Methane (CH₄) is a powerful greenhouse gas, and is the second-largest contributor to climate warming after carbon dioxide (CO₂). A molecule of methane traps more heat than a molecule of CO₂, but methane has a relatively short lifespan of 7 to 12 years in the atmosphere, while CO₂ can persist for hundreds of years or more.

Methane comes from both natural sources and human activities. An estimated 60% of today’s methane emissions are the result of human activities. The largest sources of methane are agriculture, fossil fuels, and decomposition of landfill waste. Natural processes account for 40% of methane emissions, with wetlands being the largest natural source. (Learn more about the Global Methane Budget.)