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“Suddenly,” says Ricarda Winkelmann, “it went dark in front of the cabin window.” That was in December 2010, the German research icebreaker “Polarstern” had just reached the edge of the ice shelf at Atka Bay in Antarctica. There she moored the expedition “ANT-XXVII / 2” to supply the research station “Neumayer III”. It was the first time that the young researcher saw the southern continent with her own eyes.
After long maneuvers, the crew found a place where the ice only protruded 20 meters from the water, where personnel and supplies could be left. “If you consider that only a tenth of the ice shelf can be seen above the water level, you get an idea of the dimensions of Antarctica,” says Winkelmann, who works at the Potsdam Institute for Climate Impact Research ( PIK).
A small part of the ice in Antarctica floats like an ice shelf in the ocean, most of it is found in the interior of the continent as a packet up to 4800 meters thick on land, for more than 30 million years. The ice of the southern continent stores more than half of the fresh water on earth. If it were to thaw completely, the global sea level would rise by around 58 meters. Of course, that would be a very long-term extreme scenario that, hopefully, won’t happen.
However, Antarctica might have some surprises in store for humanity. Together with his colleagues, Winkelmann calculates in the specialized journal “Science” how much the ice will melt with certain temperature increases and contribute to the rise in sea level. “There are a number of self-reinforcing effects in Antarctica,” warns Winkelmann in an interview with SPIEGEL.
If the temperature rises two degrees compared to pre-industrial times, simulations suggest that larger parts of the West Antarctic ice sheet will collapse. This is due to the warm water of the ocean, which attacks the ice shelf areas from below. This also causes glaciers on land to slide, which in turn carries ever larger amounts of ice to the sea, where they in turn melt.
Accelerating processes
“The 2 degree scenario in particular shows how dramatically sea levels can rise with this warming,” confirms Thomas Ronge of the Alfred Wegener Institute (AWI), who was not involved in the study. “Two and a half meters of sea level rise due to Antarctica alone is huge.”
With a plus of four degrees, the eastern marine areas of the continent would also be affected by the loss of ice, warns Winkelmann. In the long term, this would lead to a level rise of around 6.5 meters worldwide. At six degrees of warming, the advantage would be around 12 meters: at this time, there would be additional acceleration processes on the surface of the ice sheet.
So far, this effect is only known in Greenland; in the case of Antarctica, it has yet to be in the public eye. In short, according to Winkelmann, a vicious cycle would occur: if the ice melted on the surface and entered lower layers, it would come into contact with warmer layers of air. As the researcher describes, the effect can also be felt when hiking in the mountains. When you go down, it’s hotter and hotter. The same is true in Antarctica. As the surface of the ice continues to sink, it melts further, and so on.
The increase has increased tenfold since 2006
Winkelmann and his colleagues deliberately make no statement about how long it would take for a certain Antarctic region to melt. One thing is clear: even if the process can take hundreds of years, the corresponding amount of COtwo in the atmosphere that ultimately triggers this loss of ice, we could arrive in the near future. One point is important to the researchers: “We are showing that certain processes will cease to be reversible at some point,” says Winkelmann. Once a tipping point is reached, the ice inexorably melts. “What we are losing from Antarctica is now lost forever,” says co-author Anders Levermann.
However, the amount of greenhouse gases that humanity still emits is important, explains his colleague Winkelmann. “Ultimately, the additional warming determines how fast the sea level rises.” Antarctica is currently raising the water level by about half a millimeter per year. For one thing, that doesn’t sound like much. On the other hand, the value has multiplied by ten since 2006.
Meanwhile, the world heads to the highest COtwo-Value in the air for 3.3 million years. The mark should be reached by the middle of the century. Furthermore, a team led by Thomas Slater from the University of Leeds recently warned in the journal “Nature Climate Change” that the ice sheets in Greenland and Antarctica are currently losing as much ice as only worst-case climate scenarios can predict.
