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 Antarctica is a key to sea level rise, which threatens coastal areas
around the world.. It has enough ice to raise seas by 57 meters (190
feet) if it ever all melted, meaning that even a tiny thaw at the
fringes is a concern.
Until now, the exact cause of the collapse of the Larsen-B ice
shelf, a floating mass of ice bigger than Luxembourg at the end of
glaciers in the Antarctic Peninsula, had been unknown. Some experts
suggested it was thinned by sea water from below.
Writing in the journal Science, a team of scientists blamed rising
air temperatures, saying that melt water and rain in the brief
Antarctic summer had flowed into deep cracks.
Water expands when it turns to ice, and the re-freezing meltwater in
the Larsen-B shelf - perhaps 200 meters thick - led to a build-up of
huge pressures that shattered the ice in 2002.
A rival theory had been that warmer sea water had destabilized ice
where the shelf was grounded on the seabed. Studying the seabed,
however, the scientists found evidence that water had flowed freely
under the ice for the past 12,000 years.
"This implies that the 2002 Larsen-B Ice Shelf collapse likely was a
response to surface warming," they wrote. Since 2002, several other
shelves have broken up around the Antarctic Peninsula, which is
below South America.
WARNING SIGN
The Larsen-B captured the public imagination and even featured in a
Hollywood disaster movie about climate change, "The Day After
Tomorrow", showing a huge crevasse appearing through a scientific
base on the ice.
"Hollywood underplayed that one," said Eugene Domack, an author of
the study at the University of South Florida. "It fractured into
thousands of icebergs, not just one huge crevasse."
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Loss of floating ice shelves does not directly affect sea levels but
can accelerate the slide of glaciers from land into the sea, raising
levels. Thursday's study was by scientists in Italy, the United
States, Portugal, Germany, Canada and Britain.
Domack told Reuters the findings could help scientists spot other
ice at risk of breaking up. Pools of summer meltwater on the surface
of ice shelves - visible from space - could be an early warning
sign, he said.
The northern part of the Larsen-C ice shelf, further south and four
times the size of the Larsen-B shelf, has been showing signs of
instability, he said.
Scientists have linked warmer air over the Antarctic Peninsula to
climate change and to a thinning of the ozone hole that shields life
from cancer-causing solar rays, driven by man-made chemicals.
A U.N. report on Wednesday said that the ozone layer is showing its
first signs of recovery after years of depletion, in a rare piece of
good news about the environment.
(Editing by Alison Williams)
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