Impact of meteorology and emissions on methane trends, 1990–2004

Over the past century, atmospheric methane (CH 4 ) rose dramatically before leveling off in the late 1990s. The processes controlling this trend are poorly understood, limiting confidence in projections of future CH 4 . The MOZART‐2 global tropospheric chemistry model qualitatively captures the observed CH 4 trend (increasing in the early 1990s and then leveling off) with constant emissions. From 1991–1995 to 2000–2004, the CH 4 lifetime versus tropospheric OH decreases by 1.6%, reflecting increases in OH and temperature. The rise in OH stems from an increase in lightning NO x as parameterized in the model. A simulation including annually varying anthropogenic and wetland CH 4 emissions, as well as the changes in meteorology, best reproduces the observed CH 4 distribution, trend, and seasonal cycles. Projections of future CH 4 abundances should consider climate‐driven changes in CH 4 sources and sinks.