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AGU: Cold outlook
There was further worrying news about the Arctic at the AGU Meeting this
morning. Igor Semiletov of the University of Alaska Fairbanks detailed results from a 12,000 nautical mile long survey of the
entire Eurasian Arctic continental shelf for International Polar Year.
Worryingly, the International Siberian Shelf Study (ISSS-08) found that methane is emerging from the East
Siberian Arctic Shelf, as evidenced by bubble clouds of methane in the sea and
methane bubbles trapped in sea ice in the winter. It looks like the sub-sea
permafrost is failing due to warmer ocean temperatures and allowing methane to
escape; because the Siberian Sea is very shallow the methane isn’t oxidized as it travels to the
surface. “We didn’t know that the huge carbon pool there is extremely
vulnerable,” said Semiletov. Some have predicted that a 6 ppm increase in
atmospheric methane concentrations could induce abrupt climate change -
Semiletov says that would require the release of only 1-2% of the methane
stored under the East Siberian Arctic Shelf.
ISSS-08 also found that most of the
Eurasian Arctic shelf is a strong source of carbon dioxide, with a small area
that acts as a carbon sink near the Chukchi Sea.
Melting in Northern Greenland this year
lasted up to 18 days longer than normal, said Marco Tedesco of The City College
of New York. While Julienne Stroeve of the US National Snow and Ice Data Center
believes that the Arctic sea-ice has entered a new state. “We’re losing
ice cover and the rest of the ice is thinning down,” she said. That means
that there’s likely to be more melting in the summer regardless of the
atmospheric conditions. Even though 2008 didn’t see the almost “perfect
storm” conditions that led to the record low summer sea-ice extent of
2007, there were still large levels of ice loss. “If you had had the
conditions of 2007 again with the thinner ice this year there would have been
record ice loss,” said Stroeve.
Stroeve and her colleagues are also
starting to see evidence of Arctic amplification - the phenomenon by which the
lower amount of ice in the summer leads the ocean to absorb more heat, which is
then released in the autumn as air temperatures drop, bringing further warming.
The researchers have found that areas where the sea-ice was gone experienced a
3 degree C warming of the ocean. And anomalies in sea ice and air temperature
occurred at the same locations.
A changing Arctic is likely to affect
temperatures and precipitation at lower latitudes. “The Arctic is the air conditioner
of the northern hemisphere,” said Stroeve. “We really don’t know how
it will play out yet.”
But can sea-ice-related ocean warming
affect the land as well? The answer from Skip Walker of the University of Alaska Fairbanks was an unequivocal yes. Walker has been
studying the “greening of the Arctic” - increases in productivity of the vegetation of Arctic
tundra. Roughly 80% of the biome is within 100 km of the coast so it’s perhaps
not surprising that it’s very sensitive to ocean conditions. Walker and
colleagues have found that the vegetation’s productivity depends on summer land
temperature and late spring sea-ice concentration. But inexplicably, while
tundra in North America is greening, that in Eurasia is becoming less productive.
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