Climate change is considered one of the most important environmental issues of our time. This concern reflects the reality that so much of human activity is sensitive to climate change, and that adapting to current and projected rates of climate change could be very challenging. It also reflects the understanding that human perturbation of the climate system is essentially irreversible, for many centuries at least. How much climate change future generations are exposed to will be determined by the actions that we take over the coming decades to reduce human impacts on the climate system.
There is a very strong body of evidence, based on a wide range of indicators, that climate change is occurring, and the climate system is warming. The evidence includes observed increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global sea level (in response to the addition of water from melting snow and ice and the expansion of water when warmed). Plants and animals are responding to climate change in ways that are consistent with the observed warming with repercussions throughout natural and managed environments.
Although climate change can be caused by both natural processes and human activities, the recent warming has been largely attributed to human activity, primarily the release of carbon dioxide and other greenhouse gases to the atmosphere. These gases enhance the insulating properties of the atmosphere, reducing heat loss, thereby warming the planet. Continued emission of these gases is the primary cause for concern about climate change now and into the immediate future. Particularly important is the emission of carbon dioxide, which is released through the combustion of carbon-based fossil fuels. In Canada, over 80 % of total national greenhouse gas emissions are associated with the production or consumption of fossil fuels for energy purposes.
As carbon dioxide stays in the atmosphere for a long time, levels of carbon dioxide continue to build-up in the atmosphere with ongoing human emissions. Even with human emissions eliminated, atmospheric levels of carbon dioxide would fall very gradually as natural processes slowly remove carbon dioxide from the atmosphere. This means that past emissions from human activity continue to affect the climate system for a very long time.
The potential impacts of climate change are far-reaching, affecting our economy, infrastructure, and health, the landscapes around us, and the wildlife that inhabit them. More specific impacts are discussed in recent reports from Natural Resources Canada and Health Canada.
The following pages provide some general introductory information about the earth's climate system, the greenhouse effect, Canadian GHG emissions and about the potential impacts of climate change to our health and the environment.