Reduced biomass burning emissions reconcile conflicting estimates of the post-2006 atmospheric methane budget

Abstract

Several viable but conflicting explanations have been proposed to explain the recent ~8 p.p.b. per year increase in atmospheric methane after 2006, equivalent to net emissions increase of ~25 Tg CH₄ per year. A concurrent increase in atmospheric ethane implicates a fossil source; a concurrent decrease in the heavy isotope content of methane points toward a biogenic source, while other studies propose a decrease in the chemical sink (OH). Here we show that biomass burning emissions of methane decreased by 3.7 (±1.4) Tg CH₄ per year from the 2001–2007 to the 2008–2014 time periods using satellite measurements of CO and CH₄, nearly twice the decrease expected from prior estimates. After updating both the total and isotopic budgets for atmospheric methane with these revised biomass burning emissions (and assuming no change to the chemical sink), we find that fossil fuels contribute between 12–19 Tg CH₄ per year to the recent atmospheric methane increase, thus reconciling the isotopic- and ethane-based results.