There is now widespread agreement among professional climate scientists that the Earth's climate is changing. New and stronger evidence summarized in the Third Assessment Report by the Intergovernmental Panel on Climate Change (January 2001) has convinced the great majority of scientists that "most of the warming observed over the last 50 years is attributable to human activity." ¹²

Earth's climate changes naturally, but it is now the rapid rate of warming, leading to enhanced climate change, that concerns scientists.

Unlike local pollutants that lead to local air quality problems such as urban smog or acid rain, it doesn't matter where greenhouse gases come from. They mix and circulate in the atmosphere of the entire planet, trapping heat and affecting everyone's climate. This makes climate change a truly global issue that requires international cooperation.

As the global energy balance is altered, Earth's climate changes. The very close relationship between increases in the concentration of atmospheric CO₂ (which traps more energy near the Earth) and a rising average global temperature (which is a direct indicator of climate change) is shown in the figure below.

Nations vary significantly in their total greenhouse gas emissions and emissions per capita, with the industrialized countries well out in front. Canada's emissions continue to rise and in 2000, Canadians contributed about 726 megatonnes of CO₂ equivalent to the global atmosphere. ¹³

We can also look at trends and research to see what has happened in the past and what scientists think might happen in the future based on data and computer models.

Big Picture Thinking – Connecting the Pieces

The cause-effect pathway from burning fossil fuels to warming temperatures to impacts on our natural resources and our economy involves several main steps and it is helpful to see the big picture of how the pieces of this puzzle connect.

By (1) burning fossil fuels or otherwise emitting greenhouse gases and by damaging carbon-storing sinks and reservoirs, human activity causes (2) an increase in the atmospheric concentration of greenhouse gases. This acts like more glass insulation on the greenhouse and causes (3) increased trapping of energy. This enhanced greenhouse effect in turn causes (4) higher average global temperatures, changing precipitation patterns and more extreme weather events, which we refer to as "climate change" itself. This extraordinary climate change leads to (5) significant changes in our physical landscape that can include cropland transformed to desert, melting permafrost, rising sea levels, and shifting forest boundaries. In turn, these changes to our natural resources can (6) cause serious impacts on our ways of life and our livelihoods. And, of more recent concern, some of these physical changes actually cause a direct release of even more greenhouse gases or cause more damage to plants that photosynthesize and store carbon, creating a positive feedback loop in the system that threatens to accelerate climate change.

Human Activities that Influence Climate Change

Four main human activities are causing atmospheric concentrations of greenhouse gases to rise:

• Combustion of fossil fuels, which releases carbon dioxide, nitrous oxide and water vapour (and sometimes many other compounds if combustion is incomplete). Burning fossil fuels is the main source of greenhouse gas emissions from human activities; emissions arising from human activities are called anthropogenic emissions.
• The direct venting and release of greenhouse gases through activities such as leaky pipes and valves, chemical processes, spreading fertilizer, and rotting garbage, to name a few. Because these are from diffuse sources and are often unintentional, air quality experts refer to them as fugitive emissions. However, a significant share of Canada's fugitive emissions do arise from the release of greenhouse gases during the production, processing, transmission, storage, and delivery of oil, gas and coal. Released gases that are burned before they are disposed of (such as flaring of natural gas at oil and gas production facilities) are also considered fugitive emissions. ¹⁴ Certain industrial processes produce fugitive emissions in the form of chlorofluorocarbons, nitrous oxide, and sulphur hexafluoride as well as CO₂.
• Erosion of carbonsinks and loss of carbon reservoirs, including reducing the ability of green plants to absorb CO₂ from the atmosphere and bind it into organic matter (biomass) in soils, forests and other vegetation.
• Other activities such as landfills and livestock production (and, in other parts of the world, rice farming), also generate greenhouse gases, particularly methane.

Countries compile their greenhouse gas inventories by measuring and reporting emissions using specific methods. It's helpful to know a few things about how greenhouse gases are measured and reported before wading into the numbers and comparisons.

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12. Source: Intergovernmental Panel on Climate Change 2001. Third Assessment Report.
13. Source: Government of Canada. 2002. Canada's Greenhouse Gas Inventory 1990-2000.
14. Source: Government of Canada. 2002. Canada's Greenhouse Gas Inventory 1990-2000.