Greenland's glaciers losing ice at faster rate

Why is it happening?
Rignot said scientists still had much to learn about the dynamics of glacial ice movement under warming conditions.

One theory is that the meltwater serves as a lubricant for the moving ice, hastening its push to the sea. "This is a complex process, because we don't exactly know how the meltwater reaches the bed," Rignot said. "Some of [the glaciers] apparently accumulate this meltwater for quite a while before they start responding."

The scientists found that the speed-up has affected Southeast Greenland's glaciers since 1996, with glaciers further north speeding up after 2000. They speculated that the pattern was due to the northward spread of warmer temperatures in Greenland.

Effect on the climate debate
The latest report provides further ammunition for those who contend industrial greenhouse-gas emissions are causing higher global mean temperatures, with potentially alarming effects over the long term. However, some researchers note that other cyclical factors could be at work.

For example, weather patterns that vary on a scale of decades, such as the North Atlantic Oscillation, are known to affect Greenland's weather. Indeed, Los Alamos National Laboratory's Petr Chylek and his colleagues noted in 2004 that Greenland went through a rapid warming trend starting in the 1920s, which was followed by cooling temperatures.

But in a 2005 study, Chylek and Swiss researcher Ulrike Lohmann found that the North Atlantic Oscillation couldn't account for Greenland's current warming trend. They estimated that the warming rate in Greenland was 2.2 times faster than the global norm — which is in line with U.N. climate models.

Rignot agreed that Greenland has gone through warming trends in the past, including the rise in the 1920s.

"It's quite probably that the glaciers reacted to that, possibly in a similar way," he said. "The difference we have here is that the warming in the 1920s lasted less than a decade, and then it stopped. We have no indication from the climate record that things are starting to cool off. We are now entering a zone of warming that has not been experienced by the ice sheet over the last century."

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