Huge Antarctic ice blocks slide into the sea

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Huge Antarctic ice blocks slide into the sea(Filed: 02/02/2005)British survey

team's discovery raises new fears about the rising level of the oceans, writes

Charles Clover

Vast ice blocks are slowly collapsing into the sea off Antarctica, increasing

the threat from the rising level of the world's oceans, British scientists said

yesterday.

Their discovery that the West Antarctic ice sheet is unstable overturns the

previous international consensus that it would take 1,000 years for the

floating ice to respond to rising temperatures. It is also likely to cause

increased concern about global fossil fuel emissions.

Scientists from the British Antarctic Survey said that far from gaining in mass,

as expected, because of increased snowfall in the polar regions, the West

Antarctic ice sheet was losing 250 cubic kilometres of ice a year.This means

Antarctica is contributing at least 15 per cent of the current 2mm annual rise

in sea levels.

Prof Chris Rapley, director of the survey, told an international conference on

climate change in Exeter called by Tony Blair: "The previous view was that the

West Antarctic ice sheet would not collapse before 2100. We now have to revise

that judgment. We cannot be so sanguine."

Four years ago, he said, the United Nation's international scientific panel on

climate change concluded that over a 100-year timescale the West Antarctic ice

sheet was very unlikely to collapse and more likely to gain mass because of

greater precipitation.

The panel concluded that Antarctica was "a slumbering giant". Prof Rapley said

the survey's discovery showed it was "a giant awakened".He said studies of the

Antarctic peninsula, which is much more accessible than the ice sheet, had

already shown that the collapse of floating ice shelves had acted like "a cork

pulled out of a bottle" and increased the flow of ice streams - larger than

glaciers - into the sea.

Several major ice sheets have broken off over the past decade.The Larsen A ice

shelf, 1,600 sq km in size, fell off in 1995. The Wilkins ice shelf, 1,100 sq

km, fell off in 1998 and the Larsen B, 13,500 sq km, dropped off in 2002.

Floating ice does not raise sea levels, but scientists began to look into

whether warm water from the sea might be causing the suspended ice to slide

faster into the sea.

Using satellite radar monitoring and a team presently on the shelf, one of the

most inaccessible places in the world, they found that the ice was indeed

discharging into the ocean at exactly the point that computer models had

predicted.

Prof Rapley said that the discharge in the area of instability was "substantial"

and there was evidence that it was a "relatively recent event". He added: "It

completely opens up the debate."It was not clear whether this was a natural

event or the result of global warming. "There is some speculation that warmer

water has encroached over the shelf."

If it was natural variability it might be expected to be taking place in only

one or two places, whereas it had been shown to be happening in all three major

ice streams in West Antarctica.Prof Rapley said: "There is more reason for

concern than there was five years ago."

The British scientists' findings are likely to form the basis of an even

stronger warning from the world's scientists in 2008 that man-made emissions

are causing the world to warm in ways that are dangerous to mankind.

There is no prospect for hundreds of years of more than a tiny fraction of the

five-metre sea level rise that a full melting of the suspended ice mass would

cause. But with many of the world's major cities either on the coast or on

estuaries, the discovery of a new source of sea level rise must be a cause for

concern.

However, as global temperatures rise, there is a 50 per cent chance of the Gulf

Stream "switching off", making Britain 5C colder, the conference was told.

Even with attempts being made to control the amount of carbon dioxide entering

the atmosphere, there is still a more than 25 per cent chance of the Gulf

Stream stopping.

Michael Schlesinger, of the University of Illinois, said there was a two in

three chance of a shutdown in the ocean's circulation within 200 years without

serious measures to tackle climate change.11 October 2004: Global warming clock

ticks faster20 March 2002: Giant ice sheet's break-up 'is a warning to world'2

February 2001: Melting of huge glacier 'is likely to raise seas'.

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