Experts challenge ice shelf claim

BBC News 7 Feb 08;

Two scientists have claimed that climate change was not the only cause of the collapse of a 500bn tonne ice shelf in Antarctica six years ago.

The 656ft (200m) thick, 1,255 sq mile (3,250 sq km) Larsen B shelf broke apart in March 2002.

But Neil Glasser of Aberystwyth University and Ted Scambos of Colorado University claim in a new study that it had been on the brink for decades.

They argue that glaciological and atmospheric factors were also invoved.

In a paper published in the Journal of Glaciology, the pair say that when Larsen B collapsed it appeared to be the latest in a long line of victims of Antarctic summer heatwaves linked to global warming.

Researchers from the British Antarctic Survey predicted in 1998 that several ice shelves around the peninsula were doomed because of rising temperatures in the region, but the speed with which Larsen B went shocked them in 2002.



But Prof Glasser said the dramatic event was "not as simple as we first thought".

He acknowledged that global warming had a major part to play in the collapse, but emphasised that it was only one of a number of contributory factors.

"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," he added.

"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."

Dr Scambos, of the University of Colorado's national snow and ice data centre, said the ice shelf had probably been in distress for decades before its demise.

"It's likely that melting from higher ocean temperatures, or even a gradual decline in the ice mass of the peninsula over the centuries, was pushing the Larsen to the brink," he added.