The carbon isotopic composition of atmospheric methane

Abstract

Recent measurements of the carbon isotopic abundance of atmospheric methane give a value of δ( 13 C/ 12 C) = −47.0 ± 0.3‰, which is significantly different from earlier values measured by others between 1950 and 1970. The isotopic composition of various sources and the possibility of a temporal trend are discussed. The average methane concentration measured was 1.66 ppm, which is in accord with the increase in concentration since 1965–1970 observed in other studies.