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Antarctic ice shelves see another big breakup.

While government positions remained virtually frozen before the latest round of international climate talks in Buenos Aires, the icy continent of Antarctica continued its accelerated thaw - adding to concern over the region's potential to lift global sea levels. On October 15, the U.S. National Oceanic and Atmospheric Administration (NOAA) reported that an iceberg one-and-a-half times the size of Delaware had "calved" off from the Antarctica's Ronne Ice Shelf. With an area of 1,073 square kilometers (approximately 57 kilometers long and 19 kilometers wide), the iceberg - named A-38 - was the biggest to break off an ice shelf in the Southern Hemisphere since the loss of the 60-kilometer-long B-9 iceberg in the Ross Sea in October 1987. Both icebergs arc considered to be much larger than average.

The A-38 iceberg was discovered by scientist Mary Keller of the National Ice Center, who was examining satellite images of the region's ice shelves. Ice shelves are the massive sheets of snow and frozen water that surround and are connected to the Antarctic mainland ice mass. While the mechanics of ice shelf fracturing are not well understood, NOAA scientists believe that the calving of icebergs plays an important role in the disintegration of ice shelves, and is "a possible indicator of global warming."

The NOAA announcement coincided with the publication, in the journal Science, of new research into the effect of Antarctic ice sheet loss on global sea level rise. A research team led by Duncan Wingham of the University College of London reported findings, based on space satellite data, that the ice sheet had thinned by less than 1 centimeter per year between 1992 and 1996, and had contributed only 1.7 centimeters to the 18 centimeter sea level rise of the last century. The thermal expansion of warming sea water and the retreat of mountain glaciers are now thought to have had a larger impact on past sea level rise. Previously, as much as 14 centimeters of the increase had been attributed to Antarctica.

While in the past Antarctic ice shelves likely played a small role in rising sea levels, Wingham warns that this could change dramatically in the future. The main Antarctic ice mass is believed to be stable, but the West Antarctic ice shelf is not: the Science study also found that the Thwaites Glacier in west Antarctica has been thinning by 12 centimeters each year. According to Wingham, the collapse of the West Antarctic ice shelf, which included the A-38 iceberg, could raise worldwide sea levels by as much as 5 meters. Ice core samples from a research team led by G.D. Clow of the U.S. Geological Survey show that Antarctica is warmer than it has been during the last 4,000 years.
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Author:Dunn, Seth
Publication:World Watch
Date:Jan 1, 1999
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