Greenhouse Gases

The earth surface absorbs energy from the sun and radiates it back into the atmosphere. Socalled greenhouse gases are gases that, when present in the atmosphere, form a layer of insulation that traps the earth's outgoing heat. This causes the earth's overall temperature to become warm, a phenomenon originally known as the greenhouse effect, now more frequently called global warming or global climate change. The latter is a broader term that includes other atmospheric changes besides the greenhouse effect. Principal greenhouse gases include carbon dioxide (CO2), methane (CH4), ozone (O3), chlorofluorocarbons (CFCs), Nitrous oxides (N2O) and sulfur hexaflouride (SF6). While greenhouse gases are entering the atmosphere from both natural and human origins (the latter known as anthropogenic), the increase in human origins of such gases is most significant, and is thus driving the overall change in climate.

Atmospheric concentration of greenhouse gases has increased over the last century due to industrial and agricultural activity. The most significant greenhouse gas by volume is carbon dioxide. This is released into the atmosphere through the burning of fossil fuels (oil, natural gas, and coal) in vehicle exhaust, coal fired power plants, and industry. Similarly, methane concentrations have increased as a result of the production and transportation of fossil fuels, rice paddy farming, livestock production, and emissions from municipal solid waste landfills. Nitrous oxide is released from agricultural and industrial activities, and the combustion of both fossil fuels and solid waste.

Each greenhouse gas has a different per-molecule capacity for heat absorption. Methane traps over 21 times more heat per molecule than carbon dioxide, and nitrous oxide absorbs 270 times more heat per molecule than carbon dioxide. CFCs are also more powerful than carbon dioxide, however, emissions of CFCs have decreased significantly since the Montreal Protocol. There is significant public confusion between greenhouse gases that contribute to global climate change and gases that contribute to ozone depletion. This confusion is magnified by the fact that chlorofluorocarbons (CFCs) contribute to both ozone depletion and climate change.