Monday, January 16th 2012, 10:38 AM EST
This Q&A is part of the Guardian's ultimate climate change FAQ
Aside from water vapour, the four principal greenhouse gases are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and the halocarbons or CFCs (gases containing fluorine, chlorine and bromine). These gases – described in more detail here – can remain in the atmosphere for different amounts of time, from months to millennia, and affect the climate on very different timescales.
The lifetime in the air of CO2, the most significant man-made greenhouse gas, is probably the most difficult to determine, because there are several processes that remove carbon dioxide from the atmosphere. Between 65% and 80% of CO2 released into the air dissolves into the ocean over a period of 20–200 years. The rest is removed by slower processes that take up to several hundreds of thousands of years, including chemical weathering and rock formation. This means that once in the atmosphere, carbon dioxide can continue to affect climate for thousands of years.
Methane, by contrast, is mostly removed from the atmosphere by chemical reaction, persisting for about 12 years. Thus although methane is a potent greenhouse gas, its effect is relatively short-lived.
Nitrous oxide is destroyed in the stratosphere and removed from the atmosphere more slowly than methane, persisting for around 114 years.
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