Global warming blamed as huge Antarctic ice shelf collapses

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Tuesday, March 19, 2002 - Web posted at 9:20:54 am GMT

Global warming blamed as huge Antarctic ice shelf collapses

AUCKLAND, March 19 (AFP) - In what is being touted as the biggest event of its kind in 30 years, an Antarctic ice shelf has collapsed and broken up into thousands of icebergs, US experts said Tuesday in a new alarm over global warming.

An area of 3,250 square kilometres (1,300 square miles) of the Larsen B ice shelf, off the Antarctic Peninsula's eastern coast, has shattered over a 35-day period, the US National Snow and Ice Data Center said.

And with continued warm summers, other ice shelves are on the brink of collapse, the NSIDC warned.

That would portend increased flows of glacial ice from Antarctica and a rise in global sea levels, endangering low-lying land areas.

On its website (www.nsidc.org), the University of Colorado-based center said the Larsen B, a 720-billion-ton block of ice which could be as old as 12,000 years, began to disintegrate on January 31.

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

The center said the rate of warming was around 0.5 degrees Celsius (32.9 Fahrenheit) per decade, and the trend could be observed back at least to the late 1940s.

NSIDC researcher Ted Scambos said the ice disintegrated because of the presence of ponded meltwater on the surface in late summer as the climate warms. Meltwater fills smaller cracks in the shelf and its weight fractures the ice mass.

In an earlier study, Scambos and others writing in the Journal of Glaciology said they believed other ice shelves may be closer to breaking point than previously thought.

"The shelf retreats that have occurred so far have had few consequences for sea-level rise, but break-ups in some other areas like the Ross Ice Shelf could lead to increases in ice flow off the Antarctic and cause sea level to rise," Scambos said.

He added: "The findings provide a solid link between climate warming and the recent extensive disintegration of some Antarctic ice shelves. The process can be expected to be more widespread if Antarctic summer temperatures continue to increase."

It had previously been believed Antarctica was always very cold and stable, but summertime temperatures were just a few degrees below what the researchers believe is the threshold for surface "ponding" and subsequent ice-cracking events.

The NSIDC 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."

The largest ice shelf in the world is the 500,000 square kilometre (200,000 square mile) Ross Shelf south of New Zealand.

Scambos said that area would have to be watched very carefully now.

"If we begin to get significant water ponding there, and the shelf is eventually destroyed, we would likely have ice pouring off the Antarctic at a much faster rate. That would increase sea level significantly." - Nampa-AFP





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