The majority of methane gas emissions on Earth come from human activities related to coal mining, petroleum, natural gas systems, landfills, the raising of livestock and fermentation. Methane gas also comes from natural sources such as sediments, termites, wildfires, oceans and volcanoes. The largest natural sources of methane gas in the world are wetlands.
The majority of methane gas emissions in the U.S. come from the storage, distribution, processing and transmission of natural gas. Large amounts of methane gas are also produced from livestock when they digest food. Landfills in the U.S. emit large amounts of methane gas, as a result of decomposing waste. Methane gas is twenty times more harmful to the atmosphere when compared to carbon dioxide, in terms of the negative impact it has on contributing to global warming.