Polar bears (Ursus maritimus) are a large, light-furred species of bear that lives only around the perimeter of the Arctic. They are the largest land predators in the world and an icon of the Arctic region, often featured in cartoons and other popular representations. Since they depend on floating sea ice for much of their access to prey, polar bears are endangered by rapid shrinkage of the north polar sea ice.
Scientists with the Canadian Wildlife Service have found that because seals are becoming less accessible to bears due to a shortened ice season, some polar bear populations are already at increased risk of starvation. U.S. government scientists have warned that two thirds of polar bears will be gone by the year 2050, even under conservative global-warming scenarios.
Historical Background and Scientific Foundations
Polar bears are an even younger species than human beings, having only speciated from brown bears about 200,000 years ago. Until about 10,000 years ago, polar bears still often bore teeth resembling those of brown bears, but now have distinct teeth. There are about 20,000 to 25,000 polar bears worldwide, slightly over half of which live in Canada.
The area covered by Arctic sea ice varies seasonally, reaching a low point every September. North polar sea ice has been declining in area for every month of the year since at least 1979; that is, in each month of the year, the ice area is smaller compared to the same month in earlier years. In August and September 2007, the north polar sea-ice area shrank to the smallest size ever recorded, and the Northwest Passage from the Atlantic to the Pacific was free of ice for the first time in recorded history.
As of September 16, 2007, U.S. government scientists announced that the ice was 1.59 million square mi (4.14 million square km) in extent, about a fifth smaller than the previous record, set in September 2005.
The impact of declining sea ice on polar bears is profound. One of the polar bears' primary food species is ringed seals, which the bears attack when the seals come to the surface in ice holes to breathe. Hudson Bay polar bears, for example, do not eat for six to eight months a year, when sea ice is not available; during the winter they go out on the ice to catch seals and feed themselves for the coming summer fast.
Impacts and Issues
In 2007, the U.S. Geological Survey released a report concluding that about two thirds of the world's polar bears would be gone by 2050 due to decreasing sea ice. The remaining bears would be found mostly near the Arctic islands of northeastern Canada and the northern coast of Greenland. According to the report, the bear population will be decimated even if the most conservative (least drastic) computer forecasts of climate change turn out to be correct. Climate change, melting, and bear losses may well be more severe than these optimistic scenarios.
In the United States, the legal status of the polar bear has been a point of contention. A nonprofit environmental group, the Center for Biological Diversity, asked the U.S. Fish and Wildlife Service (FWS) to classify the polar bear as an endangered species in 2005, saying that the agency had been deliberately stalling on the issue for years. The FWS did not respond in the legally mandated 90 days, so the center, together with other environmental groups, brought a lawsuit to force action. Under a settlement, the FWS was required to make a decision by the end of 2006.
The FWS met the deadline by submitting a proposal in late December 2006 to list the polar bear as “threatened” under the terms of the Endangered Species Act of 1973. A final decision was not expected before the end of 2007. Declaration of the bear's endangered status is important because it will obligate the U.S. government to take action to save the bears' habitat, presumably by reducing greenhouse-gas emissions.
WORDS TO KNOW
ENDANGERED SPECIES ACT: U.S. federal law passed in 1973 that protects endangered animals and their habitats. It has been cited in climate disputes because an official government finding that polar bears are endangered would mandate, under the act, action to protect their habitat by mitigating climate change.
GREENHOUSE GASES: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth's surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth's atmosphere, causing global warming and global climate change.
SPECIATION: Speciation is the process by which new species arise. Although there are a variety of definitions, all involve an isolation event that separates an interbreeding population until the daughter lineages evolve in separate trajectories.
Controversy arose again in early 2007 when the media reported that the Alaskan division of the U.S. Fish and Wildlife Service had issued a requirement to several employees, who were going to attend international meetings, that they should not discuss polar bears or climate change. Activists alleged that the agency was trying to silence discussion of global warming by its employees. As reported in the New York Times, agency director H. Dale Hall defended the requirement, stating that the directive was “consistent with staying with our commitment to the other countries to talk about only what's on the agenda.”
Broder, John M. “Warming Is Seen as Wiping Out Most Polar Bears.” New York Times (September 8, 2007).
Eilperin, Juliet. “Inquiry Sought on Agency Memo About Polar Bears, Climate Change.” The Washington Post (March 10, 2007).
Pennisi, Elizabeth. “U.S. Weighs Protection for Polar Bears.” Science 315 (2007): 25.
Amstrup, Steven C., et al. “Forecasting the Range-Wide Status of Polar Bears at Selected Times in the 21st Century.” U.S. Geological Survey, 2007. <http://www.usgs.gov/newsroom/special/polar_bears/docs/USGS_PolarBear_Amstrup_Forecast_lowres.pdf> (accessed October 10, 2007).
Barringer, Felicity. “Protocol Is Cited in Limiting Scientists' Talks on Climate.” New York Times, March 9, 2007. <http://www.nytimes.com/2007/03/09/us/09polar.html?ex=1331096400&en=7706d47e846fc1ab&ei=5088&partner=rssnyt&emc=rss> (accessed November 12, 2007).