A vast Antarctic ice shelf is in danger of collapsing after the ice bridge that pinned it to land shattered. The Wilkins ice shelf would be the largest slab of ice to be lost by Antarctica in recent times, in what researchers say is a sign of how global warming is reshaping the map of Antartica.

The shelf, almost half the size of Wales, is the tenth to break away or shrink to a fraction of its original size in the past 50 years.

David Vaughan, of the British Antarctic Survey (BAS), said that warmer conditions in the Antarctic Peninsula caused the ice bridge to melt and that it is likely to be linked to global warming. Temperatures in the peninsula have risen 3C (5.4F) in 50 years. “The ice shelves that have retreated over the last few decades are the ones we would have expected to retreat because of atmospheric climate change in Antarctica,” he said. “We are beginning to connect that to global changes.”

He said that he was amazed by the speed of the breakup of the ice bridge and the retreat of the ice shelf. “This one was a very extensive ice shelf until the 1990s when it started retreating.”

In the 1990s it measured 6,200 square miles (16,000km), since when it is thought to have retreated by at least half. If the remaining ice breaks up it will be the biggest collapse on record, dwarfing the break up of the 770 square miles of Larsen B in 2002.

The ice bridge holding the ice shelf to the Antarctic coastline and Charcot Island was 25 miles (40km) long but only 500 metres wide at its narrowest point – in 1950 it was 62 miles wide. It shattered over an area measuring 12.5 miles by 1.5 miles. “The ice bridge has collapsed,” said Professor Vaughan. “It has turned into hundreds, if not more, icebergs. It’s the rapidity with which this ice shelf broke up that’s surprising. It’s a significant change in terms of the map of Antarctica. Charcot Island will be a real island for the first time in history.”

BAS scientists suspected the breakup of the ice bridge was imminent and were able to monitor it using European Space Agency satelite images. A GPS beacon placed on the ice bridge in January revealed that there were movements of several yards every few days, and in the two weeks preceding the breakup these movements had speeded up.

With the Antarctic summer coming to an end and sea ice forming, the Wilkins ice shelf is likely to be locked in position intact for the next few months. Once winter in the southern hemisphere ends and temperatures start rising again it could float away from the continent and break up.

There is still a possibility that it will move into a position where it is protected, perhaps by grounding on an island. Professor Vaughan said: “The question is whether the rest of the ice shelf will break away. The chances are quite difficult to predict. My feeling is that we will lose more of the ice.”

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