Global and Regional CH4Emissions for 1995-2013 Derived From Atmospheric CH4, δ13C-CH4, and δD-CH4Observations and a Chemical Transport Model

To better understand the current global CH(4)budget, biogenic, fossil fuel, and biomass burning CH(4)fluxes for the period 1995-2013 were inversely estimated from the observed mole fraction data of atmospheric CH(4)using a three-dimensional chemical transport model. Then, forward simulations of carbon and hydrogen isotope ratios of atmospheric CH4(delta C-13-CH(4)and delta D-CH4) were conducted using the inversion fluxes to evaluate the source proportion of the global total CH(4)emission. Model-simulated spatiotemporal variations of atmospheric CH(4)reproduce the observational results well; however, the simulated delta C-13-CH(4)and delta D-CH(4)values significantly underestimate their observed values as a whole. This implies that the proportion of biogenic CH(4)sources in the global CH(4)emission, deduced by inverse modeling, is overestimated, although the proportion is fairly comparable with the medians of recent multiple CH(4)inverse modeling. To reduce the disagreement between the observed and calculated isotope ratios, the CH(4)fluxes of individual source categories were adjusted using our atmospheric delta C-13-CH(4)and delta D-CH(4)data observed at Arctic and Antarctic surface stations. The resultant global average biogenic, fossil fuel, and biomass burning CH(4)fluxes over 2003-2012 are 346 +/- 11, 162 +/- 2, and 50 +/- 2 TgCH(4)year(-1), respectively. It is also strongly suggested that the leveling-off of atmospheric CH(4)in the early 2000s and the renewed growth after 2006/2007 are, respectively, explainable by the decrease in biogenic and biomass burning CH(4)emissions for 2000-2006 and the increase in biogenic CH(4)emissions after that period. These emission changes mainly originate in the tropics.