Methane (CH4) is a hydrocarbon, the primary constituent of natural gas and is a potent greenhouse gas (GHG). Current atmospheric concentration levels of methane are more than double the known natural range over the last 650,000 years.
Methane is 21 times more effective at trapping heat than carbon dioxide (CO2), so although global emissions are small by comparison, its effect on global warming is significant, accounting for about 14% of global GHG emissions.
Major sources of methane:
Man-made (60%) = coal mining, landfills, agriculture, oil & gas
Natural (40%) = wetlands, permafrost, gas hydrates, termites