We present a time-dependent inverse modeling approach to estimate the magnitude of CH4 emissions and the average isotopic signature of the combined source processes from geographical regions based on the observed spatiotemporal distribution of CH4 and C-13/C-12 isotopic ratios in CH4. The inverse estimates of the isotopic signature of the sources are used to partition the regional source estimates into three groups of source processes based on their isotopic signatures. Compared with bottom-up estimates, the inverse estimates call for larger CH4 fluxes in the tropics (266 +/- 25 Tg CH4/yr) and southern extratropics (98 +/- 15 Tg CH4/yr) and reduced fluxes in the northern extratropics (252 +/- 18 Tg CH4/yr). The observations of C-13/C-12 isotopic ratios in CH4 indicate that the large a posteriori CH4 source in the tropics and Southern Hemisphere is attributable to a combination both bacterial sources and biomass burning and support relatively low estimates of fossil CH4 emissions.

A time-dependent inverse modeling approach that estimates the global magnitude of atmospheric methane sources from the observed spatiotemporal distribution of atmospheric CH4, C-13/C-12 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 CH4 flux from sources with strong spatial footprints in the tropics and Southern Hemisphere and decreases in sources in the Northern Hemisphere. The CH4 and C-13/C-12 isotopic ratio observations suggest an unusually high CH4 flux from swamps (similar to200 +/- 44 Tg CH4/yr) and biomass burning (88 +/- 18 Tg CH4/yr) with relatively low estimates of emissions from bogs (similar to20 +/- 14 Tg CH4/yr), and landfills (35 +/- 14 Tg CH4/yr). The model results support the hypothesis that the 1998 CH4 growth rate anomaly was caused in part by a large increase in CH4 production from wetlands, and indicate that wetland sources were about 40 Tg CH4/yr higher in 1998 than 1999.