Big Part of an Antarctic Ice Shelf Breaks Off; Whole Mass Periled

Satellite pictures show that a big section of an Antarctic ice shelf has broken off and the whole mass may now rapidly crumble, Colorado researchers said Thursday.

A team at the University of Colorado at Boulder’s National Snow and Ice Data Center said a section about 25 miles long and 3 miles wide had broken off the Larsen B Ice Shelf.

“This is the biggest ice shelf yet to be threatened,” researcher Ted Scambos said. “The total size of the Larsen B Ice Shelf is more than all the previous ice that has been lost from Antarctic ice sheets in the past two decades.”

The researchers said their pictures seemed to confirm earlier studies by the British Antarctic Survey that predicted the 4,800-square-mile ice shelf, about the size of Connecticut, was nearing its limits of stability.

Last year, the environmental group Greenpeace released pictures it said showed the ice shelf was about to break up.

Ice shelves are thick plates of floating ice surrounding portions of Greenland and Antarctica. Fed by glaciers and snowfall, some are up to half a mile thick.

The Colorado scientists said the Larsen B shelf had shrunk so much that it could no longer brace itself against the rocky peninsulas and islands that flanked it, and the whole shelf could now disintegrate.

Scientists say global warming has been steadily shrinking the Antarctic ice shelves. Regional temperatures have risen an average of 4.5 degrees Fahrenheit since the 1940s.

“Ice shelves appear to be good bellwethers for climate change, since they respond to change within decades, rather than the years or centuries sometimes typical of other climate systems,” Scambos said.

However, some scientists say there is evidence the changes caused by global warming are also causing other Antarctic ice shelves to grow. They say they doubt melting shelves will significantly raise overall ocean levels.