Thursday April 8 2:08 AM ET

Antarctic Ice Shelves Said Breaking Up Fast

By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - Two Antarctic ice shelves have broken up more quickly than anyone predicted, indicating that the effects of global warming may be accelerating, scientists said Wednesday.

They published satellite images showing the Larsen B and Wilkins ice shelves in ``full retreat'', having lost nearly 1,100 square miles of their total area in the last year.

Ted Scambos of the University of Colorado at Boulder said his team and colleagues at the British Antarctic Survey in Cambridge had predicted the break-up would happen, but not this quickly.

``It happened much faster than we thought,'' Scambos said in a telephone interview. ``Within this last calendar year we saw a retreat not only on Larsen but the Wilkins.''

The Larsen Ice Shelf is on the eastern half of the peninsula, which is the part of the Antarctic that sticks up toward Argentina. The Wilkins is on the southwest side.

``It was nearly as much activity in a single year as we've seen in 10 or 15 years up to now on average,'' Scambos said.

``To have retreats totaling 3,000 square kilometers in a single year is clearly an escalation,'' David Vaughan of the British Antarctic Survey said in a statement.

``Within a few years, much of the Wilkins ice shelf will likely be gone.''

The researchers usually publish their findings in scientific journals and have submitted their findings to the Journal of Glaciology. But they were so alarmed by their findings that they decided to publicize them.

Images can be seen on the Internet at: http://www-nsidc.colorado.edu/NSIDC/ICESHELVES/lars-wilk-news.

The effects will not be immediate. Ice shelves are floating on the ocean, so they do not cause sea levels to rise when they break up and melt.

But Scambos said the glaciers behind them could melt faster if the protective ice shelves disappear.

``Other ice shelves have huge glaciers behind them and large areas of ice to drain that are continental,'' Scambos said. That means the water locked up as ice in those glaciers would add to the sea level.

According to the U.S. Geological Survey, global sea level has risen about four inches during the past century. It says if all the Earth's glaciers melted, which is unlikely, sea levels would rise by 260 feet.

Antarctica, the fifth largest continent, contains about 90 percent of the world's glacial ice.

Scambos thinks the satellite pictures have helped explain why the ice shelves are melting.

``Ice shelves are so large -- they are a thousand feet thick and many square miles -- that warming at the top won't actually cause the ice to melt,'' he said.

``What we think instead is going on is that as these things crack naturally in the summer, the meltwater goes into the cracks.''

Because the melted water is denser, it forces the cracks to open even wider.

``What we are seeing ... is an ice shelf that is essentially shattered, already being swept out. There are thousands of relatively small icebergs,'' he said.

Scientists believe the Larsen B ice shelf has existed for at least 400 years. But the local climate is inching toward an average summertime temperature just above 32 degrees Fahrenheit-- the melting point of water.

The British Antarctic Survey reports an increase in mean annual temperature in the region of about 4.5 degrees Fahrenheit since the 1940s.