Collapse
Of Arctic Sea Ice
'Has Reached Tipping-Point'
By Steve Connor
17 March, 2007
The
Independent
A
catastrophic collapse of the Arctic sea ice could lead to radical climate
changes in the northern hemisphere according to scientists who warn
that the rapid melting is at a "tipping point" beyond which
it may not recover.
The scientists attribute
the loss of some 38,000 square miles of sea ice - an area the size of
Alaska - to rising levels of carbon dioxide in the atmosphere as well
as to natural variability in Arctic ice.
Ever since satellite measurements
of the Arctic sea ice began in 1979, the surface area covered by summer
sea ice has retreated from the long-term average. This has increased
the rate of coastal erosion from Alaska to Siberia and caused problems
for polar bears, which rely on sea ice for hunting seals.
However, in recent years
the rate of melting has accelerated and the sea ice is showing signs
of not recovering even during the cold, dark months of the Arctic winter.
This has led to even less sea ice at the start of the summer melting
season.
Mark Serreze, a senior glaciologist
at the University of Colorado at Boulder, said the world was heading
towards a situation where the Arctic will soon be almost totally ice-free
during summer, which could have a dramatic impact on weather patterns
across the northern hemisphere.
"When the ice thins
to a vulnerable state, the bottom will drop out and we may quickly move
into a new, seasonally ice-free state of the Arctic," Dr Serreze
said.
"I think there is some
evidence that we may have reached that tipping point, and the impacts
will not be confined to the Arctic region," he said.
Some studies have linked
the loss of sea ice in the Arctic to changes in atmospheric weather
patterns that influence such things as rainfall in southern and western
Europe and the amount of snow in the Rocky Mountains of the American
Midwest.
The Arctic is one of the
fastest warming regions on Earth and scientists fear that temperatures
could rise even faster once sea ice melts to expose dark ocean, which
absorbs heat more easily without its reflective cap of ice.
"While the Arctic is
losing a great deal of ice in the summer months, it now seems that it
also is regenerating less ice in the winter. With this increasing vulnerability,
a kick to the system just from natural climate fluctuations could send
it into a tailspin," Dr Serreze said.
During the late 1980s and
early 1990s, changing wind patterns flushed much of the thick sea ice
out of the Arctic Ocean and into the North Atlantic, where it drifted
south and melted away.
A thinner layer of young
ice formed in its place, which more readily melts during the warmer,
summer months - leading to the appearance of a greater area of open
water that absorbs sunlight and heat. The summer sea ice reached an
all-time minimum in September 2005, with September 2006 the second lowest.
"This ice-flushing even
could be a small-scale analogue of the sort of kick that could invoke
rapid collapse, or it could have been the kick itself. At this point,
I don't think we really know," Dr Serreze said.
Julienne Stroeve from the
US National Snow and Ice Data Centre in Colorado said that the winter
sea ice failed again this year to recover fully.
"The freeze-up this
year was again delayed, and ice extents from October through to December
set new record lows during the satellite era," she said.
Computer models suggest that
summer sea ice could disappear altogether by 2080. Some forecasts even
predict an ice-free summer by 2040.
© 2007 Independent News and Media Limited