Ice mass changes in the Greenland Ice Sheet have been estimated since the early 1990s from the GRACE (Gravity Recovery and Climate Experiment) satellite gravity mission, of ice sheet thinning from satellite radar altimetry and airborne laser altimetry, and of increased velocities of outlet glaciers from radar interferometric surveys. Prior to 2000 existing altimetry data provides comparatively limited spatial resolution and ice losses near ice sheet margins are most likely underestimated and existing data is unable to document the persisting change within outlet glaciers. Subsequent estimates for the entire ice sheet show increased mass loss from 137 Gt/yr in 2002–2003 to 286 Gt/yr in 2007–2009. Also evidence from the GRACE, GPS (Global Positioning System), and ICESat (Ice, Cloud and land Elevation Satellite) as well as surface mass balance data suggests there is an ongoing northward migration of increasing dynamic induced ice loss. GRACE data show that this increased mass loss initiated in 2005 ceased in late 2009, thus, defining a dynamic thinning event as seen previous along the coast in southeast Greenland.

Here, we present a multi-decadal perspective on ice mass change from northwestern Greenland using the stereoscopic coverage by aerial photographs recorded in 1985, which captures the beginning of the present warming in the late 1980s. The derived Digital Elevation Model (DEM) based on the aerial photographs are superior in coverage and spatial resolution to other early surface change records with a 25 m grid resolution and vertical uncertainty of 4.1 m. Comparative DEMs were derived from laser altimetry data recorded in 2005 and 2010. Ice loss from the Greenland Ice Sheet (GrIS) can be partitioned into surface mass balance (SMB) processes (runoff and precipitation) and ice dynamics. For the marginal part of northwestern Greenland, we calculate a mass loss between 1985-2005 to 248 km3 and between 2005-2010 to 190 km3. The SMB contribute with respective 17 km3 and 63 km3 for the two periods. Therefore, dynamic thinning is the principal process associated with ice mass loss in northwestern Greenland, which is supported by ice front retreat data from the main outlet glaciers matching the thinning pattern. We further conclude, that dynamic thinning also occurred prior to 2005 - i.e. the latest thinning event in northwestern Greenland, implying that the south-north migration of recent mass-loss is not unprecedented and dynamic thinning is reoccurring in a multi-decadal pattern.