What do we know about the global methane budget? Results from four decades of atmospheric CH 4 observations and the way forward

Abstract

Atmospheric CH 4 is arguably the most interesting of the anthropogenically influenced, long-lived greenhouse gases. It has a diverse suite of sources, each presenting its own challenges in quantifying emissions, and while its main sink, atmospheric oxidation initiated by reaction with hydroxyl radical (OH), is well-known, determining the magnitude and trend in this and other smaller sinks remains challenging. Here, we provide an overview of the state of knowledge of the dynamic atmospheric CH 4 budget of sources and sinks determined from measurements of CH 4 and δ 13 C CH4 in air samples collected predominantly at background air sampling sites. While nearly four decades of direct measurements provide a strong foundation of understanding, large uncertainties in some aspects of the global CH 4 budget still remain. More complete understanding of the global CH 4 budget requires significantly more observations, not just of CH 4 itself, but other parameters to better constrain key, but still uncertain, processes like wetlands and sinks. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'.