in the u.s., the number of landfill gas projects increased from 399 in 2005, to 594 in 2012 according to the environmental protection agency. these projects are popular because they control energy costs and reduce greenhouse gas emissions. these projects collect the methane gas and treat it, so it can be used for electricity or upgraded to pipeline-grade gas. (methane gas has twenty-one times the global warming potential of carbon dioxide). for example, in the u.s., waste management uses landfill gas as an energy source at 110 landfill gas-to-energy facilities. this energy production offsets almost two million tons of coal per year, creating energy equivalent to that needed by four hundred thousand homes. these projects also reduce greenhouse gas emissions into the atmosphere.