Vast ice sheet in smithereens

An antarctic ice sheet almost the size of Cambridgeshire has collapsed after five years of disintegration caused by global warming, the British Antarctic Survey announced today.

The Larsen B ice sheet, 3,250 sq km in area, and at 200 metres about the same height as the cliffs of Dover, contained 500 million billion tonnes of ice attached to the Antarctic Peninsula.

It has disintegrated in the last month, according to surveys by British research ship the James Clark Ross, Nasa satellites and aerial surveys by Argentinian scientists.

The shelf has collapsed into small icebergs and fragments. It will not affect sea levels, but it might lead to further collapses, according to glaciologist David Vaughan of the British Antarctic Survey (BAS).

The collapse of the shelf is the latest drama in a region of Antarctica that has experienced unprecedented warming over the last 50 years.

Dr Vaughan said: "In 1998, BAS predicted the demise of more ice shelves around the Antarctic Peninsula. Since then warming on the peninsula has continued and we watched as, piece by piece, Larsen B has retreated. We knew what was left would collapse eventually, but the speed of it is staggering. It is hard to believe. The Peninsula has been warming at five times the average global rate."

He added: "There will be no immediate consequences of this that should worry us. But as an example of climate change, it should be very worrying. I think global warming will work like this, having big local effects - and the places in which this happens will really suffer."

During the last 50 years five ice sheets - floating extensions of the cap that covers the continent - have retreated as the Antarctic Peninsula has warmed by 2.5C until it is now warmer than at any time in the last 1,800 years, said Dr Vaughan.

But he said: "As [the ice sheet] is already floating the disintegration of Larsen will have no impact on sea level.

"Sea level will rise only if the ice held back by the ice shelf flows more quickly onto the sea. That will not happen just from this collapse. If others collapse, then perhaps over the next 50 or 100 years we may see that begin to happen."

But scientists are concerned that they still do not know the mechanism behind this exaggerated warming in the peninsula.

"It may be an amplification of global warming, and it could even be a change of current. We just do not know," said Dr Vaughan.