CH₄ sources estimated from atmospheric observations of CH₄ and its ¹³C/¹²C isotopic ratios: 2. Inverse modeling of CH₄ fluxes from geographical regions

摘要

We present a time-dependent inverse modeling approach to estimate the magnitude of CH emissions and the average isotopic signature of the combined source processes from geographical regions based on the observed spatiotemporal distribution of CH and C-13/C-12 isotopic ratios in CH. 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 CH fluxes in the tropics (266 ± 25 Tg CH/yr) and southern extratropics (98 ± 15 Tg CH/yr) and reduced fluxes in the northern extratropics (252 ± 18 Tg CH/yr). The observations of C-13/C-12 isotopic ratios in CH indicate that the large a posteriori CH 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 CH emissions. [References: 40]