• DOI:10.1073/pnas.1616426114
• Corpus ID: 5013516

Role of atmospheric oxidation in recent methane growth

@article{Rigby2017RoleOA,
  title={Role of atmospheric oxidation in recent methane growth},
  author={Matthew L. Rigby and Stephen A. Montzka and Ronald G. Prinn and James W. C. White and Dickon Young and Simon J. O'Doherty and Mark F. Lunt and Anita L. Ganesan and Alistair J. Manning and Peter G. Simmonds and Peter K. Salameh and Christina M. Harth and Jens M{\"u}hle and Ray F. Weiss and Paul J. Fraser and L. Paul Steele and Paul B. Krummel and Archie Mcculloch and Sunyoung Park},
  journal={Proceedings of the National Academy of Sciences},
  year={2017},
  volume={114},
  pages={5373 - 5377}
}

• M. Rigby, S. Montzka, +16 authors Sunyoung Park
• Published 17 April 2017
• Environmental Science
• Proceedings of the National Academy of Sciences

Significance Methane, the second most important greenhouse gas, has varied markedly in its atmospheric growth rate. The cause of these fluctuations remains poorly understood. Recent efforts to determine the drivers of the pause in growth in 1999 and renewed growth from 2007 onward have focused primarily on changes in sources alone. Here, we show that changes in the major methane sink, the hydroxyl radical, have likely played a substantial role in the global methane growth rate. This work has significant implications for our understanding of the methane budget, which is important if we are to better predict future changes in this potent greenhouse gas and effectively mitigate enhanced radiative forcing caused by anthropogenic emissions. The growth in global methane (CH4) concentration, which had been ongoing since the industrial revolution, stalled around the year 2000 before resuming globally in 2007. 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 concentrations 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 CH3CC3 emissions, which have uncertainty that previously limited the accuracy of OH estimates. We find a 64–70% 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 can explain some of the decline in the atmospheric 13CH4/12CH4 ratio and the recent growth in C2H6. 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.