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magazine / so04
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July/August 2004 issue |
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Arctic meltdown
The polar ice cap is shrinking, affecting everything from foraging bears to ship traffic
By Jodi Di Menna and Steven Fick
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| Click map to enlarge |
It is starting to become clear that as temperatures rise around the globe, the Arctic is
experiencing some of the world’s most demonstrable changes, particularly to its permanent
cap of sea ice.
Every 10 years since 1981, summer temperatures in the Arctic have crept up by an average
of 1.22°C, dramatically changing the thermal distribution around the North Pole (bottom).
And, as a result, the area covered by perennial sea ice — the same ice that once jammed up
the Northwest Passage for 19th-century explorers — shrank by about 15 percent between 1978
and 2003 (right). The summers of 2002 and 2003 saw ice cover at a 25-year low, creating conditions
that, in 2002, broke up the 3,000-year-old Ward Hunt Ice Shelf (inset).
Separation anxiety
In 2002, a crack 15 kilometres long and 80 metres wide triggered the collapse of the
Ward Hunt Ice Shelf. At 443 square kilometres, it was the Arctic’s largest expanse
of sea ice. Scientists lamented the loss of a rare freshwater lake along the ice surface,
the largest remaining of its kind. It drained into the Arctic Ocean, along with its
unique algae, viruses, bacteria and minute animals that may have helped explain how
life survived past ice ages and whether life could exist on Jupiter’s frozen moon Europa. |
All these trends have been triggered by a feedback loop that accelerates Arctic warming.
As ice cover diminishes, less of the sun’s radiation is reflected back into space by the
white surface and more is absorbed by the now exposed dark ocean, which traps radiation at
the Earth’s surface.
As temperatures rise, spring starts sooner and autumn arrives later, adding about two weeks
to the melt season every 10 years. Just one extra day of melting can cause sea ice to thin
by as much as €ve centimetres, which is bad news for €sh, bird and mammal species that rely
on ice cover for shelter and foraging. One recent study suggests that for every week earlier
that sea ice in Hudson Bay breaks up, polar bears come ashore 10 kilograms lighter and in
poorer condition.
Humans are also at risk. Less ice means Arctic coastlines are increasingly exposed to erosion,
putting coastal communities in danger of flooding, while traditional marine-mammal hunting
and ice fishing become more perilous as the ice is more likely to shift and break under a
hunter’s feet.
Larger-scale shifts in global weather patterns and storm systems are expected to occur as
freshwater ice melts and upsets the balance of ocean salinity and temperatures. And hazards
increase as ice islands weighing tens of millions of tonnes break off and drift into subarctic
waters, where they threaten ships and drilling platforms. Less ice could also clear the way
for more offshore development and new shipping routes, both of which raise pollution concerns.
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