Copenhagen climate summit: eight greenhouse gases and what they do

Several greenhouse gases contribute to global warming by trapping heat in the lower layers of the atmosphere. The top six below have been recognised by the IPCC as man-made causes of climate change, but water vapour and ozone also play major roles.

By Matthew MoorePublished: 11:00AM GMT 11 Dec 2009

Carbon dioxide is the gas with the greatest influence on climate change Photo: PA
1) Carbon dioxide (CO2)While composing just 0.04 per cent of the atmosphere, carbon dioxide is the focus of efforts to counter global warming because levels have increased significantly since industrialisation, through the burning of fossil fuels and deforestation.

2) Methane (CH4)Tonne for tonne, methane is around 30 times more damaging to the atmosphere than CO2. Produced mainly through agriculture – from burping cows to rotting vegetable matter – its levels have also shot up in the last 250 years. Generally considered a secondary threat to CO2 as it is found in smaller concentrations.
3) Nitrous oxide (N20)Emitted by animal manure, synthetic fertilisers and some industrial processes such as the production of nylon, nitrous oxide is considered the third most influential greenhouse gas in terms of its contribution to global warming. More commonly known as laughing gas because of its anaesthetic properties.
4) Hydrofluorocarbons (HFCs)Widely used in air-conditioning and refrigeration systems since CFCs were phased out in the 1990s because of their effect on the ozone layer, HFCs are now responsible for one per cent of human-caused warming. The chemicals' potency as greenhouse gases has led to legislation to limit their use and trade.
5) Perfluorocarbons (PFCs)Primarily released through aluminium production and semiconductor manufacture. They are largely immune to the processes that break down most pollutants in the atmosphere, where they can remain for thousands of years.
6) Sulfur Hexafluoride (SF6)The most potent greenhouse gas studied by climate change scientists, Sulfur Hexafluoride is used in small quantities in various industrial and electrical process such as the manufacture of circuit breakers.
7) Water vapour (H20)Gaseous water is the single largest contributor to the greenhouse effect, amplifying the warming caused by other gases because it occurs in greater quantities as temperatures rise. But water vapour is rarely discussed in debates about climate change because human activity has little impact on its overall levels in the atmosphere.
8) Ozone (O3)Scientists now believe that the destruction of the ozone layer by CFCs, long lamented by environmentalists, has actually helped counteract global warming as the gas is a significant contributor to the greenhouse effect. As the hole is repaired, climate change is expected to speed up.