Methane is one of the seven greenhouse gases marked for emissions reduction during the second commitment period (starting in 2013) of the Kyoto Protocol. The seven greenhouse gases are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6) and nitrogen trifluoride. Major sources of methane include sites for final disposal of organic waste, swamp bottoms, body waste from livestock, and the anaerobic breakdown process of sewage sludge.