- WASHINGTON (Reuters) -- Two Antarctic ice shelves have broken up more quickly
than anyone predicted, indicating that the effects of global warming may
be accelerating, scientists said on Wednesday.
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- They published satellite images showing
the Larsen B and Wilkins ice shelves in "full retreat," having
lost nearly 1,100 square miles (3,000 square km) of their total area in
the last year.
-
- Ted Scambos of the University of Colorado
at Boulder said his team and colleagues at the British Antarctic Survey
in Cambridge had predicted the break-up would happen, but not this quickly.
-
- "It happened much faster than we
thought," Scambos said in a telephone interview. "Within this
last calendar year we saw a retreat not only on Larsen but the Wilkins."
-
- The Larsen Ice Shelf is on the eastern
half of the peninsula, which is the part of the <http://www.cnn.com/NATURE/9904/08/antarctic.ice.reut/antarctica.lg.gif
Antarctic that sticks up toward Argentina. The Wilkins is on the southwest
side.
-
- Alarmed by findings
-
- "It was nearly as much activity
in a single year as we've seen in 10 or 15 years up to now on average,"
Scambos said.
-
- "To have retreats totaling 3,000
square kilometers in a single year is clearly an escalation," David
Vaughan of the British Antarctic Survey said in a statement.
-
- "Within a few years, much of the
Wilkins ice shelf will likely be gone."
-
- The researchers usually publish their
findings in scientific journals and have submitted their findings to the
Journal of Glaciology. But they were so alarmed by their findings that
they decided to publicize them.
-
- The effects will not be immediate. Ice
shelves are floating on the ocean, so they do not cause sea levels to rise
when they break up and melt.
-
- But Scambos said the glaciers behind
them could melt faster if the protective ice shelves disappear.
-
- "Other ice shelves have huge glaciers
behind them and large areas of ice to drain that are continental,"
Scambos said. That means the water locked up as ice in those glaciers would
add to the sea level.
-
- Sea level rising
-
- According to the U.S. Geological Survey,
global sea level has risen about 4 inches (10 cm) during the past century.
It says if all the Earth's glaciers melted, which is unlikely, sea levels
would rise by 260 feet (80 meters).
-
- Antarctica, the fifth largest continent,
contains about 90 percent of the world's glacial ice.
-
- Scambos thinks the satellite pictures
have helped explain why the ice shelves are melting.
-
- "Ice shelves are so large -- they
are a thousand feet (300 meters) thick and many square miles (km) -- that
warming at the top won't actually cause the ice to melt," he said.
-
- "What we think instead is going
on is that as these things crack naturally in the summer, the meltwater
goes into the cracks."
-
- Because the melted water is denser, it
forces the cracks to open even wider.
-
- "What we are seeing ... is an ice
shelf that is essentially shattered, already being swept out. There are
thousands of relatively small icebergs," he said.
-
- Scientists believe the Larsen B ice shelf
has existed for at least 400 years. But the local climate is inching toward
an average summertime temperature just above 32 degrees Fahrenheit (0 degrees
Celsius) -- the melting point of water.
-
- The British Antarctic Survey reports
an increase in mean annual temperature in the region of about 4.5 degrees
Fahrenheit (2.5 degrees Celsius) since the 1940s.
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