Maria Stenzel)
Researchers say that what happens at the cold “ends” of the world can have a significant impact in their hot middle: The ice losses in the Arctic and in the Antarctic will together contribute to significant climate change in the Earth’s tropical belt, according to their model calculations. Accordingly, the forecast ice loss at both poles is linked to warming of the tropical oceans as well as more rain and stronger winds.
Ice loss is dramatic: in the past four decades, Arctic sea ice has shrunk to an ever smaller area in the summer months – since 1979 it has almost halved. At the other pole, there is now also a clear decline: Between 2017 and 2018, researchers recorded record values for the annual minimum ice cover. As development continues with sustained high greenhouse gas emissions, models predict that the first ice-free summer will come in the Arctic in the middle of this century and that by 2100 the Antarctic may lose half of its sea ice cover.
In previous studies, researchers have already shown that dwindling ice surfaces can have a significant impact on the weather. Because of the changes in radiation absorption, there is a shift in the energetic balance in the atmosphere. So far, the focus has been on developments in the Arctic. It became clear how complex the climatic processes are in regions of our planet, some of which are far apart. Model simulations in connection with the Arctic ice losses showed that the influences of the air currents and thus also the ocean currents in the far north can have far-reaching effects that affect the tropical regions of the earth.
The effect of the Antarctic has so far been unclear
So far, however, little has been done to investigate how massive ice loss in the Antarctic could affect distant climatic events, say the researchers led by Mark England from Columbia University in New York. As part of their study, they have now simulated the effects of the ice loss in Antarctica forecast by the end of the century using the most modern modeling methods, which include both atmospheric and effects on currents in the oceans. They compared the effects with those of ice loss in the north and investigated the extent to which the ice losses at both poles could have an additive effect on the climate in the tropical region.
The model simulations show that the changed conditions due to the reduced sea ice cover lead in the case of the Antarctic to similar far-reaching effects as in the Arctic. The forecast sea ice loss for the end of the century in the tropics would therefore result in considerable warming in the upper troposphere, increased surface warming in the eastern Pacific and increased rainfall. The models also show that the influences from the north and the south will add up. It is becoming apparent that the polar ice losses create unusual wind patterns in the Pacific, which suppress the upward movement of cold deep water.
Polar ice losses work together on tropical weather
Combined, the sea ice losses in the Arctic and Antarctic make up 20 to 30 percent of the projected tropical warming and precipitation changes in the high-emission scenario, the scientists write. Specifically, this means that the loss of ice at both poles will lead to additional heating of the surface water at the equator of 0.5 to 0.9 degrees Celsius and to more than 0.3 millimeters more rain per day.
As the researchers emphasize, these effects can in turn be linked to other effects. For example, it is known that the warming of surface water in the eastern equatorial Pacific is a well-known characteristic of the El Niño pattern. This notorious climate phenomenon in turn means that heavy rains often occur in North and South America, while drought strikes Australia and other countries in the western Pacific.
“Through our study, we were able to show that ice loss at both poles is crucial for understanding future climate change in the tropical region,” summarizes England. “We also hope that our pioneering work will motivate other scientists to investigate the effects of Antarctic sea ice loss on the climate system in more detail,” said the scientist.
Source: University of California – San Diego, technical article: Nature Geoscience, doi: 10.1038 / s41561-020-0546-9