Atmospheric methane: Its contribution to global warming

Methane, a significant atmospheric trace-gas, controls numerous chemical processes and species in the troposphere and stratosphere. Its concentration in the Earth's atmosphere has been increasing at a rate of about 1% per year during the last century, and reached 1·72 ppmv in 1990. Methane is a strong greenhouse gas with significantly adverse environmental impacts. On a molecule-for-molecule basis, it is more than 20 times as potent a greenhouse gas as carbon dioxide. The contribution of methane to global warming between 1880 and 1980 has been estimated to be about 15%, with an increasing share, ~18%, during the 1980s. In this paper methods for estimating the change in atmospheric concentration of methane, and for predicting its global-warming effect, are described. Influences of some of the suggested emission-control policies are also discussed. Methane concentration in the atmosphere might reach a value of more than 4 ppmv by the end of the next century with no control policies implemented. This could produce an unavoidable long-term mean rise in the surface temperature of the Earth of more than 0·5°C.