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Melting Arctic sea ice. |
The current warming trends in the Arctic may shove the Arctic system into
a seasonally ice-free state not seen for more than one million years, according
to a new report. The melting is accelerating, and a team of researchers were unable
to identify any natural processes that might slow the de-icing of the Arctic.
Such substantial additional melting of Arctic glaciers and ice sheets will
raise sea level worldwide, flooding the coastal areas where many of the world's
people live.
Melting sea ice has already resulted in dramatic impacts for the indigenous
people and animals in the Arctic, which includes parts of Alaska, Canada, Russia,
Siberia, Scandinavia and Greenland.
“What really makes the Arctic different from the rest of the non-polar
world is the permanent ice in the ground, in the ocean and on land,” said
lead author University of Arizona geoscientist Jonathan T. Overpeck. “We
see all of that ice melting already, and we envision that it will melt back
much more dramatically in the future as we move towards this more permanent
ice-free state.”
The report by Overpeck and his colleagues is published in the Aug. 23 Eos,
the weekly newspaper of the American Geophysical Union. A complete list of authors
and their affiliations is at the end of this release.
The report is the result of weeklong meeting of a team of interdisciplinary
scientists who examined how the Arctic environment and climate interact and
how that system would respond as global temperatures rise. The workshop was
organized by the NSF Arctic System Science Committee, which is chaired by Overpeck.
The National Science Foundation funded the meeting.
The past climates in the Arctic include glacial periods, where sea ice coverage
expanded and ice sheets extended into Northern America and Europe, and warmer
interglacial periods during which the ice retreats, as it has during the past
10,000 years.
By studying natural data loggers such as ice cores and marine sediments, scientists
have a good idea what the “natural envelope” for Arctic climate
variations has been for the past million years, Overpeck said.
The team of scientists synthesized what is currently known about the Arctic
and defined key components that make up the current system. The scientists identified
how the components interact, including feedback loops that involve multiple
parts of the system.
“In the past, researchers have tended to look at individual components
of the Arctic,” said Overpeck. “What we did for the first time is
really look at how all of those components work together.”
The team concluded that there were two major amplifying feedbacks in the Arctic
system involving the interplay between sea and land ice, ocean circulation in
the North Atlantic, and the amounts of precipitation and evaporation in the
system.
Such feedback loops accelerate changes in the system, Overpeck said. For example,
the white surface of sea ice reflects radiation from the sun. However, as sea
ice melts, more solar radiation is absorbed by the dark ocean, which heats up
and results in yet more sea ice melting.
While the scientists identified one feedback loop that could slow the changes,
they did not see any natural mechanism that could stop the dramatic loss of
ice.
“I think probably the biggest surprise of the meeting was that no one
could envision any interaction between the components that would act naturally
to stop the trajectory to the new system,” Overpeck said. He added that
the group investigated several possible braking mechanisms that had been previously
suggested.
In addition to sea and land ice melting, Overpeck warned that permafrost—the
permanently frozen layer of soil that underlies much of the Arctic—will
melt and eventually disappear in some areas. Such thawing could release additional
greenhouse gases stored in the permafrost for thousands of years, which would
amplify human-induced climate change.
Overpeck said humans could step on the brakes by reducing carbon dioxide emissions.
“The trouble is we don’t really know where the threshold is beyond
which these changes are inevitable and dangerous," Overpeck said. “Therefore
it is really important that we try hard, and as soon as we can, to dramatically
reduce such emissions.”
Overpeck’s coauthors on the Aug. 23 Eos paper are Matthew Sturm of the
Cold Regions Research and Engineering Laboratory in Fort Wainwright, Alaska;
Jennifer A. Francis of Rutgers University in New Brunswick, N.J.; Donald K.
Perovich of the Cold Regions Research and Engineering Laboratory in Hanover,
N.H.; Mark C. Serreze of the University of Colorado, Boulder; Ronald Benner
of the University of South Carolina in Columbia; Eddy C. Carmack of the Institute
of Ocean Sciences in Sidney, BC, Canada; F. Stuart Chapin III of the University
of Alaska, Fairbanks; S. Craig Gerlach of the University of Alaska, Fairbanks;
Lawrence C. Hamilton of the University of New Hampshire in Durham; Larry D.
Hinzman of the University of Alaska, Fairbanks; Marika Holland of the National
Center for Atmospheric Research in Boulder, Colo.; Henry P. Huntington of Huntington
Consulting in Eagle River, Alaska; Jeffrey R. Key of the National Oceanic and
Atmospheric Administration’s National Environmental Satellite, Data, and
Information Service in Madison, Wis.; Andrea H. Lloyd of Middlebury College
in Middlebury, Va.; Glen M. MacDonald of the University of California, Los Angeles;
Joe McFadden of the University of Minnesota in St. Paul; David Noone of the
California Institute of Technology in Pasadena, Calif.; Terry D. Prowse of the
University of Victoria, in BC, Canada; Peter Schlosser of Columbia University
in Palisades, N.Y.; and Charles Vörösmarty of the University of New
Hampshire in Durham.