Variability in Greenland's glaciers.

One of the central claims made by those worried about global warming is that Greenland's glaciers are melting rapidly. The influx of fresh melt water into the ocean, they say, will catastrophically raise sea levels and shut down the Gulf Stream, causing extreme climatic shifts in Europe and elsewhere. Indeed, one of the criticisms environmentalists have leveled at the recent report released by the UN's Intergovernmental Panel on Climate Change (IPCC) is that it underestimates the rise in sea levels resulting from the disappearance of Greenland's glaciers. The IPCC doesn't "take into account the gorillas--Greenland and Antarctica," Ohio State University earth sciences professor Lonnie Thompson told USA Today on January 28. "I think there are unpleasant surprises as we move into the 21st century."

There are surprises, but so far they are not that unpleasant. One of the surprises is that the loss of mass has slowed for at least two of Greenland's major glaciers. In a paper published in the journal Science in early February, scientists Ian Howat of the University of Washington and two collaborators found that earlier accelerations in the loss of ice mass from the glaciers has been reversed. According to the paper's abstract, the "combined rate of mass-loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates" for the two glaciers studied.