By Mike Collett-White

LONDON (Reuters) - The sudden collapse of a huge shelf of Antarctic ice into the sea, described by scientists as "staggering," reignited fears on Wednesday of global warming (news - web sites) and its catastrophic knock-on effects.

Photos Reuters Photo

About 500 billion tons of ice known as the Larsen B shelf has disintegrated over the last month, the result of 50 years of sharp temperature rises on the Antarctic Peninsular unmatched elsewhere on the icy continent and in the rest of the world.

The British glaciologist tracking the movement of ice on the Earth's southern tip said the link between the shifting shelf and global climate change was not proven and that the dramatic events of recent weeks need not give people sleepless nights.

"A prime candidate is global climate change, but there are other reasons why the climate in that area may have changed, including ocean currents and atmospheric circulation," said David Vaughan of the British Antarctic Survey.

"What we've seen in the last month is the final phase of the collapse of that ice shelf. It may not be driven by climate change, but was structural," he told Reuters, adding that the collapse did not affect sea levels because the shelf was afloat.

But Vaughan said eroding ice shelves could affect mainland ice sheets over time, raising the specter of rising ocean levels.

"There are ice shelves which do help control the sea level," he said. "The question is, when we are looking far into the future -- decades and centuries -- how long will those big shelves remain intact?"

Environmentalists said the sudden erosion in a remote part of the world was symptomatic of a broader problem -- the world is getting warmer with potentially catastrophic results.

WORRYING SIGNS

"It is hard to attribute each case like this to man-made activity, but we can say that such changes are consistent with global warming and what is predicted in the future," said Friends of the Earth (news - web sites) climate campaigner Kate Hampton.

"There is a high probability that this (shelf collapse) has something to do with global warming and this is something we expect to see more of. We are extremely concerned about it."

Britain's Meteorological Office predicted that global temperatures will rise between 2.52 degrees Fahrenheit and nearly 10.8 degrees Fahrenheit (1.4 degrees Celsius and nearly six degrees Celsius) by the end of the century, depending on the policies adopted by governments to cut down on greenhouse gas emissions.

"The worst case scenario would be catastrophic," a Met Office spokesman said.

Temperatures rose by between 1.08 degrees Fahrenheit and 1.26 degrees Fahrenheit (0.6 and 0.7 degrees Celsius) over the last 150 years.

"There is very strong reason to believe that in the last century on top of natural changes there have been man-made additions," Vaughan said.

The implications of a sharp rise in temperatures are apocalyptic, according to environmentalists.

"Everybody will suffer in some way or another," Hampton said. "Temperatures will rise, there will be more intense precipitation, the increased risk of floods and landslides, changes in disease patterns and crop productivity."

She called on industrialized nations, notably the United States which has rejected the Kyoto Protocol (news - web sites) on greenhouse gas emissions, to heed the warning signs and cut pollution.

President Bush (news - web sites) rejected the pact, saying it would hurt the economy. He has offered an alternative voluntary plan to slow the growth of emissions of harmful gases.

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