Methane (CH4) is the second most important long-lived anthropogenic greenhouse gas. Since 2007 the growth rate has increased noticeably, the reason for this remains unexplained (1).

We performed a model synthesis inversion to fit TOMCAT CH4 and δ13C to surface sites by varying sources and sinks (2). Results show a prolonged decrease in OH since 2007 and increasing energy sector emissions (3).

For the first time we include measurements of δ13C in our inversion, which provides improved representation of not only CH4 but also δ13C variability.