Greenhouse gas
A greenhouse gas (GHG) is a natural or human-produced atmospheric gas that absorbs and emits radiation at particular wavelengths, contributing to the greenhouse effect. Major examples include carbon dioxide, methane, nitrous oxide, ozone, water vapour, and several manufactured halogenated gases.
In simple terms
Greenhouse gases let much incoming sunlight pass through the atmosphere while absorbing some heat radiated by Earth. This natural effect makes the planet habitable. Human activities increase concentrations of several gases, strengthening the effect and changing the climate. Different gases remain in the atmosphere for different periods and influence warming differently, so inventories commonly compare them using global warming potential and express totals as carbon dioxide equivalent.
Why it matters
Knowing which gases come from which activities helps organizations and governments choose effective reductions. A greenhouse gas inventory separates sources and gases before combining them, while an emission factor can estimate releases from activity data. Preserving gas-level information matters because an identical carbon dioxide equivalent total can represent gases with different lifetimes and physical effects.
Example
For example, a food company may identify carbon dioxide from fuel combustion, methane from organic waste, and refrigerant leakage from cooling equipment. It can quantify each gas separately, convert them to a common reporting unit, and prioritize actions suited to each source rather than treating all emissions as physically identical.
How it differs
Carbon dioxide equivalent
A greenhouse gas is an atmospheric substance with heat-trapping properties; carbon dioxide equivalent is a comparison unit used to express the climate effect of an amount of that gas.