Fig. 1: Time series (1850 to 2100) of key components in the global methane cycle.

Shown are trajectories for a long-lived and b short-lived climate forcers and drivers of the global methane cycle and responses, separated into c sources and d sinks of methane, respectively. Data depicted in each case represent a composite of ensemble simulations, with three ensemble members in each case, over the historic period (1850 to 2014) and SSP1-2.6 for the period 2015 to 2100. CO₂ surface mole fractions, anthropogenic nitrogen oxide (NO_x) and carbon monoxide (CO) emissions and emissions of methane from anthropogenic and wildfire sources are prescribed rather than simulated in the model. The panels depict a CO₂ surface mole fraction (ppm; the model is constrained by prescribing CO₂ mole fractions) and resultant surface temperature (insert I_a1) and tropospheric specific humidity (insert I_a2); b emissions of NO_x (emitted as NO) and CO from anthropogenic sources (A-NO_x in insert I_b1), and natural emissions of NO_x from lightning activity (L-NO_x in insert I_b1); c methane emissions from dominant anthropogenic and natural sources and resultant whole atmosphere methane burden (insert I_c1); the main sources of methane are anthropogenic emissions (red), wetland emissions (blue) and emissions from forest and grassland fires (yellow). Anthropogenic and fire emissions are prescribed while wetland emissions are simulated interactively; d dominant atmospheric methane sinks including reaction with hydroxyl (OH) in the troposphere (blue), stratospheric loss (red), and uptake by the soil (yellow). Also shown is the time series of the whole atmosphere methane lifetime (insert I_d1), as defined by Prather et al.³² and calculated as the whole atmosphere methane burden divided by the tropospheric CH₄ + OH reaction flux. All data shown represent annual global totals (for sources and sinks) and global annual averages (all other data), respectively. Solid lines denote the historic period, dotted lines represent SSP1-2.6. Where applicable, variation around the ensemble means is shown as shaded areas with a one-standard deviation width.