Greenland is still covered by a kilometer-thick layer of ice, but climate change is already gnawing at its edges. In 2019, ice loss from the Greenland ice sheet reached new record levels, researchers are now reporting. 532 billion tons of ice thawed and poured into the sea this year – more than in at least 100 years. They alone raise the sea level by 1.5 millimeters. The new record confirms the increasing melting of this second largest ice reservoir on earth.
Only the Antarctic contains more ice than the Greenland ice sheet – the ice fields and glaciers of this huge island are correspondingly important for the global climate and also for sea levels. But climate change is causing the thick ice sheet of Greenland to melt more and more. According to studies, its melting rate has more than quadrupled in the past decade. Above all, the ice on the coastal glaciers is thinning and sliding faster and faster into the sea.
Strong burst of ice loss
Now there is new bad news: After the ice loss seemed to have stabilized a little in 2017 and 2018, there was another strong boost in defrosting in 2019. “After a two-year pause for breath, the mass losses rose sharply again in 2019 and exceeded all annual losses since 1948, probably for more than 100 years,” reports first author Ingo Sasgen from the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI ) in Bremerhaven. According to this, the Greenland ice sheet lost 532 billion tons of ice in 2019 – more than ever before.
The researchers determined the loss of ice using satellite data from the GRACE and GRACE Follow-On (GRACE-FO) missions. The satellite pairs in these projects measure the earth’s gravitational field and can thus also register the subtle gravitational pull exerted by large ice masses such as the Greenland ice sheet. Their measurement accuracy is so high that they also record changes in the mass balance of the Greenland ice sheet. Sasgen and his team combined the satellite data from the last 20 years with glaciological models and weather data to determine how much mass the Greenland glaciers gained through snowfall and how much they lost through melt.
Snow-poor winter and abnormally warm, sunny summer
In 2019, the gap between the gain and loss of ice was extremely wide: the loss of mass exceeded the increase due to snowfall by more than 80 percent. “In 2019 the snowfall was lower than the long-term average, which also contributed to the record,” explains co-author Marco Tedesco from Columbia University in New York. “By comparing satellite data with regional climate models, we were able to see exactly which process was involved, how much and which general weather conditions were decisive.” It was found that, in addition to the lack of snow supply, abnormally warm summers with high defrost rates drive the loss of ice.
“More and more often we have stable high pressure areas above the ice sheet, which favor the influx of warmer air from the middle latitudes and thus the melting”, reports Sasgen. That was also the case in summer 2019: A high pressure area lay over the ice sheet in such a way that the warming rays of the sun in the south could hit the ice unhindered. Because no insulating snow fell either, the ice surfaces thawed particularly quickly there. At the same time, the outer areas of the high pressure vortex transported warm and humid air from the Atlantic along the west coast of Greenland to far north. Because these high-pressure algae lasted a particularly long time, there was a drastic loss of ice.
Even if 2019 may have been extreme and the annual climatic conditions vary, in the opinion of many climatologists and glaciologists, the trend towards ever greater ice losses on Greenland is no coincidence or just a natural fluctuation. You see this as a clear symptom of climate change. On the one hand, the Arctic is warming around twice as fast and as strongly as the global average. On the other hand, however, changed wind currents mean that high pressure areas and warm air are increasingly pushing their way to Greenland and then staying there for longer. According to a study published a few days ago, this could tip the Greenland ice sheet into a new state of equilibrium, in which the ice loss is now permanently greater than the gain.
Source: Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research; Technical article: Communications Earth and Environment, doi: 10.1038 / s43247-020-0010-1