Sunday, April 03, 2016

Climate Catastrophe, Coming Even Sooner?

[New Yorker] One of the first people to propose that climate change could result in rapid sea-level rise was an eccentric British geographer named John Mercer. A hesitant speaker in public, Mercer was less restrained in private. He was once arrested for jogging naked. It was said that he liked to do his fieldwork in the nude—a curious habit for a man who studied glaciers.
In a seminal paper published in 1968, Mercer proposed that the West Antarctic Ice Sheet, known in scientific circles as WAIS, was vulnerable to collapse. The reason, he wrote, was that the ice sheet rests on land that is below sea level. It is buttressed by floating ice shelves that extend far out to sea, but were these to disintegrate, Mercer wrote, then “changing horizontal forces” would cause the ice sheet to lift off its base. At that point, the sea would rush in and WAIS would start to warm from below as well as above. This would initiate the ice sheet’s demise, which would be “rapid, perhaps even catastrophic.” Several meters of sea-level rise would ensue.
More recent research has tended to confirm Mercer’s worst fears. The latest example comes from a study published Wednesday, in the journal Nature. “Antarctic Model Raises Prospect of Unstoppable Ice Collapse,” ran the headline in the news story that accompanied it.
The new paper, coauthored by Rob DeConto, of the University of Massachusetts at Amherst, and David Pollard, of Pennsylvania State University, arose out of frustration. The two researchers had spent years working on a computer model that did not seem to capture rises in sea level that were already known to have taken place. Before the last ice age, about a hundred and twenty thousand years ago, for instance, sea levels were at least twenty feet higher than they are now. But DeConto and Pollard found that unless they programmed the model with temperatures that were unrealistically high for that period it could not account for such levels.
Then the two got an idea from a colleague, Richard Alley, also of Penn State. Alley suggested that they look at what would happen if the floating ice shelves were lost. This would leave towering cliffs of ice exposed to the sea, which could make them vulnerable to rapid collapse. (A version of this process seems already to be under way in parts of Greenland.) Read More