General Circulation Models (GCMs) are created to simulate the Earth's climate. These computer models are made up of many complicated mathematical equations, but are only an approximation of the real climate system. There are still many aspects of our climate that we do not fully understand and many interactions that cannot be accurately represented by these models.

Over the last 200 years, human-induced greenhouse gas emissions have begun to accumulate in the atmosphere. These gases may now be strengthening the natural greenhouse effect with the potential of accelerating planet- wide climate change.

Projected CO2 concentrations (Environment Canada, 1999a)

Many climate change predictions depend on the future concentrations of atmospheric CO₂. These future concentrations will depend on global development and our commitment to the reduction of greenhouse gas emissions. In the figure (left), the high estimate assumes an increase in the burning of fossil fuels, while the low estimate assumes a switch to alternative energy sources.

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Climate models predict the greatest warming to occur in Arctic regions.

Projected temperature changes: 1975-1995 average vs. 2080-2100 (Environment Canada, 1999a)

GCMs project an overall increase in the annual mean temperature of 1°C to 3.5°C over the next 100 years. Not all areas will be affected equally, however, and the Canadian Arctic is expected to experience more substantial changes than southern regions. In the west, temperature increases of 5-7°C are predicted, while in the east warming is predicted to be much less. Temperature changes will also differ between seasons with more overall warming occurring in the winter months.

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Heavy rains and snowfalls are predicted to increase in frequency and intensity.

Projected precipitation change: 1975-1995 average vs. 2080-2100 (Environment Canada, 1999a)

Annual precipitation is predicted to increase by up to 25% over the next century; however, these changes will vary seasonally. This means that the amount and type of precipitation will vary by season. For example, in the northern regions winter snow cover may be reduced by up to 30 days and in western regions snow may be replaced by rain or freezing rain in early spring and autumn.

GCMs project major changes in sea ice cover in the northern hemisphere. In fact, if they are correct virtually all summer ice cover in the North will disappear by 2100.

Projected seasonal ice extent change: 1971-1990 vs. 2041-2060 (Flato et al., in press)