Atmospheric methane: where did you come from, where did you go?

Abstract:

Atmospheric methane plays a major role in controlling climate, yet contemporary methane trends (1982-present) have defied explanation with numerous, often conflicting, hypotheses proposed in the literature. Specifically, atmospheric observations of methane from 1982 to present have exhibited periods of both increasing concentrations (from 1982 to 2000 and from 2007 to present) and stabilization (from 2000 to 2007). Explanations for the increases and stabilization have invoked changes in tropical wetlands, livestock, fossil fuels, biomass burning, and the hydroxyl radical (OH; the primary sink of methane). This talk will present results from some of my work on this topic: Turner et al., PNAS (2017, 2018, 2019). In particular, this talk will summarize the contemporary methane trends and arguments for variations with a particular focus on the role of potential changes in OH. It will discuss mechanisms by which global mean OH can change as well as how well-known climate oscillations (e.g., the El Nino-Southern Oscillation) can impact OH and, in turn, atmospheric methane.