The Greenland Ice Sheet recorded a new record ice loss in 2019. This was the conclusion of a team of international researchers through the evaluation of satellite observations and model data. At 532 billion tonnes, total losses were higher than in the previous record year of 2012, with a loss of 464 billion tonnes of ice. This corresponds to a global average sea level rise of 1.5 millimeters.

After two years of smaller losses in 2017 and 2018, the ice sheet is now on the path of increasing mass loss. The five biggest years of losses have occurred within the last ten years. The loss of ice exceeded the growth due to snowfall in 2019 by more than 80%. The study was published August 21, 2020 in the journal Communications Earth & Environment.

In order to determine the ice losses, the researchers from the Alfred-Wegener-Institute for Polar and Marine Science AWI, together with international partners, evaluated satellite data from the GRACE mission and its successor mission GRACE Follow-On (GRACE-FO). The satellites provide high-precision measurements from which monthly maps of the earth’s gravitational pull are calculated. Due to the redistribution of masses, the earth’s gravitational pull changes temporally and spatially, in Greenland, for example, due to ice losses in the oceans. The researchers compared the satellite data with simulations of regional climate models that specialize in mapping snowfall and melting of the ice sheet.

“After two years of ‘catching a breath’, mass losses have risen sharply again in 2019, surpassing all annual losses since 1948, probably even for more than 100 years,” says Ingo Sasgen, glaciologist at the AWI in Bremerhaven and lead author of the study. “More and more often we have stable high pressure areas above the ice sheet, which promotes the flow of warmer air from the middle latitudes and thus promotes melting. We have seen a similar pattern in the record year 2012 so far.”

The mass balance of a year results from the difference between ice increase due to snowfall and ice loss due to melting and calvings at the edge of the ice sheet. “In 2019, snowfall was lower than the long-term average; that also contributed to the record,” said Marco Tedesco, a columbia University professor and co-author of the study. “By comparing satellite data with regional climate models, we were able to see exactly which process was involved and which major weather conditions were decisive,” he adds.

The two satellite missions GRACE and GRACE-FO for the observation of the Earth’s gravity field are crucial for the continuous observation of greenlandic ice masses. Their measurements make it possible to quantify mass changes of the ice sheet in a monthly resolution. “The GRACEsatellite mission, which ended in the summer of 2017, provided us with essential observations on ice losses in polar regions over 15 years,” says Christoph Dahle, responsible for calculating the gravity fields from the raw data of both missions at the German Georesearch Center GFZ. “After a gap of about one year, we were able to successfully continue monitoring in the summer of 2018 with the GRACE-FOfollow-up mission.”

In the summer, the Arctic is warming about one and a half times the global average. In addition, there are various feedback effects that increase ice losses. “In 2017 and 2018, we had very cold and snowy years in Greenland,” says Sasgen. However, the GRACE/GRACE-FO data show that even in these years the mass balance was negative due to the strong emissions of glaciers calving in the sea.

Heiner Kubny, PolarJournal

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