Research into landfill methane suggests daily emissions as large as 250 tonnes/sq km of landfill. Collection systems can help recover much of this, but efficiency of recovery can vary from 30% for surface gas collection systems (least efficient) to 55% for pipe collection systems installed during landfill operation (least costly).
Total anthropogenic sources of methane are estimated at about 275 Mt per year. However, as with natural sources, these estimates have large uncertainties.
In 1996, UK methane emissions were 3.7 million tonnes, 16 per cent lower than in 1990. The main sources of methane emissions in 1996 were landfill (46 per cent) and farm animals (28 per cent).