The New York Times (pg. F1)  [Printer-friendly version]
January 25, 2005

ANTARCTICA, WARMING, LOOKS EVER MORE VULNERABLE

By Larry Rohter

DATELINE: OVER THE ABBOTT ICE SHELF, Antarctica

From an airplane at 500 feet, all that is visible here is a vast white
emptiness. Ahead, a chalky plain stretches as far as the eye can see,
the monotony broken only by a few gentle rises and the wrinkles
created when new sheets of ice form.

Under the surface of that ice, though, profound and potentially
troubling changes are taking place, and at a quickened pace. With
temperatures climbing in parts of Antarctica in recent years, melt
water seems to be penetrating deeper and deeper into ice crevices,
weakening immense and seemingly impregnable formations that have
developed over thousands of years.

As a result, huge glaciers in this and other remote areas of
Antarctica are thinning and ice shelves the size of American states
are either disintegrating or retreating -- all possible indications of
global warming. Scientists from the British Antarctic Survey reported
in December that in some parts of the Antarctic Peninsula hundreds of
miles from here, large growths of grass are appearing in places that
until recently were hidden under a frozen cloak.

"The evidence is piling up; everything fits," Dr. Robert Thomas, a
glaciologist from NASA who is the lead author of a recent paper on
accelerating sea-level rise, said as the Chilean Navy plane flew over
the sea ice here on an unusually clear day late in November. "Around
the Amundsen Sea, we have surveyed a half dozen glaciers. All are
thinning, in some cases quite rapidly, and in each case, the ice shelf
is also thinning."

The relationship between glaciers (essentially frozen rivers) and ice
shelves (thick plates of ice protruding from the land and floating on
the ocean) is complicated and not fully understood. But scientists
like to compare the spot where the "tongue" of a glacier flows to
sea in the form of an ice shelf to a cork in a bottle. When the ice
shelf breaks up, this can allow the inland ice to accelerate its march
to the sea.

"By themselves, the tongue of the glacier or the cork in the bottle
do not represent that much," said Dr. Claudio Teitelboim, the
director of the Center for Scientific Studies, a private Chilean
institution that is the partner of the National Aeronautics and Space
Administration in surveying the ice fields of Antarctica and
Patagonia. "But once the cork is dislodged, the contents of the
bottle flow out, and that can generate tremendous instability."

Glaciologists also know that by itself, free-floating sea ice does not
raise the level of the sea, just as an ice cube in a glass of water
does not cause an overflow as it melts. But glaciers are different
because they rest on land, and if that vast volume of ice slides into
the sea at a high rate, this adds mass to the ocean, which in turn can
raise the global sea level.

Through their flights over this and other areas of Antarctica, NASA
and the Chilean center hope to help glaciologists and other scientists
interested in climate change understand what is taking place on the
continent and why. To do that, they need to compile data not only on
ice thicknesses but also the underlying geology of the region,
information that is most easily obtained from the air.

The flights are taking place aboard a Chilean Navy Orion P-3 plane
that has been specially equipped with sophisticated instruments. The
devices include a laser-imaging system that shoots 5,000 pulses of
light per second at the ground to map the ice surface, as well as ice-
penetrating radar to determine the depth of the ice sheets, a
magnetometer and digital cameras.

For most parts of Antarctica, reliable records go back less than 50
years, and data from satellites and overflights like the ones going on
here have been collected over only the past decade or so. But that
research, plus striking changes that are visible to the naked eye, all
point toward the disturbance of climate patterns thought to have been
in place for thousands of years.

In 1995, for instance, the Larsen A ice shelf disintegrated, followed
in 1998 by the collapse of the nearby Wilkins ice shelf. Over a 35-day
period early in 2002, at the end of the Southern Hemisphere summer,
the Larsen B ice shelf shattered, losing more than a quarter of its
total mass and setting thousands of icebergs adrift in the Weddell
Sea.

"The response time scale of ice dynamics is a lot shorter than we
used to think it was," said Dr. Robert Bindschadler, a NASA scientist
who is director of the West Antarctic Ice Sheet Initiative. "We don't
know what the exact cause is, but what we observe going on today is
likely to be what is also happening tomorrow."

Thus far, all of the ice shelves that have collapsed are located on
the Antarctic peninsula. In reality a collection of islands, mountain
ranges and glaciers, the peninsula juts northward toward Argentina and
Chile and is "really getting hot, competing with the Yukon for the
title of the fastest warming place on the globe," in the words of Dr.
Eric Steig, a glaciologist who teaches at the University of
Washington.

According to a recent study published in Geophysical Research Letters,
the discharge rate of three important glaciers still remaining on the
peninsula accelerated eightfold just from 2000 to 2003. "Ice is
thinning at the rate of tens of meters per year" on the peninsula,
with glacier elevations in some places having dropped by as much as
124 feet in six months, the study found.

But the narrow peninsula contains relatively little inland ice.
Glaciologists are more concerned that they are now beginning to detect
similar signs closer to the South Pole, on the main body of the
continent, where ice shelves are much larger -- and could contribute
far more to sea level changes. Of particular interest is this remote
and almost inaccessible region known as "the weak underbelly of West
Antarctica," where some individual ice shelves are as large as Texas
or Spain and much of the land on which they rest lies under sea level.

"This is probably the most active part of Antarctica," said Dr. Eric
Rignot, a glaciologist at the Jet Propulsion Laboratory in Pasadena,
Calif., and the principal author of the Geophysical Research Letters
paper. "Glaciers are changing rapidly and increasingly discharging
into the ocean, which contributes to sea level rise in a more
significant way than any other part of Antarctica."

According to another paper, published in the journal Science in
September, "the catchment regions of Amundsen Sea glaciers contain
enough ice to raise sea level by 1.3 meters," or about four feet.
While the current sea level rise attributable to glacier thinning here
is a relatively modest 0.2 millimeters a year, or about 10 percent of
the total global increase, the paper noted that near the coast the
process had accelerated and might continue to do so.

As a result, the most recent flights of NASA and the Chilean center
have been directed over the Thurston Island and Pine Island zones of
West Antarctica, near the point where the Bellinghausen and Amundsen
Seas come together. The idea is to use the laser and radar readings
being gathered to establish a base line for comparison with future
measurements, to be taken every two years or so.

"We're not sure yet how to connect what we see on the peninsula with
what we observe going on further south, but both are very clearly
dramatic and dynamic events," Dr. Bindschadler said. "On the
peninsula, large amounts of melt water are directly connected to
disintegration of the ice shelf, but the actual mechanism in West
Antarctica, whether melt water, a slippery hill or a firmer bedrock,
is not yet clear. Hence the need for more data."

The information being gathered here coincides with the recent
publication of a report on accelerating climate change in the Arctic,
an area that has been far more scrutinized than Antarctica. That
study, commissioned by the United States and seven other nations,
found permafrost there to be thawing and glaciers and sea ice to be
retreating markedly, raising new concerns about global warming and its
impact.

"The Arctic has lots of land at high latitudes, and the presence of
land masses helps snow melt off more quickly," said Dr. Steig. "But
there's not a lot of land to speak of in the high latitudes of the
Southern Hemisphere," making the search for an explanation of what is
going on here even more complicated.

The hypotheses scientists offer for the causes of glacier and ice
shelf thinning in Antarctica are varied. Rising air, land and ocean
temperatures or some combination of them have all been cited.

Some scientists have even proposed that a healing of the seasonal
ozone hole over the South Pole and southernmost Chile, a phenomenon
expected to take place in the next 50 years or so, could change the
circulation of the atmosphere over the frozen continent in ways that
could accelerate the thinning of Antarctic ice fields. But even
without that prospect, the situation developing in Antarctica is
already sobering, glaciologists agree. The data being collected here
in West Antarctica and on the peninsula farther north make that
obvious, they say, though the degree to which that should be cause for
concern around the rest of the planet will become clear only with more
research.

"If Antarctica collapses, it will have a major effect on the whole
globe," Dr. Rignot cautioned. He warned that "this is not for
tomorrow, and Antarctica is such a big place that it's important to
look at other areas" around the perimeter of the giant continent, but
added, "Nature is playing a little experiment with us, showing us
what could happen if the plug were to be removed."