EVERY 40 hours, the Greenland ice sheet loses a cubic kilometre of water as icebergs crash into the Atlantic. That鈥檚 the same amount of water as Los Angeles consumes in a year. The most detailed study yet of the 鈥渋ce balance鈥� of the world鈥檚 second largest ice sheet puts the total annual loss, after allowing for snowfall, at 220 cubic kilometres. That is more than twice the amount lost a decade ago.
鈥淭hese results absolutely floored us,鈥� says Eric Rignot of the California Institute of Technology in Pasadena, who led the study (Science, vol 311, p 986). 鈥淭he glaciers are sending us a signal. Greenland is probably going to contribute more and faster to sea-level rise than predicted by current models.鈥�
Virtually all the glaciers south of the Arctic circle have speeded up their discharges into the ocean, as a result of a regional warming of 3 掳C. That is the threshold beyond which glaciologists think the ice sheet may be doomed.
Advertisement
Much of the acceleration, Rignot says, is caused by meltwater penetrating crevasses and lubricating the glaciers鈥� flow. The ice is in effect sliding into the ocean on rivers of water. He warns that the models glaciologists are using to predict ice-flow rates do not include these physical processes.
