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Ice Shelf Break Up Antartica500 M B*

Large Antarctica ice shelf breaks up with surprising speed

Associated Press

Published Mar 20, 2002

An enormous floating ice shelf in Antarctica, which has existed since the last Ice Age 12,000 years ago, collapsed this month with staggering speed during one of the warmest summers on record in the region, scientists say.

Scientists stopped short of blaming the collapse on global warming caused by human activity. But they noted that the ice shelf had persisted through previous climate changes well before civilization began altering the environment.

"It's a profound event," said geologist Christina Hulbe of Portland State University. "This ice shelf has endured many climate oscillations over many thousands of years. Now it's gone."

Satellite images show that a piece of the Larsen Ice Shelf collapsed during a five-week period that ended March 7. It splintered into a plume of drifting icebergs.

The collapsed area was designated Larsen B. It is 650 feet thick and with a surface area of 1,250 square miles, or about the size of Rhode Island.

Larsen B is separate from a new, giant iceberg that satellites are tracking off Antarctica.

The Larsen ice shelf is on the Antarctic Peninsula and extends about 1,000 miles closer to the tip of South America than the rest of Antarctica.

In recent months, with the polar summer just beginning, temperatures were already creeping above freezing in the peninsula region. Scientists said there has also been a 50-year warming trend in the peninsula, which is considered a sensitive, early indicator of global climate change.

"We're seeing a very rapid and profound response by the ice sheet to a warming that's been around for just a few decades," said Ted Scambos, a glaciologist at the National Snow and Ice Data Center at the University of Colorado. The center has been monitoring the loss of ice in the Antarctic along with the British Antarctic Survey.

"We can use this as sort of a guide for what's going to happen if the rest of the Antarctic should begin to warm because of climate change," he said.

The Larsen Ice Shelf, which is now about 40 percent of its original size, has been under careful observation since 1995.

"We knew what was left would collapse eventually, but the speed of it is staggering," said David Vaughan, a glaciologist at the British Antarctic Survey. "Hard to believe that 500 million billion tons of ice sheet has disintegrated in less than a month."

Previous measurements showed the Antarctic Peninsula has warmed an average of more than 4 degrees Fahrenheit during the past half-century, a rate as much as five times faster than the global average.

But the overall climate picture in Antarctica is anything but consistent. In fact, glaciers elsewhere on the continent are both thickening and thinning as temperatures show conflicting climate trends.

Even larger ice shelves on the continent may be just a few summertime degrees away from the same fate as the Larsen shelf.

"Breakups in some other areas, such as the Ross Ice Shelf, could lead to increases in ice flow off the Antarctic and cause sea level to rise," Scambos said.

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