Warming melts last stable edge of Greenland icesheet

The last edge of the Greenland ice sheet that had resisted global warming has now become unstable, adding billions of tonnes of meltwater to rising seas, scientists said on Sunday. In a study published in the journal Nature Climate Change, they said a surge in temperature from 2003 had eased the brakes on a long "river" of ice that flows to the coast in northeastern Greenland. Known as an ice stream, the "river" takes ice from a vast basin and slowly shifts it to the sea -- in the same way that the Amazon River drains water. In the past, the flow from this ice stream had been constrained by massive buildups of ice debris choking its mouth. But a three-year spell of exceptionally high temperatures removed this blockage -- and like a cork removed from a bottle helped accelerate the flow, the study said. The ice stream, called Zachariae, is the largest drain from an ice basin that covers a whopping 16 percent of the Greenland ice sheet. From 2003 to 2012, northeastern Greenland disgorged 10 billion tonnes of ice annually into the ocean, the study found. "Northeast Greenland is very cold. It used to be considered the last stable part of the Greenland ice sheet," said Michael Bevis, an Earth sciences professor at Ohio State University, who led the study. "This study shows that ice loss in the northeast is now accelerating. So, now it seems that all the margins of the Greenland ice sheet are unstable." Greenland is estimated to contribute 0.5mm (0.012 inches) to the 3.2 mm (0.13 inches) annual rise in global sea levels. The main tool in the study was data from a network of 50 Global Positioning System (GPS) sensors along the Greenland coast. The monitors use Earth's natural elasticity as a stethoscope of the ice sheet. Ice is heavy, so when it melts in massive quantities the land rebounds and the position of the sensors changes slightly. To get a wider picture, the GPS data was then overlaid with data from three US satellites and a European one that measured ice thickness from space. "The Greenland ice sheet has contributed more than any other ice mass to sea level rise over the last two decades and has the potential, if it were completely melted to raise global sea level by more than seven metres (22.75 feet)," said Jonathan Bamber, a professor at Britain's University of Bristol. "About half of the increased contribution of the ice sheet is due to the speedup of glaciers in the south and northwest. Until recently, northeast Greenland has been relatively stable. This new study shows that it is no longer the case."