Man-made climate change endangers the ice masses in the polar and mountain regions of the world. When they melt, this creates additional global warming. The mechanisms have been known for a long time. So far, however, it was unclear how large the effect of the various ice sheets is and what role feedback mechanisms play. Researchers have now quantified this using a simplified Earth system model. According to this, the melting of the ice will lead to additional global warming of around 0.43 ° C in the long term. Although the effects stretch over centuries or millennia, we set the course for them within a few decades.
The large ice surfaces at the poles and in mountain regions reflect some of the sunlight back into space and thus reduce the warming of the earth. However, since the late 1970s, for example, the ice surface that covers the Arctic Ocean in summer has shrunk by ten percent every decade. If this trend continues, the summer ice in the Arctic could have completely disappeared between 2030 and 2050, depending on the scenario. The situation is similarly bad for parts of the ice surface in the Antarctic, Greenland and in mountain glacier regions.
Sunlight is reflected less
Researchers led by Nico Wunderling from the Potsdam Institute for Climate Impact Research have now calculated what impact the melting of the ice sheets will have on further global warming. “When the global ice masses shrink, this changes how much of the sunlight that hits the earth’s surface is reflected back into space,” explains Wunderling. “The waning ice cover in the Arctic releases more of the darker sea water, which absorbs more energy. This is known as albedo feedback. It’s like wearing white or black clothes in summer. If you wear dark, you warm up more easily. “
There are also other effects: The melting ice increases the water vapor in the atmosphere. This in turn increases the greenhouse effect, similar to carbon dioxide (CO2). The basic mechanisms for these processes have long been known, but the Potsdam scientists were able to calculate for the first time the total warming that the global ice loss can trigger. They put the additional warming at 0.43 ° C if all four examined ice sheets melt. The proportion of individual ice sheets is 0.05 ° C for the West Antarctic Ice Sheet, 0.13 ° C for the Greenland Ice Sheet, 0.08 ° C for mountain glaciers and 0.19 ° C for the loss of summer ice on the Arctic Sea. These calculations are based on the assumption that the CO2 content of the atmosphere corresponds to that of today, i.e. around 400 ppm. Similar results were found for assumed CO2 concentrations between 280 and 700 ppm.
Long term effects
“It’s not a short-term risk. The earth’s ice masses are huge, which makes them very important for our earth system as a whole – this also means that their reaction to anthropogenic climate change, especially that of the ice sheets on Greenland and the Antarctic, unfolds over longer periods of time, “says Wunderling’s colleague Ricarda Winkelmann. “But even if some of the changes take hundreds or thousands of years, it is possible that we will trigger them within a few decades.”
In their computer simulation, the scientists also took into account complex interactions: For example, it is possible that the ground is covered with snow even after the massive ice sheets on land have melted. This would continue to reflect the sunlight and reduce the additional warming. In addition, the researchers differentiated between influences on the local and global climate. In the Arctic itself, the average warming can therefore be up to 5 ° C, in the equatorial region around 0.2 ° C. “Every tenth of a degree of warming counts for our climate,” says Winkelmann. “It is therefore more urgent than ever to avoid feedback loops and vicious circles.”
Source: Nico Wunderling (Potsdam Institute for Climate Impact Research) et al., Nature Communications, doi: 10.1038 / s41467-020-18934-3