Satellite photos show that about 7 ? cubic miles of ice have eroded from the Antarctic ice sheet in the last 8 years, confirming that long-term changes are under way in the ice fields that cover the South Pole.
The ice sheet has shrunk mainly due to the speeded-up movement of an ice stream known as the Pine Island Glacier, which thinned by 30 to 36 feet during that period. "The Pine Island Glacier is the key," said Andrew Shepherd, a University College London geologist. "It is totally exposed to the sea, and people have identified it as the weak underbelly of the West Antarctica Ice Sheet.
"The thinning is 10 times greater than the rate of snowfall in the basin," he said. "The speed of the glacier means that much more mass is going out than is coming in."
Shepherd noted that if the present rate of change continues, the main stem of the Pine Island Glacier will be undercut by the sea and lifted up in about 600 years. When the glacier floats, it would cause a rise in sea level of 25 to 45 feet.
Antarctica contains about 7 ? million cubic miles of ice, which is about 84% of all the glacial ice on earth. If all this ice melted, it would cause a global sea level of about 240 feet, wiping out coastlines worldwide and ending the existence of many island nations.
The glacier "is moving faster than we thought," said Jane Ferrigno, a U.S. Geologic Survey geologist. "This doesn't mean it could have an effect on coastal areas around the world within the next few decades, but this is a yellow warning flag. This is an area that should be watched carefully."
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