The Vanishing Arctic
4th October, 2007
One of the most memorable parts of Al Gore’s film 'An Inconvenient Truth' was the cartoon polar bear trying to climb on the last piece of sea-ice in the Arctic, failing, and despondently swimming off into the sunset. With scientists this week reporting that autumn Arctic sea-ice coverage reached a record low this year, Al Gore’s cartoon may not be as far-fetched as it seems.
Factors that contributed to this extreme decline include the fact that the ice entered the warmer weather in an already weakened state. An unusual atmospheric pattern, with persistent high atmospheric pressures over the central Arctic Ocean and lower pressures over Siberia also pumped warm air into the region and helped push ice away from the shore.
As the sea-ice disappears, open ocean is revealed. Dark-coloured water replacing pale-coloured ice has global consequences known as the albedo effect. Pale ice reflects incoming solar radiation and keeps the Arctic cool. Perennial sea-ice, which grows thicker each year, also acts as a blanket, insulating the air above the sea-ice from the ocean below it. When the sea-ice melts, the ocean revealed absorbs rather than reflects incoming radiation and heats the overlying air. As Arctic temperatures rise, more sea-ice melts, exposing yet more ocean.
Al Gore’s polar bear cartoon wouldn’t have been as cute if he’d shown the bear drowning or starving. Polar bears depend on Arctic sea-ice to reach their favoured prey, seals, and depend on seals to get them through a hungry summer. Although polar bears are strong swimmers, prolonged trips through open water in search of food exhaust them, and eventually cause them to drown. Polar bear populations are expected to decline by two-thirds by the middle of next century, as a result of the disappearing ice. Sad as that is these shocking results could mean those predictions are optimistic.
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