Humans to blame, say scientists
2006-10-17 10:49
Oslo - Scientists said on Monday that they
had found the first direct evidence linking the collapse of an
ice shelf in Antarctica to global warming widely blamed on human
activities.
Shifts in winds whipping around the southern Ocean, tied to
human emissions of greenhouse gases, had warmed the Antarctic
peninsula jutting up towards South America and contributed to
the break-up of the Larsen B ice shelf in 2002, they said.
"This is the first time that anyone has been able to
demonstrate a physical process directly linking the break-up of
the Larsen Ice Shelf to human activity," said Gareth Marshall,
lead author of the study at the British Antarctic Survey.
The chunk that collapsed into the Weddell Sea in 2002 was
3 250 sq kms, bigger than Luxembourg or the
US state of Rhode Island.
Most climate experts say greenhouse gases, mainly from
fossil fuels burnt in power plants, factories and cars, are
warming the globe and could bring more erosion, floods or rising
seas. They are wary of linking individual events - such as a
heatwave or a storm - to warming.
But the British and Belgian scientists, writing in the
Journal of Climate, said there was evidence that global warming
and a thinning of the ozone layer over Antarctica, caused by
human chemicals, had strengthened winds blowing clockwise around
Antarctica.
The Antarctic peninsula's chain of mountains, about 2 000 metres high, used to shield the Larsen ice shelf on
its eastern side from the warmer winds.
"If the westerlies strengthen the number of times that the
warm air gets over the mountain barrier increases quite
dramatically," John King, a co-author of the study at the
British Antarctic Survey, said.
King said temperature records in Antarctica went back only
about 50 years but that there was evidence from sediments on the
seabed - which differ if covered by ice or open water - that
the Larsen ice shelf had been in place for 5 000 years.
"Further south on the main Antarctic continent temperatures
are pretty stable," he said. "There is no clear direct evidence
of human activity affecting the main area."
The collapse of the Larsen B ice shelf did not raise world
sea levels because the ice was floating. A brimful glass of
water with an ice cube jutting out will not spill if it melts
because ice contracts as it melts.
But King said the removal of the floating ice barrier could
accelerate the flow of land-based glaciers towards the sea, at
least in the short term. That extra ice could raise sea levels.