A hydrocarbon that is a greenhouse gas with a global warming potential (GWP) most recently estimated at 25 times that of carbon dioxide (CO2). Methane is produced through several means, including anaerobic (without oxygen) decomposition of waste in landfills; as a product of animal digestion; by decomposition of animal wastes; by production and distribution of natural gas and petroleum; through coal production; and through incomplete fossil fuel combustion.