If just 10 percent of the water locked in these frozen reservoirs is added to the oceans, geologists predict that sea levels will rise by more than 20 feet, drowning lowlying islands and inundating continental coasts. So far, these ice sheets have seemed to be stable and firmly anchored to islands and the nearby coasts, but new data indicate that they, too, are crumbling in the face of the thermal onslaught. Over the past 50 years, the Antarctic has warmed by about 4.5 degrees Celsius. In a 1978 article J. H. Mercer of Ohio State University predicted that if the south polar regions were warmed five degrees Celsius, the floating ice shelves surrounding the West Antarctic ice sheet would quickly disintegrate, flooding coastlines around the world in the process. Satellite images document that the Larsen B ice shelf in Antarctica has caved off more than 1,714 square kilometers of area since November 1998.
Dark areas are warmer, indicating open water.
Last October, Mercer's once controversial idea gained credibility when scientists at the National Oceanic and Atmospheric Administration's National Ice Center revealed satellite data showing a massive iceberg 92 miles long by 30 miles wide, with an area of 2,751 square miles, breaking free from the Ronne Ice Shelf in Antarctica. Surface features on the Larsen B indicate that it has existed for at least 400 years. But as climate inches toward an average summertime temperature just above the melting point of water, the Larsen and Wilkins ice shelves have begun to disintegrate. Images recorded by the Advanced Very High Resolution Radiometers on NOAA weather satellites show that the Larsen B ice shelf has begun to crumble rapidly after an initial retreat in the spring of 1998. On the opposite side of the Antarctic peninsula, the Wilkins Ice Shelf, which is nearly twice the size of Delaware, has retreated by nearly 1,100 square kilometers since early March 1998.