CO2 contributes about 50% to the greenhouse effect. The other greenhouse gases are methane, chlorofluorocarbons (CFCs) and nitrous oxide (N2O).
Methane - is released during coal-mining activities, oil exploration and when vegetation is burnt during land clearance. The main source of methane though is agricultural activity. It is released from wetlands such as rice paddies and from animals, particularly cud-chewing species like cows. The problem with methane is that as the world population increases, agricultural activity must increase and so emissions of methane will also increase. Since the 1960s the amount of methane in the air has increased by 1% per year - twice as fast as the build up of CO2 .
Nitrous oxide - comes from both natural and man-made processes. Human influenced sources, which represent about 45% of output to the atmosphere, are mainly: fossil fuel combustion, as in power stations; use of nitrogenous fertilisers; burning rainforests and human and animal waste. N2O contributes about 6% to the greenhouse effect at the moment.
CFCs - once found in fridges, air conditioners, aerosols etc. are extremely effective greenhouse gases. Although there are lower concentrations of CFCs in the atmosphere than CO2 they trap more heat. A CFC molecule is 10,000 times more effective in trapping heat than a CO2 molecule, methane is about 30 times more effective. Methane molecules survive for 10 years in the atmosphere and CFCs for 110 years.
Due to their effect on the ozone, and their role in the ozone layer hole CFCs were widely banned and their use discontinued. In 2013 a report that was issued in the journal Nature Geoscience suggested that this halt in CFC production and emissions actually contributed to the pause in rising global temperatures.
For more information see Pollution and to find out more about fossil fuels take a look at Energy. Related factsheets include Acid Rain, Meat free Mondays, Our Battered Biosphere.
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