OSLO, Dec 23 (Reuters) - West Antarctica is warming almost
twice as fast as previously believed, adding to worries of a
thaw that would add to sea level rise from San Francisco to
Shanghai, a study showed on Sunday.
Annual average temperatures at the Byrd research station in
West Antarctica had risen 2.4 degrees Celsius (4.3F) since the
1950s, one of the fastest gains on the planet and three times
the global average in a changing climate, it said.
The unexpectedly big increase adds to fears the ice sheet is
vulnerable to thawing. West Antarctica holds enough ice to raise
world sea levels by at least 3.3 metres (11 feet) if it ever all
melted, a process that would take centuries.
"The western part of the ice sheet is experiencing nearly
twice as much warming as previously thought," Ohio State
University said in a statement of the study led by its geography
professor David Bromwich.
The warming "raises further concerns about the future
contribution of Antarctica to sea level rise," it said. Higher
summer temperatures raised risks of a surface melt of ice and
snow even though most of Antarctica is in a year-round deep
freeze.
Low-lying nations from Bangladesh to Tuvalu are especially
vulnerable to sea level rise, as are coastal cities from London
to Buenos Aires. Sea levels have risen by about 20 cms (8
inches) in the past century.
The United Nations panel of climate experts projects that
sea levels will rise by between 18 and 59 cms (7-24 inches) this
century, and by more if a thaw of Greenland and Antarctica
accelerates, due to global warming caused by human activities.
GLACIERS
The rise in temperatures in the remote region was comparable
to that on the Antarctic Peninsula to the north, which snakes up
towards South America, according to the U.S.-based experts
writing in the journal Nature Geoscience.
Parts of the northern hemisphere have also warmed at
similarly fast rates.
Several ice shelves - thick ice floating on the ocean and
linked to land - have collapsed around the Antarctic Peninsula
in recent years. Once ice shelves break up, glaciers pent up
behind them can slide faster into the sea, raising water levels.
"The stakes would be much higher if a similar event occurred
to an ice shelf restraining one of the enormous West Antarctic
ice sheet glaciers," said Andrew Monaghan, a co-author at the
U.S. National Center for Atmospheric Research.
The Pine Island glacier off West Antarctica, for instance,
brings as much water to the ocean as the Rhine river in Europe.
The scientists said there had been one instance of a
widespread surface melt of West Antarctica, in 2005. "A
continued rise in summer temperatures could lead to more
frequent and extensive episodes of surface melting," they wrote.
West Antarctica now contributes about 0.3 mm a year to sea
level rise, less than Greenland's 0.7 mm, Ohio State University
said. The bigger East Antarctic ice sheet is less vulnerable to
a thaw.
Helped by computer simulations, the scientists reconstructed
a record of temperatures stretching back to 1958 at Byrd, where
about a third of the measurements were missing, sometimes
because of power failures in the long Antarctic winters.
(Reporting By Alister Doyle; Editing by Janet Lawrence)