Scientists recognize carbon dioxide (CO₂), methane (CH₄), chlorofluorocarbons (CFCs), nitrous oxide (N₂0), and water vapor as significant greenhouse gases. Greenhouse gases account for less than one percent of Earth’s atmosphere. These gases trap heat in Earth’s atmosphere, preventing the heat from escaping back into space. Human activities, such as using gasoline in automobiles for fuel, account for the release of carbon dioxide and nitrogen oxides.

* HFCs = hydrofluorocarbons, PFCs = perfluorocarbons, SF₆ = sulfur hexafluoride.