Satellite observations and a state-of-the art regional atmospheric model have independently confirmed that the Greenland ice sheet is loosing mass at an accelerating rate, reports a new study in Science. Collaborating on the paper were scientists from Utrecht University, the Netherlands Royal Meteorological Institute, Delft University of Technology, Bristol University (UK) and the Jet Propulsion Laboratory (USA).
The researchers used the Regional Atmospheric Climate Model (RACMO2/GR) at high (~11 km) horizontal resolution to calculate surface processes over Greenland, satellite radar measurements to determine iceberg production and ice sheet mass loss from the Gravity Recovery and Climate Mission (GRACE) satellites.
They found that the mass loss is equally distributed between increased iceberg production, driven by acceleration of Greenland’s fast-flowing outlet glaciers, and increased meltwater 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.
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.—Professor Jonathan Bamber, University of Bristol, co-author
The Greenland ice sheet contains enough water to cause a global sea level rise of seven metres. 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 meltwater refroze in the cold snowpack 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.
Michiel van den Broeke, Jonathan Bamber, Janneke Ettema, Eric Rignot, Ernst Schrama, Willem Jan van de Berg, Erik van Meijgaard, Isabella Velicogna, Bert Wouters (2009) Partitioning Recent Greenland Mass Loss. Science 326, 984. doi: 10.1126/science.1178176