Global Warming
Last Update: 12/02/2001

GREENHOUSE GASES

Since the beginning of the industrial revolution, atmospheric concentrations of carbon dioxide have increased nearly 40%, methane concentrations have more than doubled, and nitrous oxide concentrations have risen about 15%.⁴ These increases have enhanced the heat-trapping capability of the earth’s atmosphere causing the greenhouse effect.

Scientists generally believe that the combustion of fossil fuels and other human activities such as deforestation are the primary reason for the increased concentration of carbon dioxide in the atmosphere. Since fossil fuels provide most of the energy used by humans, everything from our factories to our cars to our refrigerators directly cause the release of some carbon dioxide. From this graph², one can see that the concentration of carbon dioxide has increased greatly after the industrial revolution.

Living forests and soil, absorb and store large amounts of carbon dioxide. Deforestation alters the carbon cycle be eliminating trees and disturbing soil. This carbon cycle involves not only forests and soil, but also oceans and the atmosphere. They act as either sinks or sources for carbon. A sink absorbs more carbon than it gives off while a source emits more carbon than it absorbs. Before the industrial revolution the amount of carbon moving around was relatively in balance. However, in the present day, with the burning of fossil fuels, at least six billion tons of carbon is introduced to the carbon cycle every year. Some good examples of this are the Canadian forests, which until the 1980s use to act as a sink for the carbon cycle. Now, however, through fires, insect infestation and harvesting, they have become a net source. Modern farming practices also disrupt the carbon cycle. Soils, which contain about 75% of carbon found on land are excellent sinks. Unfortunately, once cultivated the organic matter that soil contains drops by 20-50%.⁵

Another important greenhouse gas which we are adding to in the atmosphere is methane. Naturally occurring methane emissions come from wetlands where anaerobic decay of material results in the production and release of methane. Other natural methane sources include fires and animals. Human industrialization is responsible for 50% of the methane in our atmosphere. Methane’s overall contribution to global warming is significant because it is estimated to be 21 times more effective at trapping heat in the atmosphere than carbon dioxide.⁴ The graph² shows us the increase in methane concentration over the past 100 years and it has doubled.

Anthropogenic sources of methane, which means man-made sources, include rice cultivation, landfills and the mining, processing and distribution of fossil fuels.⁶

Nitrous oxide emissions are primarily due to microbial action in the soils. However, as one can see from the graph⁷, anthropogenic activities have contributed to a 15% growth in nitrous oxide concentrations in the atmosphere over the last 200 years.

While nitrous oxide emissions are much lower than carbon dioxide emissions, nitrous oxide is approximately 310 times more powerful than carbon dioxide at trapping heat in the atmosphere.⁴ Anthropogenic sources include land clearing, fossil fuel consumption, and fertilizer.⁶

Man-made gases, such as hydrofluorocarbon, perfluorocarbon and sulphur hexafluoride, each contribute to global warming. The first two were developed as an alternative to CFC’c which were blacklisted internationally in 1987. The hydrofluorocarbon gas has a global warming potential of up to 10 000 times that of carbon dioxide, and its main uses are in refrigeration, cleaning agents and in semi-conductor manufacturing. The perfluorocarbon gas has the same global warming potential, and it is used as a purging agent for semi-conductor manufacture and small amounts are produced during the uranium enrichment processes. Sulphur hexafluoride has a global warming potential of 25 000 times that of carbon dioxide, and it is used as an insulating material for high voltage equipment and also in water leak detection.⁴

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