By Andrew Darby in Hobart
 Scientists
studying a key piece in the global climate change puzzle, the
West Antarctic Ice Sheet, have found the largest and most abrupt
warming "spike" in Southern Hemisphere history.
The discovery
of the seven degree temperature hike over a few decades about
19,000 years ago showed climate change could be dramatically fast,
rather than gradual, according to an American scientist.
The evidence
is so strong that the region may have been a trigger area for
the end of the last ice age, said Associate Professor James White
of the University of Colorado.
He said the
warming correlated with an abrupt sea level rise documented by
researchers at the Australian National University, and with less
dramatic increases seen in other ice cores from Antarctica.
The core examined
by Professor White was taken from the West Antarctic Ice Sheet,
which is seen as a vital component in climate change because of
its potential instability.
The world's
largest remaining marine ice sheet, much of the West sheet lies
on bedrock that averages 300 metres below sea level. Were it to
melt, it contains enough grounded ice to raise the global sea
level five metres.
In recent
years, scientists studying the West sheet have found it is undergoing
rapid and dramatic change in some areas.
But they have
been unable to determine whether these changes are manifestations
of natural short-term change or impending collapse.
However, findings
presented to a recent workshop of the American Geophysical Union
have allayed fears.
A NASA scientist
told the workshop the West sheet was retreating more slowly than
thought.
"Our
previous best estimates that the ice sheet was adding one millimetre
per year to global sea level are almost certainly too high,"
said Mr Robert Bindschadler, a glaciologist at NASA's Goddard
Space Flight Centre.
The NASA revision
is based on a synthesis of data, including past sea level rise
estimates and a reconstruction of the sheet's size in the last
glacial maximum, when it was three times the size it is now.
Mr Bindschadler
said geological evidence showed that the sheet had shrunk in fits
and starts, and was now in a stage of near-zero retreat.
"But
what it will do in the future is still uncertain," he said.
"If you
extend the new evidence and the new line of reasoning into the
future, the behaviour of the ice sheet is more difficult to predict.
"It suggests,
however, that if the ice sheet loses its hold on the present shallow
bed it is resting on, the final retreat could be very rapid."
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