Total anthropogenic sources of methane are estimated at about 275 Mt per year. However, as with natural sources, these estimates have large uncertainties. Measurements of fluxes into the atmosphere from this source vary from a small sink to a source of more than 50 mg/sq m/day. Net global emissions from rice paddies are now estimate at 60 to 100 Mt/year, with China and India collectively contributing between 15 and 30% of this amount. Research into landfill methane suggests daily emissions as large as 250 tonnes/sq km of landfill. Methane emissions from energy use are dominated by methane leakage and venting during production, transportation and /or distribution of natural gas and coal. Certain types of hydro power projects may also be significant sources of methane during the first few years after biomass flooding, although recent assessments indicated that most hydro reservoirs are deep enough to allow methane generated from bottom sediments to oxidize before being released into the atmosphere, and hence contribute little to methane emissions. Finally, increased deforestation and wood fuel use may be releasing about 34 Mt of methane each year.
It is estimated that in the UK the long-term greenhouse effect of methane from domestic and commercial waste is equivalent to over 50% of all carbon dioxide (CO2) produced from coal-fired power stations. Canadian emissions of methane from anthropogenic (non-natural) sources were estimated to be 3.7 megatonnes in 1990, comprising landfills (38%), oil and gas production (29%), domesticated animals (27%), coal mining (4%) and other miscellaneous sources.