How the world’s largest ice sheet is responding to climate change

How the world’s largest ice sheet is responding to climate change

Mountain peaks protrude from the East Antarctic Ice Sheet. © Jan Lenaerts

The East Antarctic Ice Sheet appears to be more sensitive to global warming than previously thought. This is shown by a new study that evaluated the reactions of the ice sheet to past global warming and combined them with current climate models. While the East Antarctic Ice Sheet is likely to remain broadly stable if climate targets are met, if it warms more than 2 degrees Celsius above pre-industrial levels, it could be more affected by melting and contribute several meters of sea level rise over the next few centuries.

The rapid increase in average global temperatures caused by human emissions of greenhouse gases is causing the ice sheets in the polar regions to melt and sea levels to rise. The effects in coastal areas can already be seen today. With the Paris Climate Agreement of 2015, 196 countries agreed to limit global temperature rise to a maximum of two degrees Celsius above pre-industrial levels and to strive not to exceed 1.5 degrees Celsius. This is intended, among other things, to avoid or reduce the serious consequences of the melting of the ice sheets.

lessons from the past

The glaciers and ice sheets of West Antarctica and Greenland are particularly at risk. In contrast, researchers previously considered the East Antarctic ice sheet, which lies in the coldest and highest part of Antarctica, to be less susceptible to climate change. However, little was known about its properties and geological history. A team led by Chris Stokes from Durham University in Great Britain has now taken a closer look at the past and possible future of this largest ice sheet on earth.

To do this, the researchers evaluated, among other things, how the East Antarctic ice sheet reacted to past interglacial periods, when the carbon dioxide concentration and temperatures were only slightly higher than today. The last time atmospheric CO2 levels exceeded today’s level of 417 parts per million (ppm) was in the mid-Pliocene about three million years ago. Although mean global temperatures were then only about two to four degrees Celsius higher than today, traces in seafloor sediments show that parts of the ice sheet collapsed at the time, causing sea levels to rise by 10 to 25 meters.

More sensitive than expected

“An important lesson from the past is that the East Antarctic Ice Sheet is very sensitive to even relatively modest warming scenarios. It’s not as stable and protected as we once thought,” says co-author Nerilie Abram of the Australian National University in Canberra. Based on this knowledge, the researchers used existing climate models to make forecasts of how the East Antarctic ice sheet could develop under different scenarios for greenhouse gas emissions and temperatures.

“If temperatures rise by more than 2 degrees Celsius beyond 2100, and this is sustained by high greenhouse gas emissions, then East Antarctica alone could rise about 1 to 3 meters by 2300 and about 2 to 5 meters by 2500 of sea level,” reports Abram. Overall, the East Antarctic Ice Sheet contains enough frozen water to raise sea levels by 52 meters if it thaws completely. “Satellite observations are already showing signs of ice thinning and retreat,” says co-author Matthew England of the University of New South Wales. “Our models show that unless we reduce greenhouse gas emissions, ocean warming will increase dramatically.”

Compliance with climate targets can protect the ice sheet

But the analysis also gives reason for hope: “Limiting global temperature rise to less than the two-degree Celsius limit set in the Paris climate agreement should mean that we avoid the worst-case scenarios or maybe even halt the melting of the East Antarctic ice sheet and with it.” limit its impact on global sea level rise,” says Stoke.

From the researchers’ point of view, this underlines how important it is to consistently pursue the climate goals. “We now have a very small window of opportunity to rapidly reduce our greenhouse gas emissions, limit the rise in global temperatures, and preserve the East Antarctic Ice Sheet,” says Abrams. “Such action would not only protect the East Antarctic Ice Sheet, but also slow the melting of other large ice sheets like Greenland and West Antarctica, which are even more vulnerable and at risk. It is therefore crucial that countries honor and strengthen their commitments under the Paris Agreement.”

Source: Chris Stoke (Durham University, UK) et al., Nature, doi: 10.1038/s41586-022-04946-0

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