Polar Bears on Thin Ice?

Yesterday I visited popular theme park Dreamworld at Queensland’s Gold Coast. The visit was to celebrate a 10 year old’s birthday. The highlight for her was the Giant Drop.

We also visited Tiger Island and enjoyed a movie about grizzly and polar bears called ‘The Bears’ shown at the Imax theatre. The photography was spectacular and included grizzly bears catching salmon.

Towards the end of the movie we were told that the survival of polar bears was threatened by global warming. We were told that as a consequence of warmer springs, the ice sheets were thinning earlier than usual at the Arctic and as a consequence the seal hunting season was shorter and bears were losing weight.

Polar bears use sea ice as a platform for hunting ringed seals. Late spring is considered a key hunting period when there are usually lots of fat recently weaned seal pups.

The idea that polar bears are withering away as a consequence of global warming gained prominance following the release of a WWF Report in 2002 titled Polar Bears at Risk. The WWF Report relied on a research paper by Stirling et al titled Long-term trends in the population ecology of polar bears in western Hudson Bay in relation to climate change, Artic, Volume 52, Pages 294-306.

This peer reviewed article concludes:

From 1981 through 1998, the condition of adult male and female polar bears has declined significantly in western Hudson Bay, as have natality and the proportion of yearling cubs caught during the open water period that were independent at the time of capture. Over this same period, the breakup of the sea ice on western Hudson Bay has been occurring earlier. There was a significant positive relationship between the time of breakup and the condition of adult females (i.e., the earlier the breakup, the poorer the condition of the bears). The trend toward earlier breakup was also correlated with rising spring air temperatures over the study area from 1950 to 1990. We suggest that the proximate cause of the decline in physical and reproductive parameters of polar bears in western Hudson Bay over the last 19 years has been a trend toward earlier breakup, which has caused the bears to come ashore in progressively poorer condition. The ultimate factor responsible for the earlier breakup in western Hudson Bay appears to be a long-term warming trend in April-June atmospheric temperatures.

While the western Hudson Bay bears appear to be a bit thinner today than they were 20-odd years ago, there has not been a corresponding decline in population numbers. WWF and others acknowledge that the western Hudson Bay population is stable at about 1,200 polar bears.

There are thought to be about 22,000 polar bears worldwide with about 60 percent in Canada. Most bear populations are thought to be stable or increasing in number. Historically hunting has impacted on population numbers and over-harvesting is still considered the main threat to polar bears.

I recently found this site that includes some photographs and a map of the arctic and where to find polar bears,
http://www.polarbearsinternational.org/arctic-map/ .

While it is important to note that western Hudson Bay bears have been losing weight, and that from 1979 to 1998 the trend has been towards an earlier breakup of ice and thus a loss of ‘feeding platforms’ for the resident bears, the evidence is hardly adequate to conclude global warming will result in the extinction of polar bears.

It is interesting to note that the mean time of freeze-up did not change. Furthermore, in eastern Hudson Bay temperatures have been cooling over the same period that they have been warming in the west and the ice has not been breaking up earlier in spring in the east. The total ice cover for Hudson Bay (east and west) did not decline over the study period. Furthermore a distinction should perhaps be made between global warming and climate change?