The East Antarctic Ice Sheet is less stable than long thought. If humanity meets the goals of the Paris climate agreement and limits global warming to a maximum of two degrees Celsius, this, by far the largest mass of ice on earth, will only melt a little, according to a study. In this case, the resulting rise in sea level would be less than half a meter by the year 2500.
However, should the earth warm up more, the sea level could rise by a few meters, as an international research team led by Chris Stokes from the University of Durham writes in the journal "Nature".
East Antarctica contains enough ice to raise sea levels by 52 meters, the team writes. For comparison: the - much smaller - West Antarctic ice sheet would "only" raise the sea level by a good 5 meters if it melted completely. From 1992 to 2017, West Antarctica lost 2,000 gigatonnes (billion tons) of ice, equivalent to a 6 millimeter rise in sea level. Ice loss is mainly due to warm ocean currents.
In contrast to the western part of the continent, the ice of East Antarctica has long been considered very stable. Stokes' team has now analyzed the behavior of the ice sheet over the past millions of years and derived forecasts for the future from these findings - each depending on different scenarios for emissions of greenhouse gases.
According to this, the concentrations of the greenhouse gas carbon dioxide (CO₂) in the atmosphere were last around 3 million years ago at a level similar to that of today, i.e. over 400 ppm (parts per million particles).
At that time, the temperatures were 2 to 4 degrees Celsius higher than today - i.e. about as high as forecast for the end of this century. However, the sea level was 10 to 25 meters higher than today. This was also due to the retreat of the ice on Greenland and in West Antarctica. However, sediment analyzes of the seabed around East Antarctica indicate that this part of the world also contributed several meters to the sea rise at the time.
And 400,000 years ago, after global warming of 1 to 2 degrees, the ice sheet probably retreated by about 700 kilometers - which caused sea levels to rise by 3 to 4 meters. For comparison: According to the Intergovernmental Panel on Climate Change (IPCC), the average global temperature has risen by around 1.1 degrees since the beginning of industrialization.
"The key lesson from the past is that the East Antarctic Ice Sheet is very sensitive to even relatively modest warming," said co-author Nerilie Abram of the Australian National University in Canberra. "It's not as stable and protected as we used to think."
In other words, if greenhouse gas emissions remain high, this ice sheet alone could raise sea levels by 1 to 3 meters by 2300 and by 2 to 5 meters by 2500. Already, studies indicate that parts of the ice sheet like Wilkesland are losing ice.
The team admits that the current understanding is not sufficient to predict at which threshold values parts of the ice sheet will lose their stability. But if we manage to keep global warming below 2 degrees, the sea level rise caused by the East Antarctic Ice Sheet will remain well under one meter in the coming centuries. "The fate of Earth's largest ice sheet rests largely in our hands," the team concludes.
The study uses the most recent data and models to make predictions about the future of East Antarctica, says Robert Larter of the British Antarctic Survey, who was not involved in the work.
In view of the long periods of time over centuries, the predictions are associated with great uncertainties. However, they underscored the region's potential to raise sea levels by several meters with sustained high levels of greenhouse gas emissions.
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