There is a nice photo of Greenland on the story.
Greenlands Glaciers Take a Breather
By John Tierney
http://tierneylab.blogs.nytimes.com/2007/02/08/greenlands-glaciers-take-a-breather/Helheim Glacier in southeast Greenland, pictured in 2005, is one of the two glaciers that have slowed down in their flow to the sea. (Photo: NASA/Wallops)Greenland isnt melting as fast as we feared.
It was big news when the rate of melting suddenly doubled in 2004 as ice sheets began moving more quickly into the sea. That inspired predictions of the imminent demise of Greenlands ice and a catastrophic rise in sea level. But a paper published online this afternoon by Science reports that two of the largest glaciers have suddenly slowed, bringing the rate of melting last year down to near the previous rate. At one glacier, Kangerdlugssuaq, average thinning over the glacier during the summer of 2006 declined to near zero, with some apparent thickening in areas on the main trunk.
I asked the lead author of the paper, Ian Howat of the University of Washington, for some perspective. Heres his take:
Over the past few years there has been a major revolution in the way scientists think about ice sheet response to climate change. Previously, it was assumed that the big ice sheets react very slowly to climate, on the order of centuries to millenia. This is because surface melting and precipitation was thought to be the dominant way in which ice sheets gain and lose mass under changes in climate. However, over the past five years we have observed that the flow speed of the ice sheets, and therefore the rate at which the ice flows to ocean can change dramatically over very short time scales.
By short, he means months or less.
I also asked Dr. Howat about the argument that, since Greenland went through decades of relatively warm weather in the first half of the 20th century without catastrophic consequences, its unlikely that the glaciers are suddenly going to plunge into the ocean because of the current warming. His response:
Greenland was about as warm or warmer in the 1930s and 40s, and many of the glaciers were smaller than they are now. This was a period of rapid glacier shrinkage world-wide, followed by at least partial re-expansion during a colder period from the 1950s to the 1980s. Of course, we dont know very much about how the glacier dynamics changed then because we didnt have satellites to observe it. However, it does suggest that large variations in ice sheet dynamics can occur from natural climate variability. The problem arises in the
possibility that, due to anthropogenic warming, warm phases will become longer and more severe, so that each time the glaciers go through a period of retreat like this, they wont fully grow back and they will retreat farther the next time.
That sounds like a reasonable concern. But for now, with the glaciers moving in fits and starts, its wise not to make any sweeping predictions based on a few measurements. Although the Intergovernmental Panel on Climate Change was criticized for not incorporating the recent scary data from Greenland into its long-range projections, these new results seem to vindicate its caution. As Dr. Howat and his co-authors warn: Special care must be taken in how these and other mass-loss estimates are evaluated, particularly when extrapolating into the future because short-term spikes could yield erroneous long-term trends.
