greenhouse gases

Trace gases present in the atmosphere, of natural or anthropogenic origin, which absorb and emit, at certain wavelengths, part of the radiation emitted by the Earth's surface, clouds, and the atmosphere itself, giving rise to the greenhouse effect. Notable among them are those known as primary, which are water vapor (H₂ O) - the most abundant, but of highly variable proportions -, carbon dioxide (CO₂), methane (CH₄), nitrous oxide (NO₂), and ozone (O₃). Apart from the above, there is a long list of gases produced exclusively by human activities, such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF₆). Both the effectiveness and the abundance of the different greenhouse gases vary greatly from one to another. They also have different atmospheric residence times.