Since the early 1990s, glaciers draining Antarctica's vast ice
sheets have dumped ice into the ocean at an an eye-popping rate.
Now, two new studies of ice cores from different parts of the
continent are yielding important clues as to why the loss rates have
been so high.
On the Antarctic Peninsula, global warming appears to be taking a
direct toll. Glaciers are melting mainly from the top down. The
peninsula is losing land ice in the summer at a rate unmatched in
the past 1,000 years.
For the West Antarctic Ice Sheet, one of two vast continental
sheets, losses also have been relatively large. There, however,
floating ice shelves that form the seaward end of glaciers are
melting from the bottom up. Today's losses are comparable to those
that have occurred a few other times over the past 2,000 years. The
authors say that for now, the evidence points to the extended reach
of naturally shifting climate patterns in the tropical Pacific as
driving the losses.
At first blush, the two might appear to be at loggerheads.
Instead, researchers suggest, the two highlight how, as on other
continents, the intensity of global warming's impact at the bottom
of the world depends on location, location, location. And both point
to the challenge researchers still face in forecasting the future of
the continent's ice chest in a warming climate.
Each in its own way "provides guidance on projecting the future
of sea-level rise," notes Richard Alley, a glaciologist at Penn
State University in University Park, Pa., who was not a participant
in either study.
Researchers have a keen interest in trying to understand and
project ice losses in Antarctica, as well as on Greenland, with
global warming. Previous studies have shown that since 1992, the
loss of ice from polar caps is raising sea levels by an average of
about 0.59 millimeters a year.
The West Antarctic Ice Sheet alone could boost sea levels an
average of 10 feet if it melts - an increase that would occur over
hundreds to thousands of years, notes Eric Steig, a researcher at
the University of Washington who led one of the two research
Between 1992 and 2011, the peninsula lost ice at rate of 20
billion tons a year, according to a study published last November in
the journal Science. The West Antarctic Ice Sheet lost 65 billion
tons a year, and the East Antarctic Ice Sheet - the continent's
largest - lost 14 billion tons a year, although the uncertainties in
that number are so large the loss could just as well have been
The Antarctic Peninsula is an extended arm of land that last
shook hands with the southern tip of South America roughly 235
million years ago when the two continents drifted apart. It's
mountainous and extends into the Southern Ocean to some 250 miles
above the Antarctic Circle.
"In some ways, it's a climate oddity," writes Robert Mulvaney, a
researcher with the British Antarctic Survey (BAS) and a member of
the team formally reporting its results on the region's ice Sunday
in the journal Nature Geoscience, in an e-mail. Relatively warm
westerly winds, laden with with ocean moisture, blow across the
peninsula. So it tends to be warmer than the mainland and
experiences higher snowfall rates.
Even so, the buildup of the loss of ozone in the stratosphere and
the buildup of greenhouse gases - both from human industrial
activity - have affected circulation patterns over the region in
ways that have left the peninsula as one of the fastest-warming
regions on the planet. …