Increase of atmospheric methane - causes and impact on the environment

In-situ measurements and analysis of air trapped in ice cores clearly indicate that the atmospheric CH4 abundance has changed with time during the last 2 centuries from about 0.6-0.7ppmv to the present level of 1.7ppmv. The increase in atmospheric CH4 is most likely due to the change of emission rates of several biogenic and non-biogenic sources such as fermentation by ruminants, anaerobic mineralisation of organic matter in rice paddies, biomass burning and emission of natural gas due to leakages. The annual total CH4 source strength is estimated to be 237 Tg for 1950 and 348 Tg for 1975 corresponding to an average rate of increase of 1.5% per year which agrees well with the observed increase of atmospheric CH4 of 1.5-1.7% per year. The CH4 production is mainly balanced by the photochemical oxidation of CH4 by OH assuming tropospheric mixing ratios of 1.1ppmv for 1950, 1.2ppmv for 1960 and 1.5ppmv for 1970. Because of the physical and chemical properties, the increase of atmospheric C H4 has considerable impact on the chemistry of the troposphere and stratosphere. (IFU)