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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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