CH 4 sources estimated from atmospheric observations of CH 4 and its 13 C/ 12 C isotopic ratios: 1. Inverse modeling of source processes

A time‐dependent inverse modeling approach that estimates the global magnitude of atmospheric methane sources from the observed spatiotemporal distribution of atmospheric CH 4 , 13 C/ 12 C isotopic ratios, and a priori estimates of the source strengths is presented. Relative to the a priori source estimates, the inverse model calls for increased CH 4 flux from sources with strong spatial footprints in the tropics and Southern Hemisphere and decreases in sources in the Northern Hemisphere. The CH 4 and 13 C/ 12 C isotopic ratio observations suggest an unusually high CH 4 flux from swamps (∼200 ± 44 Tg CH 4 /yr) and biomass burning (88 ± 18 Tg CH 4 /yr) with relatively low estimates of emissions from bogs (∼20 ± 14 Tg CH 4 /yr), and landfills (35 ± 14 Tg CH 4 /yr). The model results support the hypothesis that the 1998 CH 4 growth rate anomaly was caused in part by a large increase in CH 4 production from wetlands, and indicate that wetland sources were about 40 Tg CH 4 /yr higher in 1998 than 1999.