There are five major greenhouse gases: water vapor, carbon dioxide, oxides of nitro gen, methane, and chlorofluorocarbons (CFCs). The last four have been significantly increased by human activities.
It’s more than just the rising atmospheric carbon dioxide levels that have been implicated in any possible global warming due to the greenhouse effect. While CO lev els are increasing at the rate of about 0.5 percent per year, methane, a very potent greenhouse gas that is also known as swamp gas, is rising at 0.8 percent per year. Atmospheric concentrations of methane, currently about 1680 parts per billion (PPB), are almost three times the 600 PPB value in pre-industrial revolution air. Methane con centrations have risen in part from increased rice cultivation and livestock numbers.
One molecule of methane has 20 times the heat-holding power of a CO molecule. And a molecule of CFC, which is produced only by humans, is 20,000 times more effi cient. Due to population increase and changes in the planet’s land use patterns, by the year 2000 atmospheric methane is expected to be six times higher than in the year 1800.

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