THE FEW MAIN GREENHOUSE GASES-

The main greenhouse gases

Carbon dioxide (CO2)Human source: Comes mostly from burning fossil fuels (oil, gas, and coal) for electricity and in cars and factories. Also from forest burning.Annual increase: 0.5%Life span: 50-200 years

Methane (CH2)Human source: Bacterial decomposition of organic matter (without oxygen) in rice paddies, swamps, garbage dumps, and intestines of ruminants like cows and sheep. Also from buning wood, mining coal.Annual increase: 1%Life span: 10-12 years

Chlorofluorocarbons (CFCs)Human Source: Chemically synthesized for use as coolants in refrigerators and air conditioners. Also in foam insulation, aerosol sprays.Annual increase: 4%Life span: up to 10 000 years

Nitrous oxide (N2O)Human source: Bacterial reactions in soil and water and from the breakdown of nitrogen-based chemical fertilizers. Also from burning fossil fuels and wood (deforestation).Annual increase: 0.4%Life span: 150 years

Note: Man-made greenhouse gases include those manufactured and those released due to processes controlled through human activity (e.g., the burning of fossil fuels). Some greenhouse gases, such as chlorofluorocarbons (CFCs), are entirely man-made, while only a small percentage of others, such as carbon dioxide, are man-made. Although man-made greenhouse gases are a small percentage of the overall total, they are changing the balance.