Emissions that trap heat in the atmosphere, causing global warming. The main greenhouse gases are carbon dioxide (CO2), Methane (CH4), Nitrous Oxide (N2O), and fluorinated gases (synthetic greenhouse gases emitted from industrial processes, including hydrofluorocarbons, perfluorocarbons, and surfur hexafluoride).[1] The Climate Registry draft update to its GHG reporting protocol now also includes NF3 (nitrogen trifluoride) for consistency with updates to the Kyoto Protocol.[2]

Sources:

[1] ARB website: http://www.arb.ca.gov/cc/inventory/inventory.htm. [2] Greenhouse Gases Overview, EPA website: http://www.epa.gov/climatechange/ghgemissions/gases.html.