A table of the main greenhouse gases and their attributes, sources and concentration levels from 1998. Naturally occurring greenhouse gases include water vapour, carbon dioxide, methane, nitrous oxide, and ozone. Greenhouse gases that are not naturally occurring include hydro-fluorocarbons (HFCs), perfluorocarbons (PFCs), and sulphur hexafl uoride (SF6), which are generated in a variety of industrial…