- New evidence strengthens fears that Antarctica
might be melting, threatening to raise sea levels and flood low-lying areas
around the world.
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- At worst, scientists say, global sea
levels might rise by about 20 feet over the next few centuries. Such a
disaster would drown many coastlines and submerge some Pacific islands.
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- Last month, in several articles in science
and nature magazines, scientists reported new data suggesting that parts
of the Antarctic ice are falling apart faster than once thought.
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- The main object of concern is the West
Antarctic Ice Sheet, or WAIS. It floats above water, like an extension
or "shelf" projecting from the Antarctic continent.
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- Among the scientists' findings:
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- Space satellites have detected Antarctic
ice changes that might, at worst, "be a first step toward the collapse
of the entire West Antarctic Ice Sheet," according to the July 24
issue of Science.
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- The European research satellites, known
as ERS 1 and ERS 2, use radar to map the distribution of ice in Antarctica.
The satellite data show that the so-called grounding line -- the boundary
between floating ice and ice atop the Antarctic continent -- "has
been retreating inland at a rate of more than a kilometer (0.6 mile) per
year," reports the Science article by Richard Kerr.
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- Why? "Presumably because the glacier
is losing mass by melting at its base," Kerr says. His article summarizes
research, published in the same issue, by Eric Rignot of the Jet Propulsion
Laboratory in Pasadena, Calif. Rignot was unavailable for comment.
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- The West Antarctic Ice Sheet is unstable
over geological time, judging by new evidence that it "wasted away
to a scrap" at some unknown time in the last 1.3 million years, according
to researchers in Sweden and Southern California.
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- The scientists base the finding partly
on fossilized marine organisms, diatoms, which they recovered from deep
within the West Antarctic ice. The find shows that the ice-covered area
was free of ice in the geological past.
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- The finding is reported in the July 3
issue of Science by Reed Scherer of Uppsala University in Sweden and Slawek
Tulaczyk of Caltech, and their colleagues.
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- "Now the question is when the WAIS
might disintegrate again as the world warms -- and how rapidly it might
flood low-lying coasts," says a Science story accompanying the Scherer
report.
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- Slick, fine-grained sediments beneath
Antarctic coastal ice might accelerate its outflow, speeding the rise of
global oceans, according to research published in the July 2 issue of Nature.
The researchers are at numerous universities and are led by R.E. Bell of
Columbia University.
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- Environmentalists have worried about
Antarctica's fate for decades.
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- In the 1970s, a few researchers warned
that "global warming" might melt part of the Antarctic ice sheet,
which is several miles thick. As a result, they said, sea levels could
rise globally.
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- Ever since, glaciologists -- scientists
who study the world's vast outcroppings of glacial ice, from Greenland
to Antarctica -- have warred over what's really happening in the southernmost
continent.
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- They fall into two camps. One argues
that Antarctic ice has been relatively stable over millions of years, and
is unlikely to undergo major collapse as the planetary temperature rises,
according to geophysicist Alan Cooper of the U.S. Geological Survey at
MenloPark, Calif.
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- Another camp, Cooper says, argues that
at least parts of the West Antarctic Ice Shelf are highly unstable, and
could rapidly fall apart during a major warming. By "rapidly,"
they mean a few centuries, extremely fast in geological terms.
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- Cooper -- who declines to side with either
camp -- says the public can learn more about Antarctic ice dynamics at
a Web site: www.usgs.gov/education/animations/.
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- While concerned by Rignot's observations,
experts caution against jumping to conclusions.
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- "Eric Rignot's observation does
not mean that the (Antarctic ice) collapse has started; it does not mean
sea level will be 20 feet higher in 100 years," says Richard Alley
of Pennsylvania State. "The easiest reason (for saying this) is that
he hasn't watched (the glacier) very long."
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- Conceivably, Alley said, the glaciers
might be undergoing some very dramatic, but normal, changes that are unrelated
to global warming.
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- "Glaciers do odd things sometimes.
They flow fast, then slowdown. ... You could anthropomorphize them and
say they have a mind of their own," says Alley, who calls for further
research.
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- The new evidence impresses at least one
veteran skeptic, Barclay Kamb, a noted glaciologist at Caltech.
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- Originally, Kamb said, "I was rather
skeptical of this idea of (Antarctic ice sheet) disintegration, it seemed
(to me) like a play for attention, like grandiosity."
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- But now, he says, the evidence for rapid
ice changes is good enough that the worst case scenarios are worth worrying
about.
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- If the ice sheet disintegrated, "sea
level would rise by about five meters, that is, about 20 feet," Kamb
says. "You'd produce a lot of these huge 'tabular' icebergs, some
as big as the state of Connecticut."
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- Scherer's work impresses John Barron,
a USGS-Menlo Park geologist who studies diatoms.
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- "I think (Scherer has) proven his
case" that the ice sheet changes substantially over time, Barron says.
"What has been lacking is direct evidence.
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- "And now he has provided direct
evidence that at some time in the last 1.3 million years, there was no
ice sheet over those sites."
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- Meteorologist Mark Fahnestock of the
University of Maryland at College Park thinks it's too early to say whether
the ice sheet is disintegrating over the centuries, or is just undergoing
routine variations in shape and size.
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- But if the ice continues to melt at high
speed, he says, "then maybe we will get to the point where we would
call it a warning signal."
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