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)

Greenland isn’t 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 Greenland’s 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. Here’s 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. Read the rest...