Carbon Dioxide or CO 2 is the most significant greenhouse gas released by human activities, mostly through the burning of fossil fuels. It is the main contributor to climate change. Methane is produced when vegetation is burned, digested or rotted with no oxygen present. Garbage dumps, rice paddies, and grazing cows and other livestock release lots of methane. You can find nitrous oxide naturally in the environment but human activities are increasing the amounts.
Nitrous oxide is released when chemical fertilizers and manure are used in agriculture.
Scientists may not agree exactly how much global warming will occur, or exactly how much the climate will change, but they do agree that some global warming has already occurred and there will likely be much more. The 12 warmest years in the past 140 years have all been since 1980, with 8 of them since 1990. For many Canadians, warmer temperatures might not seem like such a bad thing. Many larger cities could experience a significant rise in the number of very hot days. Air pollution problems would increase, placing children, the elderly and people suffering from respiratory problems at greatest risk of health effects.