Climate change : The great melt and its consequences

In climate models is, among other things, how much the ice sheets are melting near the poles. Because it seems downright absurd that the possible consequences of the melting, in turn, have played to date in climate models. The melting end of the Antarctic and Greenland glaciers flowed into them as constant values. Although, there were studies that had about the local influence of melt water on sea currents to the subject.

But what an international team of researchers now presents it: The scientists refer to these ice sheets and changes in global calculations for the whole of the current century. Their modeling, which they publish in the journal "Nature", suggests that the melting of the ice sheets could have an immense impact on the climate of 2050.

combined, The climate model is used for policy decisions

Nicholas Golledge and his colleagues from the "Victoria University of Wellington" in new Zealand, high-resolution satellite resolution data of the ice melting in the last few years, with complex mathematical models, to simulate future scenarios on the Computer.

based on the the framework of the model, which is also the IPCC (Intergovernmental Panel on Climate Change, IPCC). There is a lot of variables and probabilities are involved, what is global advance is to say over several decades to centuries. Worldwide, these simulations serve as a Basis for political decisions on Climate. This is also the 1.5-degree target agreed in Paris.

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The researchers assumed for their calculation by 2100, a warming of three to four degrees Celsius compared to the pre-industrial era. This increase is not considered to be likely to occur if greenhouse gas emissions reduce drastically.

Antarctic ice sheets to melt irregular

According to the calculations, the fresh water passes through a slow melting of the ice sheets into the sea will affect the climate in several ways. As a model, the researchers modelled, such as the melting of the ice sheets in Greenland and the Antarctic will have an impact on the sea level. Thus, the Greenland ice sheet is likely to melt by the year 2100 rather evenly, while the Antarctic ice sheet will melt in the forecasts, first slowly, but later much faster.

This would have the consequence that the sea level rises each time with the same speed. According to the data of the scientists, the fastest increase between 2065 and 2075, it would be expected, under the condition that the emissions of greenhouse gases over the 21st century. Century will continue to increase.

melt-water slows down the sea currents

The scientists Nicholas Golledge describe a further feedback effect. The increasing melt water will weaken in a couple of decades of the Atlantic meridional overturning circulation (Atlantic Meridional Overturning Circulation, AMOC). This gigantic pump brings warm surface water from the tropics towards Europe and ensures the mild climate in this country.

The melt water of the ice sheets might work for this pump as the Sand in the gearbox. "It is the sinking of cold, and salt prevents water, which acts normally as a drive for the AMOC", says Torsten Albrecht from the Potsdam Institute for climate impact research. At the same time, the melt water forms a layer of insulation. Under this relatively warmer water accumulates to Depths of 400 to 500 meters. "A temperature increase of 0.1 degrees at this depth could increase the melting of the ice Shelf is enormous," says Albrecht.

Young sea ice in the Antarctic Bellingshausen sea. In the haze shreds above the water is "Sea Smoke". He...photo: Mark Brandon

This, in turn, would lead to more and more melt water is weakening the AMOC and the sea level continues to rise. But it should not be thought of as in a bath, in which the water level increases evenly, if water comes. While certain regions of the earth, such as some island States in the Pacific, would have a fighting stands, with significantly higher water, would sink in the vicinity of the ice sheets, the sea level is even, predict the authors. Also this is mainly due to the currents and the heat distribution in the ocean, explains Marilena Oltmanns, physical Ozeanologin at the Geomar Helmholtz centre for ocean research in Kiel.

Also, the air temperature is affected

But these currents not only have an impact on the sea level, but also on the temperature of the air. And these differ significantly between the Northern and southern hemisphere. While to be expected in the North-East of Greenland, and the Arctic and slightly higher temperatures compared to the reference year 2000, it came from a South latitude of approximately 40° to a marked cooling of the air, sometimes even up to four degrees Celsius, approximately over the Antarctic.

Central Europe have to be expected according to the data of the researchers with about a half a degree cooling. "But, it is important to note that only the influence of the ice sheets is described," says Oltmanns. The calculated temperature drop of half a degree must be in proportion to the greenhouse gas-induced temperature increase. This will balance the effect is probably more than.

"A warming of 1.5 degree must remain the goal,"

"Overall, the study clearly shows that the inclusion of the Change of the ice sheets has a strong influence on the global ocean circulation, sea-level rise and surface temperature," says Oltmanns. The results should be included in any case in future research activities. What specific changes would result from it, let them, however, difficult to derive. The sun is also a "coarse resolution" of the model used.

The advantage of this approach is in contrast to long periods of time capture, says Torsten Albrecht from the SPADES. "I think the study is very well done and their results are robust". So far, we have neglected the feedback effects that arise from the melting of the ice sheets, often. Now for the first time in this Form, examines the enormous impact of the melt water have on the global System.

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"The more we know, the better we understand how sensitive this System for change," says Albrecht. "Everything we have found so far, there had to be conservative assumptions." The researcher is sure that the new findings can also be found in the "Sixth progress report" of the IPCC's booth to enter, should appear at the beginning of 2021. For the policy, however, the existing target is in the future still valid: "We must continue to remain at 1.5 degrees warming."