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” … major changes are sweeping the Arctic, researchers say.”
“Five years ago, I was not sure it’s very serious, but now I’m
sure something is going on and we should warn people,” says
Igor Semiletov from the University of Alaska in Fairbanks…”
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Nature
Published online 17 December 2008
doi:10.1038/news.2008.1314
News
Arctic warming spurs record melting
Greenland and Siberia see rapid changes.
Rich Monastersky
Record melting in northern Greenland and the
widespread release of methane gas from formerly
frozen deposits off the Siberian coast suggest
that major changes are sweeping the Arctic,
researchers say.
The recent observations, reported on 16 December
at the autumn meeting of the American Geophysical
Union in San Francisco, California, have
surprised scientists who-although used to
Arctic changes-did not expect to see them so
dramatically over the past year.
Parts of southwestern Greenland, along with the
northern part of the island’s ice cap, saw record
melting in summer 2008.Parts of southwestern
Greenland, along with the northern part of the
island’s ice cap, saw record melting in summer
2008.ESA
“Five years ago, I was not sure it’s very
serious, but now I’m sure something is going on
and we should warn people,” says Igor Semiletov
from the University of Alaska in Fairbanks, chief
scientist of the International Siberian Shelf
Study, an oceanographic expedition that surveyed
the entire Siberian coastline this summer. The
study found methane bubbling up from the seafloor
over hundreds of square kilometres in the Laptev
and East Siberian Seas, according to Semiletov.
Changes a-coming
Water measurements indicate that methane
concentrations were up to 200 times higher than
the background levels, he says. In earlier, less
extensive studies in the 1990s, Semiletov did not
find such significant releases of methane. “Based
on the newly obtained data, we suggest an
increase of methane releases from the East
Siberian Arctic Shelf,” he says.
Methane is a potent greenhouse gas, and
scientists estimate that the Arctic permafrost-
both on land and underwater-could hold
trillions of tons of methane stored mostly in the
form of frozen gas hydrates, says Semiletov. The
submerged permafrost is on the threshold of
melting, and air temperatures in the East
Siberian Arctic Shelf have increased by as much
as five degrees Celsius over the last decade, he
says. “We didn’t know that this huge carbon pool
is extremely vulnerable.”
The impact of such methane releases remains
unknown, however. At this point, researchers lack
enough data to say whether enough methane is
escaping from the Siberian continental shelf to
affect the globe, says Edward Brook of Oregon
State University in Corvallis, who says he has
not seen the new data that Semiletov presented.
In a report also released on 16 December by the
US Climate Change Science Program, Brook and his
colleagues concluded that a catastrophic release
of methane is very unlikely this century,
although they project that climate change will
speed up methane emissions from hydrates and
other sources. The report calls for more
monitoring of atmospheric methane to determine if
any abrupt changes are developing.
Not-so-icy north
Across the Arctic from Siberia, Greenland was
also keeping researchers busy this summer, as
satellite measurements revealed record melting
along the far northern margin of its ice cap. In
most summers, temperatures rise enough to permit
melting in that region on only 10-15 days on
average. But in 2008, the melt period totalled 35
days. “It’s a place where you do not expect to
see this extreme melting because it’s a northern
area,” says Marco Tedesco of the City College of
New York, who analyzed microwave data collected
by a defence meteorological satellite.
Record melting also happened last summer along
the edge of southwestern Greenland, Tedesco
reported. The changes in 2008 mark a continuation
of rapid climate change in Greenland over the
past few years. Estimates based on satellite
measurements of the entire ice cap suggest that
the island is now losing hundreds of billions of
tons of ice each year. In another example of
extreme changes, a 29-square-kilometre patch
broke off the end of the Petermann glacier in
northern Greenland during the summer of 2008.
“We’re now seeing the emergence of the Arctic
amplification that we’ve been projecting,” says
Julienne Stroeve of the National Snow and Ice
Data Center at the University of Colorado at
Boulder.
Climate models have projected that greenhouse
gases should warm the Arctic far more than the
rest of the globe because the loss of sea ice
allows heat to penetrate the oceans, which drives
up regional temperatures and causes further
melting. In 2007 the amount of summertime sea ice
dropped to a record low, followed by near-record
ice loss in 2008.
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