Greenhouse gas
An atmospheric gas that absorbs and emits infrared radiation at wavelengths relevant to Earth's energy balance.
Example
Carbon dioxide, methane and nitrous oxide are greenhouse gases. Their effects and lifetimes differ.
The catch
Comparisons require a stated metric and time horizon.
Related terms
Carbon dioxide, Methane, Nitrous oxide, Albedo, Atmospheric lifetime, Carbon budget
In more depth
Greenhouse gas, explained.
A gas traps heat when its molecules vibrate in ways that absorb infrared light, which is why nitrogen and oxygen, the bulk of the air, play no part while trace gases matter so much. Water vapour is the most abundant greenhouse gas, yet inventories leave it out, because its concentration follows temperature and human emissions do not set it directly.
Accounting standards work from a defined basket. The GHG Protocol and national inventories cover carbon dioxide, methane and nitrous oxide plus several fluorinated industrial gases, which are rare but potent. Black carbon warms the climate too, yet it is a particle and belongs with the short-lived pollutants. When a claim mentions greenhouse gases, check which basket it uses, since leaving one gas out can make a footprint look smaller.
In the journal