Fact Sheet
Polar Bears and Climate Change
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The Arctic's climate is changing, with a noticeable warming trend that is affecting polar bears. The circumpolar region, in which polar bears make their home, is experiencing the warmest air temperatures in four centuries.
The Intergovernmental Panel on Climate Change, the United States Environmental Protection Association and the Arctic Climate Impact Assessment all report on the effect of this climatic change on sea-ice patterns. A recent report notes that there has been a 7% reduction in ice cover in just 25 years, and a 40 % loss of ice thickness.
It also predicts a mostly ice-free Arctic summer by 2080 if present trends continue. There is a very clear consensus among scientists that human activity, namely, the introduction into the atmosphere of increasing quantities of carbon dioxide and other "greenhouse gases" is the most significant factor contributing to a warming Arctic.
The Importance of Sea Ice
Polar bears prefer to remain on the sea ice all year because they depend on a frozen platform from which to hunt seals. Without ice, the bears are unable to reach their prey: they seldom catch seals in open water.
Polar bears are considered to be marine mammals. In the water, seals, with their sleek and powerful bodies, can easily outmaneouver polar bears. Polar bears hunt by ambush, waiting by holes in the ice for their prey to surface. In the spring when the ice begins to recede, polar bears either retreat with it or move onto land. Staying with the ice means they will continue to have access to seals but at lower rates of success as the melt progresses.
The annual ice that lies between the permanent pack ice and the Arctic coastlines is the polar bear's favourite hunting ground because this ice cover tends to be less stable and these near-shore areas over the continental shelf are more productive. When the wind changes, this ice cracks, creating a "lead", or polynya, an area where seals will surface to breathe.
Since animals in the circumpolar Arctic ecosystem perform a very delicate balancing act between expending energy to hunt for food and the energy that the food gives, polar bears will favour hunting by ambush at leads. In these areas, migrating marine mammals can be sure to find breathing and feeding areas and polar bears can be sure to find prey.
Months of Fasting
The sea ice varies significantly throughout the circumpolar region. In some areas, the pack ice recedes little, and in other areas, such as Hudson Bay and James Bay, the ice melts completely in summer. Polar bears living there are forced ashore to fast -- sometimes for as long as eight months in the case of pregnant females -- until freeze-up the following winter.
For these bears, it is crucial to hunt in the most productive areas in order to store enough fat to see them through the lean months. A warmer Arctic means that the sea ice in Hudson Bay and James Bay is freezing later in winter and melting earlier in spring. Researchers have correlated earlier melting of spring ice with reduced body condition in the bears and lower reproduction success. Further north, ice conditions have not yet changed as much.
There is little doubt that all ice-dependent animals will be adversely affected by continued warming in the Arctic. Ringed seals (Pusa hispida) and bearded seals (Erignathus barbatus) need the ice as a place to birth their pups. Arctic cod (Boreogadu saida), a major prey for seals, live in the ice cracks. There are even ice algae that need it as a surface on which to grow. If the ice disappears, the whole ecosystem will shift. Because polar bears are a top predator in the Arctic, safeguarding them and their habitat will mean protecting most animal species that share their Arctic home.