Greenland Ice Cap Melt Accelerating

The total 2000–2008 mass loss of about 1,500 gigatons is equivalent to 0.46 millimeters per year of global sea level rise, the scientists said.

This loss of mass 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.

Professor Jonathan Bamber from the Bristol Glaciology Centre at 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," said Bamber, a glaciologist who has done previous studies of the melting taking place in Antarctica.

A glacier off the coast of Greenland (Photo by Jonathan Bamber courtesy U. Bristol)

Mass budget calculations were validated with satellite gravity observations from the twin Gravity Recovery and Climate Experiment (GRACE) satellites, enabling the scientists to quantify the individual components of the recent Greenland mass loss.

The gravity variations that GRACE studies include changes due to surface and deep currents in the ocean and exchanges between ice sheets or glaciers and the oceans.

Warm summers in the period 2006-2008 have further accelerated the mass loss to 273 gigatons per year, said Bamber, explaining that one gigaton is the mass of one cubic kilometer of water.

This represents 0.75 millimeters of global sea level rise per year, he said.

If it all melted, the Greenland ice sheet contains enough water to cause a global sea level rise of seven meters (23 feet), Bamber said.

Since 2000, the ice sheet has lost about 1,500 gigatons in total, representing on average a global sea level rise of about half a millimeter per year, or five millimeters since 2000.

At the same time that surface melting started to increase around 1996, snowfall on the ice sheet also increased at about 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, Bamber explained, post-1996 Greenland mass loss would have been double the amount of mass loss observed now.

Scientists from NASA's Jet Propulsion Laboratory and from the Department of Earth System Science, University of California, Irvine are co-authors on the study along with scientists from three Dutch institutions: the Institute for Marine and Atmospheric Research at Utrecht University; the Delft Institute of Earth Observation and Space Systems at the Delft University of Technology; and the Royal Netherlands Meteorological Institute.

The study is published in the current issue of the journal "Science."

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