Satellite images and computer model output of ice melt analysed by an international research team, including scientists from the University of Sheffield, have revealed that 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.
The finding, observed on a sector of the ice sheet that terminates on land rather than in the ocean, will help scientists improve predictions of how quickly Greenland’s ice will be lost in a warming climate.
Until recently, experts thought that 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 that in recent decades, ice movement in some areas that terminate on land has slowed down rather than accelerated. The discovery suggests that further increases in ice melting, fuelled 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 in an 8000km2 area of Greenland over three decades.
They found that, despite a 50 per cent rise in meltwater from the ice surface in recent years, overall movement in the past 10 years was slower than in previous decades.
The study showed this was caused by large amounts of meltwater produced in summer producing channels at the base of the ice sheet, which drain away water efficiently, slowing the glacier’s movement the subsequent winter.
Scientists say more research is needed to understand the movement of other parts of the ice sheet which terminate in the ocean and have seen acceleration in recent decades.
Professor Edward Hanna, from the Department of Geography at the University of Sheffield, said: “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 study, published in Nature, was carried out in collaboration with the University of Edinburgh and Université Savoie Mont-Blanc in France.
Andrew Tedstone of the University of Edinburgh’s School of GeoSciences, who led the study, said: “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.”