Tuesday, March 25, 2008

Massive ice shelf on verge of breakup

  • A large chunk of the Wilkins ice shelf in Antarctica broke away last month
  • Only a narrow strip of ice is protecting the shelf from further breakup
  • "I didn't expect to see things happen this quickly," scientist says
  • Ice shelves are floating ice sheets attached to the coast

(CNN) -- Some 220 square miles of ice has collapsed in Antarctica and an ice shelf about the size of Connecticut is "hanging by a thread," the British Antarctic Survey said Tuesday, blaming global warming.

"We are in for a lot more events like this," said professor Ted Scambos, a glaciologist at the National Snow and Ice Data Center at the University of Colorado at Boulder.

Scambos alerted the British Antarctic Survey after he noticed part of the Wilkins ice shelf disintegrating on February 28, when he was looking at NASA satellite images.

Late February marks the end of summer at the South Pole and is the time when such events are most likely, he said. VideoWatch aerial footage of the area »

"The amazing thing was, we saw it within hours of it beginning, in between the morning and the afternoon pictures of that day," Scambos said of the large chunk that broke away on February 28.

The Wilkins ice shelf lost about 6 percent of its surface a decade ago, the British Antarctic Survey said in a statement on its Web site

Another 220 square miles -- including the chunk that Scambos spotted -- had splintered from the ice shelf as of March 8, the group said.

"As of mid-March, only a narrow strip of shelf ice was protecting several thousand kilometers of potential further breakup," the group said.

Scambos' center put the size of the threatened shelf at about 5,282 square miles, comparable to the state of Connecticut, or about half the area of Scotland. See a map and photos as the collapse progressed »

Once Scambos called the British Antarctic Survey, the group sent an aircraft on a reconnaissance mission to examine the extent of the breakout.

"We flew along the main crack and observed the sheer scale of movement from the breakage," said Jim Elliott, according to the group's Web site.

"Big hefty chunks of ice, the size of small houses, look as though they've been thrown around like rubble -- it's like an explosion," he said.

"Wilkins is the largest ice shelf on the Antarctic Peninsula yet to be threatened," David Vaughan of the British Antarctic Survey said, according to the Web site.

"I didn't expect to see things happen this quickly. The ice shelf is hanging by a thread -- we'll know in the next few days or weeks what its fate will be."

But with Antarctica's summer ending, Scambos said the "unusual show is over for this season."

Ice shelves are floating ice sheets attached to the coast. Because they are already floating, their collapse does not have any effect on sea levels, according to the Cambridge-based British Antarctic Survey.

Scambos said the ice shelf is not currently on the path of the increasingly popular tourist ships that travel from South America to Antarctica. But some plants and animals may have to adapt to the collapse.

"Wildlife will be impacted, but they are pretty adept at dealing with a topsy-turvy world," he said. "The ecosystem is pretty resilient."

Several ice shelves -- Prince Gustav Channel, Larsen Inlet, Larsen A, Larsen B, Wordie, Muller and Jones -- have collapsed in the past three decades, the British Antarctic Survey said.

Larsen B, a 1,254-square-mile ice shelf, comparable in size to the U.S. state of Rhode Island, collapsed in 2002, the group said.

Scientists say the western Antarctic peninsula -- the piece of the continent that stretches toward South America -- has warmed more than any other place on Earth over the past 50 years, rising by 0.9 degrees Fahrenheit each decade.

Scambos said the poles will be the leading edge of what's happening in the rest of the world as global warming continues.

"Even though they seem far away, changes in the polar regions could have an impact on both hemispheres, with sea level rise and changes in climate patterns," he said.

News of the Wilkins ice shelf's impending breakup came less than two weeks after the United Nations Environment Program reported that the world's glaciers are melting away and that they show "record" losses.

"Data from close to 30 reference glaciers in nine mountain ranges indicate that between the years 2004-2005 and 2005-2006 the average rate of melting and thinning more than doubled," the UNEP said March 16.

The most severe glacial shrinking occurred in Europe, with Norway's Breidalblikkbrea glacier, UNEP said. That glacier thinned by about 10 feet in 2006, compared with less than a foot the year before, it said.

CNN's Marsha Walton contributed to this report.

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Vast Antarctic Ice Shelf on Verge of Collapse

Andrea Thompson
LiveScience Staff Writer
LiveScience.com
Tue Mar 25, 6:11 PM ET

A vast ice shelf hanging on by a thin strip looks to be the next chunk to break off from the Antarctic Peninsula, the latest sign of global warming's impact on Earth's southernmost continent.

Scientists are shocked by the rapid change of events.

Glaciologist Ted Scambos of the University of Colorado was monitoring satellite images of the Wilkins Ice Shelf and spotted a huge iceberg measuring 25 miles by 1.5 miles (41 kilometers by 2.5 kilometers) that appeared to have broken away from the shelf.

Scambos alerted colleagues at the British Antarctic Survey (BAS) that it looked like the entire ice shelf - about 6,180 square miles (16,000 square kilometers - about the size of Northern Ireland)- was at risk of collapsing.

David Vaughan of the BAS had predicted in 1993 that the northern part of the Wilkins Ice Shelf was likely to be lost within 30 years if warming on the Peninsula continued at the same rate.

"Wilkins is the largest ice shelf on the Antarctic Peninsula yet to be threatened," he said. "I didn't expect to see things happen this quickly. The ice shelf is hanging by a thread - we'll know in the next few days and weeks what its fate will be."

Aircraft reconnaissance

The BAS scientists sent an aircraft out on a reconnaissance mission to survey the extent of damage to the ice shelf.

Jim Elliot, who captured video of the breakout said, "I've never seen anything like this before - it was awesome. We flew along the main crack and observed the sheer scale of movement from the breakage. Big hefty chunks of ice, the size of small houses, look as though they've been thrown around like rubble - it's like an explosion."

An initial iceberg calved away from the Wilkins Ice Shelf on Feb. 28. A series of images shows the edge of the ice shelf proceeding to crumble and disintegrate in a pattern characteristic of climate-caused ice shelf retreats throughout the northern Antarctic Peninsula. The disintegration left a sky-blue patch of hundreds of large blocks of exposed old glacier ice floating across the ocean surface.

Though these broken chunks of ice have spread into the sea, they won't raise sea levels because the ice shelf was already floating on the water.

By March 8, the ice shelf had lost just over 160 square miles (414 square kilometers) of ice, and the disintegrated ice had spread over 540 square miles (1,400 square kilometers). As of mid-March only a narrow strip of shelf ice between Charcot and Latady islands was protecting several thousand more kilometers of the ice shelf from potentially breaking up.

The region where the Wilkins Ice Shelf lies has experienced unprecedented warming in the past 50 years, with several ice shelves retreating in the past 30 years. Six of these ice shelves have collapsed completely: Prince Gustav Channel, Larsen Inlet, Larsen A, Larsen B, Wordie, Muller and the Jones Ice Shelf.

Antarctic warming

The Wilkins Ice Shelf was stable for most of the last century until it began retreating in the 1990s. A previous major breakout occurred there in 1998 when 390 square miles (1,000 square kilometers) of ice was lost in just a few months.

"We believe the Wilkins has been in place for at least a few hundred years, but warm air and exposure to ocean waves are causing it to break up," Scambos said.

The Antarctic Peninsula has warmed faster than anywhere else in the Southern Hemisphere; temperature records show that the region has warmed by nearly 3 degrees Celsius during the past 50 years - several times the global average and only matched in Alaska.

Other parts of Antarctica, including the East Antarctic Ice Sheet, seem to be more stable, though areas of melt have been observed in recent years.

Melting in the Antarctic is different than the recent record melt in the Arctic. Antarctica is composed of ice sheets, or huge masses of ice up to 2.5 miles (4 kilometers) thick that lie on top of bedrock and flow toward the coast, and ice shelves, the floating extensions of ice sheets. Arctic ice is primarily sea ice, some of which persists year-round and some of which melts in the summer and freezes again in the winter.

Video: Antarctic Ice Shelf Disintegration North vs. South Poles: 10 Wild Differences Images: Ice of the Antarctic

Original Story: Vast Antarctic Ice Shelf on Verge of Collapse

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