Science 337, 569–573 (2012)

Global warming is predicted to affect the Greenland Ice Sheet and lead to sea-level rise. Ice loss can be a result of surface melting exceeding snow accumulation (surface mass balance) or loss from the marine end, by iceberg calving causing accelerated movement, leading to thinning of the ice-sheet (dynamic loss). There were limited observations of ice-sheets available prior to this century, from which to track ice-sheet changes and their causes. Kurt Kjær, of the University of Copenhagen, Denmark, and co-workers used aerial photographs to produce digital elevation models for northwestern Greenland back to 1985. The models allowed analysis of thinning of the ice sheet. The results show two independent dynamic loss events during 1985–2010. These events seem to be the primary cause of ice-mass changes, rather than melting events. Future ice-sheet responses to climate change, and associated sea-level rise, will be difficult to predict until the cause of the dynamic loss events is resolved.