6.1.3—Greenhouse gases and aerosols
- Syllabus
- First assessment 2026
- Objective
- 6.1.3
- Level
- SL
Classify a Gas or Particle by Its Radiation Path
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.