March
15, 2007
ARCTIC
SEA
ICE DECLINE MAY TRIGGER CLIMATE CHANGE CASCADE, SAYS UNIVERSITY
OF COLORADO
STUDY
Arctic sea ice that
has been dwindling for several decades
may have reached a tipping point that could trigger a cascade of
climate change
reaching into Earth's temperate regions, says a new University
of Colorado
at Boulder
study.
Mark Serreze, a
senior research scientist at CU-Boulder's
National Snow and Ice Data Center
who led the study synthesizing results from recent research, said the
Arctic
sea-ice extent trend has been negative in every month since 1979, when
concerted satellite record keeping efforts began. The team attributed
the loss
of ice, about 38,000 square miles annually as measured each September,
to
rising concentrations of greenhouse gases and strong natural
variability in
Arctic sea ice.
"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,"
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."
A review paper by
Serreze and Julienne Stroeve of
CU-Boulder's NSIDC and Marika Holland of the National
Center for
Atmospheric Research titled
"Perspectives on the Arctic's
Shrinking
Sea Ice Cover" appears in the March 16 issue of Science.
The loss of Arctic
sea ice is most often tied to negative
effects on wildlife like polar bears and increasing erosion of
coastlines in Alaska
and Siberia, he
said. But other studies have linked Arctic sea ice loss to changes in
atmospheric patterns that cause reduced rainfall in the American West
or
increased precipitation over western and southern Europe,
he said.
The decline in
Arctic sea ice could impact western states
like Colorado,
for example, by reducing the severity of Arctic cold fronts dropping
into the
West and reducing snowfall, impacting the ski industry and agriculture,
he
said. "Just how things will pan out is unclear, but the bottom line is
that Arctic sea ice matters globally," Serreze said.
Because temperatures
across the Arctic
have risen from 2 degrees to 7 degrees F. in recent decades due to a
build-up
of atmospheric greenhouse gases, there is no end in sight to the
decline in
Arctic sea ice extent, said Serreze of CU-Boulder's Cooperative
Institute for
Research in Environmental Sciences. Arctic sea ice extent is defined as
the
total area of all regions where ice covers at least 15 percent of the
ocean
surface.
"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," said Serreze. "With this
increasing vulnerability, a kick to the system just from natural
climate
fluctuations could send it into a tailspin."
In the late 1980s
and early 1990s, shifting wind patterns
from the North Atlantic Oscillation flushed much of the thick sea ice
out of
the Arctic Ocean and into the North
Atlantic
where it drifted south and eventually melted, he said. The thinner
layer of
"young" ice that formed it its place melts out more readily in the
succeeding summers, leading to more open water and more solar radiation
being
absorbed by the open ocean and fostering a cycle of higher temperatures
and
earlier ice melt, he said.
"This ice-flushing
event could be a small-scale analog
of the sort of kick that could invoke rapid collapse, or it could have
been the
kick itself," he said. "At this point, I don't think we really
know."
Researchers also
have seen pulses of warmer water from the
North Atlantic entering the Arctic
Ocean
beginning in the mid-1990s, which promote ice melt and discourage ice
growth
along the Atlantic ice margin, he said. "This is another one of those
potential kicks to the system that could evoke rapid ice decline and
send the Arctic
into a new state."
The potential for
such rapid ice loss was highlighted in a
December 2006 study by Holland
and her colleagues published in Geophysical Research Letters. In one of
their
climate model simulations, the Arctic
Ocean in
September became nearly ice-free between 2040 and 2050.
"Given the growing
agreement between models and
observations, a transition to a seasonally ice-free Arctic Ocean as the system warms
seems increasingly certain," the
researchers wrote in Science. "The unresolved questions regard when
this
new Arctic state will be realized, how rapid the transition will be,
and what
will be the impacts of this new state on the Arctic
and the rest of the globe."
##
Contact:
Mark
Serreze
University
of Colorado at Boulder
303-492-2963
serreze@kryos.colorado.edu
This text derived from:
http://www.colorado.edu/
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