tag:theconversation.com,2011:/global/topics/ice-shelves-15731/articlesIce shelves – The Conversation2023-06-28T15:12:36Ztag:theconversation.com,2011:article/2073552023-06-28T15:12:36Z2023-06-28T15:12:36ZFrom 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>
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<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">
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<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>
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<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>
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<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>
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<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>
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<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>
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<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p class="fine-print"><em><span>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 BrightonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1788282022-06-07T12:31:51Z2022-06-07T12:31:51ZIce world: Antarctica’s riskiest glacier is under assault from below and losing its grip<figure><img src="https://images.theconversation.com/files/451768/original/file-20220313-22-7yym4g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The front of Thwaites Glacier is a jagged, towering cliff.</span> <span class="attribution"><span class="source">David Vaughan/British Antarctic Survey</span></span></figcaption></figure><p>Flying over Antarctica, it’s hard to see what all the fuss is about. Like a gigantic wedding cake, the frosting of snow on top of the world’s largest ice sheet looks smooth and unblemished, beautiful and perfectly white. Little swirls of snow dunes cover the surface.</p>
<p>But as you approach the edge of the ice sheet, a sense of tremendous underlying power emerges. Cracks appear in the surface, sometimes organized like a washboard, and sometimes a complete chaos of spires and ridges, revealing the pale blue crystalline heart of the ice below.</p>
<p>As the plane flies lower, the scale of these breaks steadily grows. These are not just cracks, but canyons large enough to swallow a jetliner, or spires the size of monuments. Cliffs and tears, rips in the white blanket emerge, indicating a force that can toss city blocks of ice around like so many wrecked cars in a pileup. It’s a twisted, torn, wrenched landscape. A sense of movement also emerges, in a way that no ice-free part of the Earth can convey – the entire landscape is in motion, and seemingly not very happy about it.</p>
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<a href="https://images.theconversation.com/files/451767/original/file-20220313-17-dn1yky.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A view across the ice from an airplane showing many fractures." src="https://images.theconversation.com/files/451767/original/file-20220313-17-dn1yky.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451767/original/file-20220313-17-dn1yky.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451767/original/file-20220313-17-dn1yky.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451767/original/file-20220313-17-dn1yky.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451767/original/file-20220313-17-dn1yky.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451767/original/file-20220313-17-dn1yky.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451767/original/file-20220313-17-dn1yky.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">Broken ice where Thwaites Glacier heads out to sea.</span>
<span class="attribution"><span class="source">Ted Scambos</span></span>
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<p>Antarctica is a continent comprising several large islands, one of them the size of Australia, all buried under a <a href="https://nsidc.org/cryosphere/sotc/ice_sheets.html">10,000-foot-thick layer of ice</a>. The ice holds enough fresh water to raise sea level by nearly 200 feet.</p>
<p>Its glaciers have always been in motion, but beneath the ice, changes are taking place that are having <a href="https://www.youtube.com/watch?v=uBbgWsR4-aw">profound effects</a> on the future of the ice sheet – and on the future of coastal communities around the world.</p>
<h2>Breaking, thinning, melting, collapsing</h2>
<p>Antarctica is where I work. As a <a href="https://scholar.google.com/citations?user=-9H1Dh0AAAAJ&hl=en">polar scientist</a> I’ve visited most areas of the ice sheet in more than 20 trips to the continent, bringing sensors and weather stations, trekking across glaciers, or measuring the speed, thickness and structure of the ice. </p>
<p>Currently, I’m the U.S. coordinating scientist for a major international research effort on Antarctica’s riskiest glacier – more on that in a moment. I have gingerly crossed crevasses, trodden carefully on hard blue windswept ice, and driven for days over the most monotonous landscape you can imagine.</p>
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<img alt="" src="https://images.theconversation.com/files/451494/original/file-20220311-23-13e04jo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451494/original/file-20220311-23-13e04jo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451494/original/file-20220311-23-13e04jo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451494/original/file-20220311-23-13e04jo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451494/original/file-20220311-23-13e04jo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451494/original/file-20220311-23-13e04jo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451494/original/file-20220311-23-13e04jo.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">
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<span class="caption">Mountains direct the flow of glaciers toward the sea.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/1nW5NPuS6hY">66 North via Unsplash</a></span>
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<p>For most of the past few centuries, the ice sheet has been stable, as far as polar science can tell. Our ability to track how much ice flows out each year, and how much snow falls on top, extends back <a href="https://climate.esa.int/en/projects/ice-sheets-antarctic/data/">just a handful of decades</a>, but what we see is an ice sheet that <a href="https://doi.org/10.1073/pnas.1812883116">was nearly in balance as recently as the 1980s</a>.</p>
<p>Early on, changes in the ice happened slowly. Icebergs would break away, but the ice was replaced by new outflow. Total snowfall had not changed much in centuries – this we knew from <a href="https://www.antarcticglaciers.org/glaciers-and-climate/ice-cores/ice-core-basics/">looking at ice cores</a> – and in general the flow of ice and the elevation of the ice sheet seemed so constant that a main goal of early ice research in Antarctica was finding a place, any place, that had changed dramatically.</p>
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<img alt="Deep cracks leaves jagged columns of ice with a layer of snow at the top ready to tip into the sea." src="https://images.theconversation.com/files/451477/original/file-20220310-27-1xzxdke.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451477/original/file-20220310-27-1xzxdke.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451477/original/file-20220310-27-1xzxdke.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451477/original/file-20220310-27-1xzxdke.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451477/original/file-20220310-27-1xzxdke.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451477/original/file-20220310-27-1xzxdke.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451477/original/file-20220310-27-1xzxdke.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">
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<span class="caption">Ice breaks off the front of a glacier in Antarctica.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/xDhpn9zx2Fo">66 North via Unsplash</a></span>
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</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/451495/original/file-20220311-25-zibl59.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A map of the ice sheet showing faster flowing ice at the ice shelves and particularly around the edges of West Antarctica." src="https://images.theconversation.com/files/451495/original/file-20220311-25-zibl59.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451495/original/file-20220311-25-zibl59.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=605&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451495/original/file-20220311-25-zibl59.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=605&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451495/original/file-20220311-25-zibl59.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=605&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451495/original/file-20220311-25-zibl59.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=761&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451495/original/file-20220311-25-zibl59.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=761&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451495/original/file-20220311-25-zibl59.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=761&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 map of Antarctica seen from above, most of it the ice sheet, shows the velocity of the ice flow ice. Thwaites Glacier is on the left.</span>
<span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/3849">NASA's Goddard Space Flight Center Scientific Visualization Studio</a></span>
</figcaption>
</figure>
<p>But now, as the surrounding air and ocean warm, areas of the Antarctic ice sheet that had been stable for thousands of years <a href="https://cires.colorado.edu/news/threat-thwaites-retreat-antarctica%E2%80%99s-riskiest-glacier">are breaking, thinning, melting</a>, or in some cases <a href="https://doi.org/10.3189/172756404781814005">collapsing in a heap</a>. As these edges of the ice react, they send a powerful reminder: If even a small part of the ice sheet were to completely crumble into the sea, the impact for the world’s coasts would be severe.</p>
<p>Like many geoscientists, I think about how the Earth looks below the part that we can see. For Antarctica, that means thinking about the landscape below the ice. What does the buried continent look like – and how does that rocky basement shape the future of the ice in a warming world?</p>
<h2>Visualizing the world below the ice</h2>
<p>Recent efforts to <a href="https://doi.org/10.5194/tc-7-375-2013">combine data from hundreds of airplane and ground-based studies</a> have given us a kind of <a href="https://doi.org/10.1038/s41561-019-0510-8">map of the continent below the ice.</a> It reveals two very different landscapes, divided by the Transantarctic Mountains.</p>
<p>In East Antarctica, the part closer to Australia, the continent is rugged and furrowed, with <a href="https://www.nsf.gov/news/news_summ.jsp?org=NSF&cntn_id=122290&preview=false">several small mountain ranges</a>. Some of these have alpine valleys, cut by the very first glaciers that formed on Antarctica 30 million years ago, when its climate resembled Alberta’s or Patagonia’s. Most of East Antarctica’s bedrock sits above sea level. This is where the city-size Conger ice shelf collapsed <a href="https://www.copernicus.eu/en/media/image-day-gallery/collapse-conger-ice-shelf">amid an unusually intense heat wave</a> in March 2022.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/451763/original/file-20220313-17-17obzrz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A view of Antarctica's bedrock beneath the ice today shows islands in the west side and more above-sea bedrock in the east." src="https://images.theconversation.com/files/451763/original/file-20220313-17-17obzrz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451763/original/file-20220313-17-17obzrz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=404&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451763/original/file-20220313-17-17obzrz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=404&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451763/original/file-20220313-17-17obzrz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=404&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451763/original/file-20220313-17-17obzrz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=508&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451763/original/file-20220313-17-17obzrz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=508&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451763/original/file-20220313-17-17obzrz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=508&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Below the ice, recent studies have mapped Antarctica’s bedrock and show much of the west side is below sea level.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.5194/tc-7-375-2013">Bedmap2; Fretwell 2013</a></span>
</figcaption>
</figure>
<p>In West Antarctica the bedrock is far different, with parts that are far deeper. This area was once the ocean bottom, a region where the continent was stretched and broken into smaller blocks with deep seabed between. Large islands made of volcanic mountain ranges are linked together by the thick blanket of ice. But the ice here is warmer, and moving faster. </p>
<p><a href="https://doi.org/10.1002/2015GL063861">As recently as 120,000 years ago</a>, this area was probably an open ocean – and definitely so in the <a href="https://doi.org/10.1016/B978-0-12-819109-5.00014-1">past 2 million years</a>. This is important because our climate today is <a href="https://www.climate.gov/news-features/climate-qa/whats-hottest-earths-ever-been">fast approaching temperatures</a> like those of a few million years ago.</p>
<p>The realization that the West Antarctic ice sheet was gone in the past is the cause of great concern in the global warming era.</p>
<h2>Early stages of a large-scale retreat</h2>
<p>Toward the coast of West Antarctica is a large area of ice called <a href="https://thwaitesglacier.org/about/facts">Thwaites Glacier</a>. This is the widest glacier on earth, at 70 miles across, draining an area nearly as large as Idaho.</p>
<p>Satellite <a href="https://doi.org/10.1038/s41586-018-0179-y">data tell us</a> that it is in the <a href="https://doi.org/10.1016/j.gloplacha.2017.04.008">early stages of a large-scale retreat</a>. The height of the surface has been dropping by up to 3 feet each year. Huge cracks have formed at the coast, and many large icebergs have been set adrift. The glacier is flowing at over a mile per year, and this speed has nearly doubled in the past three decades.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/AmSovbt5Bho?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Two decades of satellite data show the fastest ice loss in the vicinity of the Thwaites Glacier. NASA.</span></figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/451765/original/file-20220313-18-462rul.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A view across the ice from an airplane showing many fractures." src="https://images.theconversation.com/files/451765/original/file-20220313-18-462rul.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451765/original/file-20220313-18-462rul.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=464&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451765/original/file-20220313-18-462rul.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=464&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451765/original/file-20220313-18-462rul.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=464&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451765/original/file-20220313-18-462rul.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=584&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451765/original/file-20220313-18-462rul.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=584&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451765/original/file-20220313-18-462rul.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=584&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">From above, fractures are evident in the Thwaites Glacier.</span>
<span class="attribution"><span class="source">Ted Scambos</span></span>
</figcaption>
</figure>
<p>This area was noted early on as a place where the ice <a href="https://doi.org/10.1126/science.1249055">could lose its grip on the bedrock</a>. The region was termed the “<a href="https://doi.org/10.3189/S002214300001159X">weak underbelly” of the ice sheet</a>.</p>
<p>Some of the <a href="https://doi.org/10.1073/pnas.1821646116">first measurements</a> of the ice depth, using radio echo-sounding, showed that the center of West Antarctica had bedrock up to a mile and a half below sea level. The coastal area was shallower, with a few mountains and some higher ground; but a wide gap between the mountains lay near the coast. This is where Thwaites Glacier meets the sea.</p>
<p>This pattern, with deeper ice piled high near the center of an ice sheet, and shallower but still low bedrock near the coast, is a recipe for disaster – albeit a very slow-moving disaster.</p>
<p>Ice flows under its own weight – something we learned in high school earth science, but give it a thought now. With very tall and very deep ice near Antarctica’s center, a tremendous potential for faster flow exists. By being shallower near the edges, the flow is held back – grinding on the bedrock as it tries to leave, and having a shorter column of ice at the coast squeezing it outward.</p>
<figure class="align-center ">
<img alt="An Antarctic glacier flows between mountains. Lines in ice show that it's flowing." src="https://images.theconversation.com/files/451489/original/file-20220311-13-xkhec.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451489/original/file-20220311-13-xkhec.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451489/original/file-20220311-13-xkhec.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451489/original/file-20220311-13-xkhec.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451489/original/file-20220311-13-xkhec.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451489/original/file-20220311-13-xkhec.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451489/original/file-20220311-13-xkhec.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">
<figcaption>
<span class="caption">An Antarctic glacier flows toward the sea.</span>
<span class="attribution"><span class="source">Erin Pettit</span></span>
</figcaption>
</figure>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/MR6-sgRqW0k?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How warmer water is undermining the glacier.</span></figcaption>
</figure>
<p>If the ice were to step back far enough, the retreating front would go from “thin” ice – <a href="https://thwaitesglacier.org/about/facts">still nearly 3,000 feet thick</a> – to thicker ice toward the center of the continent. At the retreating edge, the ice would flow faster, because the ice is thicker now. By flowing faster, the glacier pulls down the ice behind it, allowing it to float, causing more retreat. This is what’s known as <a href="https://en.wikipedia.org/wiki/Marine_ice_sheet_instability">a positive feedback loop</a> – retreat leading to thicker ice at the front of the glacier, making for faster flow, leading to more retreat.</p>
<h2>Warming water: The assault from below</h2>
<p>But how would this retreat begin? Until recently, Thwaites had not changed a lot since it was <a href="https://thwaitesglacier.org/sites/default/files/2020-09/ThwaitesGlacierFactsSheetJune2020_1.pdf">first mapped</a> in the 1940s. Early on, scientists thought a retreat would be a result of warmer air and surface melting. But the cause of the changes at Thwaites seen in satellite data is not so easy to spot from the surface.</p>
<p><a href="https://antarcticsun.usap.gov/science/4457/">Beneath the ice</a>, however, at the point where the ice sheet first lifts off the continent and begins to jut out over the ocean as a floating ice shelf, the cause of the retreat becomes evident. Here, ocean water well above the melting point is <a href="https://doi.org/10.5194/tc-16-397-2022">eroding the base of the ice</a>, erasing it as an ice cube would disappear bobbing in a glass of water.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/451479/original/file-20220311-13-145nx3v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An illustration of an ice shelf and glacier with water flowing under the ice shelf and eroding it at the seabed" src="https://images.theconversation.com/files/451479/original/file-20220311-13-145nx3v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451479/original/file-20220311-13-145nx3v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=264&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451479/original/file-20220311-13-145nx3v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=264&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451479/original/file-20220311-13-145nx3v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=264&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451479/original/file-20220311-13-145nx3v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=332&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451479/original/file-20220311-13-145nx3v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=332&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451479/original/file-20220311-13-145nx3v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=332&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Warming water is reaching under the ice shelf and eroding it from below.</span>
<span class="attribution"><a class="source" href="https://www.sciencedirect.com/science/article/pii/S092181811630491X?via%3Dihub">Scambos et al 2017</a></span>
</figcaption>
</figure>
<p>Water that is capable of melting as much as 50 to 100 feet of ice every year meets the edge of the ice sheet here. This erosion lets the ice flow faster, pushing against the floating ice shelf.</p>
<p>The ice shelf is one of the restraining forces holding the ice sheet back. But pressure from the land ice is <a href="https://doi.org/10.1038/d41586-021-03758-y">slowly breaking this ice plate</a>. Like a board splintering under too much weight, it is developing huge cracks. When it gives way – and mapping of the fractures and speed of flow <a href="https://www.youtube.com/watch?v=uBbgWsR4-aw">suggests this is just a few years away</a> – it will be another step that allows the ice to flow faster, feeding the feedback loop.</p>
<h2>Up to 10 feet of sea level rise</h2>
<p>Looking back at the ice-covered continent from our camp this year, it is a sobering view. A huge glacier, flowing toward the coast, and stretching from horizon to horizon, rises up to the middle of the West Antarctic Ice Sheet. There is a palpable feeling that the ice is bearing down on the coast.</p>
<p>Ice is still ice – it doesn’t move that fast no matter what is driving it; but this giant area called West Antarctica could soon begin a multicentury decline that would add <a href="https://cires.colorado.edu/news/threat-thwaites-retreat-antarctica%E2%80%99s-riskiest-glacier">up to 10 feet</a> to sea level. In the process, the rate of sea level rise would increase severalfold, posing large challenges for people with a stake in coastal cities. Which is pretty much all of us.</p><img src="https://counter.theconversation.com/content/178828/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ted Scambos receives funding from the National Science Foundation and NASA.</span></em></p>Thwaites Glacier’s ice shelf appears to be splintering, and scientists fear it could give way in the next few years. A polar scientist takes us on a tour under the ice to explain the forces at work.Ted Scambos, Senior Research Scientist, CIRES, University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1800772022-03-28T13:39:06Z2022-03-28T13:39:06ZConger ice shelf has collapsed: what you need to know, according to experts<figure><img src="https://images.theconversation.com/files/454695/original/file-20220328-23-181gryz.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3965%2C2641&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/icebergs-weddell-sea-off-east-coast-1557644912">Steve Allen/Shutterstock</a></span></figcaption></figure><p>East Antarctica’s Conger ice shelf – a floating platform the size of Rome – broke off the continent on March 15, 2022. Since the beginning of satellite observations in the 1970s, the tip of the shelf had been disintegrating into icebergs in a series of what glaciologists call calving events. </p>
<p>Conger was already reduced to a 50km-long and 20km-wide strip attached to Antarctica’s vast continental ice sheet at one end and the ice-covered Bowman Island at the other. Two calving events on March 5 and 7 reduced it further, detaching it from Bowman and precipitating its final collapse a week later.</p>
<p>The world’s largest ice shelves fringe Antarctica, extending its ice sheet into the frigid Southern Ocean. Smaller ice shelves are found where continental ice meets the sea in Greenland, northern Canada and the Russian Arctic. By restraining how much the grounded ice flows upstream, they can control the loss of ice from the interior of the sheet into the ocean. When an ice shelf like Conger is lost, the grounded ice once kept behind the shelf may start to flow faster as the restraining force of the ice shelf is lost, resulting in more ice tumbling into the ocean. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/454677/original/file-20220328-23-1fwihl4.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Image of Antarctica overlain with ice flow speeds." src="https://images.theconversation.com/files/454677/original/file-20220328-23-1fwihl4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454677/original/file-20220328-23-1fwihl4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=317&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454677/original/file-20220328-23-1fwihl4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=317&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454677/original/file-20220328-23-1fwihl4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=317&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454677/original/file-20220328-23-1fwihl4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=398&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454677/original/file-20220328-23-1fwihl4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=398&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454677/original/file-20220328-23-1fwihl4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=398&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">East Antarctica, where Conger once was, has seen fewer ice shelves collapse than West Antarctica.</span>
<span class="attribution"><a class="source" href="https://its-live.jpl.nasa.gov/">Bertie Miles/Nasa</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>What caused the collapse?</h2>
<p>Ice shelves are sometimes referred to as <a href="https://www.nature.com/articles/nclimate2912">the “safety band” of Antarctica</a> because they buttress the upstream flow of ice from <a href="https://www.nature.com/articles/s41558-017-0020-x">the bordering ice sheet</a>. Little of the Antarctic ice sheet melts at its surface, where snow piles up. Instead, most of the continent loses ice through <a href="https://doi.org/10.1029/2019GL085027">calving and melting</a> along the underside of the floating ice shelves. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/454678/original/file-20220328-17770-cfno7u.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A satellite image of the Conger ice shelf with coloured lines denoting historical extent." src="https://images.theconversation.com/files/454678/original/file-20220328-17770-cfno7u.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/454678/original/file-20220328-17770-cfno7u.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=677&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454678/original/file-20220328-17770-cfno7u.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=677&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454678/original/file-20220328-17770-cfno7u.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=677&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454678/original/file-20220328-17770-cfno7u.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=850&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454678/original/file-20220328-17770-cfno7u.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=850&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454678/original/file-20220328-17770-cfno7u.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=850&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Conger mapped from satellite images taken between 1973 and 2022. The ice shelf had been slowly breaking apart for 50 years.</span>
<span class="attribution"><span class="source">Bertie Miles/US Geological Survey</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The breaking and detachment of parts of ice shelves is <a href="https://doi.org/10.5194/tc-13-2771-2019">a natural process</a>: ice shelves generally go through cycles of slow growth punctuated by isolated calving events. But in recent decades, scientists have seen several large ice shelves undergoing total disintegration. </p>
<p>Along the Antarctic Peninsula, the whip-like land mass which extends from the West Antarctic mainland, these include Prince Gustav ice shelf (from 1989 to 1995), Larsen A ice shelf (1995), Larsen B (2002), and Wilkins ice shelf (2008 to 2009). In East Antarctica, where Conger once was, Cook ice Shelf was partially lost in the 1970s. Taken together, this series of collapses suggests that some underlying environmental conditions, such as ocean and atmosphere temperatures, are changing.</p>
<p>It is too soon to say what triggered the collapse of the Conger ice shelf, but it appears unlikely to have been caused by melting at the surface – there are no indications of any ponds atop the ice shelf. The most recent sequence of events also preceded the record high air temperatures recorded in Antarctica on March 18. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/record-smashing-heatwaves-are-hitting-antarctica-and-the-arctic-simultaneously-heres-whats-driving-them-and-how-theyll-impact-wildlife-179659">Record-smashing heatwaves are hitting Antarctica and the Arctic simultaneously. Here’s what’s driving them, and how they’ll impact wildlife</a>
</strong>
</em>
</p>
<hr>
<h2>What the future holds</h2>
<p>As glaciologists, we see the impact of global warming on Antarctica in increasing ice loss with time. And what happens in Antarctica does not stay in Antarctica. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/454679/original/file-20220328-21-1npk17e.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two satellite images of the Conger ice shelf side-by-side show its pre- and post-collapse state." src="https://images.theconversation.com/files/454679/original/file-20220328-21-1npk17e.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454679/original/file-20220328-21-1npk17e.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=287&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454679/original/file-20220328-21-1npk17e.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=287&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454679/original/file-20220328-21-1npk17e.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=287&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454679/original/file-20220328-21-1npk17e.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=361&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454679/original/file-20220328-21-1npk17e.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=361&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454679/original/file-20220328-21-1npk17e.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=361&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 Conger ice shelf (outlined in blue) before and after its final calving events.</span>
<span class="attribution"><span class="source">Bertie Miles/US Geological Survey/European Space Agency</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The consequences of the Conger ice shelf collapse are unlikely to be of global significance as the catchment area feeding ice into the former shelf is small. And due to its shape, the Conger ice shelf was most likely not a significant buttress to the flow of ice upstream. </p>
<p>But global warming is making events like this more likely. And as more and more ice shelves around Antarctica collapse, ice loss will increase, and with it global sea levels. There is enough ice in the West Antarctic ice sheet to raise sea levels by several meters, and if East Antarctica starts losing significant amounts of ice, the impact on sea levels could be measured in tens of meters.</p>
<p>Not everything that happens in nature is due to global warming alone. Antarctica loses mass through the discharge of icebergs and waxing and waning ice shelves as part of a natural cycle. But what we are seeing now, with the collapse of the Conger ice shelf and others, is the continuation of a worrying trend whereby Antarctic ice shelves undergo area-wide collapse one after another.</p>
<hr>
<figure class="align-right ">
<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
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<hr><img src="https://counter.theconversation.com/content/180077/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hilmar Gudmundsson receives funding from UKRI, NSF and the European Union’s Horizon 2020 research and innovation programme.</span></em></p><p class="fine-print"><em><span>Adrian Jenkins receives funding from UKRI and the European Union’s Horizon 2020 research and innovation programme.</span></em></p><p class="fine-print"><em><span>Bertie Miles receives funding from the Leverhulme Trust. </span></em></p>For the first time since satellites started studying the continent, East Antarctica has lost an entire ice shelf.Hilmar Gudmundsson, Professor of Glaciology, Northumbria University, NewcastleAdrian Jenkins, Professor of Ocean Science, Northumbria University, NewcastleBertie Miles, Leverhulme Early Career Fellow, Geosciences, The University of EdinburghLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1585402021-04-09T13:26:49Z2021-04-09T13:26:49ZAntarctica’s ice shelves are trembling as global temperatures rise – what happens next is up to us<p>Images of colossal chunks of ice plunging into the sea accompany almost every news story about climate change. It can often make the problem seem remote, as if the effects of rising global temperatures are playing out elsewhere. But the break-up of the world’s vast reservoirs of frozen water – and, in particular, Antarctic ice shelves – will have consequences for all of us.</p>
<p>Before we can appreciate how, we need to understand what’s driving this process.</p>
<p>Ice shelves are gigantic floating platforms of ice that form where continental ice meets the sea. They’re found in Greenland, northern Canada and the Russian Arctic, but the largest loom around the edges of Antarctica. They are fed by frozen rivers of ice called glaciers, which flow down from the steep Antarctic ice sheet.</p>
<p>Ice shelves act as a barrier to glaciers, so when they disappear, it’s like pulling the plug in a sink, allowing glaciers to flow freely into the ocean, where they contribute to sea level rise. </p>
<p>If you cast your mind back to 2002, you may remember the sudden demise of Larsen B, an ice shelf on the Antarctic Peninsula – the tail-like land mass which stretches out from the West Antarctic mainland – which splintered over just six weeks.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/394255/original/file-20210409-23-1rmrqmg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A map of Antarctica with the peninsula highlighted by a red box." src="https://images.theconversation.com/files/394255/original/file-20210409-23-1rmrqmg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/394255/original/file-20210409-23-1rmrqmg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=545&fit=crop&dpr=1 600w, https://images.theconversation.com/files/394255/original/file-20210409-23-1rmrqmg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=545&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/394255/original/file-20210409-23-1rmrqmg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=545&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/394255/original/file-20210409-23-1rmrqmg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=685&fit=crop&dpr=1 754w, https://images.theconversation.com/files/394255/original/file-20210409-23-1rmrqmg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=685&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/394255/original/file-20210409-23-1rmrqmg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=685&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 Antarctic Peninsula, highlighted in red, is the northernmost part of the continent.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Antarctic_Peninsula#/media/File:Antarctica_map_indicating_Antarctic_Peninsula.JPG">Anna Frodesiak/Wikipedia</a></span>
</figcaption>
</figure>
<p>Before Larsen B broke up, satellite images showed meltwater collecting in <a href="https://earthobservatory.nasa.gov/world-of-change/LarsenB">huge ponds on the surface</a>, the precursor to a process called “hydrofracturing”, which literally means “cracking by water”.</p>
<p>Ice shelves are not solid blocks of ice: they’re made up of layers with fresh snow at the top, which contains lots of air gaps. Over many seasons, layers of snow build up and become compacted, with the bottom of the shelf containing the densest ice. In the middle, there is a porous medium called firn, which contains air pockets that soak up meltwater every summer like a sponge.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/H2a3Oemo1e4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>In the Antarctic summer, ice shelves get warm enough to melt at the surface. That meltwater trickles into the firn layer, where it refreezes when temperatures dip below freezing again. If the rate of melting every year is greater than the rate at which that firn can be replenished by fresh snow, then those air pockets eventually fill up, causing the ice shelf to become one solid chunk.</p>
<p>If that happens, then the following summer when melting occurs, the water has nowhere to go and so collects in ponds on the surface. That is what we can see in the satellite images of Larsen B before it collapsed.</p>
<p>At this stage, meltwater begins to flow into crevasses and cracks within the ice shelf. The weight of water filling these rifts causes them to widen and deepen, until suddenly, all at once, the cracks reach the bottom of the shelf and the whole thing disintegrates.</p>
<p>Scientists believe the collapse of Larsen B was <a href="https://earthdata.nasa.gov/learn/sensing-our-planet/after-the-larsen-b">caused</a> by a combination of persistently warm weather and a background of ongoing atmospheric warming, which drove unusually high melt rates.</p>
<p>After its collapse, the glaciers that previously fed Larsen B sped up, spitting more ice into the ocean than before. Currently, the Antarctic Peninsula, an area that has seen more than half its ice shelves lose mass, is responsible for <a href="https://theconversation.com/the-worlds-mountain-water-towers-are-melting-putting-1-9-billion-people-at-risk-128501">around 25%</a> of all ice loss from Antarctica. It holds enough ice to raise global sea levels by <a href="http://www.antarcticglaciers.org/antarctica-2/antarctic-peninsula-2">around 24cm</a>.</p>
<h2>Three future outcomes</h2>
<p>But what might happen to the rest of Antarctica’s ice shelves in the future is still uncertain. As the climate warms, ice shelves are more likely to collapse and accelerate global sea level rise, but by how much? This is something myself and a colleague have explored in a <a href="https://doi.org/10.1029/2020GL091733">new study</a>.</p>
<p>We used the latest modelling techniques to predict the susceptibility of ice shelves to hydrofracturing at 1.5°C, 2°C and 4°C of global warming – scenarios that are all still plausible. Like with Larsen B, the presence of liquid water on the surface of an ice shelf indicates that it is becoming less stable, and so vulnerable to collapse by hydrofracturing.</p>
<p>In our paper, we identified four ice shelves – including two on the Antarctic Peninsula – which are at risk of collapse if global temperatures rise 4°C above the pre-industrial average. If both were to disintegrate, the glaciers they hold back could account for tens of cm of sea level rise – 10-20% of what’s predicted this century.</p>
<p>But limiting global warming to 2°C would halve the amount of ice shelf area at risk of collapse around Antarctica. At 1.5°C, just 14% of Antarctica’s ice shelf area would be at risk. Cutting that risk reduces the likelihood of this vast and remote continent significantly contributing to sea level rise.</p>
<p>Clearly, reducing climate change will be better not just for Antarctica, but for the world.</p><img src="https://counter.theconversation.com/content/158540/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ella Gilbert received funding from the British Antarctic Survey.</span></em></p>In a new study, we found that a third of Antarctica’s ice shelves could collapse at 4°C of global warming.Ella Gilbert, Postdoctoral Research Associate in Climate Science, University of ReadingLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1243622019-10-02T11:49:12Z2019-10-02T11:49:12ZAntarctica now has more than 65,000 ‘meltwater lakes’ as summer ice melts<figure><img src="https://images.theconversation.com/files/294835/original/file-20190930-194873-1pu7cau.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Meltwater on the ice shelf near the McMurdo research station, Antarctica.</span> <span class="attribution"><span class="source">Nicholas Bayou / UNAVCO</span>, <span class="license">Author provided</span></span></figcaption></figure><p>During the Antarctic summer, thousands of mesmerising blue lakes form around the edges of the continent’s ice sheet, as warmer temperatures cause snow and ice to melt and collect into depressions on the surface. Colleagues of mine at Durham University have recently used satellites to record <a href="https://www.nature.com/articles/s41598-019-50343-5">more than 65,000 of these lakes</a>. </p>
<p>Though seasonal meltwater lakes have formed on the continent for decades, lakes had not been recorded before in such great numbers across coastal areas of East Antarctica. This means parts of the world’s largest ice sheet may be more vulnerable to a warming climate than previously thought.</p>
<h2>Lakes affect ice shelves</h2>
<p>Much of Antarctica is surrounded by floating platforms of ice, often as tall as a skyscraper. These are “ice shelves”. And when some of these ice shelves have collapsed in the past, satellites have recorded networks of lakes growing and then abruptly disappearing shortly beforehand. For instance, <a href="https://earthobservatory.nasa.gov/world-of-change/LarsenB">several hundred lakes disappeared</a> in the weeks before the the catastrophic disintegration of the Larsen B Ice Shelf – when 3,250 km² of ice broke up in just two months in 2002.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/294838/original/file-20190930-194876-1jt1nkh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/294838/original/file-20190930-194876-1jt1nkh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/294838/original/file-20190930-194876-1jt1nkh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=241&fit=crop&dpr=1 600w, https://images.theconversation.com/files/294838/original/file-20190930-194876-1jt1nkh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=241&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/294838/original/file-20190930-194876-1jt1nkh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=241&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/294838/original/file-20190930-194876-1jt1nkh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=302&fit=crop&dpr=1 754w, https://images.theconversation.com/files/294838/original/file-20190930-194876-1jt1nkh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=302&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/294838/original/file-20190930-194876-1jt1nkh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=302&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Blue meltwater ponds cover the surface of Larsen B Ice Shelf in January 2002 (left) before its abrupt collapse two months later (right). Open ocean appears as black in both images.</span>
<span class="attribution"><span class="source">NASA/Goddard Space Flight Center</span></span>
</figcaption>
</figure>
<p>The collapse may have depended on water from these lakes filling crevasses and then acting like a wedge as the weight of the water expanded the crevasses, triggering a network of fractures. The weight of lakes can also cause the ice shelf surface to flex, leading to <a href="https://www.cam.ac.uk/research/news/surface-lakes-cause-antarctic-ice-shelves-to-flex">further fracturing</a>, which is thought to have helped the shelf become unstable and collapse. </p>
<p>Ice shelves act as door stops, supporting the huge mass of ice further inland. Their removal means the glaciers feeding the ice shelf are no longer held back and flow faster into the ocean, contributing to sea-level rise.</p>
<h2>Melting the ice sheet surface</h2>
<p>Scientists already knew that lakes form on the Antarctic ice sheet. But the latest study, published in <a href="https://www.nature.com/articles/s41598-019-50343-5">Scientific Reports</a>, shows that many more lakes are forming than previously thought, including in new parts of the ice sheet and much further inland and at higher elevations.</p>
<p>Since the cold and remoteness makes it logistically challenging to measure and monitor Antarctica’s lakes <a href="https://epic.awi.de/id/eprint/42771/1/Lenaerts_etal_2016-Nature_Climate_Change_meltwater.pdf">in the field</a>, we largely know all this thanks to satellite imagery. In this case, one of the satellites used was the European Space Agency’s <a href="https://www.bbc.co.uk/news/science-environment-39183353">Sentinel-2</a> which provides global coverage of the Earth’s surface every five days and can detect features as small as ten metres. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/294845/original/file-20190930-194873-yfu5fp.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/294845/original/file-20190930-194873-yfu5fp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/294845/original/file-20190930-194873-yfu5fp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=289&fit=crop&dpr=1 600w, https://images.theconversation.com/files/294845/original/file-20190930-194873-yfu5fp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=289&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/294845/original/file-20190930-194873-yfu5fp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=289&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/294845/original/file-20190930-194873-yfu5fp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=363&fit=crop&dpr=1 754w, https://images.theconversation.com/files/294845/original/file-20190930-194873-yfu5fp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=363&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/294845/original/file-20190930-194873-yfu5fp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=363&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Meltwater lakes on Sørsdal Glacier, Antarctica (red dot on larger map).</span>
<span class="attribution"><span class="source">Google Maps</span></span>
</figcaption>
</figure>
<p>My colleagues analysed satellite images of the East Antarctic Ice Sheet taken in January 2017. In total, the images covered 5,000,000 km² (that’s more than 20 times the area of the United Kingdom). </p>
<p>Because water reflects certain wavelengths very strongly compared to ice, lakes can be detected in these images by classifying pixels in the image as “water” or “non-water”. From these images we can pinpoint when lakes form, their growth and drainage, and how their extent and depth <a href="https://www.independent.co.uk/environment/global-warming-climate-change-langhovde-glacier-east-antarctica-dronning-maud-land-scientists-a7204691.html">change over time</a>. The largest lake detected so far was nearly 30 km long and estimated to hold enough water to fill 40,000 Olympic-sized swimming pools.</p>
<h2>Cause for concern?</h2>
<p>In a warming world, scientists are particularly interested in these lakes because they may contribute to destabilising the ice shelves and ice sheet in future.</p>
<p>Like a sponge, the more that ice shelves become saturated with meltwater, the less they are able to absorb, meaning more water pools on their surfaces as lakes. More surface lakes mean a greater likelihood that water will drain out, fill crevasses and potentially trigger flexing and fracturing. If this were to occur, <a href="https://cosmosmagazine.com/climate/scientists-warn-on-antarctic-ice-shelf-vulnerability">other ice shelves</a> around Antarctica may start to disintegrate like Larsen B. Glaciers with floating <a href="https://theconversation.com/when-an-antarctic-iceberg-the-size-of-a-country-breaks-away-what-happens-next-39257">ice tongues</a> protruding into the ocean may also be vulnerable.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/294841/original/file-20190930-194832-7n89gh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/294841/original/file-20190930-194832-7n89gh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/294841/original/file-20190930-194832-7n89gh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/294841/original/file-20190930-194832-7n89gh.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/294841/original/file-20190930-194832-7n89gh.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/294841/original/file-20190930-194832-7n89gh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/294841/original/file-20190930-194832-7n89gh.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/294841/original/file-20190930-194832-7n89gh.jpeg?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">Meltwater drains away through a</span>
<span class="attribution"><span class="source">Sanne Bosteels</span></span>
</figcaption>
</figure>
<p>Meanwhile in Greenland, scientists have observed entire lakes draining away <a href="https://www.livescience.com/2448-icy-lake-drains-faster-niagara-falls.html">within a matter of days</a>, as meltwater plunges through vertical shafts in the ice sheet known as “moulins”. A warm, wet base lubricated by meltwater allows the ice to slide quicker and flow faster into the ocean. </p>
<p>Could something similar be happening in Antarctica? Lakes disappearing in satellite imagery suggests they could be draining in this way, but scientists have yet to observe this directly. If we are to understand how much ice the continent could lose, and how much it could contribute to global sea-level rise, we must understand how these surface meltwater lakes behave. Though captivating, they are potentially a warning sign of future instability in Antarctica. </p>
<hr>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=140&fit=crop&dpr=1 600w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=140&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=140&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=176&fit=crop&dpr=1 754w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=176&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=176&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption"></span>
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<p><em><a href="https://theconversation.com/imagine-newsletter-researchers-think-of-a-world-with-climate-action-113443?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=Imagineheader1124362">Click here to subscribe to our climate action newsletter. Climate change is inevitable. Our response to it isn’t.</a></em></p><img src="https://counter.theconversation.com/content/124362/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jennifer Arthur receives funding from the Natural Environment Research Council (NERC).</span></em></p>These lakes could threaten the future stability of parts of the Antarctic ice sheet.Jennifer Arthur, PhD student, Cryospheric Remote Sensing, Durham UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/981772018-06-13T20:36:43Z2018-06-13T20:36:43ZOcean waves and lack of sea ice can trigger Antarctic ice shelves to disintegrate<p>Large waves after the loss of sea ice can trigger Antarctic ice shelf disintegration over a period of just days, according to our <a href="https://www.nature.com/articles/s41586-018-0212-1">new research</a>.</p>
<p>With other research <a href="https://www.nature.com/articles/s41586-018-0179-y">also published today in Nature</a> showing that the rate of annual ice loss from the vulnerable Antarctic Peninsula has quadrupled since 1992, our study of catastrophic ice shelf collapses during that time shows how the lack of a protective buffer of sea ice can leave ice shelves, already weakened by climate warming, wide open to attack by waves.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/antarctica-has-lost-3-trillion-tonnes-of-ice-in-25-years-time-is-running-out-for-the-frozen-continent-98176">Antarctica has lost 3 trillion tonnes of ice in 25 years. Time is running out for the frozen continent</a>
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</em>
</p>
<hr>
<p>Antarctica is covered by an ice sheet that is several kilometres thick in places. It covers an area of 14 million square kilometres – roughly twice the size of Australia. This ice sheet holds more than 90% of the world’s ice, which is enough to <a href="https://www.the-cryosphere.net/7/375/2013/tc-7-375-2013.pdf">raise global mean sea level by 57 metres</a>.</p>
<p>As snow falls and compacts on the ice sheet, the sheet thickens and flows out towards the coast, and then onto the ocean surface. The resulting “ice shelves” (and glacier tongues) buttress three-quarters of the Antarctic coastline. Ice shelves act as a crucial braking system for fast-flowing glaciers on the land, and thus moderate the ice sheet’s contribution to sea-level rise. </p>
<p>In the southern summer of 2002, scientists monitoring the Antarctic Peninsula (the northernmost part of mainland Antarctica) by satellite witnessed a dramatic ice shelf disintegration that was stunning in its abruptness and scale. In just 35 days, 3,250 square km of the Larsen B Ice Shelf (twice the size of Queensland’s Fraser Island) shattered, releasing an estimated <a href="https://visibleearth.nasa.gov/view.php?id=2288">720 billion tonnes of icebergs into the Weddell Sea</a>. </p>
<p>This wasn’t the first such recorded event. In January 1995, roughly 1,500 square km of the nearby Larsen A Ice Shelf <a href="https://www.tandfonline.com/doi/pdf/10.3402/polar.v18i2.6568">suddenly disintegrated</a> after several decades of warming and years of gradual retreat. To the southwest, the Wilkins Ice Shelf suffered a series of strikingly similar disintegration events in 1998, 2008 and 2009 — not only in summer but also in two of the Southern Hemisphere’s coldest months, May and July.</p>
<p>These sudden, large-scale fracturing events removed features that had been stable for centuries – up to <a href="https://www.nature.com/articles/nature03908">11,500 years in the case of Larsen B</a>. While ice shelf disintegrations don’t directly raise sea level (because the ice shelves are already floating), the removal of shelf ice allows the glaciers behind them to accelerate their discharge of land-based ice into the ocean – and this does raise sea levels. <a href="https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2004GL020697">Previous</a> <a href="https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2004GL020670">research</a> has shown that the removal of Larsen B caused its tributary glaciers to flow eight times faster in the year following its disintegration.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/cold-and-calculating-what-the-two-different-types-of-ice-do-to-sea-levels-59996">Cold and calculating: what the two different types of ice do to sea levels</a>
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</em>
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<hr>
<p>The ocean around ice shelves is typically covered by a very different (but equally important) type of ice, called sea ice. This is formed from frozen seawater and is generally no more than a few metres thick. But it stretches far out into the ocean, <a href="http://ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter04_FINAL.pdf">doubling the area of the Antarctic ice cap</a> when at its maximum extent in winter, and varying in extent throughout the year.</p>
<p>The response of Antarctic sea ice to climate change and variability is complex, and differs between regions. Around the Antarctic Peninsula, in the Bellingshausen and northwestern Weddell seas, it has clearly <a href="https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2012GL050874">declined in extent and annual duration</a> since satellite monitoring began in 1979, at a similar rate to the Arctic’s rapidly receding sea ice.</p>
<p>The Southern Ocean is also host to the largest waves on the planet, and these waves are <a href="http://science.sciencemag.org/content/332/6028/451?sid=acdfca77-ed06-">becoming more extreme</a>. Our <a href="https://www.nature.com/articles/s41586-018-0212-1">new study</a> focuses on “long-period” swell waves (with swells that last up to about 20 seconds). These are generated by distant storms and carry huge amounts of energy across the oceans, and can potentially flex the vulnerable outer margins of ice shelves. </p>
<p>The earliest whalers and polar pioneers knew that sea ice can damp these waves — Sir Ernest Shackleton reported it in his iconic book <a href="https://books.google.com.au/books/about/South.html?id=xr4g1G4O-4IC&printsec=frontcover&source=kp_read_button&redir_esc=y#v=onepage&q&f=false">South!</a>. Sea ice thus acts as a “buffer” that protects the Antarctic coastline, and its ice shelves, from destructive ocean swells. </p>
<p>Strikingly, all five of the sudden major ice shelf disintegrations listed above happened during periods when sea ice was abnormally low or even absent in these regions. This means that intense swell waves crashed directly onto the vulnerable ice shelf fronts.</p>
<h2>The straw that broke the camel’s back</h2>
<p>The Antarctic Peninsula has experienced particularly strong climate warming (roughly <a href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.591.9578&rep=rep1&type=pdf">0.5°C per decade since the late 1940s</a>), which has caused intense surface melting on its ice shelves and exacerbated their structural weaknesses such as fractures. These destabilising processes are the underlying drivers of ice shelf collapse. But they do not explain why the observed disintegrations were so abrupt. </p>
<p>Our new study suggests that the trigger mechanism was swell waves flexing and working weaknesses at the shelf fronts in the absence of sea ice, to the point where they calved away the shelf fronts in the form of long, thin “sliver-bergs”. The removal of these “keystone blocks” in turn led to the catastrophic breakup of the ice shelf interior, which was weakened by years of melt. </p>
<p>Our research thus underlines the complex and interdependent nature of the various types of Antarctic ice – particularly the important role of sea ice in forming a protective “buffer” for shelf ice. While much of the focus so far has been on the possibility of ice shelves melting from below as the sea beneath them warms, our research suggests an important role for sea ice and ocean swells too.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/222936/original/file-20180613-153677-j5wbww.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/222936/original/file-20180613-153677-j5wbww.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/222936/original/file-20180613-153677-j5wbww.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/222936/original/file-20180613-153677-j5wbww.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/222936/original/file-20180613-153677-j5wbww.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/222936/original/file-20180613-153677-j5wbww.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/222936/original/file-20180613-153677-j5wbww.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/222936/original/file-20180613-153677-j5wbww.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The edge of an ice shelf off the Antarctic Peninsula, with floating sea ice beyond (to the left in this image).</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Edge_of_Ice_Shelf_(8136346793).jpg">NASA/Maria Jose Vinas</a></span>
</figcaption>
</figure>
<p>In July 2017 an <a href="https://theconversation.com/dont-worry-about-the-huge-antarctic-iceberg-worry-about-the-glaciers-behind-it-80314">immense iceberg broke away</a> from the Larsen C Ice Shelf, just south of Larsen B, prompting fears that it could disintegrate like its neighbours. </p>
<p>Our research suggests that four key factors will determine whether it does: extensive flooding and fracturing across the ice shelf; reduced sea ice coverage offshore; extensive fracturing of the ice shelf front; and calving of sliver-bergs.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/dont-worry-about-the-huge-antarctic-iceberg-worry-about-the-glaciers-behind-it-80314">Don't worry about the huge Antarctic iceberg – worry about the glaciers behind it</a>
</strong>
</em>
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<hr>
<p>If temperatures continue to rise around the Antarctic, ice shelves will become weaker and sea ice less extensive, which would imply an increased likelihood of future disintegrations. </p>
<p>However, the picture is not that clear-cut, as not all remaining ice shelves are likely to respond in the same way to sea ice loss and swell wave impacts. Their response will also depend on their glaciological characteristics, physical setting, and the degree and nature of surface flooding. Some ice shelves may well be capable of surviving prolonged absences of sea ice.</p>
<p>Irrespective of these differences, we need to include sea ice and ocean waves in our models of ice sheet behaviour. This will be a key step towards better forecasting the fate of Antarctica’s remaining ice shelves, and how much our seas will rise in response to projected climate change over coming decades. In parallel, our new findings underline the need to better understand and model the mechanisms responsible for recent sea ice trends around Antarctica, to enable prediction of likely future change in the exposure of ice shelves to ocean swells.</p><img src="https://counter.theconversation.com/content/98177/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Luke Bennetts has previously funding from the Australian Research Council and the Australian Antarctic Science Program. </span></em></p><p class="fine-print"><em><span>Rob Massom receives funding from Australian Antarctic Division and the Australian Antarctic Science Program</span></em></p><p class="fine-print"><em><span>Vernon Squire currently receives funding from the US Office of Naval Research and the University of Otago. </span></em></p>Since 1995, several ice shelves off the Antarctic Peninsula have abruptly disintegrated. A new analysis suggests that these events are triggered when ice shelves lose their buffer of floating ice.Luke Bennetts, Lecturer in applied mathematics, University of AdelaideRob Massom, Leader, Sea Ice Group, Antarctica & the Global System program, Australian Antarctic Division and Antarctic Climate and Ecosystems CRC, Australian Antarctic DivisionVernon Squire, Deputy Vice-Chancellor Academic, Professor of Applied Mathematics, University of OtagoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/952072018-06-13T17:21:48Z2018-06-13T17:21:48ZShort-term changes in Antarctica’s ice shelves are key to predicting their long-term fate<figure><img src="https://images.theconversation.com/files/222991/original/file-20180613-32347-12ej8ho.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The northeast edge of the Venable Ice Shelf, near Antarctica's Allison Peninsula.</span> <span class="attribution"><a class="source" href="https://flic.kr/p/H84yYt">NASA/John Sonntag</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Antarctica’s ice sheet contains enough ice to raise global sea levels by around 180 feet if it all melted. But dramatic, eye-catching changes to Antarctica’s floating ice shelves, such as calving icebergs, are often highlighted in the news without a sense of long-term context or a clear connection to what is causing the changes. </p>
<p>Antarctica is <a href="https://theconversation.com/cold-and-calculating-what-the-two-different-types-of-ice-do-to-sea-levels-59996">losing land ice</a> at an accelerating rate, and current observations suggest it will become the <a href="https://www.nasa.gov/feature/goddard/2018/new-study-finds-sea-level-rise-accelerating">largest contributor to sea level rise</a> by the middle of this century. Understanding variations in the height of Antarctic ice shelves – the floating edges of the continent’s ice sheet – can tell us how and why Antarctica is changing, and what that could mean for future sea levels.</p>
<p>We study <a href="https://scholar.google.com/citations?user=JI_DpHwAAAAJ&hl=en">changes</a> in <a href="https://scholar.google.com/citations?user=J4DvU4oAAAAJ&hl=en">Antarctic</a> <a href="https://scholar.google.com/citations?user=ybHJBncAAAAJ&hl=en">ice</a> shelves, along with our colleague <a href="https://www.esr.org/staff/laurence-padman/">Laurie Padman</a> at <a href="https://www.esr.org/">Earth & Space Research</a>, a nonprofit institute in Seattle. One of us, <a href="https://scholar.google.com/citations?user=5prTIdoAAAAJ&hl=en">Helen Amanda Fricker</a>, contributed to two articles in a <a href="https://www.nature.com/collections/jwwltflrpn">special issue of the journal Nature</a> that brings together current understanding of the state of Antarctica. Here’s what we see happening.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/222802/original/file-20180612-112614-1nf8oyd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/222802/original/file-20180612-112614-1nf8oyd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/222802/original/file-20180612-112614-1nf8oyd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=501&fit=crop&dpr=1 600w, https://images.theconversation.com/files/222802/original/file-20180612-112614-1nf8oyd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=501&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/222802/original/file-20180612-112614-1nf8oyd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=501&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/222802/original/file-20180612-112614-1nf8oyd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=629&fit=crop&dpr=1 754w, https://images.theconversation.com/files/222802/original/file-20180612-112614-1nf8oyd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=629&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/222802/original/file-20180612-112614-1nf8oyd.jpg?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">Antarctica’s major geographical features, including the West and East Antarctic ice sheets, the Antarctic Peninsula and some of the larger ice shelves around the continent’s edges.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Antarctica_major_geographical_features.jpg">NASA</a></span>
</figcaption>
</figure>
<h2>Ice shelves hold back the grounded ice</h2>
<p>Antarctic ice shelves provide mechanical support to hold back the flow of ice from the continent to the ocean, regulating the pace of mass loss from the enormous ice sheet. Scientists call this process “buttressing,” since it works in the same way that an <a href="https://www.britannica.com/technology/buttress-architecture">architectural buttress</a> prevents a building from collapsing. </p>
<p>Reducing the mass of an ice shelf does not contribute directly to sea level rise, since this ice is already floating on the ocean, but it promotes faster discharge of grounded ice, which increases sea level. To understand how Antarctic mass loss varies, we need to understand how ice shelves grow and shrink.</p>
<p>Ice shelves gain mass mainly through ice flowing from the continent and local snowfall on their surfaces. They lose mass primarily through melting by the ocean and by iceberg calving. </p>
<p>Antarctica has more than 300 ice shelves, and the net change in their mass is a delicate balance between gains and losses. Determining this balance requires understanding how ice, ocean, and atmosphere interact to drive changes around Antarctica. Climate change will alter the overall balance between gains and losses, and will determine the <a href="http://dx.doi.org/10.1038/s41586-018-0173-4">future of Antarctica’s ice loss</a>.</p>
<h2>The critical role of satellites</h2>
<p>Antarctica’s small ice shelves are roughly the area of small cities, and its largest is the size of Spain. The total ice-shelf area is around 1.5 million square kilometers (580,000 square miles), about as large as Mongolia. The only viable way to routinely monitor changes in their mass is with satellites. </p>
<p>Since the launch of <a href="https://landsat.usgs.gov/landsat-missions-timeline">Landsat 1</a> in 1972, satellite data have taught us a lot about the ice sheet, including its large-scale structure, surface properties and flow rates. A <a href="http://dx.doi.org/10.1038/s41586-018-0179-y">recent synthesis</a> combined 150 independent estimates of ice-sheet mass loss from satellite data and atmospheric models to show that the ice sheet is losing more mass to the ocean with every passing year. The largest changes have occurred in places where ice shelves have either thinned or collapsed.</p>
<p>Single satellite missions typically only last five to 10 years, but we can stitch together data from consecutive missions to increase the length of the record. This helps us separate long-term trends from natural climate variability and unravel processes that drive changes around the margins of Antarctica.</p>
<p>The European Space Agency (ESA) has launched four ice-observing satellites since 1992, carrying radar altimeters to precisely determine the distance between the satellite and the Earth’s surface beneath it. These data have now provided a continuous time series of variations in ice-shelf surface height since the early 1990s. Combining measured increases and decreases in surface height with the latest generation of climate models to infer how the atmosphere has changed, we can estimate the amount of mass an ice shelf can lose to the ocean.</p>
<figure>
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<figcaption><span class="caption">Work by researchers at Scripps Institution of Oceanography reveals that strong El Niño events can cause significant ice loss in some Antarctic ice shelves.</span></figcaption>
</figure>
<h2>El Niño and La Niña affect ice shelves</h2>
<p>The Pacific Ocean sector of the Antarctic Ice Sheet is experiencing exceptionally high mass loss. This sector contains the rapidly changing Thwaites Glacier, which is the focus of a <a href="http://www.bbc.com/news/science-environment-43936372">new major research initiative</a> between the U.S. National Science Foundation and the United Kingdom’s National Environmental Research Council. </p>
<p>The 23-year altimeter record revealed <a href="https://doi.org/10.1038/s41561-017-0033-0">long-term mass loss in the Pacific sector ice shelves</a>. Further analysis of these data showed that in addition, the <a href="https://oceanservice.noaa.gov/facts/ninonina.html">El Niño/Southern Oscillation (ENSO)</a> – a periodic variation in sea surface temperatures and pressure over the tropical eastern Pacific Ocean – caused additional height change fluctuations. </p>
<p>Strong El Niño events, which typically bring warmer ocean waters and increase precipitation, increase snowfall over these ice shelves. But they also increase ocean-driven melting, removing ice from the ice-shelf base. Since snow is less dense than solid ice, mass lost through melting exceeds that added by snowfall. The result is that total ice-shelf mass, and hence its buttressing capability, actually decreases during El Niño events even though the height of the ice shelf may increase. </p>
<p>The opposite occurs during La Niñas, the counter to El Niño, where tropical ocean waters cool. Scientists expect that total precipitation and the <a href="https://doi.org/10.1038/nclimate2100">frequency of extreme ENSO events will increase as Earth’s atmosphere warms</a>, which implies that yearly fluctuations of ice shelf thickness and mass will also increase.</p>
<h2>Atmospheric conditions affect the Antarctic Peninsula</h2>
<p>A region further north in Antarctica, the Antarctic Peninsula, has experienced <a href="https://nsidc.org/news/newsroom/larsen_B/2002.html">startling changes over the past three decades</a>. Here several ice shelves have catastrophically collapsed due to warming in the atmosphere. Scientists see this as a canary in the coal mine: Similar warming events could drive the collapse of more southern ice shelves, which can play a larger role in future sea level rise. </p>
<p>Extensive press coverage of the 2017 calving of a <a href="https://www.youtube.com/watch?v=8Aw0kHAnY28">Delaware-sized iceberg</a> from Larsen C Ice Shelf has aggravated such concerns. However, in a recent study we showed that the height of the remaining Antarctic Peninsula ice shelves across the region has <a href="https://doi.org/10.1002/2017GL076652">increased since 2009</a>. Using atmospheric models backed up by field observations, we connected this height recovery to a regional cooling that persisted for several years and reduced summertime surface melting. The large calving event was likely a normal mass loss process, similar to a <a href="https://www.tandfonline.com/doi/abs/10.1080/01431169508954407">larger event in 1986</a>. There is so far no clear indication that Larsen C is on the brink of collapse.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/222800/original/file-20180612-112599-s3do2q.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/222800/original/file-20180612-112599-s3do2q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/222800/original/file-20180612-112599-s3do2q.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=264&fit=crop&dpr=1 600w, https://images.theconversation.com/files/222800/original/file-20180612-112599-s3do2q.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=264&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/222800/original/file-20180612-112599-s3do2q.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=264&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/222800/original/file-20180612-112599-s3do2q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=332&fit=crop&dpr=1 754w, https://images.theconversation.com/files/222800/original/file-20180612-112599-s3do2q.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=332&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/222800/original/file-20180612-112599-s3do2q.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=332&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Height changes observed over Larsen C Ice Shelf from Four European Space Agency satellites, one NASA satellite and an extensive airborne survey from NASA’s Operation IceBridge.</span>
<span class="attribution"><span class="source">Helen Fricker</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The role of the atmosphere is only part of this story. After removing the effect of higher air temperatures, we found that the ocean continued to melt the ice shelves’ bases at a rate that tipped the scales toward net mass loss. In fact, we found that the atmosphere recently played a stabilizing role while the ocean exerts a continuing destabilizing influence, highlighting the complex interplay between the atmosphere, ice and ocean around Antarctica.</p>
<h2>New satellites will provide more insight</h2>
<p>With existing data, scientists can begin to decode the intricacies of ice-shelf evolution to improve our understanding of what is influencing ice-shelf mass changes and stability. </p>
<p>Satellites have shown that the ice shelves are shrinking overall due to increased ocean-induced melting. In addition to the overall trend, signals corresponding to atmospheric and oceanic processes are becoming apparent, such as influences from El Niño and La Niña cycles in the tropics and local atmospheric changes. </p>
<p>As the satellite record lengthens with the launch of new polar-orbiting satellites like NASA’s <a href="https://icesat-2.gsfc.nasa.gov/">ICESat-2</a> in September 2018 and <a href="https://nisar.jpl.nasa.gov/">NISAR</a> in 2020, scientists expect to reach the point where we can confidently include these processes in models of ice-sheet response to climate changes, which will improve projections of future sea level rise.</p><img src="https://counter.theconversation.com/content/95207/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Helen Amanda Fricker receives funding from NASA and NSF.</span></em></p><p class="fine-print"><em><span>Fernando Paolo receives funding from NASA. </span></em></p><p class="fine-print"><em><span>Matthew Siegfried receives funding from NSF and NASA. </span></em></p><p class="fine-print"><em><span>Susheel Adusumilli receives funding from NASA. </span></em></p>Last summer one of Antarctica’s floating ice shelves calved an iceberg the size of Delaware – but scientists say other less dramatic changes reveal more about how and why Antarctica is changing.Helen Amanda Fricker, Professor, Scripps Institution of Oceanography, University of California, San DiegoFernando Paolo, Postdoctoral Scholar, Jet Propulsion Laboratory, California Institute of TechnologyMatthew Siegfried, Postdoctoral Fellow, Stanford University, Stanford UniversitySusheel Adusumilli, Graduate Student Researcher, University of California, San DiegoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/820162017-10-19T11:59:54Z2017-10-19T11:59:54ZWarm waters melting Antarctic ice shelves may have appeared for the first time in over 7,000 years<figure><img src="https://images.theconversation.com/files/190803/original/file-20171018-32375-b0ry26.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Eastern ice.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/full-moon-setting-over-ice-bergs-734422477?src=SRShHMLkzs0tA0kSpxHusA-2-61">Shutterstock/Hall</a></span></figcaption></figure><p>The vast expanse of the Antarctic is a region of the world particularly vulnerable to climate change, where ice loss has the potential to significantly increase sea levels. </p>
<p>Now, for possibly the first time in 7,000 years, a phenomenon known as “upwelling” (the upward flow of warmer ocean water to the surface), is thought to have caused recent ice shelf collapse around the continent – and the glacial thinning associated with it. </p>
<p>Ice shelves floating on water are the oceanic extension of land glaciers and ice sheets, and the primary region for ice loss. As these shelves break apart, the flow of continental ice held up behind them accelerates.</p>
<p>The ocean surrounding Antarctica is extremely cold, but water over 300m deep, Circumpolar Deep Water (CDW), is about 3⁰C above the melting point of ice. Normally, the very cold water above keeps this away from ice shelves. But in some areas, CDW is spilling onto the shallow Antarctic continental shelf, causing the ice to thin.</p>
<p>Ice shelf thinning has <a href="https://www.scientificamerican.com/article/antarctica-s-ice-shelves-thin-threaten-significant-sea-level-rise/">accelerated in recent decades</a>, but the picture is not the same everywhere. While the east of the Antarctic has shown modest gains in ice thickness, the west has outstripped this with significant ice loss – <a href="http://science.sciencemag.org/content/348/6232/327">up to 18%</a> in vulnerable areas like the Amundsen and Bellingshausen Seas.</p>
<p>The pattern of ice loss and <a href="http://science.sciencemag.org/content/343/6167/174">other observations</a> indicate that warmer water upwelling beneath these ice shelves is driving it. But what has caused this upwelling? Is it related to human activity? And how concerned should we be?</p>
<p>Two teams led by scientists from the <a href="https://www.bas.ac.uk/team/science-teams/palaeo-environments-or-past-climates/#about">British Antarctic Survey</a>, both of which I have been working with, set out to tackle these precise questions by focusing on two vulnerable areas. One site is in <a href="http://www.nature.com/nature/journal/v547/n7661/full/nature22995.html">Pine Island Bay, in the Amundsen Sea</a>, and the other is in <a href="http://www.sciencedirect.com/science/article/pii/S0277379115001444">Marguerite Bay, in the Bellingshausen Sea</a>.</p>
<p>The aims of the studies are similar – to monitor the extent of upwelling warm water onto the continental shelf over the past 10,000 years, in order to understand when this last occurred and what the impact was. </p>
<p>This involves collecting and sampling “cores” of sediment up to 10m long from the sea bed at a range of depths up to 900m. Obtaining suitable cores is particularly challenging in these remote locations, where glacial dynamics often disturb the sediment.</p>
<h2>Core evidence</h2>
<p>Much of the evidence for past oceanography comes from tiny shells of amoeboid organisms called foraminifera. A huge variety of species colonise habitats on the sea floor and make up much of the sediment collected. There can be hundreds of shells in just one gram of sediment.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/190841/original/file-20171018-32375-1sna4uw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/190841/original/file-20171018-32375-1sna4uw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=593&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190841/original/file-20171018-32375-1sna4uw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=593&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190841/original/file-20171018-32375-1sna4uw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=593&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190841/original/file-20171018-32375-1sna4uw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=745&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190841/original/file-20171018-32375-1sna4uw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=745&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190841/original/file-20171018-32375-1sna4uw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=745&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Electron microscope images of planktonic foraminifera N. pachyderma from Pine Island Bay. Scale bar: 100µm equals 0.1mm.</span>
<span class="attribution"><span class="source">Nature Publishing Group</span></span>
</figcaption>
</figure>
<p>Forams are extremely valuable, as their shells are made of calcium carbonate precipitated from the ocean water in which they lived. Examining these shells allows us to reconstruct the chemistry of ocean water. </p>
<p>There were two geochemical tracers used for warm CDW in Pine Island Bay – the proportion of carbon isotopes, and the magnesium to calcium ratio controlled by water temperature. Both of these showed CDW was last on the inner shelf over 7,500 years ago.</p>
<p>In Marguerite Bay, shells of another plankton group called diatoms were also analysed. These indicate past productivity and sea surface temperatures. They showed that CDW was persistently on the shelf here over 7,000 years ago, and more sporadically since then.</p>
<p>Tellingly, the enhanced upwelling of warm CDW in both locations negatively impacted the local extent of ice. </p>
<h2>Winds of change</h2>
<p>Both studies suggest that the cause of the CDW upwelling before 7,000 years ago was a more southerly position of the southern hemisphere westerly winds (SHWW). These winds are thought to drive circulation of the warmer deep water. A recent shift in the position of the SHWW towards the poles could be the cause of greater CDW upwelling in Pine Island Bay since the 1940s. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/190847/original/file-20171018-32370-cmhboe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/190847/original/file-20171018-32370-cmhboe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=267&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190847/original/file-20171018-32370-cmhboe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=267&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190847/original/file-20171018-32370-cmhboe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=267&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190847/original/file-20171018-32370-cmhboe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=336&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190847/original/file-20171018-32370-cmhboe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=336&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190847/original/file-20171018-32370-cmhboe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=336&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Data llustrating the apparent link between winds and ocean around western Antarctica. The migration of the southern hemisphere westerly winds (SHWW) coincide with upwelling of Circumpolar Deep Water (CDW) in the Amundsen Sea.</span>
</figcaption>
</figure>
<p>This coincidence of timing with the onset of industrialisation shows it is possible that human made greenhouse gasses, thought to cause atmospheric warming, are having an impact on the position of the winds, the increase in warm water reaching the surface, and ultimately the melting of more ice in the Antarctic.</p>
<p>Irrespective of the causes of past changes in SHWW positions, the link between winds and ocean upwelling is cause for concern, as future projected global warming may shift SHWW belts and promote further upwelling and melting. More research is now needed to fully understand the link between CDW and past climate, and to estimate the strength of upwelling since the 1940s compared to upwelling before 7,000 years ago. But the emerging picture is one of the potentially increased vulnerability of West Antarctic ice sheets, and possible future sea level rise.</p><img src="https://counter.theconversation.com/content/82016/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sev Kender receives funding from the Natural Environment Research Council. He is affiliated with the University of Exeter and the British Geological Survey. </span></em></p>Warm waters run very deep.Sev Kender, Lecturer in Palaeontology, University of ExeterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/803142017-07-05T20:09:38Z2017-07-05T20:09:38ZDon’t worry about the huge Antarctic iceberg – worry about the glaciers behind it<p>Icebergs breaking off Antarctica, even massive ones, do not typically concern glaciologists. But the impending birth of a <a href="http://www.projectmidas.org/blog/another-step-closer/">new massive iceberg</a> could be more than business as usual for the frozen continent. </p>
<p>The Larsen C ice shelf, the fourth-largest in Antarctica, has attracted <a href="http://www.bbc.com/news/science-environment-40113393">worldwide attention</a> in the lead-up to calving an iceberg one-tenth of its area – or about half the area of greater Melbourne. It is still <a href="http://www.projectmidas.org/blog/berg-acceleration/">difficult to predict exactly when it will break free</a>.</p>
<p>But it’s not the size of the iceberg that should be getting attention. Icebergs calve all the time, including the occasional very large one, with nothing to worry about. Icebergs have only a <a href="https://theconversation.com/cold-and-calculating-what-the-two-different-types-of-ice-do-to-sea-levels-59996">tiny direct effect</a> on sea level. </p>
<p>The calving itself will simply be the birth of another big iceberg. But there is valid concern among scientists that the entire Larsen C ice shelf could become unstable, and eventually break up entirely, with knock-on effects that could take decades to play out.</p>
<p>Ice shelves essentially act as corks in a bottle. Glaciers flow from land towards the sea, and their ice is eventually absorbed into the ice shelf. Removal of the ice shelf causes glaciers to flow faster, increasing the rate at which ice moves from the land into the sea. This has a much larger effect on sea level than iceberg calving does.</p>
<p>While the prediction that Larsen C could become unstable is based partly on physics, it is also based on observations. Using aerial and satellite images, scientists have been able to track very similar ice shelves in the past, some of which have been seen to retreat and collapse. </p>
<h2>The death of an ice shelf</h2>
<p>The most dramatic ice shelf collapse observed so far is that of Larsen C’s neighbour to the north – the imaginatively named Larsen B. Over the course of just six weeks in 2002 the <a href="https://earthobservatory.nasa.gov/Features/WorldOfChange/larsenb.php">entire ice shelf splintered into dozens of icebergs</a>. Almost immediately afterwards, the glaciers feeding into it sped up by two to six times. Those glaciers <a href="https://www.nasa.gov/press-release/nasa-study-shows-antarctica-s-larsen-b-ice-shelf-nearing-its-final-act">continue to flow faster</a> to this day. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/176544/original/file-20170703-8225-1h27706.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/176544/original/file-20170703-8225-1h27706.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/176544/original/file-20170703-8225-1h27706.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/176544/original/file-20170703-8225-1h27706.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/176544/original/file-20170703-8225-1h27706.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/176544/original/file-20170703-8225-1h27706.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/176544/original/file-20170703-8225-1h27706.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/176544/original/file-20170703-8225-1h27706.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"></a>
<figcaption>
<span class="caption">Satellite photo series of Larsen B Ice Shelf collapse from January 2002 to April 2002.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>In our new study, <a href="https://authors.elsevier.com/a/1VKFJ,Ig49NjA">published in Earth and Planetary Science Letters</a>, we turn the clock back even further to look at the Wordie ice shelf, on the west coast of the southern Antarctic Peninsula, which began to retreat in the 1960s and eventually <a href="https://landsat.gsfc.nasa.gov/landsat-documents-rapid-disappearance-of-antarcticas-ice-shelves/">disappeared in January 2017</a>. </p>
<p>Over the past 20 years, observations have shown that the main glacier feeding into the Wordie ice shelf, the Fleming Glacier, has sped up and thinned. Compared with the glaciers feeding Larsen B and C, Fleming Glacier is massive: 80km long, 12km wide, and 600m thick at its front.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/176862/original/file-20170705-16510-iymhsl.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/176862/original/file-20170705-16510-iymhsl.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/176862/original/file-20170705-16510-iymhsl.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=380&fit=crop&dpr=1 600w, https://images.theconversation.com/files/176862/original/file-20170705-16510-iymhsl.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=380&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/176862/original/file-20170705-16510-iymhsl.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=380&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/176862/original/file-20170705-16510-iymhsl.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=477&fit=crop&dpr=1 754w, https://images.theconversation.com/files/176862/original/file-20170705-16510-iymhsl.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=477&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/176862/original/file-20170705-16510-iymhsl.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=477&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Locations of the Larsen C Ice Shelf and the Wordie Ice Shelf-Fleming Glacier system with ice front positions from 1947 to 2016.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We used historic aerial photographs from 1966 to create an elevation map of the Fleming Glacier, and compared it to elevation measurements from 2002 to 2015. Between 1966 and 2015 the Fleming Glacier thinned by at least 100m near the front. The thinning rate, which is the elevation change rate, rapidly increased: the thinning rate after 2008 is more than twice that during 2002 to 2008, and four times the average rates from 1966 to 2008.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/176322/original/file-20170629-5317-1j5zalo.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/176322/original/file-20170629-5317-1j5zalo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/176322/original/file-20170629-5317-1j5zalo.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=255&fit=crop&dpr=1 600w, https://images.theconversation.com/files/176322/original/file-20170629-5317-1j5zalo.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=255&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/176322/original/file-20170629-5317-1j5zalo.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=255&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/176322/original/file-20170629-5317-1j5zalo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=320&fit=crop&dpr=1 754w, https://images.theconversation.com/files/176322/original/file-20170629-5317-1j5zalo.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=320&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/176322/original/file-20170629-5317-1j5zalo.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=320&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 thinning rate of the Fleming Glacier region during (a) 2002-2008 and (b) 2008-2015.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>Ice flow speeds have also increased by more than 400m per year at the front since 2008. This is <a href="http://www.the-cryosphere-discuss.net/tc-2017-75/">the largest speed change in recent years of any glacier in Antarctica</a>. These changes all point to ice shelf collapse as the cause.</p>
<p>We estimate the total glacier ice volume lost from all glaciers that feed the Wordie is 179 cubic kilometres since 1966, or 319 times the volume of Sydney Harbour. The weight of this ice moving off the land and into the ocean has caused the bedrock beneath the glaciers to lift by more than 50mm. </p>
<p>Other research has suggested this lift could have acted to slow the glacier’s retreat, but it’s clear that the bedrock deformation has not stopped the ice movement speeding up. It seems the Fleming Glacier has a long way to go before it will return to a new stable state (in which snowfall feeding the glacier equals the ice flowing into the oceans).</p>
<p>Fifty years after the Wordie Ice Shelf began to collapse, the major feeding glaciers continue to thin and flow faster than before. </p>
<p>We can’t yet predict the full consequences of the new iceberg calving from Larsen C. But if the ice shelf does begin to retreat or collapse, history tells us it is very possible that its glaciers will flow faster – making yet more sea level rise inevitable.</p><img src="https://counter.theconversation.com/content/80314/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chen Zhao is a PhD student from the School of Land and Food, University of Tasmania. She receives funding from the Australian Government Research Training Program. </span></em></p><p class="fine-print"><em><span>Christopher Watson receives funding from the Australian Research Council and the Department of Environment.</span></em></p><p class="fine-print"><em><span>Matt King receives funding from the Australian Research Council and the Department of Environment.</span></em></p>A huge iceberg is set to break free from Antarctica. While the iceberg isn’t hugely concerning, it could herald the breakup of the entire Larsen C ice shelf, which could trigger more sea-level rise.Chen Zhao, PhD candidate of Antarctic Science, University of TasmaniaChristopher Watson, Senior Lecturer, Surveying and Spatial Sciences, School of Land and Food, University of TasmaniaMatt King, Professor, Surveying & Spatial Sciences, School of Land and Food, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/599962016-07-12T19:41:14Z2016-07-12T19:41:14ZCold and calculating: what the two different types of ice do to sea levels<figure><img src="https://images.theconversation.com/files/126463/original/image-20160614-12948-157moyq.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Knowing where the ice comes from can help work out what it will do to sea levels.</span> <span class="attribution"><span class="license">Author provided</span></span></figcaption></figure><p>It was back in 250ʙⅽ when Archimedes reportedly stepped into his bathtub and had the world’s first <a href="https://en.wikipedia.org/wiki/Eureka_(word)">Eureka</a> moment – realising that putting himself in the water made its level rise. </p>
<p>More than two millennia later, the <a href="http://arstechnica.com/science/2016/07/recent-antarctic-sea-ice-growth-boosted-by-la-ninas/?comments=1">comments sections of news stories</a> still routinely reveal confusion about how this same thing happens when polar ice melts and sea levels change. </p>
<p>This is in marked contrast to the confidence that scientists have in their collective understanding of what is happening to the ice sheets. Indeed, the <a href="https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter04_FINAL.pdf">2014 Assessment Report of the Intergovernmental Panel on Climate Change</a> reported “very high confidence” that the Greenland Ice Sheet was melting and raising sea levels, with “high confidence” of the same for the Antarctic Ice Sheet. </p>
<p>Despite this, commenters below the line on news stories frequently wonder how it can be true that Antarctica is melting and contributing to sea-level rise, when satellite observations show Antarctic ice expanding.</p>
<p>Unravelling the confusion depends on appreciating the difference between the two different types of ice, which we can broadly term “land ice” and “sea ice” – although as we shall see, there’s a little bit more to it than that. The two different types of ice have very different roles in Earth’s climate, and behave in crucially different ways. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/126202/original/image-20160610-29209-17b9pep.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/126202/original/image-20160610-29209-17b9pep.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=372&fit=crop&dpr=1 600w, https://images.theconversation.com/files/126202/original/image-20160610-29209-17b9pep.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=372&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/126202/original/image-20160610-29209-17b9pep.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=372&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/126202/original/image-20160610-29209-17b9pep.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=467&fit=crop&dpr=1 754w, https://images.theconversation.com/files/126202/original/image-20160610-29209-17b9pep.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=467&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/126202/original/image-20160610-29209-17b9pep.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=467&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Sea levels rise when ice resting on land, <em>grounded ice</em>, melts (often after forming icebergs). Floating sea ice that melts has a very important role in other areas of our climate system.</span>
</figcaption>
</figure>
<h2>Land ice</h2>
<p><a href="https://theconversation.com/au/topics/ice-sheets">Ice sheets</a> form by the gradual accumulation of snow on land over long periods of time. This “grounded” ice flows in glaciers to the ocean under the influence of gravity, and when it arrives it eventually melts. If the amount of ice flowing into the oceans is balanced by snowfall on land, the net change in global sea level due to this ice sheet is zero. </p>
<p>However, if the ice begins to flow more rapidly or snowfall declines, the ice sheet can be out of balance, resulting in a net rise in sea level. </p>
<p>But this influence on sea level is only really relevant for ice that is grounded on land. When the ice sheet starts to float on the ocean it is called an “ice shelf”. The contribution of ice shelves to sea-level rise is negligible because they are already in the sea (similar to an <a href="http://www.physlink.com/education/askexperts/ae389.cfm">ice cube in a glass of water</a>, although the ocean is salty unlike a glass of water). But they can nevertheless play an important role in sea-level rise, by governing the rate at which the grounded ice can discharge into the oceans, and therefore how fast it melts.</p>
<h2>Sea ice</h2>
<p>When viewed from space, all polar ice looks pretty much the same. But there is a second category of ice that has effectively nothing to do with the ice sheets themselves. </p>
<p>“Sea ice” is formed when ocean water is frozen due to cooling by the air. Because it is floating in the ocean, sea ice does not (directly) affect sea level. </p>
<p>Sea ice is generally no more than a few metres thick, although it can grow to more than 10 metres thick if allowed to grow over many winters. Ice shelves, on the other hand, are hundreds of metres thick, <a href="https://www.youtube.com/watch?v=IxfORXWph2Q">as seen when an iceberg is created and rolls over</a>. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/IxfORXWph2Q?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A big breakup.</span></figcaption>
</figure>
<p>In the ocean around Antarctica, almost all the sea ice melts in the southern hemisphere spring. This means that every year an area of ocean twice the size of Australia freezes over and then melts – arguably the largest seasonal change on our planet. </p>
<p>So, while ice sheets change over decades and centuries, the time scale of sea ice variability is measured in months. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/MLCfF7BLii4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Antarctic sea ice grows and shrinks dramatically over the course of the year. These changes do not directly affect sea level. Land ice changes are slower but do affect sea levels, at least until the land ice becomes afloat.</span></figcaption>
</figure>
<p>The seasonal cycle of Arctic sea ice is much smaller. This is because the Arctic retains much more of its sea ice in the summer, and its winter extent is limited by land that surrounds the Arctic Ocean.</p>
<h2>What is happening to land ice?</h2>
<p>The two great ice sheets are in Greenland and Antarctica. Thanks to <a href="http://science.sciencemag.org/content/338/6111/1183">satellite measurements</a>, we now know that since the early 1990s both have been contributing to sea-level rise.</p>
<p>It is thought that most of the Antarctic changes are caused by seawater melting the ice shelves faster, causing the land ice to flow faster and hence leading to sea-level rise as the ice sheet is tipped out of balance.</p>
<p>In Greenland, both surface and ocean melting play important roles in driving the accelerated contribution to sea levels. </p>
<h2>What about sea ice?</h2>
<p>Over the last four decades of satellite measurements, there has been a rapid <a href="http://www.the-cryosphere.net/9/269/2015/tc-9-269-2015.html">decrease and thinning</a> of summer Arctic sea ice. This is due to human activity warming the atmosphere and ocean. </p>
<p>In the Antarctic there has been a modest <a href="http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter04_FINAL.pdf">increase</a> in total sea ice cover, but with a complex pattern of localised increases and decreases that are related to changes in winds and ocean currents. What’s more, satellite measurement of changes in sea ice thickness is much more difficult in the Antarctic than in the Arctic mainly because Antarctic sea ice has a lot of poorly measured snow resting on it.</p>
<p>The Southern Ocean is arguably a much more complex system than the Arctic Ocean, and determining humans’ influence on these trends and projecting future change is challenging. </p>
<p>Observations of the changes happening in the Arctic and Antarctic reveal complex stories that vary from place to place and over time. </p>
<p>These changes require ongoing monitoring and greater understanding of the causes of the observed changes. And public confusion can be avoided through careful use of the different terms describing ice in the global climate system. It pays to know your ice sheets from your sea ice.</p><img src="https://counter.theconversation.com/content/59996/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matt King receives funding from the Australian Research Council and the Department of Environment.</span></em></p><p class="fine-print"><em><span>Ben Galton-Fenzi works for the Australian Antarctic Division. He receives funding from the Department of the Environment.</span></em></p><p class="fine-print"><em><span>Will Hobbs is employed by the Antarctic Climate and Ecosystems Cooperative Research Centre, and receives funding from the Australian Research Council. </span></em></p>Polar ice isn’t all the same - it can be divided roughly into “land ice” and “sea ice”. What matters most for sea levels is how much ice slides off the land and melts in the sea.Matt King, Professor, Surveying & Spatial Sciences, School of Land and Food, University of TasmaniaBen Galton-Fenzi, Senior Scientist, Australian Antarctic DivisionWill Hobbs, Physical Oceanographer, Antarctic Climate and Ecosystems Cooperative Research Centre, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/392732015-03-26T22:25:23Z2015-03-26T22:25:23ZShrinking of Antarctic ice shelves is accelerating<figure><img src="https://images.theconversation.com/files/76037/original/image-20150325-14494-1nivjgq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Antarctica's Brunt Ice Shelf photographed in October 2011 from NASA's DC-8 research aircraft during an Operation IceBridge flight.</span> <span class="attribution"><span class="source">Michael Studinger/NASA</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Ask people what they know about Antarctica and they usually mention cold, snow and ice. In fact, there’s so much ice on Antarctica that if it all melted into the ocean, average sea level around the entire world would rise about 200 feet, roughly the height of a 20-story building.</p>
<p>Could this happen? There’s evidence that at various times in the past there was much less ice on Antarctica than there is today. For example, during an extended warm period called the <a href="http://www.sciencemag.org/content/333/6042/620.short">Eemian interglacial</a> about 100,000 years ago, Antarctica probably lost enough ice to raise sea level by several meters. </p>
<p>Scientists think that global average temperature back then was only about two degrees Fahrenheit warmer than today. Assuming we continue to burn fossil fuels and add greenhouse gases to the atmosphere, global temperature is expected to rise by at least two degrees Fahrenheit by <a href="https://www.ipcc.ch/publications_and_data/ar4/wg1/en/spmsspm-projections-of.html">2100</a>. What will that do to Antarctica’s ice sheet? Even one meter of worldwide sea level rise – that is, melting only a fiftieth of the ice sheet – would cause massive displacements of coastal populations and require major investments to protect or relocate cities, ports and other coastal infrastructure. </p>
<p>Ice leaving Antarctica enters the ocean through ice shelves, which are the floating edges of the ice sheet. We expect that any changes to the ice sheet caused by changes in the ocean will be felt first by the ice shelves. Using satellite data, we analyzed how Antarctica’s ice shelves have changed over nearly two decades. Our <a href="http://www.sciencemag.org/content/early/2015/03/25/science.aaa0940">paper</a> published in Science shows that not only has ice shelf volume gone down, but losses have accelerated over the past decade, a result that provides insight into how our future climate will affect the ice sheet and sea level. </p>
<h2>Cork in a champagne bottle</h2>
<p>The link between changing global temperature and ice loss from Antarctica’s ice sheet is not straightforward. By itself, air temperature has a fairly small influence on the ice sheet, since most of it is already well below freezing. </p>
<p>It turns out that, to understand ice loss, we need to know about changes in winds, snowfall, ocean temperature and currents, sea ice, and the geology under the ice sheets. We don’t yet have enough information on any of these to build reliable models for predicting ice sheet response to climate changes.</p>
<p>We do know that one important control on ice loss from Antarctica is what happens where the ice sheet meets the ocean. The Antarctic Ice Sheet gains ice by snowfall. The ice sheet spreads under its own weight forming glaciers and ice streams that flow slowly downhill towards the ocean. Once they lift off the bedrock and begin to float, they become ice shelves. To stay in balance, ice shelves have to shed the ice they gained from glacier flow and local snowfall. Chunks break off to form icebergs and ice is also lost from the bottom by melting as warm ocean water flows under it.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/76128/original/image-20150326-8680-em68zv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/76128/original/image-20150326-8680-em68zv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/76128/original/image-20150326-8680-em68zv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=367&fit=crop&dpr=1 600w, https://images.theconversation.com/files/76128/original/image-20150326-8680-em68zv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=367&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/76128/original/image-20150326-8680-em68zv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=367&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/76128/original/image-20150326-8680-em68zv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=462&fit=crop&dpr=1 754w, https://images.theconversation.com/files/76128/original/image-20150326-8680-em68zv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=462&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/76128/original/image-20150326-8680-em68zv.jpg?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"></a>
<figcaption>
<span class="caption">Schematic diagram of an Antarctic ice shelf showing the processes causing the volume changes measured by satellites. Ice is added to the ice shelf by glaciers flowing off the continent and by snowfall that compresses to form ice. Ice is lost when icebergs break off the ice front, and by melting in some regions as warm water flows into the ocean cavity under the ice shelf. Under some ice shelves, cold and fresh meltwater rises to a point where it refreezes onto the ice shelf.</span>
<span class="attribution"><span class="source">Helen Amanda Fricker, Professor, Scripps Institution of Oceanography, UC San Diego</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>An ice shelf acts a bit like a cork in a champagne bottle, slowing down the glaciers flowing from the ground into it; scientists call this the buttressing effect. Recent observations show that when ice shelves thin or collapse, the <a href="http://nsidc.org/news/newsroom/20040921_acceleration.html">glacier flow</a> from the land into the ocean speeds up, which contributes to sea level rise. So understanding what makes ice shelves change size is an important scientific question.</p>
<h2>Building an ice shelves map</h2>
<p>The first step towards understanding ice shelves is to work out just how much and how quickly they have changed in the past. In our <a href="http://www.sciencemag.org/content/early/2015/03/25/science.aaa0940">paper</a>, we show detailed maps of changes in ice shelves all around Antarctica based on the 18 years from 1994 to 2012. The data came from continuous measurements of surface height collected by three European Space Agency radar altimeter satellites. By comparing surface heights at the same point on the ice shelf at different times, we can build a record of ice height changes. We can then convert that to thickness changes using ice density and the fact that <a href="http://physics.weber.edu/carroll/archimedes/principle.htm">ice shelves float</a>.</p>
<p>Prior studies of changes in ice shelf thickness and volume have given averages for individual ice shelves or approximated the changes in time as straight-line fits over short periods. In contrast, our new study presents high-resolution (about 30 km by 30 km) maps of thickness changes at three-month time steps for the 18-year period. This data set allows us to see how the rate of thinning varies between different parts of the same ice shelf, and between different years.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/76131/original/image-20150326-8713-1fyzwcb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/76131/original/image-20150326-8713-1fyzwcb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/76131/original/image-20150326-8713-1fyzwcb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=538&fit=crop&dpr=1 600w, https://images.theconversation.com/files/76131/original/image-20150326-8713-1fyzwcb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=538&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/76131/original/image-20150326-8713-1fyzwcb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=538&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/76131/original/image-20150326-8713-1fyzwcb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=676&fit=crop&dpr=1 754w, https://images.theconversation.com/files/76131/original/image-20150326-8713-1fyzwcb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=676&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/76131/original/image-20150326-8713-1fyzwcb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=676&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This map shows eighteen years of change in thickness and volume of Antarctic ice shelves. Rates of thickness change (meters/decade) are color-coded from -25 (thinning) to +10 (thickening). Circles represent percentage of thickness lost (red) or gained (blue) in 18 years. The central circle demarcates the area not surveyed by the satellites (south of 81.5ºS). Original data were interpolated for mapping purposes.</span>
<span class="attribution"><span class="source">Scripps Institution of Oceanography, UC San Diego</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We find that, if recent trends continue, some ice shelves will thin dramatically within centuries, reducing their ability to buttress the ice sheet. Other ice shelves are gaining ice, and so could slow down the loss of ice from the ground.</p>
<p>When we sum up losses around Antarctica, we find that the change in volume of all the ice shelves was almost zero in the first decade of our record (1994-2003) but, on average, over 300 cubic kilometers per year were lost between 2003 and 2012. </p>
<p>The pattern of acceleration in ice loss varies between regions. During the first half of the record, ice losses from West Antarctica were almost balanced by gains in East Antarctica. After about 2003, East Antarctic ice shelf volume stabilized, and West Antarctic losses increased slightly. </p>
<p>Changes in climate factors like snowfall, wind speed and ocean circulation will lead to different patterns of ice shelf thickness change in time and space. We can compare the “fingerprints” of these factors with our new, much clearer maps to identify the primary causes, which might be different in different regions around Antarctica.</p>
<p>Our 18-year data set has demonstrated the value of long and continuous observations of the ice shelves, showing that shorter records cannot capture the true variability. We expect that our results will inspire new ways of thinking about how the ocean and atmosphere can affect ice shelves and, through them, ice loss from Antarctica.</p><img src="https://counter.theconversation.com/content/39273/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Laurence Padman receives funding from NASA, grants NNX10AG19G and NNX13AP60G.</span></em></p><p class="fine-print"><em><span>Fernando Paolo receives funding from NASA Earth System Science Fellowship (NESSF), grant NNX12AN50H 002 (93735A).</span></em></p><p class="fine-print"><em><span>Helen Amanda Fricker receives funding from NASA, grants NNX10AG19G and NNX13AP60G.</span></em></p>Researchers find that ice around Antarctica shrank quickly last decade, raising concerns over this buttress against melting land-based ice and future sea-level rise.Laurence Padman, Senior Scientist, Earth and Space ResearchFernando Paolo, PhD candidate, Scripps Institution of Oceanography, University of California, San DiegoHelen Amanda Fricker, Professor, Institute of Geophysics and Planetary Physics , University of California, San DiegoLicensed as Creative Commons – attribution, no derivatives.