Estimating emissions of methane consistent with atmospheric measurements of methane and δ 13 C of methane

[摘要] We have constructed an atmospheric inversion framework based on TM5-4DVAR to jointly assimilate measurements of methane and δ 13 C of methane in order to estimate source-specific methane emissions. Here we present global emission estimates from this framework for the period 1999–2016. We assimilate a newly constructed, multi-agency database of CH 4 and δ 13 C measurements. We find that traditional CH 4 -only atmospheric inversions are unlikely to estimate emissions consistent with atmospheric δ 13 C data, and assimilating δ 13 C data is necessary to derive emissions consistent with both measurements. Our framework attributes ca. 85 % of the post-2007 growth in atmospheric methane to microbial sources, with about half of that coming from the tropics between 23.5 ∘  N and 23.5 ∘  S. This contradicts the attribution of the recent growth in the methane budget of the Global Carbon Project (GCP). We find that the GCP attribution is only consistent with our top-down estimate in the absence of δ 13 C data. We find that at global and continental scales, δ 13 C data can separate microbial from fossil methane emissions much better than CH 4 data alone, and at smaller scales this ability is limited by the current δ 13 C measurement coverage. Finally, we find that the largest uncertainty in using δ 13 C data to separate different methane source types comes from our knowledge of atmospheric chemistry, specifically the distribution of tropospheric chlorine and the isotopic discrimination of the methane sink.

[学科分类] 医学（综合）