METHANE : A BUNCH OF INFORMATION FOR CLIMATE RESEARCH

Methane is a radiatively and chemically active trace gas of the earth\u27s atmosphere. Its atmospheric concentration has been measured continuously and directly since 1978 (STEELE et al., J. Atmos. Chem., 5,125,1987; BLAKE and ROWLAND, Science, 239,1129,1988; DLUGOKENCKY et al., J. Geophys. Res., 99,17021,1994). Before that the CH_4 concentration history has to be reconstructed from paleo records. Ice sheets and glaciers are so far the only archives which have stored the atmospheric gas composition directly. Results from various ice cores are consistent and prove the reliability of this archive. The pre-industrial CH_4 concentration changes, with some exceptions, in concert with the main climate features of the northern hemisphere. That is, lower concentrations of about 350 ppbv during ice ages, and higher concentrations, around 700 ppbv, during warm periods. Natural variations are most probably linked to the extent and source intensity of wetlands, the main natural source. The anthropogenic increase from 700 to over 1700 ppbv over the last 200yr is caused by emissions linked to the human population growth like domestic ruminants, rice paddies, human-induced fires, landfills, and fossil fuel exploitation (FUNG et al., J. Geophys. Res., 96,13033,1991 and references therein). CH_4 can, due to its global signal (neglecting a pole to pole difference of a few percent), be used to synchronise ice core data from various sites. This is extremely useful in investigating the causes of climate change