Fig. 6: Modelled influence of evolving OH concentrations and individual emission sectors on the δ¹³C_CH4 isotopic ratio.

Anomaly in globally averaged δ¹³C_CH4 (‰) from observations and from the difference between box model simulations (see Methods and Supplementary Fig. 10) that are run with evolving vs. constant (a) OH concentrations, (b) anthropogenic emissions (from 2007), and (c) wetland emissions. In (a), three different OH datasets have been used (AerChemMIP, CCMI and OsloCTM3), and the green shading represents the range for the three different AerChemMIP models while dotted lines assume constant OH for the remaining time period (CCMI and AerChemMIP datasets end in 2010 and 2014, respectively). In (b) and (c), shading represent +/−1σ uncertainty in the isotopic signature for individual anthropogenic emission sectors (b) and wetland emissions (c). Observations are from Table S4 in Schaefer, et al.¹⁰⁰ (black line) and WMO/GAW² (grey line and shading).