The mass loss is equally distributed between increased iceberg production, driven by acceleration of Greenland's fast-flowing outlet glaciers, and increased melt water production at the ice sheet surface. Recent warm summers further accelerated the mass loss to 273 Gt per year (1 Gt is the mass of 1 cubic kilometer of water), in the period 2006-2008, which represents 0.75 mm of global sea level rise per year.
The Greenland ice sheet contains enough water to cause a global sea level rise of seven meters. Since 2000, the ice sheet has lost about 1500 Gt in total, representing on average a global sea level rise of about half a millimeter per year, or 5 mm since 2000.
At the same time that surface melting started to increase around 1996, snowfall on the ice sheet also increased at approximately the same rate, masking surface mass losses for nearly a decade. Moreover, a significant part of the additional melt water refroze in the cold snow
pack that covers the ice sheet. Without these moderating effects, post-1996 Greenland mass loss would have been double the amount of mass loss observed now.
"It is clear from these results that mass loss from Greenland has been accelerating since the late 1990s and the underlying causes suggest this trend is likely to continue in the near future. We have produced agreement between two totally independent estimates, giving us a lot of confidence in the numbers and our inferences about the processes," says co-author Jonathan Bamber from the University of Bristol.
Citation: Michiel van den Broeke, Jonathan Bamber, Janneke Ettema, Eric Rignot, Ernst Schrama, Willem Jan van de Berg, Erik van Meijgaard, Isabella Velicogna, Bert Wouters, 'Partitioning Recent Greenland Mass Loss', Science, November 2009, doi: 10.1126/science.1178176