Greenland is melting faster than previous predictions suggested and is losing ice seven times faster than it was in the 1990s, according to the most complete picture of the country’s ice loss to date.
“On current trends, Greenland ice melting will cause 100 million people to be flooded each year by the end of the century, so 400 million in total due to all sea-level rise. These are not unlikely events or small impacts; they are happening and will be devastating for coastal communities,” said researcher Andrew Shepherd from the University of Leeds in a statement. Shepherd was one of 96 international polar scientists from a number of governmental agencies – including NASA’s Jet Propulsion Lab and the European Space Agency – to create the Ice Sheet Mass Balance Intercomparison Exercise (IMBIE).
Researchers turned to 26 different surveys to compute changes in the ice sheet between 1992 and 2018, assessing data from 11 different satellite missions that measured changes in ice volume, flow, and gravity. The team used regional climate models to show that half of the ice loss is a result of melting from rising air temperatures while the other half is due to increased glacier flows from rising ocean temperatures.
Since 1992, Greenland has lost 3.8 trillion tonnes of ice, which is enough to increase global sea levels by up to 10.6 millimeters (0.4 inches). Additionally, the annual rate of loss has risen from 33 billion tonnes in the 1990s to 254 billion tonnes within the last decade – a seven-fold increase. Ice loss peaked at 10 times the rates seen in the 1990s, resulting in a 335-billion-tonne loss in 2011. Since then, the average rate of ice loss has declined to an average of 238 billion tonnes per year.
However, the authors are quick to note that their data does not include numbers from 2019 and so may be limited.
“More satellite estimates of ice sheet mass balance at the start (1990s) and end (2010s) of our record would help to reduce the dependence on fewer data during those periods; although new missions will no doubt address the latter, further analysis of historical satellite data is required to address the former,” wrote the authors in Nature.
Greenland holds enough water to raise global sea level by 7.4 meters (24 feet). Fluctuations in ice flow to the ocean through glaciers and ice streams are due to variations in snow accumulation, meltwater runoff, ocean-driven melting, and iceberg calving. These can be exacerbated by air and ocean temperature increases. By 2100, the Intergovernmental Panel on Climate Change predicts that sea levels will rise by as much as 70 centimeters (27 inches) with Greenland expected to contribute between 5 and 16 centimeters (2-6 inches). An estimated 360 million people will be exposed to annual coastal flooding under this high-end climate warming scenario by the end of the century.