THE collapse of an Antarctic ice-shelf that is the size of Cambridgeshire has caused a surge in the flow of the region’s glaciers, with potentially grave consequences for global sea levels.

New research by Nasa scientists has revealed that nearby glaciers began to flow up to eight times more quickly after the break-up of the Larsen B ice-shelf on the Antarctic Peninsula, which cast 500 billion tonnes of ice into the Weddell Sea two years ago.

The discovery suggests that global warming could bring significant rises in sea levels much more quickly than was generally thought, as inland glaciers course into the ocean at ever faster rates.

Larsen B, which covered 1,255 square miles, disintegrated over the course of 35 days in 2002 in an event attributed by most scientists to global warming. The Antarctic Peninsula has warmed by more than 2.5C (4.5F) over the past 50 years and the shelf’s neighbour, Larsen A, collapsed in 1995.

The break-up of the 650ft-thick shelf did not itself have an impact on the sea level, as it was already floating on the ocean, but experts predicted that it might remove a vital “brake” on the flow of onshore glaciers that would contribute to sea-level rise, were they to melt into the sea.

This effect has now been confirmed by two Nasa studies, which used satellite images to chart the flow of the region’s glaciers. Scientists compared a series of photographs of five glaciers taken in 2000, before the collapse of Larsen B, and again in 2003, tracking the movement of crevasses on their surface to calculate their speed of flow.

Both studies, details of which are published today in the journal Geophysical Review Letters, found evidence of sharp acceleration. The Hektoria, Green and Evans glaciers were flowing eight times faster in 2003 than in 2000, while the Jorum and Crane glaciers had doubled in speed by early 2003. All five glaciers are among those whose path to the sea was previously “blocked” by Larsen B.

Adjacent glaciers that are held up by other ice-shelves that remain showed no significant increase in flow rate.

Eric Rignot, of the Nasa Jet Propulsion Laboratory in Pasadena, California, who led one of the studies, said:

“Glaciers in the Antarctic Peninsula accelerated in response to the removal of the Larsen B ice-shelf.

“These two papers clearly illustrate, for the first time, the relationship between the ice-shelf collapses caused by climate warming and accelerated glacier flow.”

Ted Scambos, of the US National Snow and Ice Data Centre in Boulder, Colorado, who led the second study, said: “We have seen 150 miles of coastline change drastically in just 15 years.”

The two papers suggest that there is an important relationship between climate change, the break-up of ice-shelves and the rate at which freshwater ice on the Antarctic mainland is transported to the sea. This means that, as temperatures around the continent rise, there may be a feedback effect in which ice is deposited into the sea at faster and faster rates. This is generally accepted to be the principal means by which climate change can affect sea level.

While the amounts of ice involved in the Larsen B break-up appear large, they are not sufficiently significant to have an appreciable effect on sea levels. As more ice-shelves melt and collapse, however, larger glaciers are likely to be affected, with more serious consequences.

The larger Ross ice-shelf, for example, is the main outlet for several glaciers that drain the West Antarctic ice-sheet, which contains enough water to increase global sea levels by more than 16ft.

The Larsen B shelf is thought to have been in existence for at least 400 years, and may have been there since the end of the Ice Age 12,000 years ago.

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