For food, polar bears enjoy phocid seals, as well as bearded seals (Smith, p. 2205) as their primary sources, although other varieties of seals, as well as walruses, will also do.
Just about all of the Arctic Ocean around the North Pole has served as a suitable habitat for the polar bear. Recent estimates of the polar bear population range between 21,500 and 25,000 (IUCN/SSC Polar Bear Specialist Group, p. 26). The primary threat in years past to the polar bear population has been overharvesting, but recent measures have been instituted to correct this trend (Prestrud and Stirling, p. 116). Because of the location of the habitats, the impact of human development has been minimal, and so the polar bear has maintained a high percentage of its original range, especially in comparison to other large carnivores. However, it is fairly clear that the effects of melting polar ice due to global warming will be far more invasive to the polar bears' habitats (Derocher).
There is a considerable body of research supporting the existence of global warming in the Arctic, and also supporting that the rate of global warming may accelerate from its present levels (Serreze e.a., Parkinson and Cavalieri, Comiso). Time has adapted most of the mammals indigenous to the Arctic marine ecosystem to the environment of sea ice; in fact, it has become crucial for pagophilic ("ice-loving") mammals and epontic marine communities, with the result that if ice continues to disappear from some parts of the Arctic region, the ecosystem will alter drastically. Specific effects could include the loss of life in the continental shelf under the ice, reductions in total sea ice area as well as in the duration of sea ice lasting during the year, thinner ice, changed snow cover, and increased ice drift (Derocher).
Scientists have documented the considerable effects that climate can have on the life history patterns of animals (Stearns, p. 102). While these effects can at times be cyclical, in response to long-term patterns in climate, the primary concern about the contemporary trend for global warming is that it will not be cyclical, but will instead increase without stopping (Derocher). There are a number of ways that this warming could affect polar bears in Arctic Canada and throughout the polar region, and there are a number of approaches to figuring out just what these effects will be, and how severe they will be.
The most unique characteristic of the polar bear is the fact that it is pagophilic. It evolved from the brown bear and moved into the large, fertile, but mostly vacant opportunity for a large predator (Stirling and Derocher, p. 244). Despite the fact that females will return to land to bear and care for their young, the polar bear depends on what is found on the sea ice for sustenance, and so will be profoundly affected by major changes to the sea ice habitat (Derocher). Of the different kinds of sea ice, polar bears tend to prefer the annual variety that forms over the continental shelf and the archipelagos that surround the polar basin. In recent years, the total sea ice has declined, near shore areas as well as in the multiyear ice layers (Parkinson and Cavalieri, Comiso). The