The Greenland ice sheet has been losing mass at an accelerating rate since the early 1990s. A substantial part of the ice loss is driven by an increase in surface meltwater production that runs off to the ocean. In a study published today in Science Advances, researchers from Utrecht and Delft show that there is a large difference between mass loss in the North and South of Greenland, with runoff increasing twice as fast in North Greenland as in the South. The northern mass loss is triggered by a rapid snowline retreat in early summer, exposing dark bare ice and causing high runoff rates.
The Greenland ice sheet is the second largest ice mass on Earth. Totally melted, it has the potential to raise global sea-level by 7.4 meters. Along the ice sheet margins stands the ablation zone, where summer meltwater runoff exceeds the mass gain from winter snowfall. Historically, the widest ablation zone is found in the warm southwest, contributing one third of the ice sheet runoff total, whereas the North only contributes ~10% annually. After 1991, runoff has increased all over Greenland, but much more so in the North. In the summer of 2012, the ice sheet experienced extreme runoff of 560 km3, about two times the pre-1990s average. The frequency of such extreme melt years has increased over the past decades.