ST. LOUIS -- Warmer temperatures over the past decade have sped up the march of Greenland's southern glaciers to the Atlantic Ocean, where the ice and water they spill contribute more to the global rise in sea levels than previously thought.
Those faster-moving glaciers now dump in a year twice as much ice into the Atlantic as they did in 1996, researchers said yesterday. The resulting icebergs, along with increased melting of Greenland's ice sheet, could account for nearly 17 percent of the estimated one-tenth of an inch annual rise in global sea levels, or twice what was previously believed, said Eric Rignot of the National Aeronautics and Space Administration's Jet Propulsion Laboratory in Pasadena, Calif.
''It's likely that Greenland is going to contribute more and faster to rising sea levels than previously estimated," Rignot told reporters at the annual meeting of the American Association for the Advancement of Science. A report by Rignot and Pannir Kanagaratnam of the University of Kansas appears today in the journal Science.
An increase in surface air temperatures appears to be causing the glaciers to flow faster, albeit at the still-glacial pace of 8 to 9 miles a year at their fastest clip, and to discharge increased amounts of ice into the Atlantic, the researchers said.
That stepped-up flow accounted for about two-thirds of the net 54 cubic miles of ice Greenland lost in 2005. That compares with 22 cubic miles in 1996. The most recent volume is more than 200 times the amount of fresh water used by Los Angeles in a year, Rignot said.
Rignot and Kanagaratnam said their report is the first to include measurements of recent changes in glacier velocity in the estimates of how much ice Greenland is losing.
Gino Casassa, who studies glaciers at Chile's Centro de Estudios Cientificos, called the study a major finding because it may expand the understanding of shrinking glaciers in Antarctica, Patagonia, Alaska, and elsewhere around the globe. Previous studies have only hinted that increased flow rates played such a prominent role, Casassa said.
Rignot and Kanagaratnam believe warmer temperatures boost the amount of melt water that reaches where the glaciers flow over rock. Extra water lubricates the rivers of ice and eases their downhill movement toward the Atlantic. The pair tracked the speeds of the glaciers from space, using satellite data collected between 1996 and 2005.