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Abstract

The Greenland Ice Sheet is a major contributor to global mean sea level rise, contributing about 20% to the global mean sea level rise since 1993. In recent years, ice losses from Greenland have accelerated, rising from 34 Gt yr^-1 in the 1990s to 244 Gt yr^-1 between 2016-2020. About a third of Greenland’s total ice losses come from the Northwest sector, which has experienced widespread retreat and thinning of its outlet glaciers. Here, we study the imbalance of the Northwest Greenland Ice Sheet with the aid of satellite altimetry, satellite gravimetry and the input-output method, from 1972 to 2022. Over the input-output record (1972-2019), the Northwest sector lost 1,200.7 ± 19.4 Gt of ice, contributing 3.3 ± 0.1 mm to sea level rise. While the rate of mass loss was of only 16.0 ± 0.9 Gt yr^-1 in 1972-2000, the pace of mass loss was more than twice as high rising to 36.8.5 ± 0.8 Gt yr^-1 in 2000-2010, before increasing further to 50.1 ± 1.0 Gt yr^-1 in 2010-2019 due to the combined effect of reduced surface mass balance and increased ice discharge. This acceleration in ice losses post 2000s is confirmed by the satellite gravimetry record (2002-2021), with a rate of mass loss of 55.1 ± 2.0 Gt yr^-1. Finally, thanks to the high spatial and temporal resolution of the CryoSat-2 altimetry record (2010-2022), we find that in 22 glacier basins, high thinning rates spread to more than 10 % of the area of these basins.