Polar bears (Ursus maritimus, which means “sea bear”) are well adapted to cold climates. They have a thick layer of water repellant fur and blubber for insulation, and skid-resistant, snowshoe style paws. These carnivores are intelligent and huge - males can weigh up to 1760 pounds. As a result, they only have one real enemy - and it is us.
Prior to passage of the Marine Mammal Protection Act in 1972, unrestricted hunting of as many as 1,250 polar bears a year was significantly impacting populations. Because they are at the top of the food chain, bears tend to accumulate man-made toxins like pesticides and PCBs in their fat, which can impact health. Now, as a result of climate change, their habitat is shrinking. Overall decreases in the distribution and abundance of sea ice have already been recorded and are expected to continue. By the year 2050, projected changes in sea ice conditions could result in the loss of approximately two-thirds of the existing polar bear population, according to a series of studies by the USGS.
We may not have polar bears in our backyards, but that does not mean we cannot cause their habitat to melt away. The majority of scientists studying climate change and atmospheric processes believe humans are a significant factor in contributing to global warming, and it’s not humans living in the Arctic – it’s humans using electricity from coal-fired power plants and commuting to work, says Steven Amstrup of the U.S. Geological Service (USGS). Because the planet’s ecosystem is so interconnected, pollution can have serious consequences far from the source. If the climate does warm up, polar bears can not go farther north. There is no more north. They already live at the top of the world, notes Amstrup.
An estimated 21,500-25,000 polar bears currently live in Alaska, Canada, Russia, Greenland and Norway (Polar Bear Specialist Group, 2002). Dr. Ian Stirling of the Canadian Wildlife Service has been studying polar bears in Hudson Bay area for 30 years. The population there has already dropped by 22% in the last decade. The overall body condition of the bears has also been steadily declining. Thinner, stressed bears have lower reproductive and survival rates. Females only breed about once every three years, since cubs usually stay with their mother for 27 months. The USGS reports that only 45 percent of cubs are surviving to their first birthday. Just fifteen years ago, that number was 65 percent.
Polar bears depend on sea ice as a platform to hunt for prey like seals. The bear usually waits at a breathing hole until a seal surfaces. Then it smashes through the snow and grabs the seal with its jaws. Polar bears need to spend more than half of their time hunting, since maybe less than ten percent of attempts to catch seals succeed. Even in good hunting areas, a bear may catch only one seal every four or five days.
When the Arctic ice melts in late summer, the bears go inland and live off their fat reserves for the next four months. If the ice shrinks or melts earlier in the year, they are driven to shore earlier. As sea ice thins and fractures more due to warmer temperatures, it is more likely to drift in response to wind and currents, and bears must walk and swim farther and farther to hunt. In 2004, the U.S. Minerals Management Service documented the apparent drowning of at least four polar bears after the sea ice retreated a record 160 miles off the coast, followed by a severe storm. That same year, there were three documented instances of polar bears stalking, killing and eating their own kind. Some bears are moving closer to human settlements, where they scavenge garbage and sometimes end up eating things that are not good for them, like plastic and engine oil. The town of Churchill Manitoba had to set up an air conditioned “polar bear jail” for marauding bears that have become aggressive towards people.
The world’s leading polar bear researchers from the USGS, American and Canadian government agencies, academia and the private sector agree that the situation is serious. Of the existing 19 populations of polar bears, five are declining, five are stable, two are increasing, and the status of the other seven is unknown. This data prompted the Center for Biological Diversity to petition, and then sue the government to grant the polar bear conservation status under the Endangered Species Act as a threatened species. A decision from the U.S. Dept. of the Interior is expected in January 2008.
Of course predicting what will happen in a complex ecosystem is difficult, depends on quality data and reliable models, and always involves some degree of uncertainty. One of the problems with polar bears is that by the time we see the clear signals, it’s going to be too late, says Dr. Andrew Derocher of the University of Alberta. Thus we must rely on the best available data from credible scientists if we are to take precautionary measures in time to make a difference.
UPDATE: In 2008, The U.S. Interior Dept. announced it will protect the polar bear as a Threatened Species because of the decline in Arctic sea ice from global warming. The State of Alaska is suing.