Polar bears serve as the key indicator of the effects of climate change in the arctic, as its ecosystem is continuously shaped by climate. When the summer ice melts, the bears willl swim between floes (floating ice chunks) that are normally within 15 miles of each other. Polar bears have webbed feet which allows them to swim at 6 miles an hour and up to 60 miles without rest. However, in 2005, wildlife biologists spotted polar bears swimming 60 miles off shore, and later found 4 floating bodies. The biologists reported that the bears had likely drowned as a result of high seas caused by rough winds. In the past few years, multiple deaths of polar bears have been recorded as a result of the melting ice shelves forcing them to swim long distances.
The Arctic Climate Impact Assessment reported in 2004 that the covering of summer ice in the Arctic has shrunk by 15-20% in the past 30 years. It has also been predicted that a 10-50% reduction in the perennial sea ice (the sea ice that remains during the entire year) and 50-100% reduction of summer sea ice in the next 50-100 years is a major and considerable threat. Some organizations are predicting that the arctic basin will be completely void of ice within 50 years.
As the ice recedes, there is less for the polar bears to hunt from, forcing them into the water. An adult polar bear will usually eat one seal every 4-5 days. The bears' method of hunting them is to wait for the seals to come up to the ice through breathing holes and catch them. However, if the seals no longer need the breathing holes, the polar bears will face another serious problem. The changes that alter the period of ice coverage could affect the polar bears in that they may spend more time on land, which could eventually effect their physical condition when they are forced to rely on stored fats. Their decreased physical conditions may effect their production and survival.
A study in the South Beaufort Sea (covering northern coasts of Alaska and western Canada) has discovered that adult males weigh less and have smaller skulls than the polar bears measured 2 decades ago. The declining sea ice is a likely reason for the smaller male adults and the smaller numbers of surviving cubs.
"We can't say unequivocally that sea ice is the only thing involved," said Steven Amstrup of the U.S. Geological Survey. "There are things we may not be aware of. However, the trends we observed are consistent with changes in nutritional status that are likely to be associated with declines in sea ice. These are the same kinds of trends that we observed in western Hudson Bay, and there we had enough data to determine the decline in sea ice was directly correlated with changing survival rates."
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