=linkback&utm_campaign=Imagine&utm_content=DontHaveTimeTop">Get a weekly roundup in your inbox instead.</a> Every Wednesday, The Conversation’s environment editor writes Imagine, a short email that goes a little deeper into just one climate issue. <a href="https://theconversation.com/uk/newsletters/imagine-57?utm_source=TCUK&utm_medium=linkback&utm_campaign=Imagine&utm_content=DontHaveTimeBottom">Join the 10,000+ readers who’ve subscribed so far.</a></em></p>
<hr><img src="https://counter.theconversation.com/content/197998/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>I am author of 'Earthrise: a Short History of the Whole Earth'. It will be out February 2023.</span></em></p><p class="fine-print"><em><span>Nick Pepin has received funding from RGS, Royal Society, NERC and other organisations for research into climate change. </span></em></p><p class="fine-print"><em><span>Oliver Gruner 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>
A new image has been taken of the whole Earth 50 years after the first - revealing noticeable changes to its surface.
Robert Poole, Professor of History, University of Central Lancashire
Nick Pepin, Reader in Climate Science, University of Portsmouth
Oliver Gruner, Senior Lecturer in Visual Culture, University of Portsmouth
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/195693
2022-12-15T15:56:27Z
2022-12-15T15:56:27Z
Glaciers have existed on Earth for at least 60 million years – far longer than previously thought
<figure><img src="https://images.theconversation.com/files/500682/original/file-20221213-1814-xh303t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Transantarctic Mountains peaks are some of the only parts of the continent not buried beneath ice.</span> <span class="attribution"><span class="source">Matt Makes Photos / shutterstock</span></span></figcaption></figure><p>Glaciers have been present somewhere on Earth for at least 60 million years, a period stretching back almost to the time of the dinosaurs. That’s the key finding of our <a href="https://www.nature.com/articles/s41467-022-33310-z">new research</a>, which pushes the date when the planet was last glacier-free back by at least 26 million years.</p>
<p>It may not feel like it due to profound recent warming, but Earth is currently in an “icehouse phase” – at least, relative to its long-term geological history. Even after a century of global warming and many glaciers shrinking or disappearing, conditions are still cold enough to support permanent ice sheets at both poles and more than 200,000 glaciers at high and low elevations and latitudes across the planet. This has not always been the case. </p>
<p>In the geological past Earth was much warmer and glaciers were almost certainly absent even from the very highest and coldest mountains. This is perhaps best demonstrated by the Late Cretaceous period (some 100 million to 66 million years ago), when dinosaurs roamed much of the planet and the climate was up to 20°C warmer than present. Then, the sort of “sub-tropical” forests you might find today in Mexico or India covered <a href="https://www.imperial.ac.uk/news/196516/traces-ancient-rainforest-antarctica-point-warmer/">most of Antarctica</a>.</p>
<p>As the climate cooled over the past 66 million years, Earth was pushed from a “greenhouse” into an “icehouse”, triggering ice ages and the growth of glaciers. The most dramatic cooling happened around 34 million years ago, when Antarctica first developed the ice sheets which now cover most of the continent in up to 4km of ice. However, it was less clear when the continent’s mountain glaciers first formed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/500689/original/file-20221213-10619-5dike1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="map of Transantarctic Mountains" src="https://images.theconversation.com/files/500689/original/file-20221213-10619-5dike1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500689/original/file-20221213-10619-5dike1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=501&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500689/original/file-20221213-10619-5dike1.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=501&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500689/original/file-20221213-10619-5dike1.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=501&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500689/original/file-20221213-10619-5dike1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=629&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500689/original/file-20221213-10619-5dike1.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=629&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500689/original/file-20221213-10619-5dike1.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=629&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 Transantarctics are almost as long as the Rocky Mountains of North America, and just as high.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Transantarctic_mountains_highlighted.jpg">NASA</a></span>
</figcaption>
</figure>
<p>Our <a href="https://www.nature.com/articles/s41467-022-33310-z">new study</a> addresses this uncertainty by investigating when small glaciers first formed in the Transantarctic Mountains, a vast mountain chain that extends some 3,500km across the Antarctic continent. It is currently largely buried under the ice sheet but the areas which sit above the surface can be used to help understand when glaciers first appeared on the continent.</p>
<h2>The onset of Antarctic glaciation</h2>
<p>We used satellite images to map tens of thousands of glacial landforms, which can be valleys, cliffs, scratches in the rock or other features that have been formed at some point by glaciers. Given these are the world’s most remote and least hospitable mountains, mapping from satellite images in this way is far quicker than by visiting in person. But since the region is so big this still took more than a year of continuous work. </p>
<p>Our specific interest was in mapping glacial cirques, which are large glacially eroded bowl-shaped hollows (such as Cwm Idwal in North Wales, which was visited by Charles Darwin and helped convince him that the mountains of Britain <a href="https://www.geolsoc.org.uk/GeositesCwmIdwal">once held glaciers</a>). Using these cirques and our understanding of the climate conditions required for glaciers to form, we found that glaciers have likely existed in the highest mountains of Antarctica for at least the past 60 million years.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/500710/original/file-20221213-16138-f7sylx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="bowl-shaped valley with lake" src="https://images.theconversation.com/files/500710/original/file-20221213-16138-f7sylx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500710/original/file-20221213-16138-f7sylx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500710/original/file-20221213-16138-f7sylx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500710/original/file-20221213-16138-f7sylx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500710/original/file-20221213-16138-f7sylx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500710/original/file-20221213-16138-f7sylx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500710/original/file-20221213-16138-f7sylx.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">Cwm Idwal: Charles Darwin realised this Welsh valley must have been formed by glaciers.</span>
<span class="attribution"><span class="source">Iolo ap Gwynn / shutterstock</span></span>
</figcaption>
</figure>
<p>This is far earlier than reported by previous studies which suggest that mountain glaciers first developed just before 34 million years ago, immediately prior to the formation of the first ice sheet.</p>
<p>Our results instead indicate that Antarctica had glaciers <a href="https://www.nature.com/articles/nature01290">even when it was much warmer than now</a> and was mostly covered by dense sub-tropical forests. At the time, those were probably the only glaciers on Earth. </p>
<p>These high elevation mountain glaciers were likely swallowed up 34 million years ago by larger ice masses which eventually became a continent-wide ice sheet. It is likely that some mountain glaciers returned as the ice sheet retreated during the Miocene Climatic Optimum, a warm period some 15 million years ago, before a widespread switch to the sort of ice that continues to the present day.</p><img src="https://counter.theconversation.com/content/195693/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Scientists used satellites to map tens of thousands of glacial landforms in Antarctica’s highest mountains.
Iestyn Barr, Reader in Physical Geography, Manchester Metropolitan University
Brice Rea, Professor, Geography, University of Aberdeen
Kathryn Adamson, Senior Lecturer in Physical Geography, Manchester Metropolitan University
Matteo Spagnolo, Professor of Geography and the Environment, School of Geosciences, University of Aberdeen
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/185590
2022-08-29T18:04:43Z
2022-08-29T18:04:43Z
What’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 Tromsø
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/187500
2022-08-10T20:27:47Z
2022-08-10T20:27:47Z
The world’s biggest ice sheet is more vulnerable to global warming than scientists previously thought
<figure><img src="https://images.theconversation.com/files/478326/original/file-20220809-26-e92enx.jpg?ixlib=rb-1.1.0&rect=9%2C2296%2C6480%2C4193&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">titoOnz / shutterstock</span></span></figcaption></figure><p>The eastern two thirds of Antarctica is covered by an ice sheet so large that if it melted the sea would rise by 52 metres. Most scientists had once thought this ice sheet was largely invulnerable to climate change, but not any more. And our new research, published in <a href="https://www.nature.com/articles/s41586-022-04946-0">Nature</a>, reveals the dire consequences if we were to awaken Antarctica’s sleeping giant. </p>
<p>Almost 70% of the Earth’s fresh water is frozen in vast continental ice sheets that cover Greenland and Antarctica. Together, they store the equivalent of around 65 metres of sea level rise. Hence, even relatively small changes in the volume of these remote polar ice sheets will have a global impact. An <a href="https://www.nature.com/articles/s41467-019-12808-z">estimated</a> 1 billion people live within 10 metres of sea level, including 230 million within 1 metre.</p>
<p>Scientists measure changes in the volume of these ice sheets by estimating the mass input, mostly via snowfall, and the mass output, mostly melting snow and ice along with icebergs that break off and float away. The difference between input and output is known as the ice sheet’s “mass balance”, which is highly sensitive to climate change.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/478540/original/file-20220810-20-4k341c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Scientists working on ice" src="https://images.theconversation.com/files/478540/original/file-20220810-20-4k341c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/478540/original/file-20220810-20-4k341c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=227&fit=crop&dpr=1 600w, https://images.theconversation.com/files/478540/original/file-20220810-20-4k341c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=227&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/478540/original/file-20220810-20-4k341c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=227&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/478540/original/file-20220810-20-4k341c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=286&fit=crop&dpr=1 754w, https://images.theconversation.com/files/478540/original/file-20220810-20-4k341c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=286&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/478540/original/file-20220810-20-4k341c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=286&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 field camp on the surface of the East Antarctic Ice Sheet.</span>
<span class="attribution"><span class="source">Nerilie Abram</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The most recent efforts to measure ice sheet mass balance paint a very worrying picture. The Greenland Ice Sheet, which contains around 7.4 metres of sea level rise, lost <a href="https://www.nature.com/articles/s41586-019-1855-2">3,900 billion tonnes of ice</a> between 1992 and 2018, causing global sea level to increase by 11 millimetres over this period. A similar story emerges from the western part of Antarctica, known as the West Antarctic Ice Sheet. It holds around 5.3 metres of sea level and lost more than <a href="https://www.nature.com/articles/s41586-018-0179-y">2,000 billion tonnes of ice</a> between 1992 and 2017, adding around 6 mm to the sea level. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/478530/original/file-20220810-10557-eziox2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Shaded map of Antarctica." src="https://images.theconversation.com/files/478530/original/file-20220810-10557-eziox2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/478530/original/file-20220810-10557-eziox2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=477&fit=crop&dpr=1 600w, https://images.theconversation.com/files/478530/original/file-20220810-10557-eziox2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=477&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/478530/original/file-20220810-10557-eziox2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=477&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/478530/original/file-20220810-10557-eziox2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=600&fit=crop&dpr=1 754w, https://images.theconversation.com/files/478530/original/file-20220810-10557-eziox2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=600&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/478530/original/file-20220810-10557-eziox2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=600&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Thickness of ice in Antarctica (UK and Ireland shown for scale).</span>
<span class="attribution"><span class="source">Data: Morlighem et al. (2020; Nature Geoscience) Image: Guy Paxman</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>More sensitive than we thought</h2>
<p>Perhaps surprisingly, much less work has focused on the East Antarctic Ice Sheet, which is by far the world’s largest but was thought to be a lot less vulnerable to global warming. This is because large parts of the ice sheet have persisted through “natural” climate changes across <a href="https://www.nature.com/articles/376412a0">millions of years</a>, and because recent measurements indicate that it has been in equilibrium or has maybe even gained mass (a warmer atmosphere can hold more moisture, which means more snow). In fact, the ice sheet may have even slightly <a href="https://www.nature.com/articles/s41558-018-0356-x">reduced sea level rise</a> over the past century.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/478545/original/file-20220810-19-hi7uym.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Icebergs in the sea" src="https://images.theconversation.com/files/478545/original/file-20220810-19-hi7uym.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/478545/original/file-20220810-19-hi7uym.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=739&fit=crop&dpr=1 600w, https://images.theconversation.com/files/478545/original/file-20220810-19-hi7uym.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=739&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/478545/original/file-20220810-19-hi7uym.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=739&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/478545/original/file-20220810-19-hi7uym.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=929&fit=crop&dpr=1 754w, https://images.theconversation.com/files/478545/original/file-20220810-19-hi7uym.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=929&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/478545/original/file-20220810-19-hi7uym.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=929&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Iceberg towers that have broken off from the East Antarctic Ice Sheet.</span>
<span class="attribution"><span class="source">Nerilie Abram</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>However, over the past two decades or so, observations suggest that the East Antarctic Ice Sheet may be far more sensitive to climate warming than previously thought. Major <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL069173">outlet glaciers</a> like the Totten and Vanderford are thinning and retreating. And there are clear signals of mass loss in Wilkes Land, the ice sheet’s “<a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL086821">weak underbelly</a>”, so-called because it rests on “land” that lies well below sea-level and so is <a href="https://blogs.egu.eu/divisions/cr/2016/06/22/marine-ice-sheet-instability-for-dummies-2/">particularly unstable</a>.</p>
<h2>Lessons from the past</h2>
<p>There is also <a href="https://www.nature.com/articles/ngeo1889">evidence</a> that parts of East Antarctica retreated quite dramatically during warm periods in the past, when carbon dioxide concentrations and atmospheric temperatures were only slightly higher than present. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/478544/original/file-20220810-9449-l5hff.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Ice meets ocean" src="https://images.theconversation.com/files/478544/original/file-20220810-9449-l5hff.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/478544/original/file-20220810-9449-l5hff.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=258&fit=crop&dpr=1 600w, https://images.theconversation.com/files/478544/original/file-20220810-9449-l5hff.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=258&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/478544/original/file-20220810-9449-l5hff.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=258&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/478544/original/file-20220810-9449-l5hff.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=324&fit=crop&dpr=1 754w, https://images.theconversation.com/files/478544/original/file-20220810-9449-l5hff.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=324&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/478544/original/file-20220810-9449-l5hff.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=324&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 edge of Vanderford Glacier, one of the major outlet glaciers that appears to be thinning and retreating in Wilkes Land, East Antarctica.</span>
<span class="attribution"><span class="source">Richard Jones</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>It is likely that East Antarctica contributed several metres to global sea level during the mid-Pliocene warm period, around 3 million years ago, with ice loss concentrated in Wilkes Land. <a href="https://www.nature.com/articles/s41586-020-2484-5">Recent work</a> has also suggested that ice in Wilkes Land retreated 700 km inland from its present position around 400,000 years ago, when global temperatures were only 1 or 2°C higher than present. A key lesson from the past, therefore, is that the East Antarctic Ice Sheet is highly sensitive to relatively modest warming, even if it is currently stable.</p>
<h2>Don’t wake a sleeping giant</h2>
<p>So what will actually happen over the next few decades and centuries? We recently analysed projections from various computer simulations to answer this question. Our results were alarming, but also offered some encouragement.</p>
<p>We found the ice sheet will probably remain broadly in balance in the short-term, because any mass loss due to global warming will be offset by increased snowfall. Although there are large uncertainties, we concluded that the ice sheet will only raise the sea level by about 2cm by the year 2100, which is much less than the contribution projected from melting ice in Greenland or West Antarctica.</p>
<p>Over the next few centuries, however, the sea-level contribution from East Antarctica will depend critically on whether we manage to curb our emissions. If warming continues beyond 2100, sustained by high emissions, then East Antarctica could contribute around 1 to 3 metres by 2300 and around 2 to 5 metres by 2500, adding to the substantial contributions from Greenland and West Antarctica and threatening millions of people who inhabit coastal areas.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/478537/original/file-20220810-12-42uevo.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Chart" src="https://images.theconversation.com/files/478537/original/file-20220810-12-42uevo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/478537/original/file-20220810-12-42uevo.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=391&fit=crop&dpr=1 600w, https://images.theconversation.com/files/478537/original/file-20220810-12-42uevo.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=391&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/478537/original/file-20220810-12-42uevo.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=391&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/478537/original/file-20220810-12-42uevo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=491&fit=crop&dpr=1 754w, https://images.theconversation.com/files/478537/original/file-20220810-12-42uevo.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=491&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/478537/original/file-20220810-12-42uevo.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=491&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 much the sea would rise thanks to melting water from the Each Antarctic Ice Sheet if warming was kept below 2C (left column in each year) and in an extreme warming scenario (right).</span>
<span class="attribution"><span class="source">Richard Jones, Monash University</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Crucially, however, our analysis suggests that if the Paris Agreement to limit warming to well below 2°C is satisfied, then East Antarctica’s sea-level contribution would remain below 0.5 metres, even five centuries from now.</p>
<p>The fate of the world’s largest ice sheet remains in our hands.</p><img src="https://counter.theconversation.com/content/187500/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Stokes received funding from the Natural Environment Research Council (grant NE/R000824/1). </span></em></p><p class="fine-print"><em><span>Guy Paxman receives funding from the Leverhulme Trust. </span></em></p>
But new research offers some hope if we are able to keep climate change under control.
Chris Stokes, Professor in the Department of Geography, Durham University
Guy Paxman, Assistant Professor (Research), Department of Geography, Durham University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/179360
2022-06-27T12:25:01Z
2022-06-27T12:25:01Z
How many ice ages has the Earth had, and could humans live through one?
<figure><img src="https://images.theconversation.com/files/468859/original/file-20220614-17290-2cjvwa.jpg?ixlib=rb-1.1.0&rect=25%2C12%2C8601%2C5729&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">During ice ages, ice sheets like the one in Greenland have covered much of Earth's surface. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/the-greenland-ice-sheet-is-the-largest-ice-sheet-in-the-news-photo/1399203109">Thor Wegner/DeFodi Images via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?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">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>How many ice ages has the Earth had, and could humans live through one? – Mason C., age 8, Hobbs, New Mexico</strong></p>
</blockquote>
<p>First, what is an <a href="https://geology.utah.gov/map-pub/survey-notes/glad-you-asked/ice-ages-what-are-they-and-what-causes-them/">ice age</a>? It’s when the Earth has cold temperatures for a long time – millions to tens of millions of years – that lead to ice sheets and glaciers covering large areas of its surface. </p>
<p>We know that the Earth has had <a href="http://iceage.museum.state.il.us/content/when-have-ice-ages-occurred">at least five major ice ages</a>. The first one happened about 2 billion years ago and lasted about 300 million years. The most recent one started about 2.6 million years ago, and in fact, we are still technically in it. </p>
<p>So why isn’t the Earth covered in ice right now? It’s because we are in a period known as an “interglacial.” In an ice age, temperatures will fluctuate between colder and warmer levels. Ice sheets and glaciers melt during warmer phases, which are called interglacials, and expand during colder phases, which are called glacials.</p>
<p>Right now we are in the most recent ice age’s warm interglacial period, which began about 11,000 years ago.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/I4EZCy14te0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Earth’s climate goes through warming and cooling cycles that are influenced by gases in its atmosphere and variations in its orbit around the sun.</span></figcaption>
</figure>
<h2>What was it like during the ice age?</h2>
<p>When most people talk about the “ice age,” they are usually referring to the last glacial period, which began about 115,000 years ago and ended about 11,000 years ago with the start of the current interglacial period. </p>
<p>During that time, the planet was much cooler than it is now. At its peak, when ice sheets covered most of North America, the average global temperature was about <a href="https://www.smithsonianmag.com/smart-news/ice-age-temperature-science-how-cold-180975674/">46 degrees Fahrenheit</a> (8 degrees Celsius). That’s 11 degrees F (6 degrees C) cooler than the global annual average today.</p>
<p>That difference might not sound like a lot, but it resulted in most of North America and Eurasia being covered in ice sheets. Earth was also much drier, and <a href="https://www.usgs.gov/media/images/coastline-eastern-us-changesslowly">sea level was much lower</a>, since most of the Earth’s water was trapped in the ice sheets. <a href="https://education.nationalgeographic.org/resource/steppe">Steppes</a>, or dry grassy plains, were common. So were <a href="http://kids.nceas.ucsb.edu/biomes/savanna.html">savannas</a>, or warmer grassy plains, and deserts.</p>
<p>Many <a href="https://ucmp.berkeley.edu/quaternary/ple.html">animals present during the ice age</a> would be familiar to you, including brown bears, caribou and wolves. But there were also megafauna that went extinct at the end of the ice age, like <a href="https://uwaterloo.ca/earth-sciences-museum/resources/ice-age-mammals">mammoths, mastodons, saber-toothed cats</a> and <a href="https://www.livescience.com/56762-giant-ground-sloth.html">giant ground sloths</a>. </p>
<p>There are different ideas about <a href="https://samnoblemuseum.ou.edu/understanding-extinction/extinctions-in-the-recent-past-and-the-present-day/pleistocene-extinctions/">why these animals went extinct</a>. One is that humans hunted them into extinction when they came in contact with the megafauna.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/468864/original/file-20220614-2525-72v0y4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Scientist and workers gather around a jawbone and horns protruding out of the ground." src="https://images.theconversation.com/files/468864/original/file-20220614-2525-72v0y4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/468864/original/file-20220614-2525-72v0y4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/468864/original/file-20220614-2525-72v0y4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/468864/original/file-20220614-2525-72v0y4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/468864/original/file-20220614-2525-72v0y4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/468864/original/file-20220614-2525-72v0y4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/468864/original/file-20220614-2525-72v0y4.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">Excavating a mastodon skeleton at Burning Tree Golf Course in Heath, Ohio, December 1989. The skeleton, found by workers who were digging a pond, was 90% to 95% complete and more than 11,000 years old.</span>
<span class="attribution"><a class="source" href="https://flic.kr/p/mF53eR">James St. John/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Wait, there were humans during the ice age?!</h2>
<p>Yes, people just like us lived through the ice age. Since our species, <em>Homo sapiens</em>, <a href="https://humanorigins.si.edu/evidence/human-fossils/species/homo-sapiens">emerged about 300,000 years ago in Africa</a>, we have spread around the world. </p>
<p>During the ice age, some populations remained in Africa and did not experience the full effects of the cold. Others moved into other parts of the world, including the cold, glacial environments of Europe. </p>
<p>And they weren’t alone. At the beginning of the ice age, there were other species of hominins – a group that includes our immediate ancestors and our closest relatives – throughout Eurasia, like the <a href="https://humanorigins.si.edu/evidence/human-fossils/species/homo-neanderthalensis">Neanderthals</a> in Europe and the mysterious <a href="https://www.newscientist.com/definition/denisovans/">Denisovans</a> in Asia. Both of these groups seem to have gone extinct before the end of the ice age. </p>
<p>There are lots of ideas about how our species survived the ice age when our hominin cousins did not. Some think that it has to do with how adaptable we are, and how we <a href="https://www.discovermagazine.com/planet-earth/how-humans-survived-the-ice-age">used our social and communication skills and tools</a>. And it appears that humans didn’t hunker down during the ice age. Instead they moved into new areas. </p>
<p>For a long time it was thought that humans did not enter North America until after the ice sheets started to melt. But <a href="https://www.nps.gov/whsa/learn/nature/fossilized-footprints.htm">fossilized footprints</a> found at <a href="https://www.nps.gov/whsa/index.htm">White Sands National Park</a> in New Mexico show that humans have been in North America since at least 23,000 years ago – close to the peak of the last ice age.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/179360/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Denise Su 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>
The Earth has had at least five major ice ages, and humans showed up in time for the most recent one. In fact, we’re still in it.
Denise Su, Associate Professor, Arizona State University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/182506
2022-05-05T18:17:57Z
2022-05-05T18:17:57Z
Scientists in Antarctica discover a vast, salty groundwater system under the ice sheet – with implications for sea level rise
<figure><img src="https://images.theconversation.com/files/461411/original/file-20220504-21-pex7jj.jpg?ixlib=rb-1.1.0&rect=0%2C338%2C4031%2C2679&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Co-author Chloe Gustafson and mountaineer Meghan Seifert install measuring equipment on an ice stream.</span> <span class="attribution"><a class="source" href="https://emlab.ldeo.columbia.edu/index.php/projects/subglacial-em-mapping/">Kerry Key/Lamont-Doherty Earth Observatory</a></span></figcaption></figure><p><em>A new discovery deep beneath one of Antarctica’s rivers of ice could change scientists’ understanding of how the ice flows, with important implications for estimating future sea level rise.</em></p>
<p><em>Glacier scientists <a href="https://scholar.google.com/citations?user=ybHJBncAAAAJ&hl=en">Matthew Siegfried</a> from Colorado School of Mines, <a href="https://scholar.google.com/citations?user=hFaSe94AAAAJ&hl=en">Chloe Gustafson</a> from Scripps Institution of Oceanography and their colleagues spent 61 days living in tents on an Antarctic <a href="https://www.antarcticglaciers.org/glacier-processes/glacier-types/ice-streams/">ice stream</a> to collect data about the land under half a mile of ice beneath their feet. They explain what the team discovered and what it says about the behavior of ice sheets in a warming world.</em></p>
<h2>What was the big takeaway from your research?</h2>
<p>First, it helps to understand that West Antarctic was an ocean before it was an ice sheet. If it disappeared today, it would be an ocean again with a bunch of islands. So, we know that the bedrock below the ice sheet is covered with a thick layer of sediments – the particles that accumulate onto ocean floors. </p>
<p>What we didn’t know was what was in the tiny pore spaces among those sediments below the ice.</p>
<p>We expected to find meltwater coming from the ice stream above, a fast-moving channel of ice that flows from the center of the ice sheet toward the ocean. What we didn’t expect, but we found in this thick layer of sediments, was a huge amount of groundwater – including saltwater from the ocean.</p>
<p><a href="https://www.science.org/doi/10.1126/science.abo1266">Our findings</a> suggest that this salty groundwater is the largest reservoir of liquid water below the ice stream we studied, and likely others, and it may be affecting how the ice flows on Antarctica.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/LSG8Dm-ZPzc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How Antarctica’s ice flows through ice streams and ice shelves to the ocean. NASA.</span></figcaption>
</figure>
<p>Liquid water is incredibly important to <a href="https://www.antarcticglaciers.org/glacier-processes/glacier-types/ice-streams/">how fast an ice stream moves</a>. If there’s liquid water at the base of an ice stream, it flows fast. If that water freezes or the base dries out, the ice screeches to a stop. </p>
<p>Models of ice streams <a href="https://doi.org/10.1029/93PA02201">typically consider only</a> whether ice at the base has reached the melting point or if water has flowed from upstream along the base of the ice. Scientists had never considered that more water was available under the ice sheet, let alone water that is much saltier, which keeps water from freezing at lower temperatures. (Think about why communities put salt on roads in winter.) </p>
<p>Our observations suggest there is so much water there, if you took the 500 to 1,900 meters (1,600 to 6,200 feet) or so of sediments below the ice stream and squeezed them like a sponge, you’d have a column of water about 220 to 820 meters (700 to 2,700 feet) deep.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/461621/original/file-20220505-22-hq5ugs.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Illustrations of subglacial lakes and groundwater show the sediment depth to 1000 meters or meter" src="https://images.theconversation.com/files/461621/original/file-20220505-22-hq5ugs.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461621/original/file-20220505-22-hq5ugs.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=387&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461621/original/file-20220505-22-hq5ugs.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=387&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461621/original/file-20220505-22-hq5ugs.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=387&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461621/original/file-20220505-22-hq5ugs.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=487&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461621/original/file-20220505-22-hq5ugs.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=487&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461621/original/file-20220505-22-hq5ugs.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=487&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Illustrations of the Whillans ice stream show liquid water under the ice from subglacial lakes (left) and groundwater within the sediment. The ice stream moves at about 300 meters per year.</span>
<span class="attribution"><a class="source" href="https://www.science.org/doi/10.1126/science.abo1266">Modified from Gustafson et al., 2022</a></span>
</figcaption>
</figure>
<p>This water can move through the pores in the subglacial groundwater system, just like groundwater elsewhere, but in Antarctica, there is a dynamic ice sheet on top. When the ice sheet gets thicker, it exerts more pressure on the sediment below, so it could <a href="https://doi.org/10.1111/j.1468-8123.2011.00360.x">drive meltwater from the base of the ice sheet</a> deeper into the sediment. When the ice gets thinner, however, it could draw water, now a little saltier, out of the sediments. That saltier water could affect how fast the ice flows.</p>
<p>Knowing that there is a massive reservoir of water that may be linked to how fast-flowing regions of Antarctica behave means scientists need to rethink our understanding of ice streams.</p>
<h2>What does finding liquid seawater in the sediments tell scientists about Antarctica?</h2>
<p>The salty groundwater was a clear sign of how far inland the boundary between the ice sheet and the ocean once reached.</p>
<p>This boundary, known as <a href="https://www.antarcticglaciers.org/glacier-processes/grounding-lines">the grounding line, is incredibly important</a>. When ice flows across the grounding line, it starts to float in the ocean. If you know how the grounding line is shifting, you have a good sense of how much ice is being <a href="https://www.antarcticglaciers.org/glaciers-and-climate/sea-level-rise-2/">contributed to the global ocean</a>.</p>
<p>The fact that there were marine waters beneath our feet meant that the grounding line was upstream of us at some point, at least 70 miles (110 kilometers) from where it is today.</p>
<figure class="align-center ">
<img alt="Map of the study site and locator map in Antarctica." src="https://images.theconversation.com/files/461413/original/file-20220504-15-rmqju5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461413/original/file-20220504-15-rmqju5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461413/original/file-20220504-15-rmqju5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461413/original/file-20220504-15-rmqju5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461413/original/file-20220504-15-rmqju5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461413/original/file-20220504-15-rmqju5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461413/original/file-20220504-15-rmqju5.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">The team’s survey points on the Whillan’s ice stream in 2018-2019 and the grounding line.</span>
<span class="attribution"><a class="source" href="https://emlab.ldeo.columbia.edu/index.php/projects/subglacial-em-mapping/">Kerry Key/Lamont-Doherty Earth Observatory</a></span>
</figcaption>
</figure>
<p>The next question is when it got there.</p>
<p>We argue in our paper that it can’t be too old. The groundwater is flowing, and fresh water is coming into the sediments from the glacier above. We estimate that most of this salty water arrived in the subglacial system within the past 10,000 years, <a href="https://doi.org/10.1029/2020GL088476">based on how much radiocarbon has been found in the upper sediment</a> in previous a study.</p>
<p>The ocean would have deposited that seawater when the ice sheet got smaller during warm periods in the past.</p>
<h2>Whillans ice stream is pretty remote. How did you determine what was happening a mile below you?</h2>
<p>Our site is about a two-hour flight from McMurdo Station, Antarctica. The plane lands on skis and drops off everything you need to live. Then it takes off, and it’s you, your field team, and a couple pallets of cargo.</p>
<p>In all, we slept 61 days in a tent that season. Each day, we packed our snowmobiles, put in the coordinates for a site, and installed <a href="https://em.geosci.xyz/content/geophysical_surveys/mt/index.html">magnetotelluric</a> stations. </p>
<p>Each station has three magnetometers – pointing east-west, north-south and vertical – and two pairs of electrodes – aligned east-west and north-south. These instruments can detect the electromagnetic signatures of different Earth materials in the subsurface.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/-9tJEyI5o38?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Installing a magnetotelluric station on the Whillans ice stream.</span></figcaption>
</figure>
<p>Natural variations in the Earth’s magnetic and electric fields are created by events across the globe, such as <a href="https://www.swpc.noaa.gov/phenomena/solar-wind">solar wind</a> interacting with the <a href="https://scied.ucar.edu/learning-zone/atmosphere/ionosphere">Earth’s ionosphere</a> and lightning strikes. A change in the Earth’s magnetic and electric fields induces secondary electromagnetic fields in the subsurface, and the strength of those fields is related to how well the material there conducts electricity.</p>
<p>So, by measuring electric and magnetic fields on the ice surface, we can figure out the conductivity of the subsurface materials, including water. It’s the same method the oil and gas industry used to find fossil fuels.</p>
<p>We could see the groundwater, and since <a href="https://mrccc.org.au/wp-content/uploads/2013/10/Water-Quality-Salinity-Standards.pdf">salt water has far greater conductivity</a> than fresh water, we could estimate how salty it was.</p>
<h2>What else might be in the groundwater?</h2>
<p>Any time we’ve poked a hole through Antarctica, <a href="https://doi.org/10.1038/nature13667">it’s been teeming with microbial life</a>. There’s no reason to think microbes aren’t gnawing away at nutrients in the groundwater, too.</p>
<p>When you have microbial ecosystems that are cut off for extended periods of time – in this case, seawater was likely deposited there 5,000-10,000 years ago – you start to have a pretty good analog for how life might exist on other planetary bodies, locked in the subsurface and buried underneath thick ice.</p>
<p>Where there’s life, there is also the question of carbon.</p>
<p>We know that there are <a href="https://doi.org/10.3389/fmicb.2016.01457">microbes in subglacial lakes and rivers</a> at the top of the sediment that are consuming carbon and transforming it into greenhouse gases like <a href="https://doi.org/10.1038/nature11374">methane</a> and <a href="https://doi.org/10.1038/ngeo2992">carbon dioxide</a>. We know all of this carbon ultimately gets <a href="https://doi.org/10.1029/2019GB006446">transferred to the Southern Ocean</a>. But we still don’t have great measurements of any of this.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/XyCYuTL71wE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">High winds, common at the authors’ camp on the Whillans ice stream, create challenges for the electromagnetic method. Each snow particle has static electricity that creates noise for the instruments.</span></figcaption>
</figure>
<p>This is a new environment, and there’s a lot of research still to do. We have observations from one ice stream. It’s like sticking a straw in the groundwater system in Florida and saying, “Yeah, there’s something here” – but what does the rest of the continent look like?</p><img src="https://counter.theconversation.com/content/182506/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Siegfried receives funding from the National Science Foundation and NASA. </span></em></p><p class="fine-print"><em><span>Chloe Gustafson receives funding from the National Science Foundation. </span></em></p>
Liquid water below the ice determines how fast an ice stream flows. As the ice sheet gets thinner, more of that salty groundwater could rise.
Matthew Siegfried, Assistant Professor of Geophysics and Hydrologic Science and Engineering, Colorado School of Mines
Chloe Gustafson, Postdoctoral Research Scientist in Geophysics, Scripps Institution of Oceanography, University of California, San Diego
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/180989
2022-04-21T10:23:38Z
2022-04-21T10:23:38Z
Warmer summers threaten Antarctica’s giant ice shelves because of the lakes they create
<figure><img src="https://images.theconversation.com/files/458844/original/file-20220420-16-5zrq74.jpg?ixlib=rb-1.1.0&rect=7%2C14%2C4737%2C3144&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Layered ice sheets can be vulnerable to fracturing.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/elisfanclub/4542347479">Eli Duke/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>During the Antarctic summer, air temperatures get warm enough to melt snow and ice on the surface of the great ice sheets that make up <a href="https://discoveringantarctica.org.uk/oceans-atmosphere-landscape/ice-land-and-sea/ice-sheets-and-glaciation/">around 99%</a> of Antarctica. This melted water collects to form thousands of lakes around the edges of this vast continent. Most of these lakes form on gigantic platforms of floating ice called <a href="https://nsidc.org/cryosphere/quickfacts/iceshelves.html">ice shelves</a>, which extend out from the continent into the sea. </p>
<p>Lakes forming on the surface of these ice shelves can sometimes cause them to <a href="http://www.antarcticglaciers.org/glaciers-and-climate/changing-antarctica/shrinking-ice-shelves/antarctic-supraglacial-lakes-and-ice-shelf-collapse/">break up</a>. The most famous example is the collapse of <a href="https://theconversation.com/antarcticas-ice-shelves-are-trembling-as-global-temperatures-rise-what-happens-next-is-up-to-us-158540">Larsen B</a> ice shelf on the Antarctic Peninsula, which shattered entirely over a matter of weeks in <a href="https://nsidc.org/cryosphere/icelights/2021/09/what-happened-larsen-ice-shelf">2002</a>. </p>
<p>Satellites recorded the appearance and drainage of <a href="https://earthobservatory.nasa.gov/world-of-change/LarsenB">thousands of lakes</a> on Larsen B’s surface before it broke up. Scientists believe meltwater from these lakes widened and deepened cracks and crevasses within the shelf in a process called hydrofracturing.</p>
<p>Ice shelves act as doorstops, supporting vast masses of ice known as glaciers that lie further inland. But if hydrofracturing forces them to break up, these rivers of ice that feed into the ice shelf flow faster into the ocean, contributing to <a href="https://nsidc.org/cryosphere/icelights/2021/09/what-happened-larsen-ice-shelf">rising sea levels</a>. </p>
<figure class="align-center ">
<img alt="A gif showing how lakes contributed to the collapse of the Larsen B ice shelf" src="https://images.theconversation.com/files/458843/original/file-20220420-13-nvcyej.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/458843/original/file-20220420-13-nvcyej.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/458843/original/file-20220420-13-nvcyej.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/458843/original/file-20220420-13-nvcyej.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/458843/original/file-20220420-13-nvcyej.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/458843/original/file-20220420-13-nvcyej.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/458843/original/file-20220420-13-nvcyej.gif?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">Blue meltwater lakes covered the surface of Larsen B before its collapse.</span>
<span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/system/downloadable_items/1161_3iceshelf-alt.gif">NASA Goddard Space Flight Center</a></span>
</figcaption>
</figure>
<p>Scientists have recently found that lakes are <a href="https://theconversation.com/antarctica-now-has-more-than-65-000-meltwater-lakes-as-summer-ice-melts-124362">more extensive</a> around the Antarctic ice sheet than previously thought. Endurance swimmer <a href="https://lewispugh.com/">Lewis Pugh</a> even swam one kilometre through one of these lakes in 2020 to raise awareness of climate change. But how much does the meltwater stored in these lakes vary between years, and how is this linked to climate conditions? This is something my colleagues and I have explored in a new study, published in <a href="https://www.nature.com/articles/s41467-022-29385-3">Nature Communications</a>.</p>
<p>Our research uncovers for the first time how meltwater lake coverage and volumes vary between years around the whole Antarctic ice sheet. We analysed over 2,000 satellite images of the East Antarctic sheet – the world’s largest – to record the changing size and volume of these lakes over the past seven years. </p>
<p>Until now, observations of surface meltwater lakes on the East Antarctic ice sheet were relatively scarce and their year-to-year changes were largely unknown, making it difficult to assess whether some ice shelves were close to breaking up under the effects of climate change. </p>
<figure class="align-center ">
<img alt="A diagram showing major lakes in East Antarctica" src="https://images.theconversation.com/files/458849/original/file-20220420-34130-dw5jnm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/458849/original/file-20220420-34130-dw5jnm.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=577&fit=crop&dpr=1 600w, https://images.theconversation.com/files/458849/original/file-20220420-34130-dw5jnm.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=577&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/458849/original/file-20220420-34130-dw5jnm.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=577&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/458849/original/file-20220420-34130-dw5jnm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=725&fit=crop&dpr=1 754w, https://images.theconversation.com/files/458849/original/file-20220420-34130-dw5jnm.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=725&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/458849/original/file-20220420-34130-dw5jnm.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=725&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Surface meltwater lakes are visible in satellite images on ice shelves around East Antarctica.</span>
<span class="attribution"><span class="source">Jennifer Arthur</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We found that total lake volume varies between years by as much as 200% on some ice shelves and by up to 72% across the entire ice sheet, with large differences between ice shelves. Across the whole ice sheet, total meltwater stored in lakes peaked in 2017. That water could have filled about 930,000 Olympic swimming pools. </p>
<h2>More warming means more lakes</h2>
<p>Melting at the surface of the sheet doesn’t just form lakes: the water also seeps into air spaces in the layers beneath the surface, where it freezes as temperatures get colder. These layers, called firn, are made up of old snow that has not yet been compressed into ice. </p>
<p>If more melting occurs than snowfall each year, air in the firn becomes replaced with refrozen meltwater. When that happens, meltwater forming the next summer is forced to collect on the surface as lakes. The more surface melting there is, the more the firn gets saturated like a sponge and so the more lakes form on the surface, increasing the risk of fracturing. </p>
<p>To investigate lake variability between years, we ran model simulations of firn air content, surface melt and runoff on Antarctic ice shelves where lakes form. We found that across the whole ice sheet, summer air temperatures and the amount of air in the firn are important factors affecting the total area and volume of meltwater lakes. We’ve noticed on satellite images that on some ice shelves lake coverage is already expanding into regions vulnerable to fracturing.</p>
<figure class="align-center ">
<img alt="A bright blue lake on an ice shelf" src="https://images.theconversation.com/files/458841/original/file-20220420-19-dk3y5k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/458841/original/file-20220420-19-dk3y5k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/458841/original/file-20220420-19-dk3y5k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/458841/original/file-20220420-19-dk3y5k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/458841/original/file-20220420-19-dk3y5k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/458841/original/file-20220420-19-dk3y5k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/458841/original/file-20220420-19-dk3y5k.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 meltwater lake formed on Sørsdal glacier in East Antarctica.</span>
<span class="attribution"><span class="source">Sue Cook, UTAS</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Interestingly, we found large differences between where we’ve observed lakes in satellite images and the amount of meltwater that can form lakes predicted by our models. This means local climate conditions are more important than we thought in predicting surface melting and therefore lake formation. Our climate models still need refining to allow these processes to be fully captured to better predict future surface meltwater around Antarctica.</p>
<p>In a <a href="https://www.carbonbrief.org/guest-post-the-fate-of-antarctic-ice-shelves-at-1-5c-2c-and-4c-of-warming">warming world</a>, these lakes are likely to continue to spread onto ice shelves that are vulnerable to breaking up. Our work is a step forward in understanding not just where lakes are forming now across the whole ice sheet, but what controls the way they change every year. This is key to predicting which ice shelves are most at risk of collapse, as well as for improving model projections of Antarctica’s contribution to sea-level rise.</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>Jennifer Arthur receives funding from a Natural Environment Research Council doctoral studentship grant.</span></em></p>
Melting lakes on ice shelves can widen cracks within them - new research shows how these lakes change across the world’s largest sheet.
Jennifer Arthur, PhD student in Cryospheric Remote Sensing, Durham University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/177211
2022-02-16T01:51:12Z
2022-02-16T01:51:12Z
What drives sea level rise? US report warns of 1-foot rise within three decades and more frequent flooding
<figure><img src="https://images.theconversation.com/files/446652/original/file-20220215-13-okbiwf.jpg?ixlib=rb-1.1.0&rect=0%2C32%2C3594%2C2360&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Tidal flooding is creeping farther into coastal towns like Alexandria, Virginia.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/jeff-bigler-turns-his-bicycle-around-after-taking-in-the-news-photo/1036298978">Matt McClain/The Washington Post via Getty Images</a></span></figcaption></figure><p>Sea levels are rising, and that will bring profound flood risks to large parts of the Gulf and Atlantic coasts over the next three decades.</p>
<p>A new report led by scientists at the National Oceanic and Atmospheric Administration warns that the U.S. should <a href="https://aambpublicoceanservice.blob.core.windows.net/oceanserviceprod/hazards/sealevelrise/noaa-nos-techrpt01-global-regional-SLR-scenarios-US.pdf">prepare for 10-12 inches</a> of relative sea level rise on average in the next 30 years. The rise is due to both sinking land and global warming. And given the greenhouse emissions released so far, the country is unlikely to be able to avoid it.</p>
<p>That much sea level rise means cities like <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</a> that see nuisance flooding during high tides today will experience more damaging floods by midcentury. Nationally, the report expects moderate coastal flooding will occur 10 times as often by 2050. Without significant adaptations, high tides will more frequently pour into streets and disrupt coastal infrastructure, including ports that are essential for supply chains and the economy. </p>
<p>The higher ocean will also <a href="https://theconversation.com/new-flood-maps-show-us-damage-rising-26-in-next-30-years-due-to-climate-change-alone-and-the-inequity-is-stark-175958">bring seawater farther inland</a>. By the end of the century, an average of 2 feet of sea level rise or more is likely, depending on how much the world its cuts greenhouse gas emissions.</p>
<p>As a <a href="https://scholar.google.com/citations?user=p0hz6e0AAAAJ&hl=en">geoscientist, I study sea level rise</a> and the effects of climate change. Here’s a quick explanation of two main ways global warming is affecting ocean levels and their threat to the coasts.</p>
<h2>Ocean thermal expansion</h2>
<p>As greenhouse gases from fossil fuel use and other human activities accumulate in the atmosphere, they trap energy that would otherwise escape into space. That energy causes average global surface temperatures to rise, especially the upper layers of the ocean.</p>
<p>Thermal expansion happens when the ocean heats up. The heat causes sea water molecules to move slightly farther apart, taking up more space. The result is the ocean rises higher, flooding more land.</p>
<p>Over 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 has been due to the effect of thermal expansion. The ocean, which covers about 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>
<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>
<h2>Melting land ice</h2>
<p>The other major factor in rising sea levels is melting land ice. Mountain glaciers and polar ice sheets are diminishing at rates faster than natural systems can replace them.</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.
<a href="https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level">About 50%</a> of global sea level rise was induced by land ice melt during the past several decades.</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 <a href="https://nsidc.org/cryosphere/quickfacts/icesheets.html">up to 200 feet</a>, or 60-70 meters – 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 ">
<img alt="An illustration of sources of sea level rise" src="https://images.theconversation.com/files/446635/original/file-20220215-17-16ewbf4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/446635/original/file-20220215-17-16ewbf4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/446635/original/file-20220215-17-16ewbf4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/446635/original/file-20220215-17-16ewbf4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/446635/original/file-20220215-17-16ewbf4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/446635/original/file-20220215-17-16ewbf4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/446635/original/file-20220215-17-16ewbf4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&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://aambpublicoceanservice.blob.core.windows.net/oceanserviceprod/hazards/sealevelrise/noaa-nos-techrpt01-global-regional-SLR-scenarios-US.pdf">NOAA</a></span>
</figcaption>
</figure>
<h2>Risk will keep rising long after emissions stabilize</h2>
<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> rises globally as the planet warms, the impact is not the same for every coastal region. The rate of rise can be several times faster in some places due to unique local conditions, such as shifts in ocean circulation or the subsidence of the land. </p>
<p>The U.S. East Coast and Gulf Coast, for example, face <a href="https://aambpublicoceanservice.blob.core.windows.net/oceanserviceprod/hazards/sealevelrise/noaa-nos-techrpt01-global-regional-SLR-scenarios-US.pdf">risks above the average</a>, according to the new report, while the West Coast and Hawaii are projected to be lower than average.</p>
<p>Nearly 4 in 10 U.S. residents live near a coastline, and a large part of the U.S. economy is there, as well.</p>
<p>Even when greenhouse gas emissions eventually fall, 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 <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">2021 report from the Intergovernmental Panel on Climate Change</a> shows 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>Get more science, health and technology news.</em> <a href="https://memberservices.theconversation.com/newsletters/?nl=science&source=inline-science-fascinating">Sign up for The Conversation’s weekly science newsletter</a>.]</p><img src="https://counter.theconversation.com/content/177211/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jianjun Yin 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>
A sea level scientist explains the two main ways climate change is threatening the coasts.
Jianjun Yin, Associate Professor of Geoscience, University of Arizona
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/175247
2022-01-23T19:09:15Z
2022-01-23T19:09:15Z
5 ways climate change increases the threat of tsunamis, from collapsing ice shelves to sea level rise
<figure><img src="https://images.theconversation.com/files/441876/original/file-20220121-9541-as4ejs.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C2983%2C1986&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>The enormous eruption of the underwater volcano in Tonga, Hunga Tonga-Hunga Ha'apai, triggered a <a href="https://www.reuters.com/business/environment/tonga-volcano-generates-tsunami-us-tsunami-monitor-said-2022-01-15/">tsunami</a> that reached countries all around the Pacific rim, even causing a <a href="https://apnews.com/article/oil-spills-business-tonga-peru-trending-news-3a92a17e2101945afcb22f5eb5bfb2ad?utm_campaign=SocialFlow&utm_source=Twitter&utm_medium=AP">disastrous oil spill</a> along 21 beaches in Peru. </p>
<p>In Tonga, waves about 2 metres high were recorded before the sea level gauge failed, <a href="https://twitter.com/ConsulateKoT/status/1483384039826464768/photo/1">and waves of up to 15m</a> hit the west coasts of Tongatapu Islands, ‘Eua, and Ha’apai Islands. Volcanic activity could continue for weeks or months, but it’s hard to predict if or when there’ll be another such powerful eruption.</p>
<p>Most tsunamis are caused by earthquakes, but a <a href="http://tsunami.org/what-causes-a-tsunami/">significant percentage</a> (about 15%) are caused by landslides or volcanoes. Some of these may be interlinked – for example, landslide tsunamis are often triggered by earthquakes or volcanic eruptions. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1482437044785889286"}"></div></p>
<p>But does <a href="https://www.un.org/en/climatechange/what-is-climate-change">climate change</a> also play a role? As the planet warms, we’re seeing more <a href="https://www.usgs.gov/faqs/how-can-climate-change-affect-natural-disasters">frequent and intense</a> storms and cyclones, the melting of glaciers and ice caps, and sea levels rising.
Climate change, however, doesn’t just affect the atmosphere and oceans, it affects the Earth’s crust as well. </p>
<p><a href="https://www.reuters.com/article/us-climate-geology-idUSTRE58F62I20090916">Climate-linked</a> geological changes can increase the incidence of earthquakes and volcanic eruptions which, in turn, can exacerbate the threat of tsunamis. Here are five ways this can happen.</p>
<h2>1. Sea level rise</h2>
<p>If greenhouse gas emissions remain at high rates, the average global sea level is <a href="https://www.ipcc.ch/srocc/chapter/chapter-4-sea-level-rise-and-implications-for-low-lying-islands-coasts-and-communities">projected to rise</a> between 60 centimetres and 1.1m. <a href="https://www.un.org/sustainabledevelopment/wp-content/uploads/2017/05/Ocean-fact-sheet-package.pdf">Almost two thirds</a> of the world’s cities with populations over five million are at risk.</p>
<p>Rising sea levels not only make coastal communities more vulnerable to flooding from storms, but also tsunamis. Even modest rises in sea level will dramatically increase the frequency and intensity of flooding when a tsunami occurs, as the tsunami can travel further inland. </p>
<p>For example, <a href="https://www.science.org/doi/10.1126/sciadv.aat1180">a 2018 study</a> showed only a 50 centimetre rise would double the frequency of tsunami-induced flooding in Macau, China. This means in future, smaller tsunamis could have the same impact as larger tsunamis would today.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1483741932970983428"}"></div></p>
<h2>2. Landslides</h2>
<p>A warming climate can increase the risk of both submarine (underwater) and aerial (above ground) landslides, thereby increasing the risk of local tsunamis. </p>
<p>The <a href="https://www.nrdc.org/stories/permafrost-everything-you-need-know">melting of permafrost</a> (frozen soil) at high latitudes decreases soil stability, making it more susceptible to erosion and landslides. More <a href="https://climate.nasa.gov/news/2951/climate-change-could-trigger-more-landslides-in-high-mountain-asia/">intense rainfall</a> can trigger landslides, too, as storms become more frequent under climate change. </p>
<p><a href="https://www.usgs.gov/faqs/how-do-landslides-cause-tsunamis#:%7E:text=Tsunamis%20are%20large%2C%20potentially%20deadly,a%20result%20of%20submarine%20earthquakes.&text=Tsunamis%20can%20be%20generated%20on,a%20rapidly%20moving%20underwater%20landslide.">Tsunamis can be generated</a> on impact as a landslide enters the water, or as water is moved by a rapid underwater landslide. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/waves-from-the-tonga-tsunami-are-still-being-felt-in-australia-and-even-a-50cm-surge-could-knock-you-off-your-feet-175056">Waves from the Tonga tsunami are still being felt in Australia – and even a 50cm surge could knock you off your feet</a>
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<p>In general, tsunami waves generated from landslides or rock falls dissipate quickly and don’t travel as far as tsunamis generated from earthquakes, but they can still lead to huge waves locally.</p>
<p>In Alaska, US, glacial retreat and melting permafrost has exposed unstable slopes. In 2015, this melting caused a landslide that sent 180 million tonnes of rock into a narrow fjord, <a href="https://www.nature.com/articles/s41598-018-30475-w">generating a tsunami reaching 193m high</a> – one of the highest ever recorded worldwide. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Scientists survey damage from a megatsunami in Taan Fiord that had occurred in October, 2015 after a massive landslide.</span>
<span class="attribution"><span class="source">Peter Haeussler, United States Geological Survey Alaska Science Center/Wikimedia</span></span>
</figcaption>
</figure>
<p>Other areas at risk include <a href="https://www.sciencedirect.com/science/article/pii/S0921818121000849">northwest British Columbia</a> in Canada, and the Barry Arm in Alaska, where an <a href="https://dggs.alaska.gov/hazards/barry-arm-landslide.html">unstable mountain slope</a> at the toe of the Barry Glacier has the potential to fail and <a href="https://www.woodwellclimate.org/wp-content/uploads/2020/05/Letter-to-Stakeholders_-Barry-Arm-Landslide-Final.pdf">generate a severe tsunami</a> in the next 20 years.</p>
<h2>3. Iceberg calving and collapsing ice shelves</h2>
<p>Global warming is accelerating the <a href="https://www.businessinsider.com.au/chasing-ice-glacier-calving-climate-change-2014-10?r=US&IR=T">rate of iceberg calving</a> – when chunks of ice fall into the ocean.</p>
<p>Studies predict large ice shelves, such as the Thwaites Glacier in Antarctica, will <a href="https://news.climate.columbia.edu/2021/12/17/crucial-antarctic-glacier-likely-to-collapse-much-earlier-than-expected/">likely collapse</a> in the next five to ten years. Likewise, the Greenland ice sheet is <a href="https://climate.nasa.gov/news/3062/warming-seas-are-accelerating-greenlands-glacier-retreat/">thinning and retreating</a> at an alarming rate.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Iceberg near ship" src="https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.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">Icebergs colliding with the seafloor can trigger underwater landslides.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>While much of the current research focus is on the sea level risk associated with melting and collapse of glaciers and ice sheets, there’s also a <a href="https://nhess.copernicus.org/articles/12/415/2012/">tsunami risk</a> from the calving and breakup process. </p>
<p>Wandering icebergs can trigger <a href="https://www.nature.com/articles/s41561-021-00767-4">submarine landslides and tsunamis</a> thousands of kilometres from the iceberg’s original source, as they hit unstable sediments on the seafloor.</p>
<h2>4. Volcanic activity from ice melting</h2>
<p>About 12,000 years ago, the last glacial period (“ice age”) ended and the melting ice triggered a dramatic <a href="https://eprints.lancs.ac.uk/id/eprint/32995/2/Tuffen_PTRSL.pdf">increase in volcanic activity</a>.</p>
<p>The correlation between climate warming and more volcanic eruptions isn’t yet well constrained or understood. But it may be related to <a href="https://pubs.er.usgs.gov/publication/70182772">changes in</a> stress to the Earth’s crust as the weight of ice is removed, and a phenomenon called “<a href="http://people.rses.anu.edu.au/lambeck_k/pdf/152.pdf">isostatic rebound</a>” – the long-term uplift of land in response to the removal of ice sheets. </p>
<p>If this correlation holds for the current period of climate warming and melting of ice in high latitudes, there’ll be an increased risk of volcanic eruptions and associated hazards, including tsunamis.</p>
<h2>5. Increased earthquakes</h2>
<p>There are a number ways climate change can increase the frequency of earthquakes, and so increase tsunami risk. </p>
<p>First, the weight of ice sheets may be <a href="https://royalsocietypublishing.org/doi/10.1098/rsta.2010.0031">suppressing fault movement and earthquakes</a>. When the ice melts, the isostatic rebound (land uplift) is accompanied by an increase in earthquakes and fault movement as the crust adjusts to the loss of weight. </p>
<p>We may have seen this already in <a href="http://www.geotimes.org/oct04/NN_glacier.html">Alaska</a>, where melting glaciers reduced the stability of faults, inducing many small earthquakes and <a href="https://www.sciencedirect.com/science/article/pii/S0921818104000487?casa_token=BGo_KzIOuJkAAAAA:UHyQvV-tvVulwAfvOFPJILcG2206iyZhOM9TCVS_VAh0UdLimWrfu_NJRTHJVtwlKBL0cfA">possibly the magnitude 7.2 St Elias earthquake</a> in 1979.</p>
<p>Another factor is low air pressure associated with storms and typhoons, which studies have also shown can trigger earthquakes in areas where the Earth’s crust is already under stress. Even relatively small changes in air pressure can trigger fault movements, as <a href="https://www.nature.com/articles/nature08042">an analysis</a> of earthquakes between 2002 and 2007 in eastern Taiwan identified. </p>
<h2>So how can we prepare?</h2>
<p>Many mitigation strategies for climate change should also include elements to improve tsunami preparedness. </p>
<p>This could include incorporating projected sea level rise into tsunami prediction models, and in building codes for infrastructure along vulnerable coastlines. </p>
<p>Researchers can also ensure scientific models of climate impacts include the projected increase in earthquakes, landslides and volcanic activity, and the increased tsunami risk this will bring.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-causes-a-tsunami-an-ocean-scientist-explains-the-physics-of-these-destructive-waves-175213">What causes a tsunami? An ocean scientist explains the physics of these destructive waves</a>
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</em>
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<img src="https://counter.theconversation.com/content/175247/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jane Cunneen 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>
Climate change doesn’t just affect the atmosphere and the oceans, it affects the Earth’s crust as well.
Jane Cunneen, Adjunct Research Fellow, Curtin University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/172136
2021-12-14T16:45:01Z
2021-12-14T16:45:01Z
2021 Arctic Report Card reveals a (human) story of cascading disruptions, extreme events and global connections
<figure><img src="https://images.theconversation.com/files/436805/original/file-20211209-188518-u3cogf.jpg?ixlib=rb-1.1.0&rect=0%2C3%2C2543%2C1686&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Community members from Utqiagvik, Alaska, look to open water from the edge of shorefast sea ice. </span> <span class="attribution"><span class="source">Matthew Druckenmiller</span></span></figcaption></figure><p>The Arctic has long been portrayed as a distant end-of-the-Earth place, disconnected from everyday common experience. But as the planet rapidly warms, what happens in this icy region, where <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/948/Surface-Air-Temperature">temperatures are rising twice as fast as the rest of the globe</a>, increasingly affects lives <a href="https://doi.org/10.1029/2018EF001088">around the world</a>.</p>
<p>On Dec. 14, 2021, a team of 111 scientists from 12 countries released the 16th annual <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021">Arctic Report Card</a>, a yearly update on the state of the Arctic system. <a href="https://cires.colorado.edu/researcher/matthew-druckenmiller">We are</a> <a href="https://cires.colorado.edu/researcher/twila-moon">Arctic</a> <a href="https://news.uaf.edu/expertsguide/rick-thoman">scientists</a> and the editors of this peer-reviewed assessment. In the report, we take a diverse look across the region’s interconnected physical, ecological and human components. </p>
<p>Like an annual checkup with a physician, the report assesses the Arctic’s vital signs – including <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/948/Surface-Air-Temperature">surface air temperatures</a>, <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/944/Sea-Surface-Temperature">sea surface temperatures</a>, <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/945/Sea-Ice">sea ice</a>, <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/947/Terrestrial-Snow-Cover">snow cover</a>, <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/946/Greenland-Ice-Sheet">the Greenland ice sheet</a>, <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/936/Tundra-Greenness">greening of the tundra</a>, and <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/937/Arctic-Ocean-Primary-Productivity-The-Response-of-Marine-Algae-to-Climate-Warming-and-Sea-Ice-Decline">photosynthesis rates by ocean algae</a> – while inquiring into other indicators of health and emerging factors that shed light on the trajectory of Arctic changes. </p>
<p>As the report describes, rapid and pronounced human-caused warming continues to drive most of the changes, and ultimately is paving the way for disruptions that affect ecosystems and communities far and wide.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/_WbWjLUTvZM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A closer look at the 2021 Arctic Report Card.</span></figcaption>
</figure>
<h2>Continued loss of ice</h2>
<p>Arctic Sea ice – a central vital sign and one of the most iconic indicators of global climate change – <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/945/Sea-Ice">is continuing to shrink</a> under warming temperatures. </p>
<p>Including data from 2021, 15 of the lowest summer sea ice extents – the point when the ice is at its minimum reach for the year – <a href="https://nsidc.org/arcticseaicenews/charctic-interactive-sea-ice-graph/">have all occurred in the last 15 years</a>, within a record dating back to 1979 when satellites began regularly monitoring the region.</p>
<p>The sea ice is also thinning at an alarming rate as the Arctic’s oldest and thickest multi-year ice disappears. This loss of sea ice diminishes the Arctic’s ability to cool the global climate. It can also <a href="https://doi.org/10.1080/15230430.2021.1942400">alter lower latitude weather systems</a> to an extent that makes previously rare and impactful weather events, like droughts, heat waves and extreme winter storms, more likely.</p>
<p>Similarly, the <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/946/Greenland-Ice-Sheet">persistent melting of the Greenland ice sheet</a> and other land-based ice is raising seas worldwide, exacerbating the severity and exposure to coastal flooding, disruptions to drinking and waste water systems, and coastal erosion for more communities around the planet. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/436435/original/file-20211208-23-p9y7vr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/436435/original/file-20211208-23-p9y7vr.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=368&fit=crop&dpr=1 600w, https://images.theconversation.com/files/436435/original/file-20211208-23-p9y7vr.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=368&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/436435/original/file-20211208-23-p9y7vr.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=368&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/436435/original/file-20211208-23-p9y7vr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=462&fit=crop&dpr=1 754w, https://images.theconversation.com/files/436435/original/file-20211208-23-p9y7vr.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=462&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/436435/original/file-20211208-23-p9y7vr.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=462&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"><span class="source">NOAA Climate.gov/NSIDC</span></span>
</figcaption>
</figure>
<h2>A warmer, wetter Arctic</h2>
<p>This transition from ice to water and its effects are evident across the Arctic system. </p>
<p>The eight major Arctic rivers are <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/953/River-Discharge">discharging more freshwater</a> into the Arctic Ocean, reflecting an Arctic-wide increase in water coming from land as a result of precipitation, permafrost thaw and ice melt. Remarkably, the summit of the Greenland ice sheet – over 10,000 feet above sea level – experienced its <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/946/Greenland-Ice-Sheet">first-ever observed rainfall during summer 2021</a>. </p>
<p>These developments point to a changed and more variable Arctic today. They also give credence to <a href="https://doi.org/10.1038/s41467-021-27031-y">new modeling studies</a> that show the potential for the Arctic to transition from a snow-dominated to rain-dominated system in summer and autumn by the time global temperatures rise to only 1.5 degrees Celisus (2.7 F) above pre-industrial times. The world has <a href="https://public.wmo.int/en/media/press-release/2020-was-one-of-three-warmest-years-record">already warmed by 1.2 C (2.2 F)</a>.</p>
<p>Such a shift to more rain and less snow would further transform landscapes, fueling faster glacier retreat and permafrost loss. The thaw of permafrost not only affects ecosystems but also further <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2019/ArtMID/7916/ArticleID/844/Permafrost-and-the-Global-Carbon-Cycle">adds to climate warming</a> by allowing previously once-frozen plant and animal remains to decompose, releasing additional greenhouse gases to the atmosphere.</p>
<p>This year’s report highlights how retreating glaciers and deteriorating permafrost are also posing growing <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/951/Glacier-and-Permafrost-Hazards">threats to human life through abrupt and localized flooding and landslides</a>. It urges coordinated international efforts to identify these hazards. More rain in the Arctic will further multiply these threats.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/436436/original/file-20211208-19-1k9eode.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/436436/original/file-20211208-19-1k9eode.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=610&fit=crop&dpr=1 600w, https://images.theconversation.com/files/436436/original/file-20211208-19-1k9eode.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=610&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/436436/original/file-20211208-19-1k9eode.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=610&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/436436/original/file-20211208-19-1k9eode.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=766&fit=crop&dpr=1 754w, https://images.theconversation.com/files/436436/original/file-20211208-19-1k9eode.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=766&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/436436/original/file-20211208-19-1k9eode.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=766&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"><span class="source">NOAA Climate.gov/CS ERA5</span></span>
</figcaption>
</figure>
<h2>Rising human impact</h2>
<p>Observed changes and disruptions in the Arctic have bearing on everyday lives and actions worldwide, either directly or as stark reminders of a range of human-caused harm to climate and ecosystems. </p>
<p>An Arctic Report Card essay on <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/955/Beaver-Engineering-Tracking-a-New-Disturbance-in-the-Arctic">beavers expanding northward into Arctic tundra</a> to exploit newly favorable conditions is a case study for how species around the world are on the move as habitats respond to climate shifts, and the need for new forms of collaborative monitoring to assess the scale of the resulting ecological transformations. </p>
<p>An essay on <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/952/2020-Foreign-Marine-Debris-Event%e2%80%94Bering-Strait">marine garbage from shipping washing ashore on the Bering Sea coast</a>, posing an immediate threat to food security in the region, reminds us that the threat of both micro- and macro-plastics in our oceans is a <a href="https://doi.org/10.17226/26132">preeminent challenge of our time</a>.</p>
<p>A report on <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/950/The-Changing-Arctic-Marine-Soundscape">shipping noise increasingly infiltrating the Arctic’s underwater marine soundscape</a>, to the detriment of marine mammals, is a call to conserve the integrity of natural soundscapes worldwide. For example, a <a href="https://doi.org/10.1038/s41467-021-26488-1">recent unrelated study</a> found that noise caused by human activities and biodiversity loss are deteriorating the spring songbird soundscapes in North America and Europe. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/436787/original/file-20211209-141213-12ddc9u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/436787/original/file-20211209-141213-12ddc9u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/436787/original/file-20211209-141213-12ddc9u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/436787/original/file-20211209-141213-12ddc9u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/436787/original/file-20211209-141213-12ddc9u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/436787/original/file-20211209-141213-12ddc9u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/436787/original/file-20211209-141213-12ddc9u.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">
<figcaption>
<span class="caption">Donna Erickson cuts fish at camp near Unalakleet, Alaska.</span>
<span class="attribution"><span class="source">Jeff Erickson</span></span>
</figcaption>
</figure>
<p>Yet, an <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/957/The-Impact-of-COVID-19-on-Food-Access-for-Alaska-Natives-in-2020">Arctic Report Card essay from members of the Indigenous Foods Knowledges Network</a> highlights how, despite the continued climate threats to Arctic food systems, Alaska Indigenous communities weathered early pandemic disruptions to food security through their cultural values for sharing and “community-first” approaches.</p>
<p>Their cooperation and ability to adapt offer an important lesson for similarly struggling communities worldwide, while reminding everyone that the Arctic itself is a homeland; a place where large-scale disruptions are not new to its over 1 million Indigenous Peoples, and where solutions have long been found in practices of reciprocity.</p>
<h2>An Arctic connected to the rest of the world</h2>
<p>The Arctic Report Card compiles observations from across the circumpolar North, analyzing them within a polar projection of our planet. This puts the Arctic at the center, with all meridians extending outward to the rest of the world. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/436816/original/file-20211209-149721-mt0if2.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/436816/original/file-20211209-149721-mt0if2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/436816/original/file-20211209-149721-mt0if2.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/436816/original/file-20211209-149721-mt0if2.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/436816/original/file-20211209-149721-mt0if2.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/436816/original/file-20211209-149721-mt0if2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/436816/original/file-20211209-149721-mt0if2.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/436816/original/file-20211209-149721-mt0if2.png?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">Some of the Arctic events of 2021 discussed in the Arctic Report Card.</span>
<span class="attribution"><span class="source">NOAA Climate.gov</span></span>
</figcaption>
</figure>
<p>In this view, the Arctic is tethered to societies worldwide through a myriad of exchanges – the natural circulation of air, ocean and contaminants, the migration of animals and invasive species, as well as human-driven transport of people, pollution, goods and natural resources. The warming of the Arctic is also allowing for <a href="https://www.pame.is/projects-new/arctic-shipping/pame-shipping-highlights/411-arctic-shipping-status-reports">greater marine access</a> as sea ice loss permits ships to move deeper into Arctic waters and for longer periods of time. </p>
<p>[<em>Over 140,000 readers rely on The Conversation’s newsletters to understand the world.</em> <a href="https://memberservices.theconversation.com/newsletters/?source=inline-140ksignup">Sign up today</a>.]</p>
<p>These realities illuminate the importance for increased international cooperation in conservation, hazard mitigation and scientific research.</p>
<p>The Arctic has already undergone unprecedented rapid environmental and social changes. A warmer and more accessible Arctic results in a world only tethered more tightly together.</p><img src="https://counter.theconversation.com/content/172136/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Druckenmiller receives funding from the National Oceanic and Atmospheric Administration (NOAA) to serve as a scientific editor of the Arctic Report Card. </span></em></p><p class="fine-print"><em><span>Rick Thoman receives funding from the National Oceanic and Atmospheric Administration (NOAA) via Cooperative Institute for Climate, Ocean, and Ecosystem Studies (CICOES) to serve as a scientific editor of the Arctic Report Card. </span></em></p><p class="fine-print"><em><span>Twila Moon receives funding from the National Oceanic and Atmospheric Administration (NOAA) to serve as a scientific editor for the Arctic Report Card. </span></em></p>
Sea ice is thinning at an alarming rate. Snow is shifting to rain. And humans worldwide are increasingly feeling the impact of what happens in the seemingly distant Arctic.
Matthew L. Druckenmiller, Research Scientist, National Snow and Ice Data Center (NSIDC), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder
Rick Thoman, Alaska Climate Specialist, University of Alaska Fairbanks
Twila A. Moon, Deputy Lead Scientist, National Snow and Ice Data Center (NSIDC), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/168729
2021-11-05T19:55:18Z
2021-11-05T19:55:18Z
East 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 Arizona
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/166652
2021-09-28T03:24:51Z
2021-09-28T03:24:51Z
Climate explained: what is an ice age and how often do they happen?
<figure><img src="https://images.theconversation.com/files/423437/original/file-20210927-21-1w4io46.jpg?ixlib=rb-1.1.0&rect=123%2C167%2C7339%2C3860&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Ulrik Pedersen/NurPhoto via Getty Images</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>What is an ice age? Do they have to last a certain amount of time to count, how did they vary and how many ice ages has the Earth experienced?</strong></p>
</blockquote>
<p>As with many definitions of natural phenomena, a precise definition of an ice age isn’t straightforward. </p>
<p>Ice ages form during protracted periods of a relatively cooler Earth. A definition must include the condition that the Earth is sufficiently cool for permanent ice formation.</p>
<p>A second part of an ice age definition is the end result of protracted cooling. Ice ages lead to the development of continental ice sheets in the northern and southern hemispheres, and the growth of glaciers in mountainous parts of the world, such as the Himalayas, Alps, Southern Alps and Andes. </p>
<p>A third part of the definition involves time. For an ice age to be recorded as significant, it must last for a geologically significant amount of time. </p>
<p>If we bring all these factors together, then an ice age occurs during times of protracted lower temperatures, resulting in significant areas covered in ice for millions to tens or even hundreds of millions of years.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/humans-inhabited-north-america-in-the-depths-of-the-last-ice-age-but-didnt-thrive-until-the-climate-warmed-142810">Humans inhabited North America in the depths of the last Ice Age, but didn't thrive until the climate warmed</a>
</strong>
</em>
</p>
<hr>
<h2>Variations within an ice age</h2>
<p>Ice ages are not uniformly cold. There can be colder and warmer periods during the overall ice-age period. Colder periods lead to more extensive areas of continental ice sheets, valley glaciers and sea ice, while warmer periods lead to reduced areas of ice. </p>
<p>Cold ice-age periods on Earth are called “stadials”, while warmer parts of an ice age are known as “inter-stadials”. An ice age ends when the Earth warms enough for the ice cover to recede, or disappear completely.</p>
<p>The regions on the fringes of extensive ice sheets and glaciers experience a cooling to the point that a consistently cold environment forms. </p>
<figure class="align-center ">
<img alt="An aerial view of the village in a permafrost region of Russia." src="https://images.theconversation.com/files/423438/original/file-20210927-25-1ghy5xr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/423438/original/file-20210927-25-1ghy5xr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=319&fit=crop&dpr=1 600w, https://images.theconversation.com/files/423438/original/file-20210927-25-1ghy5xr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=319&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/423438/original/file-20210927-25-1ghy5xr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=319&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/423438/original/file-20210927-25-1ghy5xr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=401&fit=crop&dpr=1 754w, https://images.theconversation.com/files/423438/original/file-20210927-25-1ghy5xr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=401&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/423438/original/file-20210927-25-1ghy5xr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=401&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">In regions close to larger ice sheets, thr ground remains frozen for most of the year.</span>
<span class="attribution"><span class="source">Alexander Ryumin\TASS via Getty Images</span></span>
</figcaption>
</figure>
<p>Usually, the ground is frozen for much of the year, growing seasons are short, and only the hardiest of flora and fauna survive. The Russian tundra is an example of this landscape.</p>
<p>These environments are called “periglacial” and occupy areas between relatively warmer ice-free regions and permanent ice fields. </p>
<h2>Ice ages and the Earth’s climate</h2>
<p>Ice ages change the Earth’s climatic belts. Temperate and tropical zones become restricted to the lower equatorial latitudes. </p>
<p>A question that follows on from the definition of an ice age is: how cold does Earth have to become to produce one? Earth’s average global temperature today is around 16°C. </p>
<p>Analysis of proxy temperature data (e.g. from the modelling of deep-ocean sediment isotope compositions) over the past 500 million years of Earth’s history indicates that average global temperatures have varied between around -10°C and +30°C. During the most recent glacial maximum (stadial, 23,000 to 11,000 years ago), the average global temperature was about 8°C, with polar regions experiencing average temperatures of -2°C. Ice-free periods over the past 500 million years correspond with average global temperatures of over 20°C. </p>
<p>There is no official minimum period of time for an ice age. Some colder periods in historical times are termed little ice ages, including between the 13th and 18th centuries. This period was characterised by longer and colder winters, and shorter, cooler summers. Rivers regularly froze over in winter in western Europe. The stunning <a href="https://www.rijksmuseum.nl/en/rijksstudio/artists/hendrick-avercamp">artwork</a> of the Dutch painter Hendrick Avercamp (1585–1634 CE) documents aspects of this period. </p>
<figure class="align-center ">
<img alt="Winter Landscape with Ice Skaters, a painting by Durch artist Hendrick Avercamp (circa 1608)." src="https://images.theconversation.com/files/423434/original/file-20210927-19-7g46c5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/423434/original/file-20210927-19-7g46c5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=346&fit=crop&dpr=1 600w, https://images.theconversation.com/files/423434/original/file-20210927-19-7g46c5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=346&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/423434/original/file-20210927-19-7g46c5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=346&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/423434/original/file-20210927-19-7g46c5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=435&fit=crop&dpr=1 754w, https://images.theconversation.com/files/423434/original/file-20210927-19-7g46c5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=435&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/423434/original/file-20210927-19-7g46c5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=435&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Winter Landscape with Ice Skaters, by Hendrick Avercamp (circa 1608).</span>
<span class="attribution"><span class="source">Sepia Times/Universal Images Group via Getty Images</span></span>
</figcaption>
</figure>
<h2>How many ice ages has the Earth experienced?</h2>
<p>Geologists agree Earth has gone through six major global ice ages. The oldest ice age occurred some 2,900-2,780 million years ago. The most recent ice age is the one we are currently experiencing, the late <a href="https://en.wikipedia.org/wiki/Quaternary">Cainozoic-Quaternary Ice Age</a>, which began around 34 million years ago with the <a href="https://www.nature.com/articles/nature01290">glaciation of Antarctica</a>.</p>
<p>Between these two ice-age periods, other ice ages occurred at 2,400-2,100, 715-550, 450-420 and 360-260 million years ago. These six major ice ages lasted between 300 and 30 million years respectively.</p>
<p>Ice ages vary in length of time, extent, and extremes of temperature. The most extensive ice age was the period referred to as “Snowball Earth” when geologists think ice reached all the way to the equator, some 700 million years ago.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-last-ice-age-tells-us-why-we-need-to-care-about-a-2-change-in-temperature-126923">The last ice age tells us why we need to care about a 2℃ change in temperature</a>
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<p>At other times within ice ages (such as today), ice is mainly restricted to polar regions and higher mountain chains. But at its greatest extent, the present glacial period produced ice sheets as far south as the southern Great Lakes in the US and the river Thames in the UK. Mountain glaciers also extended much further and sea levels were some 120 metres lower than today. </p>
<p>There are many factors that cause ice ages. The main ones include variations in Earth’s orbit, known as <a href="https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/">Milankovitch cycles</a>, reductions in solar energy emissions, lower atmospheric greenhouse gas concentrations, variations in ocean currents, tectonic activity, continental configurations, mountain building periods and global volcanism.</p><img src="https://counter.theconversation.com/content/166652/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Petterson has received funding from a range of sources such as research grants and international aid grants throughout his career. </span></em></p>
Three things define an ice age: Earth has to be cold enough for a long time, ice grows to cover significant areas, and it lasts for millions of years.
Michael Petterson, Professor of Geology, Auckland University of Technology
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/166567
2021-08-25T03:03:03Z
2021-08-25T03:03:03Z
What Greenland’s record-breaking rain means for the planet
<p>For three days this month, <a href="https://nsidc.org/greenland-today/2021/08/rain-at-the-summit-of-greenland/">7 billion tonnes of rain</a> fell across Greenland — the largest amount since records began in 1950. It’s also the first time since then that rain, not snow, fell on Greenland’s highest peak. </p>
<p>This is alarming. Greenland’s ice sheet is the second largest on the planet (after Antarctica) and any rain falling on its surface accelerates melting. By August 15, the amount of ice lost was seven times greater than is normal for mid-August.</p>
<p>This is just the latest extreme climate event on the island, which sits in the North Atlantic Ocean. In <a href="https://www.theguardian.com/environment/2021/jul/30/greenland-ice-sheet-florida-water-climate-crisis">a single day</a> in July this year, the amount of ice that melted in Greenland would have covered the US state of Florida with 5 centimetres of water. And last October, <a href="https://www.nature.com/articles/s41586-020-2742-6">research showed</a> ice in Greenland is melting faster than at any other time in the past 12,000 years.</p>
<p>Melting in Greenland threatens to significantly hamper humanity’s efforts to mitigate climate change. That’s because, after a certain point, it may create catastrophic “feedback loops”. Let’s look at the issue in more detail.</p>
<h2>Rising temperatures in the Arctic</h2>
<p>Greenland’s vast <a href="https://nsidc.org/cryosphere/quickfacts/icesheets.html">ice sheet</a> comprises almost 1.7 million square kilometres of glacial land ice. It covers most of the territory and contains enough ice to raise sea levels by more than <a href="https://advances.sciencemag.org/content/5/6/eaav9396">7 metres</a> if melted. </p>
<p>The Greenland and Antarctica ice sheets lost a <a href="https://www.esa.int/Applications/Observing_the_Earth/Space_for_our_climate/Greenland_and_Antarctica_losing_ice_six_times_faster_than_expected">combined 6.4 trillion tonnes of ice</a> between 1992 and 2017. Melting in Greenland has <a href="https://climate.nasa.gov/news/2958/greenland-antarctica-melting-six-times-faster-than-in-the-1990s/">contributed to 60%</a> (17.8 millimetres) of the Earth’s overall sea-level rise due to melting ice sheets, even though Greenland is much smaller than Antarctica. </p>
<p>This may be partly because half of Greenland’s melting is the <a href="https://www.esa.int/Applications/Observing_the_Earth/Space_for_our_climate/Greenland_and_Antarctica_losing_ice_six_times_faster_than_expected">result of rising air temperatures</a>, which cause surface melting. In Antarctica, most ice loss is from ocean water melting glaciers that spill from land into the sea. And the rate of ice loss in both Greenland and Antarctica <a href="https://www.nature.com/articles/d41586-019-03595-0">is accelerating</a> — increasing sixfold since the 1990s.</p>
<p>Rain falling on ice exacerbates this process. So what’s behind the recent unprecedented weather?</p>
<p>Temperatures in the Arctic are <a href="https://theconversation.com/climate-explained-why-is-the-arctic-warming-faster-than-other-parts-of-the-world-160614">rising twice as quickly</a> as the rest of the planet for a number of reasons, <a href="https://www.nasa.gov/topics/earth/features/warmingpoles.html">including</a> changes in cloud cover and water vapour, the reflectivity of the surface, and how weather systems transport energy from the tropics to the polar regions. This has made extreme weather events more common.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/climate-explained-why-is-the-arctic-warming-faster-than-other-parts-of-the-world-160614">Climate explained: why is the Arctic warming faster than other parts of the world?</a>
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</em>
</p>
<hr>
<p>In recent years in Greenland, rain has fallen further north, and more rain has fallen in winter. This is not normal for these regions, which usually get snow, not rain, in below-freezing temperatures.</p>
<p>This month’s rain is <a href="https://nsidc.org/greenland-today/2021/08/rain-at-the-summit-of-greenland/">the result of</a> warm, moist air flowing up from south-west of Greenland and remaining for several days. In the morning of August 14, temperatures at the 3,216-metre summit of Greenland’s ice sheet surpassed freezing point, peaking at 0.48°C. Rain fell on the summit for several hours that morning and on August 15. </p>
<p>This was <a href="https://www.npr.org/2021/08/20/1029633740/rain-fall-peak-of-greenland-ice-sheet-first-climate-change">particularly shocking</a> given the above-freezing temperatures occurred so late in Greenland’s normally short summer. At this time of year, large areas of bare ice are exposed from a lack of snow, which leads to greater runoff of rainwater and meltwater into the oceans.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/417529/original/file-20210824-21-641ihm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/417529/original/file-20210824-21-641ihm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/417529/original/file-20210824-21-641ihm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/417529/original/file-20210824-21-641ihm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/417529/original/file-20210824-21-641ihm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/417529/original/file-20210824-21-641ihm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/417529/original/file-20210824-21-641ihm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/417529/original/file-20210824-21-641ihm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Temperatures rarely surpass freezing at Greenland’s highest point.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>When melting is self-reinforcing</h2>
<p>Rainfall makes the ice sheet more prone to surface melt since it exacerbates the so-called “ice-albedo positive feedback”. In other words, the melting reinforces itself. </p>
<p>When rain falls, its warmth can melt snow, exposing the underlying darker ice, which absorbs more sunlight. This increases temperatures at the surface, leading to more melting.</p>
<p>Unfortunately, this isn’t the only <a href="https://www.pnas.org/content/118/21/e2024192118">positive feedback loop</a> destabilising the Greenland ice sheet. </p>
<p>The “positive melt-elevation feedback” is another, where the lower height of the ice sheet leads to faster melting because higher temperatures occur at lower altitudes. </p>
<p>Also worrying is when higher temperatures cause coastal glaciers to thin, allowing <a href="https://advances.sciencemag.org/content/5/6/eaav9396">more ice to slip into the sea</a>. This both speeds up the rate of glacier flow towards the sea and lowers the ice surface, exposing it to warmer air temperatures and, in turn, increasing melting.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/417527/original/file-20210824-17-drt768.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/417527/original/file-20210824-17-drt768.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/417527/original/file-20210824-17-drt768.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/417527/original/file-20210824-17-drt768.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/417527/original/file-20210824-17-drt768.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/417527/original/file-20210824-17-drt768.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/417527/original/file-20210824-17-drt768.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/417527/original/file-20210824-17-drt768.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">The rate of ice loss in both Greenland and Antarctica is accelerating.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>What does this mean for the planet?</h2>
<p>These positive feedbacks can lead to tipping points — abrupt and irreversible changes in the climate system after a certain threshold is reached. We are more likely to reach these tipping points as emissions increase and global temperatures rise. </p>
<p>While the science on tipping points is still emerging, the <a href="https://www.ipcc.ch/report/ar6/wg1/">most recent report</a> from the Intergovernmental Panel on Climate Change said <a href="https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf">they cannot be ruled out</a>. The report identified likely tipping points such as widespread Arctic sea-ice melting and the thawing of methane-rich permafrost. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/failure-is-not-an-option-after-a-lost-decade-on-climate-action-the-2020s-offer-one-last-chance-158913">'Failure is not an option': after a lost decade on climate action, the 2020s offer one last chance</a>
</strong>
</em>
</p>
<hr>
<p>Recent studies show what humanity may be up against. <a href="https://www.pnas.org/content/118/21/e2024192118">A study from May this year</a> showed a substantial part of the Greenland ice sheet is either at, or about to reach, a tipping point where melting will accelerate, even if global warming is stopped. <a href="https://www.nature.com/articles/d41586-019-03595-0">Scientists are concerned</a> reaching this point may trigger a cascade effect, leading to other tipping points being reached.</p>
<p>Melted ice from both the Arctic Ocean and Greenland have caused an influx of freshwater into the North Atlantic Ocean. This <a href="https://www.metoffice.gov.uk/weather/learn-about/weather/oceans/amoc">has contributed to</a> the slowing of a system of crucial ocean currents, which carry warm water from the tropics into the colder North Atlantic. This current, called the Atlantic Meridional Overturning Circulation (AMOC), has slowed by 15% since the 1950s.</p>
<p>If the AMOC slows down any further, the consequences for the planet could be profound. It could destabilise the West African monsoon, cause more frequent drought in the Amazon rainforest and accelerate ice loss in Antarctica.</p>
<h2>An existential threat</h2>
<p>The rising likelihood of tipping points being reached beyond 1.5°C of warming represents a potential, looming existential threat to human civilisation. However, even if we’ve already crossed some tipping points, as <a href="https://www.theguardian.com/environment/2019/nov/27/climate-emergency-world-may-have-crossed-tipping-points">some scientists suggest</a>, how fast the impacts unfold is still within our control.</p>
<p>If we limit global warming to 1.5°C this century, we give ourselves longer to adapt to heating already locked into the Earth’s system. But the window is rapidly closing; estimates indicate we may reach the crucial 1.5°C threshold <a href="https://www.weforum.org/agenda/2021/08/ipcc-report-on-climate-change/">as soon as the mid-2030s</a>.</p>
<p>The message for humanity is urgent: hard science, not cloying political spin, needs to dictate climate action in the coming years. As with COVID-19, listening to the scientists gives us the best hope of saving the planet.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/when-greenland-was-green-rapid-global-warming-55-million-years-ago-shows-us-what-the-future-may-hold-166342">When Greenland was green: rapid global warming 55 million years ago shows us what the future may hold</a>
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</p>
<hr>
<img src="https://counter.theconversation.com/content/166567/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Willow Hallgren 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>
Greenland’s melting ice sheets threaten to significantly hamper humanity’s efforts to mitigate climate change.
Willow Hallgren, Adjunct Research Fellow, Centre for Planetary Health and Food Security, Griffith University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/164657
2021-08-11T12:27:50Z
2021-08-11T12:27:50Z
Melting Mongolian ice reveals fragile artifacts that provide clues about how past people lived
<figure><img src="https://images.theconversation.com/files/413205/original/file-20210726-21-1ouh7m9.png?ixlib=rb-1.1.0&rect=13%2C4%2C868%2C541&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Archaeologist and paleoenvironmental researcher Isaac Hart of the University of Utah surveys a melting ice patch in western Mongolia.</span> <span class="attribution"><span class="source">Peter Bittner</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>In the world’s high mountain regions, life needs ice. From the Rockies to the Himalayas, glaciers and other accumulations of snow and ice persist throughout the year. Often found on shaded slopes protected from the sun, these ice patches transform barren peaks into biological hot spots.</p>
<p><a href="https://scholar.google.com/citations?user=mlo_aD8AAAAJ&hl=en&oi=sra">As an archaeologist</a>, I value these snow and ice patches for the rare peek they can provide back in time through the fog of alpine prehistory. When people lose objects in the ice, ice patches act as natural deep-freezers. For thousands of years, they can store snapshots of the culture, daily life, technology and behavior of the people who created these artifacts. </p>
<p>Frozen heritage is melting from mountain ice <a href="https://secretsoftheice.com/findings/globally/">in every hemisphere</a>. As it does so, small groups of archaeologists are scrambling to cobble together the funding and staffing needed to identify, recover and study these objects before they are gone. </p>
<p>Alongside a group of scholars from the University of Colorado, the National Museum of Mongolia and partners from around the world, I’m working to identify, analyze and preserve ancient materials emerging from the ice in the grassy steppes of Mongolia, where such discoveries have a tremendous impact on how scientists understand the past. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/413209/original/file-20210726-13-1jd4m2.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="left panel: reindeer lounge on ice; right panel: reindeer lounge on bare ground" src="https://images.theconversation.com/files/413209/original/file-20210726-13-1jd4m2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/413209/original/file-20210726-13-1jd4m2.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=223&fit=crop&dpr=1 600w, https://images.theconversation.com/files/413209/original/file-20210726-13-1jd4m2.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=223&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/413209/original/file-20210726-13-1jd4m2.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=223&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/413209/original/file-20210726-13-1jd4m2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=281&fit=crop&dpr=1 754w, https://images.theconversation.com/files/413209/original/file-20210726-13-1jd4m2.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=281&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/413209/original/file-20210726-13-1jd4m2.png?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"></a>
<figcaption>
<span class="caption">Domestic reindeer in northern Mongolia cool themselves on an ice patch to escape heat and insects (left). Others attempt the same in an area that recent melting has left devoid of perennial ice, hurting herd health.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1371/journal.pone.0224741">© 2019 Taylor et al.</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Life at the ice’s edge</h2>
<p>During the warm summer months, unique plants thrive at the well-watered margins of ice patches. Large animals such as caribou, elk, sheep and <a href="https://doi.org/10.14430/arctic4191">even bison seek the ice</a> to cool off or escape from insects. </p>
<p>Because ice patches are predictable sources of these plants and animals, as well as fresh water, they are important to the subsistence of nearby people nearly everywhere they’re found. In the dry steppes of Mongolia, meltwater from mountain ice feeds summer pastures, and <a href="https://doi.org/10.1371/journal.pone.0224741">domestic reindeer seek out the ice</a> in much the same way as their wild counterparts. Climate warming aside, ice margins act as magnets for people – and repositories of the materials they leave behind. </p>
<p>It’s not just their biological and cultural significance that makes ice patches important tools for understanding the past. The tangible objects made and used by early hunters or herders in many mountainous regions were constructed from soft, organic materials. These fragile objects rarely survive erosion, weather and exposure to the severe elements that are common in alpine areas. If discarded or lost in the ice, though, items that would otherwise degrade can be preserved for centuries in deep-freeze conditions. </p>
<p>But high mountains experience extreme weather and are often far from urban centers where modern researchers are concentrated. For these reasons, significant contributions by mountain residents to the human story are sometimes left out of the archaeological record.</p>
<p>For example, in Mongolia, the high mountains of the Altai hosted the region’s oldest pastoral societies. But these cultures are known only through a small <a href="http://archsib.ru/articles/A501.pdf">handful of burials</a> and the ruins of a few <a href="https://doi.org/10.1038/s41598-020-57735-y">windswept stone buildings</a>. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/XVQaZZ_nDk0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<h2>More artifacts are melting out of the ice</h2>
<p>One of our discoveries was a finely woven piece of animal hair rope from a melting mountaintop ice patch in western Mongolia. On survey, we spotted it lying among the rocks exposed at the edge of the retreating ice. The artifact, which may have been part of a bridle or harness, appeared as though it might have been dropped in the ice the just day before – our guides even recognized the technique of traditional manufacture. However, scientific radiocarbon dating revealed that the artifact is <a href="https://doi.org/10.1038/s41598-021-93765-w">actually more than 1,500 years old</a>. </p>
<p>Objects like these provide rare clues about daily life among the ancient herders of western Mongolia. Their excellent preservation allows us to perform advanced analyses back in the lab to reconstruct the materials and choices of the early herding cultures that <a href="https://doi.org/10.1016/j.cell.2020.10.015">eventually gave rise to pan-Eurasian empires</a> like the Xiongnu and the Great Mongol Empire. </p>
<p>For example, scanning electron microscopy allowed to us to pinpoint that camel hair was chosen as a fiber for making this rope bridle, while collagen preserved within ancient sinew revealed that deer tissue was used to haft a Bronze Age arrowhead to its shaft. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/413208/original/file-20210726-16-xdnvps.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="two metal arrowheads, one lashed with sinew to a wooden shaft" src="https://images.theconversation.com/files/413208/original/file-20210726-16-xdnvps.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/413208/original/file-20210726-16-xdnvps.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/413208/original/file-20210726-16-xdnvps.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/413208/original/file-20210726-16-xdnvps.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/413208/original/file-20210726-16-xdnvps.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/413208/original/file-20210726-16-xdnvps.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/413208/original/file-20210726-16-xdnvps.png?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">Ice patches in western Mongolia preserved a nearly intact arrow from the region’s Bronze Age past – along with sinew lashing and red pigmentation that reveal previously unknown details about the region’s early occupants.</span>
<span class="attribution"><span class="source">Peter Bittner</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Sometimes, the objects that emerge end up overturning some of archaeologists’ most basic assumptions about the past. People in the region have long been classified as herding societies, but my colleagues and I found that Mongolian glaciers and ice patches also contained hunting artifacts, like spears and arrows, and skeletal remains of big game animals like argali sheep <a href="https://doi.org/10.1038/s41598-021-93765-w">spanning a period of more than three millennia</a>. These finds demonstrate that big game hunting on mountain ice has been an essential part of pastoral subsistence and culture in the Altai Mountains for thousands of years.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/413207/original/file-20210726-22-1w55foo.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a pile of sheep skulls and horns on stones at the edge of the ice" src="https://images.theconversation.com/files/413207/original/file-20210726-22-1w55foo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/413207/original/file-20210726-22-1w55foo.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/413207/original/file-20210726-22-1w55foo.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/413207/original/file-20210726-22-1w55foo.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/413207/original/file-20210726-22-1w55foo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/413207/original/file-20210726-22-1w55foo.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/413207/original/file-20210726-22-1w55foo.png?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">A 1,500-year-old pile of argali sheep skulls and horn curls, perhaps intentionally stacked by ancient hunters, melts from a glacier margin in western Mongolia.</span>
<span class="attribution"><span class="source">William Taylor</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>But the clock is ticking. The summer of 2021 is shaping up to be one of the hottest ever recorded, as <a href="https://theconversation.com/extreme-heat-waves-in-a-warming-world-dont-just-break-records-they-shatter-them-164919">scorching summer temperatures</a> fry the rainforests of the Pacific Northwest and <a href="https://www.nytimes.com/2021/07/17/world/europe/siberia-fires.html">wildfires ravage the Siberian Arctic</a>. The impact of escalating temperatures is particularly severe <a href="https://nsidc.org/cryosphere/arctic-meteorology/climate_change.html">in the world’s cold regions</a>. </p>
<p>In the area my colleagues and I study in western Mongolia, satellite photos show that more than <a href="https://doi.org/10.1038/s41598-021-93765-w">40% of the surface cover of ice has been lost</a> over the past three decades. After each artifact is exposed by the melting ice, it may have only a limited window of time for recovery by scientists before it is damaged, degraded or lost because of the combination of freezing, thawing, weather and glacial activity that can affect previously frozen artifacts.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/413211/original/file-20210726-17-1d2dppd.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="satellite image showing outlines of ice getting smaller over the years" src="https://images.theconversation.com/files/413211/original/file-20210726-17-1d2dppd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/413211/original/file-20210726-17-1d2dppd.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=408&fit=crop&dpr=1 600w, https://images.theconversation.com/files/413211/original/file-20210726-17-1d2dppd.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=408&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/413211/original/file-20210726-17-1d2dppd.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=408&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/413211/original/file-20210726-17-1d2dppd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=513&fit=crop&dpr=1 754w, https://images.theconversation.com/files/413211/original/file-20210726-17-1d2dppd.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=513&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/413211/original/file-20210726-17-1d2dppd.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=513&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Satellite photos show the extent of glacier and ice melting in the author’s western Mongolia study zone over less than three decades.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1038/s41598-021-93765-w">Taylor, W., Hart, I., Pan, C. et al. High altitude hunting, climate change, and pastoral resilience in eastern Eurasia. Sci Rep 11, 14287 (2021).</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Because of the scale of modern climate change, it’s difficult to quantify how much material is being lost. Many of the high mountains of Central and South Asia have never been systematically surveyed for melting artifacts. In addition, many international projects have been unable to proceed since summer 2019 because of the COVID-19 pandemic – which has also prompted reductions, pay cuts and even <a href="https://www.museumsassociation.org/museums-journal/news/2021/07/outrage-as-sheffield-university-confirms-closure-of-archaeology-department/">complete closures of archaeology departments</a> at leading universities.</p>
<h2>Revealed by warming, providing climate clues</h2>
<p>Ice patch artifacts are irreplaceable scientific datasets that can also help researchers characterize ancient responses to climate change and understand how modern warming may affect today’s world.</p>
<p>In addition to human-made artifacts left behind in the snow, ice patches also preserve “ecofacts” – natural materials that trace important ecological changes, like shifting tree lines or changing animal habitats. By collecting and interpreting these datasets along with artifacts from the ice, scientists can gather insights into how people adapted to significant ecological changes in the past, and maybe expand the toolkit for facing the 21st-century climate crisis. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/413210/original/file-20210726-23-1vssn46.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="reindeer on a patch of white ice in 2006, contrasted with the same hillside with no ice at all in 2018" src="https://images.theconversation.com/files/413210/original/file-20210726-23-1vssn46.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/413210/original/file-20210726-23-1vssn46.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=244&fit=crop&dpr=1 600w, https://images.theconversation.com/files/413210/original/file-20210726-23-1vssn46.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=244&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/413210/original/file-20210726-23-1vssn46.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=244&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/413210/original/file-20210726-23-1vssn46.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=307&fit=crop&dpr=1 754w, https://images.theconversation.com/files/413210/original/file-20210726-23-1vssn46.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=307&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/413210/original/file-20210726-23-1vssn46.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=307&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Domestic reindeer cool themselves on a formerly permanent ice patch (left) that melted away completely during the summer of 2018 for the first time in local memory.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1371/journal.pone.0224741">© 2019 Taylor et al.</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Meanwhile, the plant, animal and human communities that depend on dwindling ice patches are also imperiled. In northern Mongolia, my work shows that summer ice loss is <a href="https://doi.org/10.1371/journal.pone.0224741">harming the health of domestic reindeer</a>. Local herders worry about the impact of ice loss on pasture viability. Melting ice also converges with other environmental changes: In western Mongolia, animal populations have <a href="https://www.biotaxa.org/mjbs/article/view/26803">dramatically dwindled</a> because of poaching and poorly regulated tourism hunting.</p>
<p>[<em>Over 100,000 readers rely on The Conversation’s newsletter to understand the world.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=100Ksignup">Sign up today</a>.]</p>
<p>As soaring heat exposes artifacts that provide insights into ancient climate resilience and other important scientific data, the ice loss itself is reducing humanity’s resilience for the years ahead.</p><img src="https://counter.theconversation.com/content/164657/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>William Taylor receives funding from The University of Colorado-Boulder Research and Innovation Office (RIO), the Franklin Research Grant from the American Philosophical Society, and the Multi-Country Research Fellowship from the Council of American Overseas Research Centers (CAORC). </span></em></p>
From the high Yukon to the mountains of Central Asia, melting ice exposes fragile ancient artifacts that tell the story of the past – and provide hints about how to respond to a changing climate.
William Taylor, Assistant Professor and Curator of Archaeology, University of Colorado Boulder
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/164312
2021-07-12T21:26:44Z
2021-07-12T21:26:44Z
A significant number of New Zealanders overestimate sea-level rise — and that could stop them from taking action
<figure><img src="https://images.theconversation.com/files/410727/original/file-20210712-17-go0sax.jpg?ixlib=rb-1.1.0&rect=4%2C89%2C2991%2C1872&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Hagen Hopkins/Getty Images</span></span></figcaption></figure><p>Following a recent storm surge in Wellington, some <a href="https://www.tvnz.co.nz/shows/breakfast/clips/world-can-expect-50cm-sea-level-rise-by-2100-even-if-warming-stays-under-2-c">media coverage</a> expressed surprise that 30cm of sea-level rise – an unavoidable amount projected to happen by the middle of this century – would turn a one-in-100-year coastal flood into an annual event. </p>
<p>Our <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0254348">research survey</a>, published last week, confirms that many New Zealanders (38.2%) indeed underestimate current and projected sea-level rise. But it also shows a similar proportion (35%) overestimate it, and only about about a quarter (26.9%) are in line with current understanding of sea-level rise.</p>
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Read more:
<a href="https://theconversation.com/with-seas-rising-and-storms-surging-who-will-pay-for-new-zealands-most-vulnerable-coastal-properties-163807">With seas rising and storms surging, who will pay for New Zealand’s most vulnerable coastal properties?</a>
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<p>Our study is part of the public engagement research of the <a href="https://www.searise.nz/about">NZ SeaRise</a> programme, which is co-led by Richard Levy and Tim Naish. We surveyed a representative sample of New Zealand adults. The finding that a significant number of New Zealanders overestimate sea-level rise might seem positive at first, as it could lead people to be more prepared, but the evidence indicates that’s not the case. </p>
<p>Overestimating the risk of sea-level rise can be as much a problem as underestimating it, because it can lead to public anxiety and <a href="https://doi.org/10.1016/j.jenvp.2017.12.003">feelings of helplessness</a>, rather than motivation to take action to mitigate and adapt. </p>
<h2>Confusion about sea-level rise projections</h2>
<p>In 2019, the Intergovernmental Panel on Climate Change (<a href="https://www.ipcc.ch/reports/">IPCC</a>) <a href="https://www.ipcc.ch/srocc/chapter/summary-for-policymakers/">reported</a> that between 1902 and 2015, global sea level rose by 16cm on average. The process has been accelerating in recent decades, as ice loss from the Greenland and Antarctic ice sheets has increased. </p>
<p>According to the IPCC, the planet will likely experience 0.24-0.32m of sea-level rise by 2050. What happens beyond 2050 depends on how successful we are at reducing carbon emissions. </p>
<p>In 2017, the Ministry for the Environment published <a href="https://environment.govt.nz/publications/preparing-for-coastal-change-a-summary-of-coastal-hazards-and-climate-change-guidance-for-local-government/">projections</a> for New Zealand of 0.46–1.05m of sea-level rise by 2100, depending on how quickly global carbon emissions are reduced. </p>
<p>The NZ SeaRise programme is working to finetune projections because the sea doesn’t rise universally along the coastline. </p>
<figure class="align-right ">
<img alt="An eroded stretch of coast, with caravan parked." src="https://images.theconversation.com/files/410734/original/file-20210712-46002-15gymdj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/410734/original/file-20210712-46002-15gymdj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/410734/original/file-20210712-46002-15gymdj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/410734/original/file-20210712-46002-15gymdj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/410734/original/file-20210712-46002-15gymdj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/410734/original/file-20210712-46002-15gymdj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/410734/original/file-20210712-46002-15gymdj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Rising seas exacerbate coastal erosion.</span>
<span class="attribution"><span class="source">Shutterstock/S Curtis</span></span>
</figcaption>
</figure>
<p>But before we start sharing these new projections, we wanted to find out what people already knew. The survey asked New Zealanders to indicate what they knew about the amount, rate and causes of sea-level rise.</p>
<p>Apart from the question about current sea-level rise, we asked about projections to 2100. Nearly 75% of respondents selected options that were in line with scientifically plausible projections, from “up to 40cm” to “up to 2m”. But 19% of respondents overestimated sea-level rise projections to 2100, selecting “up to 5m” (10.7%) or “more than 5m” (8.2%). </p>
<p>When asked how much global sea levels could rise by 2100 under “a scientifically credible worst-case scenario”, only 33.1% of respondents gave an answer in line with current science, answering “1m or more” (16.7%) or “2m or more” (16.4%). </p>
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Read more:
<a href="https://theconversation.com/managing-retreat-why-new-zealand-is-drafting-a-new-law-to-enable-communities-to-move-away-from-climate-risks-157394">Managing retreat: why New Zealand is drafting a new law to enable communities to move away from climate risks</a>
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</em>
</p>
<hr>
<p>Another 22.5% of respondents underestimated the worst-case scenario by selecting “up to 1m”, while 37.4% overestimated it, selecting “5m or more” (18%) or higher (19.4%). In fact, “15m or more” by 2100 (selected by 6.8%) would defy physical laws around how fast ice can melt, even under extreme temperature forcing.</p>
<p>Respondents were also asked to identify and rank the major causes of sea-level rise from a list of ten items. Here, 28.7% of respondents erroneously identified melting sea ice (which does not directly contribute to sea-level rise) as their top ranked cause. </p>
<figure class="align-center ">
<img alt="Sea ice in the Arctic" src="https://images.theconversation.com/files/410732/original/file-20210712-17-115sfwu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/410732/original/file-20210712-17-115sfwu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/410732/original/file-20210712-17-115sfwu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/410732/original/file-20210712-17-115sfwu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/410732/original/file-20210712-17-115sfwu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/410732/original/file-20210712-17-115sfwu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/410732/original/file-20210712-17-115sfwu.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">While Arctic sea ice is reducing, the melting of floating ice doesn’t directly contribute to sea-level rise.</span>
<span class="attribution"><span class="source">Vincent LECOMTE/Gamma-Rapho via Getty Images</span></span>
</figcaption>
</figure>
<p>The public’s association of melting sea ice with sea-level rise may be due to the significant media coverage given to melting sea ice in the Arctic, rather than the factors contributing to sea-level rise, such as melting of land-based ice sheets and glaciers, the expansion of the ocean as it warms, and land subsidence. </p>
<figure class="align-center ">
<img alt="Graphic that shows how sea level rise affects coastal communities" src="https://images.theconversation.com/files/410733/original/file-20210712-49042-ud1v2c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/410733/original/file-20210712-49042-ud1v2c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=263&fit=crop&dpr=1 600w, https://images.theconversation.com/files/410733/original/file-20210712-49042-ud1v2c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=263&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/410733/original/file-20210712-49042-ud1v2c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=263&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/410733/original/file-20210712-49042-ud1v2c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=330&fit=crop&dpr=1 754w, https://images.theconversation.com/files/410733/original/file-20210712-49042-ud1v2c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=330&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/410733/original/file-20210712-49042-ud1v2c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=330&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"><span class="source">Katy Kelly/GNS Science/NZ SeaRise porgramme</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Respondents who overestimated the amount and speed of sea-level rise were more likely to express greater concern. But concern is not always helpful. A focus on extreme (and often unsound) projections of sea-level rise can lead to more anxiety instead of greater motivation to act. </p>
<p>Nevertheless, our research shows New Zealanders are aware of, and concerned about, 21st-century sea-level rise, which is already affecting coastal communities and infrastructure. </p>
<h2>Site specific projections</h2>
<p>The NZ SeaRise programme is preparing a set of location-specific sea-level rise projections, taking into account global and regional projections of sea-level changes and new knowledge of local vertical land movements, including subsidence and earthquake uplift. </p>
<p>New Zealand straddles a tectonic plate boundary and the land moves up and down as a result. This movement can be large and rapid during major earthquakes, but is relatively continuous along most coastal regions between earthquakes. </p>
<p>For example, measurements from satellites show that today, regions of the lower east coast of the North Island are going down at rates up to 8mm per year and areas along the central Bay of Plenty coast are rising at rates over 10mm per year. Sea-level rise is amplified in places where land is subsiding and dampened where it is going up. </p>
<p>Adding continuous estimates of vertical land movement to our sea-level projections shows future increases in the frequency of coastal flooding due to global sea-level rise will happen decades sooner than expected in areas that are going down, and vice versa.</p>
<p>Criticisms of the “deficit model” of science communication show that encouraging action on an issue – such as sea-level rise – is not as simple as ensuring that people are fully informed. But it is essential they have access to reliable scientific information that can inform their decisions. </p>
<p>Our goal is to provide location-specific projections so all New Zealanders have the information they need to help with decisions and discussions about how we manage life on the coast.</p><img src="https://counter.theconversation.com/content/164312/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rebecca Priestley receives funding from the NZ Ministry for Business Innovation and Employment through the NZ SeaRise Programme</span></em></p><p class="fine-print"><em><span>Richard Levy receives funding from the NZ Ministry for Business Innovation and Employment through the NZ SeaRise Programme</span></em></p><p class="fine-print"><em><span>Taciano L. Milfont receives funding from the Biological Heritage National Science. </span></em></p><p class="fine-print"><em><span>Timothy Naish receives funding from the NZ Ministry for Business Innovation and Employment through the NZ SeaRise Programme.</span></em></p><p class="fine-print"><em><span>Zoë Heine receives funding from the NZ Ministry for Business Innovation and Employment through the NZ SeaRise Programme</span></em></p>
Survey respondents who overestimated the amount and speed of sea-level rise were more likely to express greater concern. But concern is not always helpful in prompting action.
Rebecca Priestley, Associate professor, Te Herenga Waka — Victoria University of Wellington
Richard Levy, Principal Scientist/Environment and Climate Research Leader, GNS Science
Taciano L. Milfont, Reader in Environmental Psychology, University of Waikato
Timothy Naish, Professor, Te Herenga Waka — Victoria University of Wellington
Zoë Heine, PhD Candidate, Te Herenga Waka — Victoria University of Wellington
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/160978
2021-05-17T20:12:26Z
2021-05-17T20:12:26Z
Antarctica is headed for a climate tipping point by 2060, with catastrophic melting if carbon emissions aren’t cut quickly
<figure><img src="https://images.theconversation.com/files/400902/original/file-20210516-13-169io22.jpg?ixlib=rb-1.1.0&rect=21%2C21%2C2400%2C1573&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The big wildcard for sea level rise is Antarctica.</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/efcqsTN-T38">James Eades/Unsplash</a></span></figcaption></figure><p>While U.S. Secretary of State Antony Blinken draws attention to climate change in the Arctic at <a href="https://arctic-council.org/en/">meetings with other national officials</a>, an even greater threat looms on the other side of the planet.</p>
<p><a href="https://doi.org/10.1038/s41586-021-03427-0">New research</a> shows it is Antarctica that may force a reckoning between the choices countries make today about greenhouse gas emissions and the future survival of their coastlines and coastal cities, from New York to Shanghai.</p>
<p>That reckoning may come much sooner than people realize.</p>
<p>While <a href="https://grace.jpl.nasa.gov/resources/30/greenland-ice-loss-2002-2020/">Arctic ice loss</a> as global temperatures rise is <a href="https://theconversation.com/in-alaska-everyones-grappling-with-climate-change-105032">directly affecting lives</a> and <a href="https://theconversation.com/wheres-the-sea-ice-3-reasons-the-arctic-freeze-is-unseasonably-late-and-why-it-matters-148918">triggering feedback loops</a>, the big <a href="https://doi.org/10.1073/pnas.1904822116">wild card for sea level rise is Antarctica</a>. It holds enough land ice to raise global sea levels by more than 200 feet (60 meters) – roughly 10 times the amount in the Greenland ice sheet – and we’re already seeing signs of trouble. </p>
<p>Scientists have long known that the Antarctic ice sheet has physical tipping points, beyond which ice loss can accelerate out of control. The <a href="https://doi.org/10.1038/s41586-021-03427-0">new study</a>, published in the journal Nature, finds that the Antarctica ice sheet could reach a critical tipping point in a few decades, when today’s elementary school kids are raising their families. </p>
<p>The results mean a <a href="https://www.hbs.edu/faculty/Pages/item.aspx?num=58516">common argument</a> for not reducing greenhouse gas emissions now – that future technological advancement can save us later – is likely to fail. </p>
<figure class="align-center ">
<img alt="Long lines are formed by the glacier's flow" src="https://images.theconversation.com/files/400905/original/file-20210516-13-tig4sq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/400905/original/file-20210516-13-tig4sq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=413&fit=crop&dpr=1 600w, https://images.theconversation.com/files/400905/original/file-20210516-13-tig4sq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=413&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/400905/original/file-20210516-13-tig4sq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=413&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/400905/original/file-20210516-13-tig4sq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=520&fit=crop&dpr=1 754w, https://images.theconversation.com/files/400905/original/file-20210516-13-tig4sq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=520&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/400905/original/file-20210516-13-tig4sq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=520&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A satellite image shows the long flow lines as a glacier moves ice into Antarctica’s Ross Ice Shelf, on the right. The red patches mark bedrock.</span>
<span class="attribution"><a class="source" href="https://www.usgs.gov/media/images/byrd-glacier">USGS</a></span>
</figcaption>
</figure>
<p>The new study shows that if emissions continue at their current pace, by about 2060 the Antarctic ice sheet will have <a href="https://doi.org/10.1038/s41586-021-03427-0">crossed a critical threshold</a> and committed the world to sea level rise that is not reversible on human timescales. Pulling carbon dioxide out of the air at that point <a href="https://www.youtube.com/watch?v=XRUxTFWWWdY">won’t stop the ice loss</a>, it shows, and by 2100, sea level could be rising more than 10 times faster than today. </p>
<h2>The tipping point</h2>
<p>Antarctica has several <a href="https://nsidc.org/cryosphere/quickfacts/iceshelves.html">protective ice shelves</a> that fan out into the ocean ahead of the continent’s constantly flowing glaciers, slowing the land-based glaciers’ flow to the sea. But those shelves can thin and break up <a href="https://www.washingtonpost.com/weather/2021/01/21/southern-ocean-warming-antarctica/">as warmer water</a> moves in under them. </p>
<p>As <a href="https://theconversation.com/antarcticas-ice-shelves-are-trembling-as-global-temperatures-rise-what-happens-next-is-up-to-us-158540">ice shelves break up</a>, that can expose towering ice cliffs that may not be able to stand on their own. </p>
<p>There are two potential instabilities at this point. Parts of the Antarctic ice sheet are grounded below sea level on bedrock that slopes inward toward the center of the continent, so <a href="https://doi.org/10.1038/s41467-020-20781-1">warming ocean water</a> can eat around their lower edges, destabilizing them and causing them to retreat downslope rapidly. Above the water, surface melting and rain can open fractures in the ice. </p>
<p>When the ice cliffs get too tall to support themselves, they can collapse catastrophically, <a href="https://nsidc.org/cryosphere/quickfacts/iceshelves.html">accelerating the rate of ice flow to the ocean</a>. </p>
<p>The study used computer modeling based on the physics of ice sheets and found that above 2 C (3.6 F) of warming, Antarctica will see a sharp jump in ice loss, triggered by the rapid loss of ice through the massive Thwaites Glacier. This glacier drains an area the size of Florida or Britain and is the focus of intense study by <a href="https://thwaitesglacier.org/projects">U.S. and U.K. scientists</a>. </p>
<p>To put this in context, the planet is on track to exceed 2 C warming <a href="https://climateactiontracker.org/global/temperatures/">under countries’ current policies</a>. </p>
<p><a href="https://doi.org/10.1038/s41586-021-03302-y">Other projections</a> don’t account for ice cliff instability and generally arrive at lower estimates for the rate of sea level rise. While much of the press coverage that followed the new paper’s release focused on differences between these two approaches, both reach the same fundamental conclusions: The magnitude of sea level rise can be drastically reduced by meeting the Paris Agreement targets, and physical instabilities in the Antarctic ice sheet can lead to rapid acceleration in sea level rise. </p>
<h2>The disaster doesn’t stop in 2100</h2>
<p>The new study, led by Robert DeConto, David Pollard and Richard Alley, is one of the few that looks beyond this century. One of us is a co-author. </p>
<p>It shows that if today’s high emissions continued unabated through 2100, sea level rise would explode, exceeding 2.3 inches (6 cm) per year by 2150. By 2300, sea level would be 10 times higher than it is expected to be if countries meet the Paris Agreement goals. A warmer and softer ice sheet and a warming ocean holding its heat for centuries all prevent refreezing of Antarctica’s protective ice shelves, leading to a very different world. </p>
<p>The vast majority of the pathways for meeting the <a href="https://climateactiontracker.org/global/cat-thermometer/">Paris Agreement expect emissions will overshoot</a> its goals of keeping warming under 1.5 C (2.7 F) or 2 C (3.6 F), and <a href="https://doi.org/10.1088/1748-9326/abfeec">then count on future advances</a> in technology to remove enough carbon dioxide from the air later to lower the temperature again. The rest require a 50% cut in emissions globally by 2030. </p>
<p>Although a majority of countries – including the U.S., U.K. and European Union – have set that as a goal, current policies globally would result in <a href="https://unfccc.int/process-and-meetings/the-paris-agreement/nationally-determined-contributions-ndcs/nationally-determined-contributions-ndcs/ndc-synthesis-report">just a 1% reduction by 2030</a>.</p>
<h2>It’s all about reducing emissions quickly</h2>
<p>Some other researchers <a href="https://doi.org/10.1029/2019GL084183">suggest</a> that ice cliffs in Antarctica might not collapse as quickly as those in Greenland. But given their size and current rates of warming – far faster than in the historic record – what if they instead collapse more quickly? </p>
<p>As countries prepare to increase their Paris Agreement pledges in the runup to a <a href="https://ukcop26.org/">United Nations meeting in November</a>, Antarctica has three important messages that we would like to highlight as <a href="https://blogs.umass.edu/jbgwebstuff/">polar and</a> <a href="http://geoscience.wisc.edu/geoscience/people/faculty/andrea-dutton/">ocean scientists</a>. </p>
<p>First, every fraction of a degree matters. </p>
<p>Second, allowing global warming to overshoot 2 C is not a realistic option for coastal communities or the global economy. The comforting prospect of technological fixes allowing a later return to normal is an illusion that will leave coastlines under many feet of water, with devastating economic impacts. </p>
<p>Third, policies today must take the long view, because they can have irreversible impacts for Antarctica’s ice and the world. Over the past decades, much of the focus on rapid climate change has been on the Arctic and its rich tapestry of Indigenous cultures and ecosystems that are under threat. </p>
<p>As scientists learn more about Antarctica, it is becoming clear that it is this continent – with no permanent human presence at all – that will determine the state of the planet where today’s children and their children will live.</p><img src="https://counter.theconversation.com/content/160978/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Julie Brigham-Grette has received funding from The US National Science Foundation over the course of her career. She currently volunteers academic service as President of the Geological Society of America's Quaternary Geology and Geomorphology Division; and President of the American Geophysical Union's Global Environmental Change section. </span></em></p><p class="fine-print"><em><span>Andrea Dutton receives funding from the National Science Foundation and the John D. and Catherine T. MacArthur Foundation. </span></em></p>
If emissions continue at their current pace, Antarctica will cross a threshold into runaway sea rise when today’s kids are raising families. Pulling CO2 out of the air later won’t stop the ice loss.
Julie Brigham-Grette, Professor of Geosciences, UMass Amherst
Andrea Dutton, Professor of Geoscience, University of Wisconsin-Madison
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/160885
2021-05-14T18:05:13Z
2021-05-14T18:05:13Z
How cables in glaciers could help forecast future sea level rise
<figure><img src="https://images.theconversation.com/files/400604/original/file-20210513-21-1wruqg3.jpg?ixlib=rb-1.1.0&rect=0%2C12%2C4025%2C3005&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Greenland Ice Sheet is the world's second largest body of ice</span> <span class="attribution"><span class="source">Robert Law</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Fibre-optic cables usually make us think of ultra-fast internet – or maybe the irritation of new installation works digging up the pavement. But there are now such cables snaking their way through the centre of the planet’s second largest body of ice, the Greenland ice sheet.</p>
<p>Fibre-optic technologies are allowing us to monitor the internal structure of glaciers in unprecedented levels of detail. <a href="https://advances.sciencemag.org/lookup/doi/10.1126/sciadv.abe7136">In our new study</a>, we show how fibre-optics are offering extraordinary new insight into how ice sheets evolve – and how the movement of Greenland’s glaciers is far more complicated than previously thought.</p>
<p>Ice loss from Greenland has <a href="https://doi.org/10.1073/pnas.1904242116">increased sixfold since the 1980s</a>, and the melting ice sheet is now the <a href="https://doi.org/10.1038/s41467-020-20011-8">single biggest contributor</a> to global sea level rise. In order to forecast the ice sheet’s future – including its worrying rates of melting – we need to understand the thermodynamic processes at work within it. That means we need to take its temperature as accurately as we can. </p>
<p>Surface conditions can be detected simply enough using satellites or <a href="https://www.businessinsider.com/greeland-ice-sheet-turned-black-melts-faster-because-of-algae-2021-3?r=DE&IR=T">in-person observations</a>, but plumbing the deepest reaches of the ice sheet, a moving block of ice a kilometre thick, is a whole different challenge.</p>
<p>This is where fibre-optics come in. In any home broadband network, information travels through fibre-optic cables as a series of light pulses. We use a similar idea in our work, firing bursts of light from a laser into a length of cable. </p>
<p>However, the cable isn’t perfectly smooth: so as the light travels, some will be reflected from tiny flaws in the cable wall, much like how light bounces off the reflective shards on a disco ball. As the cable changes temperature, or is stretched slightly by tiny earthquakes, the flaws changes: and so do the characteristics of the reflections. By continually monitoring these changes, we build up a detailed picture of what the glacier is like deep under its icy surface. </p>
<figure class="align-center ">
<img alt="A man raises a hammer above an icy tundra surrounded by equipment" src="https://images.theconversation.com/files/400580/original/file-20210513-23-156xfs1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/400580/original/file-20210513-23-156xfs1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/400580/original/file-20210513-23-156xfs1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/400580/original/file-20210513-23-156xfs1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/400580/original/file-20210513-23-156xfs1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/400580/original/file-20210513-23-156xfs1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/400580/original/file-20210513-23-156xfs1.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">Taking a sledgehammer to the ice mimics seismic shockwaves.</span>
<span class="attribution"><span class="source">Adam Booth</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>As part of the EU-funded <a href="https://www.erc-responder.eu/">RESPONDER project</a> based at the <a href="https://www.spri.cam.ac.uk/">Scott Polar Research Institute</a>, University of Cambridge, we installed a kilometre-long stretch of fibre-optic cable to explore the properties of Sermeq Kujalleq, also known as Store Glacier, in West Greenland. Situated 28km from the front of the glacier, our study site creeps west at a rate of around 500 metres per year. </p>
<p>To get the cable in place, colleagues from <a href="https://www.aber.ac.uk/en/dges/research/centre-glaciology/">Aberystwyth University</a> used a hot-water drill to bore a 1,040-metre hole downwards through the ice before we threaded the cable in. The cable connects at the surface to a computer, called an interrogator, which fires and records the laser pulses. </p>
<p>Over six weeks, we monitored the cable to determine the temperature differences throughout the glacier’s layers. We also investigated ice stiffness, an indicator of how easily ice flows, by measuring variations in how quickly <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL088148">seismic vibrations</a> travel through the ice along the cable length: faster vibrations can indicate stiffer ice. For this, we made our own <a href="https://www.nature.com/articles/s43017-021-00176-6.epdf?sharing_token=0yan-HW5Qlwtkn524n42J9RgN0jAjWel9jnR3ZoTv0OwAreHKMhA7jKEtPMDxjS257nBx0-e_jzrqs7Lr8pBnLgy9pCUkVhbcrwhO5fyOv0ViYJsavEMtLn41vwpk6xbzf5jDj6Km9JFp4UzVgTXYOHnH84SmUtN90ksyxDJ7pI%3D">DIY shockwaves</a> by hitting the surface of the glacier with a sledgehammer.</p>
<figure> <img src="https://media.giphy.com/media/RUTAHot2ogFTCodPvx/giphy.gif"> <figcaption>Adam Booth makes mini earthquakes. Video by Poul Christoffersen</figcaption></figure>
<h2>The anatomy of a glacier</h2>
<p>The result is the most detailed description to date of the thermal and mechanical structure of the glacier. The internal temperature of glaciers is controlled by a few key processes. At their centre lies a core of extremely cold, stiff ice. As it continues its journey coastwards, the glacier surface is heated to -6.5°C – tropical in comparison – by sunlight and warmer air. </p>
<p>But nearest to the ground, the glacier is warmer still, as the constant churning of internal ice crystals generates heat. Add the heat naturally radiating from within the earth, and ice temperature approaches 0°C. </p>
<p>At these depths, ice coexists with small pockets of liquid water, similar to how snow becomes slush. We call such ice “temperate” and, in terms of glacier flow and eventual ice loss, it’s where the action is. That means it’s vital to understand how much temperate ice we’ve got.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/400754/original/file-20210514-13-fj4wad.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/400754/original/file-20210514-13-fj4wad.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=778&fit=crop&dpr=1 600w, https://images.theconversation.com/files/400754/original/file-20210514-13-fj4wad.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=778&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/400754/original/file-20210514-13-fj4wad.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=778&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/400754/original/file-20210514-13-fj4wad.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=978&fit=crop&dpr=1 754w, https://images.theconversation.com/files/400754/original/file-20210514-13-fj4wad.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=978&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/400754/original/file-20210514-13-fj4wad.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=978&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Our temperature results (black line). The coldest ice is in the very centre of the ice column, heated at the surface by the atmosphere and at the bottom by the ice deforming around itself and heat radiated out from the Earth.</span>
<span class="attribution"><span class="source">Robert Law</span></span>
</figcaption>
</figure>
<p>So what did we find?</p>
<p>First, the heat map of our glacier showed far more variability than we’d expected. We found concentrated patches of heat in areas where the ice was particularly deformed, even at relatively shallow depths – something never previously observed in glacier ice. </p>
<p>Second, we observed three distinct ice layers within the glacier. Two of these were predictable. The upper 890 metres of the glacier was made of cold and stiff ice. Beneath that was older, weaker ice dating back to the last ice age. This ice is weaker because it contains particles of ice age dust, which disrupts the bonds between individual ice crystals. </p>
<figure class="align-center ">
<img alt="People stand around large equipment on an icy surface" src="https://images.theconversation.com/files/400581/original/file-20210513-15-cq4ym.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/400581/original/file-20210513-15-cq4ym.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/400581/original/file-20210513-15-cq4ym.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/400581/original/file-20210513-15-cq4ym.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/400581/original/file-20210513-15-cq4ym.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/400581/original/file-20210513-15-cq4ym.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/400581/original/file-20210513-15-cq4ym.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The research team bores through the ice to install the fibre-optic cable.</span>
<span class="attribution"><span class="source">Adam Booth</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>But the biggest surprise of all was hiding in the lowermost 70 metres of the glacier, where we found a large quantity of temperate ice. This might be expected in warm Alpine environments, but at such depths in Sermeq Kujalleq, the heat required to produce liquid water can only be produced by significant ice deformation: evidence of just how dynamic the base of the ice sheet is. </p>
<p>These observations not only help explain why the Greenland ice sheet is losing so much mass, they also help us predict future patterns of ice loss and sea level rise.</p><img src="https://counter.theconversation.com/content/160885/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robert Law receives funding from Natural Environment Research Council and European Research Council.</span></em></p><p class="fine-print"><em><span>Adam Booth 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>
New research shows how fibre-optic cables can monitor the hidden structure of glaciers, teaching us about past and future ice flow.
Robert Law, PhD candidate, University of Cambridge
Adam Booth, Associate Professor in Applied Geophysics, School of Earth and Environment, University of Leeds
Licensed as Creative Commons – attribution, no derivatives.