Study: Arctic Sea Ice Melting Faster
Pastor Dale Morgan
Apr 30, 8:34 PM EDT
*
Study: Arctic Sea Ice Melting Faster
*
BOULDER, Colo. (AP) -- Arctic sea ice is melting three times faster than
many scientists project, U.S. researchers reported Monday, just days
ahead of the next major international report on climate change.
Scientists at the National Center for Atmospheric Research and the
University of Colorado in Boulder concluded, using actual measurements,
that Arctic sea ice has declined at an average rate of about 7.8 percent
per decade between 1953 and 2006.
By contrast, 18 computer models used by the Intergovernmental Panel on
Climate Change, a U.N.-sponsored climate research group, estimated an
average rate of decline of 2.5 percent per decade over the same period,
the researchers said.
International delegates are meeting in Bangkok, Thailand, this week to
hammer out the final wording of the third IPCC report.
Both the observations cited in the new study and projections from the
IPCC computer models are for September, when Arctic sea ice is typically
at its low point for the year. For March, when the ice is typically at
its most extensive, the new study found the rate of decline was 1.8
percent per decade, about three times larger than the mean from the
computer models.
The researchers said their observations indicate the retreat of
summertime Arctic sea ice is about 30 years ahead of the pace projected
by climate models.
"While the ice is disappearing faster than the computer models indicate,
both observations and the models point in the same direction: the Arctic
is losing ice at an increasingly rapid pace and the impact of greenhouse
gases is growing," said NCAR scientist Marika Holland, one of the
study's co-authors.
Gavin Schmidt, a climate researcher at the Goddard Institute for Space
Studies who wasn't involved in the study, said the study is "a good
reminder that uncertainty in model projections cuts both ways." Critics
of some global warming scenarios say the models exaggerate the potential
problems.
"My feeling (along with the authors) is that it is likely that the
models are insufficiently sensitive," Schmidt said in an e-mail to The
Associated Press. He said the reasons for the lack of sensitivity are
unclear.
"Overall, the models have a track record of getting large scale changes
right, particularly in temperatures, but at the regional scale (like in
the Arctic), there is more variability," he wrote.
The Boulder-based researchers used a combination of early reports from
aircraft and ships and more recent satellite measurements to come up
with their observations of the ice melt.
They said the discrepancy between their observations and computer
projections indicate computer models may have failed to portray the
entire impact of increasing levels of greenhouse gases such as carbon
dioxide in the atmosphere.
The computer models indicated that increased greenhouse gases and
natural climate variations were about equally responsible for ice loss
between 1979 and 2006, the researchers said. They said their own study
indicates greenhouse gases may have a "significantly greater" role than
the models suggested.
A number of factors may lead the computer models to underestimate the
rate of decline in sea ice, the researchers said. Several models
overestimated the thickness of the ice, and the models may have failed
to fully account for changes in currents in the atmosphere and oceans
that transfer heat to polar regions, they said.
The study, "Arctic Sea Ice Decline: Faster Than Forecast," will appear
in the online edition of Geophysical Research Letters on Tuesday, three
days before the IPCC issues its report.
---
On the Net:
Geophysical Research Letters: http://www.agu.org/journals/gl/
Intergovernmental Panel on Climate Change: http://www.ipcc.ch/