A brief review of atmospheric methane is presented with emphasis on the isotopic composition of 13CH4-12CH4. A tentative budget of the fluxes from natural and anthropogenic sources based on isotopic data is given. The trends of ??13C for atmospheric CH4 in the southern and northern hemisphere since 1978 are discussed with the following conclusions: (1) in the southern hemisphere an increasing ??13C trend is attributed to increasing fluxes of isotopically heavy CH4 from biomass burning; and (2) in the northern hemisphere the average ??13C of the source fluxes decreased from 1978 to 1983 at a rate much greater than can be reasonably accounted for by increasing fluxes of isotopically light CH4 from anthropogenic sources and therefore is attributed to increasing fluxes from natural sources. After 1982-1983 the ??13C increased at a greater rate in both hemispheres, which is attributed most plausibly to a decrease in the flux of isotopically light CH4 from natural sources. ?? 1988.
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