Scientific Symposium Presentation Abstracts
September 19
Dr. Eric Rignot: Changes in the Greenland Ice Sheet and Implications for Global Sea Level Rise
Using satellite radar interferometry observations of Greenland, we detect widespread acceleration of glaciers in the last decade, which is rapidly expanding from south to north. Accelerated ice discharge in the west, and particularly in the east, doubled the ice sheet mass deficit from 90 cubic kilometers per year (about 22 cubic miles per year) to 220 cubic kilometers per year (about 53 cubic miles per year) in less than 10 years. This mass loss is larger than the excess discharge from Arctic rivers. It is equivalent to the yearly water consumption of 200 cities like Los Angeles. It represents 40 percent of Greenland’s annual accumulation, and is sufficient to raise global sea level by half a millimeter per year or 6 cm per century (about 2.4 inches per century). Yet it represents only a small fraction of the ice contained in Greenland. If all ice were removed, it would raise global sea level by more than 5 meters (over 16 feet).
Acceleration of glaciers is proceeding north. As more glaciers speed up in the northwest, the mass deficit could double again in the near future. We do not see any slow down or reversal of glacier acceleration, indicating the irreversible character of this evolution, which is unique in at least the last 50 years of Greenland’s glacial history.
Enhanced snowfall and enhanced ice/snow melt, which are both predicted by climate models in response to climate warming, matter less and less; the dominant control on the evolution of Greenland is determined by glacier flow. Models used to predict the future of Greenland in a warmer climate do NOT include variability in ice flow and therefore largely under-predict the contribution of Greenland to sea level rise. Despite these serious limitations, the Greenland ice sheet is projected to contribute 3-4 meters (about 10-13 feet) to global sea level rise over the next 1000 years as a result of projected changes in climate. In the light of recent observations of glacier behavior in Greenland, this time scale of 1,000 years must be revised downwards significantly. Making reliable predictions of the Ice Sheet’s evolution, however, remains a major challenge due to limitations in observations of key processes taking place at the glacier beds, and the need to develop a new generation of ice sheet models that more fully represent all processes being observed to play a role.
