OSLO – The West Antarctic ice sheet may start to collapse if sea temperatures rise by five degrees, triggering a thaw that would raise world ocean levels by five metres (16ft), US scientists say.
Such a rise in sea levels – taking thousands of years – would swamp many coasts and cities and wipe some lowlying Pacific islands off the map.
West Antarctica, the part of the frozen continent most vulnerable to climate change, has thawed several times in the past few million years, most recently 400,000 years ago, according to today’s edition of the journal Nature.
The study “suggests the western Antarctic ice sheet will begin to collapse when nearby ocean temperatures warm by roughly five degrees”, write David Pollard of Pennsylvania State University and Robert DeConto of the University of Massachusetts.
The study helps plug significant gaps in understanding Antarctica’s likely reaction to modern global warming by improving knowledge of the history of the ice.
Dr Pollard said the five-degree estimate for triggering a collapse was a rough guide, based on an computer model. The bigger East Antarctic ice sheet had not thawed in past warm periods studied.
The UN Intergovernmental Panel on Climate Change has projected a best estimate that global atmospheric temperature will rise by between 1.8 and four degrees by 2100 because of emissions of greenhouse gases that could give rise to floods, droughts, heatwaves and more powerful storms. Higher rises were possible unless the world reined in the growth of emissions, it said.
Ocean temperatures lag far behind the rise in air temperatures. “The required ocean warmings, of the order of five degrees, may well take several centuries to develop,” wrote Philippe Huybrechts of Vrije University in Brussels in a commentary.
“But such an outcome could result from the accumulation of total greenhouse-gas emissions projected for the 21st century, if emissions are not greatly reduced.” – (Reuters)