| Summary: | Understanding the mechanisms that drive the mass imbalance of the Greenland ice sheet (GrIS) is critical to the accurate projection of its contribution to future sea level rise. Greenland's ice mass loss has been accelerating recently. Using satellite Earth-gravity and regional climate model data, we show that the acceleration rate of Greenland ice mass loss from 2003 to 2012 is -13.9 +/- 2.0 Gt/yr(2), which results mainly from an increase of meltwater runoff (-6.3 +/- 1.1 Gt/yr(2)) and a decrease of precipitation (-4.8 +/- 1.1 Gt/yr(2)). Before the extreme surface melting in the summers of 2010 and 2012, the decrease of precipitation (-9.7 +/- 2.5 Gt/yr(2)) was a larger contributor to the ice mass loss acceleration than the increase of runoff (-2.1 +/- 2.2 Gt/yr(2)). Furthermore, we show that the North Atlantic Oscillation (NAO) is linked to the precipitation decrease during summer, and its recent influence to Greenland is anomalously large possibly due to the change in atmospheric circulation in the North Atlantic. These results indicate that inter-annual climate variability is playing a significant role in the recently observed Greenland ice mass loss acceleration, underscoring the difficulty of projecting future sea level rise based on the recent observations of GrIS mass loss. (C) 2015 Elsevier B.V. All rights reserved.
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