© Author(s) 2007. This work is licensed under a Creative Commons License. Atmospheric Chemistry and Physics Centennial evolution of the atmospheric methane budget: what do the carbon isotopes tell us?

Abstract. Little is known about how the methane source in-ventory and sinks have evolved over recent centuries. New and detailed records of methane mixing ratio and isotopic composition (12CH4, 13CH4 and 14CH4) from analyses of air trapped in polar ice and firn can enhance this knowl-edge. We use existing bottom-up constructions of the source history, including “EDGAR”-based constructions, as inputs to a model of the evolving global budget for methane and for its carbon isotope composition through the 20th century. By matching such budgets to atmospheric data, we exam-ine the constraints imposed by isotope information on those budget evolutions. Reconciling both 12CH4 and 13CH4 bud-gets with EDGAR-based source histories requires a combi-nation of: a greater proportion of emissions from biomass burning and/or of fossil methane than EDGAR construction