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interglacial (120,000 years ago), which was about 1°C warmer 

 than today, the West Antarctic ice sheet may have completely 

 disappeared. -*-8/ 



Several ice sheets that contain significant quantities of 

 water are thought to be vulnerable to warming. Thousands of 

 feet thick and resting mainly on land, these sheets are held 

 in place and prevented from entering the ocean by floating 

 "ice shelves" and pinnings below sea level. As global warming 

 occurs, the waters around these shelves and pinnings may become 

 warmer and melt them, allowing the ice sheets to begin to slide 

 into the oceans. Furthermore, meltwater that does not run off, 

 but percolates into the sheets and then refreezes, will tend to 

 soften the ice, making rapid movement of ice more likely. 

 Polar warming, which may be several times the magnitude of the 

 average global increase, thus makes it possible for "the bottle 

 to be uncorked." 



Because it is marine-based (resting on the ocean floor), 

 the ice sheet most vulnerable to such a deglaciation is the 

 West Antarctic ice sheet. If all of that ice enters the ocean, 

 sea level will rise five to six meters. Bentley has estimated 

 500 years, and Hughes 200 years, as the earliest time this 

 could possibly happen. 19/ Although both estimates were 

 made in the absence of detailed information about melting 

 rates, sea ice retreat, and ocean and air temperatures, the 

 possibility of a complete disintegration in 200 to 500 years 

 cannot be ruled out. 



