The Earth's temperature is determined in part by a naturally occurring process known as "greenhouse effect". While certain greenhouse gases occur naturally, human activities are realizing additional greenhouse gases into the atmosphere.

Data collected from polar ice cores show that concentrations of
CO₂ , which had been stable at about 280 parts per million by volume for the 10,000 years between the last ice age and the start of the 19 th century, have today increased by about 30 percent. If current trends in greenhouse gas emissions continue, by the end of this century their concentration in our atmosphere could be double what they had been prior to the industrial revolution.

While uncertainties exist about the timing and rate of future changes in this concentration, the UN Intergovernmental Panel on Climate Change (IPCC) - an international body made up of 2,000 of the world's top climate scientists - estimates that the average global surface temperature is likely to increase by between 1.4 and 5.8°C by 2100. While these changes may seem modest, even small changes in global average temperatures can have a dramatic impact on out climate. The last time the earth's average temperature was 5°C colder, for example, Canada was covered with three kilometers of ice.

Scientists have also concluded that changes consistent with global warming are already occurring in different parts of the world. Mountain glaciers are retreating, the global sea level is raising and climate zones are shifting. The 20 th century was the warmest century of the last millennium; the 1990s were the warmest decade of the last century and the years 1999 and 2001 were the warmest years yet. This is well beyond the range of natural climate variability.

Because scientists expect that northern nations will be more affected by climate change than those closer to the equator, Canada is particularly vulnerable. We are already feeling the effects: increasing heat waves and related health problems, declining water levels in the Great Lakes, changes in fish migration and melting polar ice caps, as well as insect infestations in British Columbia's forests.

What is more, we are only beginning to get a sense of the costs related to climate change, such as hotter summers, higher level of smog in major urban centres and more extreme weather events such as droughts on the Prairies, ice storms in the eastern Canada or flooding in Manitoba and Quebec. There are also the costs associated with distributing ecosystems, from fish stocks to forestry.

All of these will have a profound effect on our economy, our health and our quality of life.