- Journal Article
The growth in global methane (CH4) concentration, which had been ongoing since the industrial revolution, was observed to stall around the year 2000, before resuming globally in 2007. Here, we evaluate the role of the hydroxyl radical (OH), the major CH4 sink, in the recent CH4 growth. We also examine the influence of systematic uncertainties in OH on CH4 emissions inferred from atmospheric observations. We use observations of 1,1,1-trichloroethane (CH3CCl3), which is lost primarily through reaction with OH, to estimate OH levels as well as CH3CCl3 emissions, whose uncertainty has previously limited the accuracy of OH estimates. We find a 61% - 73% probability that a decline in OH has contributed to the post-2007 methane rise. Our median solution suggests that CH4 emissions increased relatively steadily during the late 1990s and early 2000s, after which, growth was more modest. This solution obviates the need for a sudden, statistically significant change in total CH4 emissions around the year 2007 to explain the atmospheric observations, and contributes to the decline in the atmospheric 13CH4/12CH4 ratio. Our approach indicates that significant OH-related uncertainties in the CH4 budget remain, and we find that it is not possible to implicate, with a high degree of confidence, rapid global CH4 emissions changes as the primary driver of recent trends, when our inferred OH trends and these uncertainties are considered.