In the southern Beaufort Sea, polar bears may be turning to cannibalism because longer seasons without ice keep them from obtaining food from their natural sources. Normally, polar bears feed primarily on ringed seals and use sea ice for basic functions like feeding, mating and giving birth.
American and Canadian scientists reviewed three examples of polar bears preying on each other from January to April 2004, in northern Alaska and western Canada. In one incident, a bear killed a female of the species in her den shortly after she had given birth.
In the wild, polar bears do kill each other for population regulation, to exert their dominance, and to gain reproductive advantage. But killing one another for food is much less common. Steven Amstrup, of the U.S. Geological Survey Alaska Science Center, says that "During the 24 years of research on polar bears in the southern Beaufort Sea region of northern Alaska and 34 years in northwestern Canada, we have not seen other incidents of polar bears stalking, killing and eating other polar bears.".
Environmentalists believe that the shrinking of the polar ice (due to global warming) may lead to the extinction of polar bears before the end of the 21st century.
The Center for Biological Diversity of Joshua Tree, CA, petitioned the federal government in 2005 to list polar bears as "threatened" under the Endangered Species Act, saying that cannibalism demonstrates the adverse effects that global warming has had on the bears.
Less than thirty years ago, there was 7 million square kilometers (2.5 million square miles) of ice at the end of each summer. Today's levels are down about 40% from those numbers. A research scientist with the National Snow and Ice Data Center in Boulder, Colorado stated that "Seven million square kilometers roughly corresponds to an area of the lower 48 United States." Imagine if, back in the early 1980s, the lower 48 states were covered in sea ice in the summer and now, the sea ice east of the Mississippi River is gone.