Has the Arctic Melt Passed the Point of No Return?

Published on
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The Independent/UK

Has the Arctic Melt Passed the Point of No Return?

by
Steve Connor

The Beaufort Sea, just north of Alaska, where near-surface air temperatures are 7C higher than normal. (ALAMY)

Scientists have found the first unequivocal evidence that the Arctic region is
warming at a faster rate than the rest of the world at least a decade before
it was predicted to happen.

Climate-change researchers have found that air temperatures in the region are
higher than would be normally expected during the autumn because the
increased melting of the summer Arctic sea ice is accumulating heat in the
ocean. The phenomenon, known as Arctic amplification, was not expected to be
seen for at least another 10 or 15 years and the findings will further raise
concerns that the Arctic has already passed the climatic tipping-point
towards ice-free summers, beyond which it may not recover.

The Arctic is considered one of the most sensitive regions in terms of climate
change and its transition to another climatic state will have a direct
impact on other parts of the northern hemisphere, as well more indirect
effects around the world.

Although researchers have documented a catastrophic loss of sea ice during the
summer months over the past 20 years, they have not until now detected the
definitive temperature signal that they could link with greenhouse-gas
emissions.

However, in a study to be presented later today to the annual meeting of the
American Geophysical Union in San Francisco, scientists will show that
Arctic amplification has been under way for the past five years, and it will
continue to intensify Arctic warming for the foreseeable future.

Computer models of the global climate have for years suggested the Arctic will
warm at a faster rate than the rest of the world due to Arctic amplification
but many scientists believed this effect would only become measurable in the
coming decades.

However, a study by scientists from the US National Snow and Ice Data Centre
(NSIDC) in Colorado has found that amplification is already showing up as a
marked increase in surface air temperatures within the Arctic region during
the autumn period, when the sea ice begins to reform after the summer
melting period.

Julienne Stroeve, of the NSIDC, who led the study with her colleague Mark
Serreze, said that autumn air temperatures this year and in recent years
have been anomalously high. The Arctic Ocean warmed more than usual because
heat from the sun was absorbed more easily by the dark areas of open water
compared to the highly reflective surface of a frozen sea. "Autumn 2008
saw very strong surface temperature anomalies over the areas where the sea
ice was lost," Dr Stroeve told The Independent ahead of her
presentation today.

"The observed autumn warming that we've seen over the Arctic Ocean, not
just this year but over the past five years or so, represents Arctic
amplification, the notion that rises in surface air temperatures in response
to increased atmospheric greenhouse gas concentrations will be larger in the
Arctic than elsewhere over the globe," she said. "The warming
climate is leading to more open water in the Arctic Ocean. As these open
water areas develop through spring and summer, they absorb most of the sun's
energy, leading to ocean warming.

"In autumn, as the sun sets in the Arctic, most of the heat that was
gained in the ocean during summer is released back to the atmosphere, acting
to warm the atmosphere. It is this heat-release back to the atmosphere that
gives us Arctic amplification."

Temperature readings for this October were significantly higher than normal
across the entire Arctic region – between 3C and 5C above average – but some
areas were dramatically higher. In the Beaufort Sea, north of Alaska, for
instance, near-surface air temperatures were more than 7C higher than normal
for this time of year. The scientists believe the only reasonable
explanation for such high autumn readings is that the ocean heat accumulated
during the summer because of the loss of sea ice is being released back into
the atmosphere from the sea before winter sea ice has chance to reform.

"One of the reasons we focus on Arctic amplification is that it is a good
test of greenhouse warming theory. Even our earliest climate models were
telling us that we should see this Arctic amplification emerge as we lose
the summer ice cover," Dr Stroeve said. "This is exactly what we
are not starting to see in the observations. Simply put, it's a case of we
hate to say we told you so, but we did," she added.

Computer models have also predicted totally ice-free summers in the Arctic by
2070, but many scientists now believe that the first ice-free summer could
occur far earlier than this, perhaps within the next 20 years.

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