FIG 1.

Sources of atmospheric methane. The proportion of atmospheric methane emissions caused by anthropogenic activities (red), produced by biogenic processes (blue), and the overlap between the two categories (purple) is shown. Percentages of each methane source were determined from atmospheric observation-based calculations reported by Dean et al. (5). The category “other natural sources” is primarily composed of biologically produced methane (8% of total) in freshwater and marine sediments and geologically produced methane (3% of total).