Nature reports:
It took decades for global warming to slowly melt the surface of the Larsen B Ice Shelf on the Antarctic Peninsula, forming nearly 3,000 lakes. But at the end of the Antarctic summer of 2002, all the lakes drained away in the space of a week. And then the 2,700-square-kilometre ice shelf, which was some 220 metres thick and probably had existed for some 12,000 years, rapidly disintegrated into small icebergs, leaving glaciologists scratching their heads.
Antarctic Ice Shelf Collapse Blamed On More Then Climate Change;
Feb. 11, 2008 — When the Larsen B Ice Shelf in Antarctica collapsed in 2002, the event appeared to be a sudden response to climate change, and this long, fringing ice shelf in the north west part of the Weddell Sea was assumed to be the latest in a long line of victims of Antarctic summer heat waves linked to Global Warming.
However in a paper published in the Journal of Glaciology, Prof. Neil Glasser of Aberystwyth University, working as a Fulbright Scholar in the US, and Dr Ted Scambos of University of Colorado’s National Snow and Ice Data Centre now say that the shelf was already teetering on collapse before the final summer.
“Ice shelf collapse is not as simple as we first thought,” said Professor Glasser, lead author of the paper. “Because large amounts of meltwater appeared on the ice shelf just before it collapsed, we had always assumed that air temperature increases were to blame. But our new study shows that ice-shelf break up is not controlled simply by climate. A number of other atmospheric, oceanic and glaciological factors are involved. For example, the location and spacing of fractures on the ice shelf such as crevasses and rifts are very important too because they determine how strong or weak the ice shelf is”.
The study is important because ice shelf collapse contributes to global sea level rise, albeit indirectly. “Ice shelves themselves do not contribute directly to sea level rise because they are floating on the ocean and they already displace the same volume of water. But when the ice shelves collapse the glaciers that feed them speed up and get thinner, so they supply more ice to the oceans,” Prof. Glasser explained.
http://www.sciencedaily.com/releases/2008/02/080210100441.htm