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.
This 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 kilometre of water), in the period 2006-2008, which represents 0.75 mm of global sea level rise per year.
Professor Jonathan Bamber from the University of Bristol and an author on the paper said: “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”.
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 millimetre 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.
These results are described in a paper in Science by scientists of Utrecht University, Institute for Marine and Atmospheric Research, in collaboration with colleagues from the Netherlands Royal Meteorological Institute, Delft University of Technology, Bristol University (UK) and the Jet Propulsion Laboratory (USA). They 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.
The paper: Partitioning Recent Greenland Mass Loss by Michiel van den Broeke, Jonathan Bamber, Janneke Ettema, Eric Rignot, Ernst Schrama, Willem Jan van de Berg, Erik van Meijgaard, Isabella Velicogna, Bert Wouters. Science, November 13 2009.
This work was funded by the Natural Environment Research Council.
J.S. Source: http://www.bristol.ac.uk