6.1.3—Greenhouse gases and aerosols

Greenhouse gases absorb outgoing infrared radiation; aerosols are suspended particles that scatter or absorb radiation.

Water vapour, CO2, methane and nitrous oxide absorb and re-emit outgoing infrared radiation. CO2 and water vapour are abundant greenhouse gases, while methane also has a strong warming effect. Many aerosols scatter sunlight; black carbon absorbs radiation and can darken snow or ice.

CO₂ is a greenhouse gas; soot on snow is black carbon aerosol that lowers albedo. Both affect radiation, but through different classes.

Classify by physical form and radiation pathway. Water vapour is a greenhouse gas but its atmospheric abundance responds dynamically to temperature, so it is usually treated as a feedback rather than a direct mitigation target.

‘Warms’ does not identify the category; classify by physical form and mechanism.