At the March 2009 range states meeting of the five polar bear nations, scientists agreed that climate change is the single biggest threat facing polar bears.
The Arctic is experiencing the warmest air temperatures in four centuries, and sea ice losses in the summer of 2012 broke all previous records. The Arctic has experienced warm periods before, but the present, rapid shrinking of sea ice is unprecedented. It has been linked to a build-up of greenhouse gases in the atmosphere caused by human activity. Scientists predict a mostly ice-free Arctic summer by 2040 unless we take action to reduce greenhouse gas emissions.
Effect on polar bears. Polar bears rely on the sea ice to hunt, breed, and, in some cases, den. Changes in their distribution or numbers affect the entire arctic ecosystem.
Scientists emphasize that we still have time to save polar bears if we significantly reduce greenhouse emissions within the next few years. Yet it will take 30 to 40 years for changes reversing the warming trend to show.
- There's some evidence that polar bears are leaving the sea ice to den on land even in winter. In Russia, many bears have been stranded on land by long summers that prevent the advance of the permanent ice pack.
- In the Western Hudson Bay area where permafrost has declined, denning areas are vulnerable to forest fires in the summer. Warm spring weather leads to increased rainfall causing dens to collapse.
- Without ice, polar bears are unable to reach their prey. Shorter hunting seasons correlate directly with a 22% drop in the population of Western Hudson Bay near Churchill in Manitoba, Canada since the early 1980s. There has also been a steep drop in cub survival rates.
- A Southern Beaufort Sea population study shows a drop in cub survival rates, as well as declines in the weight and skull size of adult males, when compared with data from 20 years ago. Similar declines were observed in the Western Hudson Bay population before it dropped.
Polar bears are finding too much open water. In 2004, four polar bears drowned off the coast of Alaska when trying to swim to the pack ice.