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 Editorials | Environmental | March 2008 
Massive Chunk of Antarctic Ice Shelf Collapses
 Seth Borenstein - Associated Press
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| | March 27, 2008 | A section of Antarctica's massive Wilkins Ice Shelf disintegrates under the impact of global warming. The collapse of the shelf was triggered on February 28 when an iceberg measuring 25.5 by 1.5 miles broke off its southwestern front. (Jim Elliott/British Antarctic Survey) | | |
A chunk of Antarctic ice bigger than the city of Montreal has suddenly collapsed, putting an even greater portion of glacial ice at risk, scientists said Tuesday.
Satellite images show the runaway disintegration of a 414-square-kilometre chunk in western Antarctica, which started Feb. 28. It was the edge of the Wilkins ice shelf and has been there for hundreds, maybe 1,500 years.
This is the result of global warming, British Antarctic Survey scientist David Vaughan said.
Because scientists noticed satellite images within hours, they diverted satellite cameras and even flew an airplane over the ongoing collapse for rare pictures and video.
"It's an event we don't get to see very often," said Ted Scambos, lead scientist at the National Snow and Ice Data Center in Boulder, Colo. "The cracks fill with water and slice off and topple. … That gets to be a runaway situation."
Although icebergs naturally break away from the mainland, collapses like this are unusual, but have been happening more frequently in recent decades, Prof. Vaughan said. The collapse is similar to what happens to glass when it is smashed with a hammer, he said.
The rest of the Wilkins ice shelf, measuring more than twice the size of Prince Edward Island, is holding on by a narrow beam of thin ice. Scientists worry that it too might collapse. Larger, more dramatic ice collapses occurred in 2002 and 1995.
Prof. Vaughan had previously predicted the Wilkins shelf would collapse about 15 years from now. The part that recently gave way makes up about 4 per cent of the overall shelf, but it's an important part that can trigger further collapse.
There's still a chance the rest of the ice shelf will survive until next year because this is the end of the Antarctic summer and colder weather is setting in, Prof. Vaughan said.
Scientists said they are not worried about a rise in sea level from the latest event, but say it's a sign of worsening global warming.
Such occurrences are "more indicative of a tipping point or trigger in the climate system," said Sarah Das, a scientist at the Woods Hole Oceanographic Institute.
"These are things that are not re-forming," Dr. Das said. "So once they're gone, they're gone."
Climate in Antarctica is complicated and more isolated from the rest of the world.
Much of the continent is not warming and some parts are even cooling, Prof. Vaughan said. However, the western peninsula, which includes the Wilkins ice shelf, juts into the ocean and is warming. This is the part of the continent where scientists are most concerned about ice-melt triggering sea-level rise.
Cracking Up: The Ice Shelf as Big as Northern Ireland
Steve Connor - The Independent UK
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It is one of the biggest in Antarctica and, for the past century, the massive Wilkins ice shelf appeared to have escaped the ravages of global warming. But now, enormous cracks have appeared in this floating ice platform the size of Northern Ireland. Scientists say it is breaking apart at an unprecedented rate after warmer temperatures weakened it.
A thin strip of ice is all that now prevents the Wilkins shelf from disintegrating and breaking away from the landmass of the Antarctic peninsula, scientists said yesterday. The peninsula is the fastest-warming region in the Antarctic and has seen some of the largest temperature rises on earth - 0.5C per decade - which is why the Wilkins ice shelf is on the verge of disappearing completely, said one of the scientists.
Observers at the British Antarctic Survey (BAS) in Cambridge and the US National Snow and Ice Data Centre in Colorado said they were astonished to discover just how fast the ice shelf was breaking apart since the first cracks were seen in February.
"Wilkins is the largest ice shelf yet on the Antarctic peninsula to be threatened, said David Vaughan of the BAS. "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.
"In this case things are happening more rapidly than we thought. We didn't really understand how sensitive these ice shelves are to climate change," said Dr Vaughan, who predicted in the 1990s that it would take 30 years for the ice shelf to break up.
Ice shelves form along the coasts and, because the ice is already floating on water, their disintegration does not affect sea levels. However, scientists believe that their rapid disappearance could lead to the faster movement into the ocean of the massive, land-based ice sheets and glaciers - which do raise sea levels.
The Wilkins ice shelf covers an area of about 5,282 square miles and satellite images taken at the end of February revealed that the rapid disintegration began after an iceberg the size of the Isle of Man broke away from its western edge.
Ted Scambos, of the snow and ice data centre, spotted the development and alerted colleagues at the BAS in Cambridge, who immediately dispatched a Twin Otter reconnaissance aircraft to map the Wilkins ice shelf with aerial photographs.
"I had never seen anything like this before - it was awesome," said Jim Elliott, who was on board the aircraft. "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, looked as though they've been thrown around like rubble - it was like an explosion."
Dr Scambos said: "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 a break-up... the collapse underscores that the Wilkins region has experienced an intense melt season. Regional sea ice has all but vanished, leaving the ice shelf exposed to the action of waves."
Several ice shelves on the peninsula have retreated in recent years and six of them - the Prince Gustav Channel, Larsen Inlet, Larsen A and Larsen B, the Wordie, Muller and the Jones ice shelves - have collapsed completely.
The Wilkins ice shelf is important because it is farther south on the Antarctic peninsula, where temperatures are generally colder than at the northern tip. "Climate warming in the Antarctic peninsula has pushed the limit of viability for ice shelves further south - setting some of them that used to be stable on a course of retreat and eventual loss," Dr Vaughan said.
"The Wilkins breakout won't have any effect on sea level because it is floating already, but it is another indication of the impact that climate change is having on the region."
The two biggest ice shelves in Antarctica - the Ross and the Ronne - lie on the edges of the Antarctic mainland farther south and so far show no signs of melting, Dr Vaughan added. |
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