Why Some Of Greenland’s Ice Sheets Have Slowed Down

Despite dramatic increases in ice melt across Greenland in recent years, the speed of ice movement in some areas has slowed down rather than accelerated.

Scientists made the discovery using satellite images and computer models. They say large amounts of meltwater in summer produce channels at the base of the ice sheet, which drain away water efficiently, slowing the glacier’s movement the subsequent winter.

The discovery could mean parts of the ice sheet could be less vulnerable to climate change than was previously thought—which could have a small but beneficial effect on sea level forecasts.

Says Edward Hanna, a geography professor at the University of Sheffield:

“Our research underscores the complexity of the relation between climate change affecting Greenland and the response of its ice sheet to the ongoing warming. We need to understand these ice-climate interactions better in order to be able to make more reliable global sea-level predictions.

It is clearly not always a simple case of more icemelt resulting in faster-flowing ice, as was originally thought by some to be the case. On the other hand, there can be little doubt of the increasing contribution of mass loss from the Greenland ice sheet to global-sea-level rise over the last couple of decades and we cannot be complacent about further changes.”

The finding were observed on a sector of the ice sheet that terminates on land rather than in the ocean. Until recently, experts thought the increased volumes of meltwater from Greenland’s ice in response to climate warming would speed up the motion of all parts of the ice sheet by helping the ice slide more rapidly.

However, the latest study shows in recent decades ice movement in some areas that terminate on land has slowed down rather than accelerated. The discovery suggests further increases in ice melting, fueled by climate change, may further slow movement of these sectors of the ice sheet.

The team of scientists used satellite data to track the shift of ice features, such as crevasses, over three decades. They found, despite a 50 percent rise in meltwater from the ice surface in recent years, overall movement in the past 10 years was slower than in previous decades.

Scientists say more research is needed to understand the movement of other parts of the ice sheet that terminate in the ocean and have seen acceleration in recent decades.

“A large sector of the Greenland ice sheet has slowed down, despite sustained warming in the past decade. However, the ice sheet’s overall contribution to sea level rise continues to accelerate in two ways: through increases in surface melting and the movement of glaciers which terminate in the ocean,”

says study leader Andrew Tedstone of the University of Edinburgh’s School of GeoSciences.

Andrew J. Tedstone, Peter W. Nienow, Noel Gourmelen, Amaury Dehecq, Daniel Goldberg & Edward Hanna
Decadal slowdown of a land-terminating sector of the Greenland Ice Sheet despite warming
Nature 526, 692–695 (29 October 2015) doi:10.1038/nature15722

Photos: Andrew Sole/University of Sheffield