The future of Antarctica on a warming planet has long been one of the great uncertainties in climate science.
The western part of that continent has a low-lying ice sheet that appears to be highly vulnerable to attack by warmer ocean water. Some signs suggest that the ice sheet is in the early stages of a collapse that could eventually have a profound effect on sea level.
The much larger, higher, colder ice sheet in eastern Antarctica is another story. Scientists have long thought that not only might it be stable in a warmer world, but it might even gain ice, as some computerized forecasts suggested. The idea was that a warmer atmosphere holding more moisture would lead to greater snowfall, but eastern Antarctica would still be cold enough to preserve that snow as glacial ice.
Some research even suggested that the gain might be enough to offset much of the water pouring into the ocean from melting ice elsewhere, helping to limit the rise in sea level.
Now a new study throws cold water, so to speak, on this notion.
The work, led by Ricarda Winkelmann and published in the journal Nature, comes from the Potsdam Institute for Climate Impact Research in Germany. Undertaking one of the most elaborate exercises yet in forecasting the future of the ice sheet, the researchers concluded that extra snowfall in Antarctica would speed up the flow of ice through the glaciers and ice shelves that ring the continent, which then dump it into the ocean.
In essence, the paper found, the increase of snowfall will steepen the gradient from the top of the ice sheet to the ocean. The ice will not just grow ever higher, however. Instead, the increasing weight will exert increased pressure on ice as it flows downhill toward the sea, causing it to speed up. Icebergs breaking off into the ocean at the mouth of glaciers, and extra ice flowing into floating ice shelves, will return much of the increased snowfall to the sea.
The paper suggests that this effect will not entirely offset ice gain over the study period, which extended to the year 2500, but will offset 30 to 65 percent of it, depending on the exact assumptions used to set up the computer modeling. Those numbers suggest that the eastern Antarctic ice gain will not be large enough to counteract the water that will probably be pouring into the ocean in coming centuries from the ice melting in Greenland and western Antarctica.
?We now know that snowfall in Antarctica will not save us from sea level rise,? one of the study?s authors, Anders Levermann, said in a statement. ?Sea level is rising ? that is a fact. Now we need to understand how quickly we have to adapt our coastal infrastructure, and that depends on how much CO2 we keep emitting into the atmosphere.?
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