Arctic indigenous communities are already noticing some of these changes: warmer winters, earlier break-up of ice in the spring, and thinner ice year round. This traditional knowledge supports scientific evidence:
- Air temperatures in the Arctic have on average increased by about 5°C over the last 100 years.
- Arctic sea ice extent has decreased by 14% since the 1970s.
The results of computer modeling of future climate vary in detail, but all show a clear trend towards an overall warming in the Arctic, and a resulting melting of the sea ice. The models suggest that by 2080, arctic sea ice will completely disappear during the summer months.
These are dramatic and rapid changes. A slight shift in temperature, bringing averages above freezing, will completely alter the character of this region. Where once ice covered the seas and permafrost stabilized the ground, open water and large tracts of barren land will dominate. The consequences for all arctic species will be severe.In the southern range of polar bears, for example the Hudson and James Bays of Canada, sea ice is now melting earlier in the spring and forming later in the autumn. The time bears have on the ice, storing up energy for the summer and autumn when there is little available food, is becoming shorter.
As the periods without food become longer, the overall body condition of these polar bears declines. This is particularly serious for bears that are pregnant or have cubs, and for the cubs themselves. In Hudson Bay, scientists have found the main cause of death for cubs to be either lack of food or lack of fat on nursing mothers.
For every week earlier the ice breaks up in Hudson Bay, bears come ashore roughly 10 kg (22 lbs) lighter and in poorer condition. Rising temperatures in the southern Arctic, therefore, mean less sea ice, leading to less healthy bears. Reduced body condition can lead to lower reproduction rates, which in the long run could lead to local extinction.
This situation could extend to other parts of the Arctic should climate change go unchecked.