Greenland's ice mass loss has spread to the northwest

Past studies have found most of Greenland's ice mass loss had occured in the south. However, new research has been published (Khan 2010) examining the pattern of mass loss over the entire Greenland ice sheet (H/T to Riccardo). Satellite gravity data and Global Positioning System (GPS) measurements both find that mass loss has been spreading up along the northwest coast of Greenland, starting in late 2005. This increase in mass loss is shown most dramatically in this animation created by co-author John Wahr:

Ice mass loss from Greenland

GPS data is obtained by placing GPS receivers on bedrock adjacent to the ice sheet. As the massive Greenland ice sheet loses mass, the bedrock undergoes vertical crustal uplift. Bedrock near the Thule Air Base on Greenland's northwest coast rose by about 4 centimeters from October 2005 to August 2009. As accelerating ice mass loss causes accelerated crustal uplift, the observed uplift show strong agreement with the loss of ice mass measured by satellite gravity data. These observations indicate that the accelerated mass loss is dominated by the increasing velocity of outlet glaciers. Large glaciers in the north-west region are sliding downhill faster and dumping more ice in the ocean.

The GPS data provides yet another line of evidence that the Greenland ice sheet has been losing mass at a significant rate. Satellite radar altimetry and airborne laser altimetry have observed thinning near ice sheet margins. Radar interferometric surveys find that glaciers are sliding faster in the ocean. And the overall picture given by the satellite gravity data shows that mass loss of the entire ice sheet is still accelerating (Velicogna 2009).

What will happen to Greenland in the future? Various independent studies predict global sea level rise of around 1 to 2 metres by 2100, with Greenland being a significant contributor (Vermeer 2009, Pfeffer 2008). Models predict that at the rate we're emitting CO2, collapse of the Greenland ice sheet is likely within the next few centuries (Stone 2010). This is backed up by studies of earth's past history which find ice sheets are highly sensitive to warmer temperatures. Global temperatures just 1 to 2°C warmer than now saw sea levels over 6 metres higher than current levels (Kopp 2009).

Science is about piecing together the full body of evidence to improve our understanding. As more data comes in, we're now seeing many lines of evidence painting the same picture. The Greenland ice sheet is highly sensitive to warming temperatures and is likely to contribute sea level rise in the order of metres.

UPDATE 2 Apr 2010: Many thanks to Robert Simmon at NASA who pointed me in the direction of another instructive animation of ice mass loss from Greenland as measured by the GRACE gravity satellites:

Posted by John Cook on Tuesday, 30 March, 2010

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