On its website (www.nsidc.org) the University of Colorado-based center said a major part of the Larsen B ice shelf, believed to have been there for up to 12,000 years, had collapsed over a 35-day period.

1995 ======== Jan 31, 2002 ======== Feb 17, 2002 ======== Mar 5, 2002 ======== An Antarctic ice shelf the size of a small country has disintegrated under the impact of global warming, scientists said March 19, 2002. Although scientists at the British Antarctic Survey predicted four years ago the eventual disintegration of the giant Larsen B ice shelf -- 1,255 square miles and 655 feet deep -- they were astounded by the speed of the break up. This satellite image shows the progression of collapse of the Larsen shelf between 1995 and March, 2002. Pictured area is approximately 300x300 km. ( NASA-Modis-NSIDC-BAS via Reuters Reuters)

On the eastern side of the Antarctic Peninsula, due south of South America's Cape Horn, Larsen has been a centre of concern for several years and is believed to be suffering the effects of global warming.

The area that collapsed totalled 3,250 square kilometres (1,300 square miles).

It contained 720 billion tons of ice. Over the last five years the shelf has lost a total of 5,700 square kilometres (2,280 square miles), and is now about 40 percent the size of its previous minimum stable extent.

The center said the latest collapse of the 220-metre (733-foot) thick shelf began on January 31.

"The shattered ice formed a plume of thousands of icebergs adrift in the Weddell Sea," it said.

"This is the largest single event in a series of retreats by ice shelves in the Peninsula over the last 30 years. The retreats are attributed to a strong climate warming in the region."

It said the rate of warming was around 0.5 degrees Celsius (0.9 Fahrenheit) per decade, and the trend has been on since at least the late 1940s.

Around the Peninsula since 1974, NSIDC said, the seven ice shelves declined by a total of about 13,500 square kilometres (5,212 square miles).

It said the break up of the Peninsula ice shelves had little consequence for the global sea level but could affect the rate of ice flow off the continent.

"Ice shelves act as a buttress, or braking system, for glaciers," the center said. "Further, the shelves keep warmer marine air at a distance from the glaciers; therefore, they moderate the amount of melting that occurs on the glaciers' surfaces.

"Once their ice shelves are removed, the glaciers increase in speed due to meltwater percolation and/or a reduction of braking forces, and they may begin to dump more ice into the ocean than they gather as snow in their catchments.."

Last November the head of the Glaciological Division of the Instituto Antartico Argentino, Pedro Skvarca, warned of a possible break-up of Larsen, due to warm spring temperatures and a dramatic 20 percent rise in the rate of flow of the ice shelf.

An NSIDC researcher Ted Scambos said the ice disintegrates because of the presence of ponded melt water on the surface in late summer as the climate has warmed in the area.

Meltwater acts to enhance fracturing of the shelf by filling smaller cracks and forcing them through the thickness of the ice due to the weight of the water.

Copyright © 2002 AFP

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