- Greenhouse Gas: : A Greenhouse Gas is any gas that absorbs Infrared radiation in the atmosphere. Greenhouse gases include water vapor, carbon dioxide (CO₂), Methane (CH₄), Nitrous Oxide (N₂O), halogenated fluorocarbons (HCFCs), ozone (O3), perfluorinated carbons (PFCs), and hydrofluorocarbons (HFCs).