 A Polar Bear on Ice
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Oct. 29, 2003 — Longer summers are causing the Arctic icecap to thin and shrink, spelling a potential catastrophe for polar bears, said a report this week. It is the second study in less than a week to warn of the perils facing the Earth's northern ice sheet.
British researchers used data from a pair of European and American radar satellites to assess the thickness of the ice covering the Arctic Ocean over eight years.
They found that, while the ice has thinned by 40 percent overall since the 1960s, the thickness can in fact fluctuate greatly during the course of the year and also from year to year.
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Averaged out over the 1993-2001 duration of the study, the mean ice thickness in winter was just less than three meters (10 feet), but over time this figure fluctuated by up to 25 centimeters (two feet) each way.
Computer models have generally assumed that variations in ice thickness are caused by changes in ocean currents and winds, which stresses the ice.
But the latest study said that those factors are far less important than global warming.
It found that the fluctuations in the ice thickness are mirrored by variations in the length of the summer melt season caused by warmer waters from April to September.
The records showed that, over time, the melt season has been getting progressively longer while the ice has thinned.
The shorter winter is potentially disastrous for polar bears, because they depend on the ice to hunt for seals, they said. If the ice breaks up earlier, the bears have less time to find food.
Last Friday, NASA published satellite images showing that the northern polar icecap has been shrinking by 10 percent per decade during the past quarter century.
The period of "perennial sea ice" — the Arctic sea ice that remains frozen all year round — reached record lows in 2002 and 2003, NASA said. It blamed global warming, noting that oceans and landmasses surrounding the Arctic Ocean had warmed by 1° C (1.8°F) over the past decade.
Lead author of the research, which appears in Thursday's issue of the British science weekly journal Nature, is Seymour Laxon of the Center for Polar Observation and Modeling, which is part of University College London.
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Name: Polar Bear (Ursus maritimus)
Primary Classification: Ursidae (Bears) Location: Arctic region surrounding the North Pole. Habitat: Glacier ice and tundra. Diet: Seals mostly. Also walrus, sea birds, lemmings, birds' eggs, some vegetation, and carrion. Size: Up to 11 ft in length and 1,500 lbs in weight. Description: Dense creamy white coat made of hollow translucent hairs; black skin; powerful build; long neck and head. Cool Facts: It is the world's largest land predator. It has been known to swim more than 60 miles without rest. Studies show that they are as intelligent as apes. Conservation Status: Lower Risk (Conservation Dependent) Major Threat(s): Habitat Loss What Can I Do?: Visit Polar Bears Alive for information on how you can help. |
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