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Naturally occurring greenhouse gases (GHGs) help to regulate the planet's climate by trapping solar energy that is radiated back from the Earth. Emissions from human activities over the past 200 years have amplified this natural process, and scientists predict that this trend will continue (Environment Canada 2005a).
Not all GHGs occur naturally. Some, such as hydrofluorocarbons and sulphur hexafluoride, are generated only by industrial processes. Others, such as carbon dioxide, methane and nitrous oxide, come from both natural and human sources.
The main concern is due to the increased atmospheric concentration of GHGs resulting from human activities such as burning fossil fuels (oil, coal and natural gas) and deforestation. Global atmospheric concentrations of the six main GHGs (see Box 3) rose by more than 50% during the past three decades (WRI n.d.). Canada's share of global GHG emissions is approximately 2%, although Canadians make up only 0.5% of the planet's population (Environment Canada 2005a).
Box 3. The greenhouse gas emissions indicator
The national greenhouse gas emissions indicator comes directly from Environment Canada's GHG inventory report (Environment Canada 2005a), which contains emissions estimates for sources categorized by economic sectori. It includes estimates for six GHGs: carbon dioxide, methane, nitrous oxide, sulphur hexafluoride, perfluorocarbons and hydrofluorocarbons.
The emissions estimates and sector definitions used for reporting are based on methodological guidance provided by the Intergovernmental Panel on Climate Change (IPCC) and reporting guidelines under the United Nations Framework Convention on Climate Change. The estimates for each sector are generally calculated by multiplying some measure of the amount of GHG-producing activity by the quantity of GHG emitted per unit of activity (e.g., carbon dioxide released per litre of gasoline burned). Emissions estimates for different gases are converted to their equivalent in carbon dioxide based on their impact on global warming compared with carbon dioxide.
For a more detailed description of the indicator and how it is calculated, see Description of the greenhouse gas emissions indicator.
i. For the purposes of estimating and reporting GHG emissions, the IPCC has identified sectors of economic activity.
Emissions of GHGs have been discussed and estimated by scientists and governments for more than a decade. In 1988, the Intergovernmental Panel on Climate Change (IPCC) was established by the United Nations Environment Programme and the World Meteorological Organization (IPCC n.d.). Originally consisting of more than 300 of the world's leading experts, the IPCC was formed to investigate climate change. The panel concluded that a doubling of GHGs in the atmosphere would lead to serious consequences for the world's social, economic and natural systems (Houghton et al. 1990). The IPCC estimated that a doubling of CO2 would lead to an average global temperature increase of 1.4°C to 5.8°C by 2100 (IPCC 2001).
According to several federal government reports (e.g., Lemmen and Warren 2004), if GHG emissions continue to grow, serious consequences will be seen globally, nationally, regionally and locally. A rise in global temperatures could affect, for example, the severity of heat waves, the migration of insects and infectious diseases, water availability and crop yields. Extreme weather events could become more frequent. Sea levels are expected to rise. Indications of these effects have already been seen throughout Canada , especially in the North, where changes have been observed in ice cover, permafrost stability and the distribution of wildlife. At the national level, the social and economic impacts of increased extreme weather events such as drought, flooding and severe storms may be among the most serious of the possible consequences of climate change. Agriculture, forests, tourism and recreation could be affected, as could related supporting industries and towns.