Drivers of persistent changes in the global methane cycle under aggressive mitigation action

Abstract

To achieve the goals under the Paris climate agreement comprehensive mitigation of greenhouse gas emissions is required. Here methane plays an important role. Therefore, better understanding of the global methane cycle is indispensable for robust climate projections and assessments of multi-gas mitigation strategies. Here we simulate the global methane cycle fully interactively over the period 1850-2100, including a Shared Socioeconomic Pathway with strong mitigation action (SSP1-2.6 ). We show that under SSP1-2.6 the atmospheric methane burden recovers to almost pre-industrial levels, but wetland methane emissions show a persistent upward trend from 166 Tg(CH4) yr-1 in the 1850s to 221 Tg(CH4) yr-1 in the 2090s. Analogously, the atmospheric methane lifetime exhibits a persistent downward trend from 9.3 to 7.3 years. We identify the trend in net primary productivity as the dominant driver behind the trend in wetland methane emissions, with a correlation coefficient of 0.7. Significantly, our work demonstrates that important components of the global methane cycle such as wetland methane emissions and the methane lifetime are subject to feedbacks in the Earth system which elude methane mitigation action. Therefore, future methane mitigation strategies will need to take into account feedbacks in the Earth system.