Antarctic ice may be more stable than we thought

• New Scientist, 04 March 2011 by Jeff Hecht
• Magazine issue 2802. 

WHETHER Antarctica's ice will survive a warmer world is one of the great puzzles of climate science. Now it seems vast expanses of ice may have hung on for the past 200,000 years, surviving the last interglacial.

The west Antarctic ice sheet's base is below sea level, which should make it unstable. If it were to collapse the torrent of fresh water could raise global sea level by 5 metres. Whether or not this will happen as temperatures climb is a hotly debated topic.

A new study by David Sugden at the University of Edinburgh, UK, and colleagues suggests the ice sheet may be more stable than we thought. They studied the Heritage range of mountains near the central dome of the west Antarctic ice sheet. Specifically, the researchers looked at blue-ice moraines, where winds erode the ice in topological depressions, exposing the rocks beneath.

They analysed the moraine for beryllium isotopes produced by cosmic radiation, which accumulate in the rock when it is exposed. Sugden's team found evidence that the moraines had been forming for at least 200,000 years, suggesting that ice has covered the area for at least that long (Palaeogeography, Palaeoclimatology, Palaeoecology, DOI: 10.1016/j.palaeo.2011.01.027), and therefore survived the last interglacial 125,000 years ago.

Don't expect this to be the final word on the matter. A recent study by Robert Kopp at Princeton University (Nature, DOI: 10.1038/nature08686) suggests sea levels were 8 to 9 metres higher than now during the last interglacial, in part due to the west Antarctic ice sheet melting. If Sugden's team is correct, that amount of sea level rise would be unlikely.

Working out who is right is a "frustrating and intriguing scientific riddle that we'd love to unravel", says Richard Alley of Pennsylvania State University in University Park.

Even if the central parts of the ice sheet can survive a warming climate, melting is likely at the extremities, says Sugden. Tim Naish of Victoria University in Wellington, New Zealand, agrees. With melting at the edges and in Greenland, "we're looking at a rise of one metre plus or minus 0.5 metres" by 2100, he says - double the maximum predicted in 2007 by the Intergovernmental Panel on Climate Change.