Sources of greenhouse gases
Carbon dioxide (CO2) is the most important greenhouse gas. However, there are several others, which, although present in much smaller quantities, have a powerful impact. They include methane, oxides of nitrogen and sulphur and water vapour. Carbon dioxide is released in the burning of fossil fuels (such as oil, natural gas and coal) in power stations, buildings and transport. Other sources include deforestation, land clearance and peat burning in the tropics. Methane is produced by landfill sites, melting permafrost and livestock. Nitrous oxides are produced from the burning of fossil fuels and agriculture – especially fertilizers. The term Carbon Dioxide equivalent (CO2 e) is used to measure all greenhouse gases.
Since the start of the industrial revolution the concentration of CO2 has risen from 280ppm in 1750 to reach around 380 parts per million (ppm) in 2005. The combined levels from carbon dioxide and all the other greenhouse gases emitted by human activities is now around 430ppm CO2 e and is rising at around 2.3ppm per year.
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Useful links
EC Europa Understanding greenhouse gases (pdf)
Reuters The heat is on for methane
NASA Carbon Dioxide emissions from fossil fuel burning
International Energy Agency CO2 emissions 2011 highlights