METHANE HAS MANY sources, both natural and human-related, but just two major sinks: its destruction in the atmosphere, and its use by certain soil bacteria. Methane is a powerful greenhouse gas, each kg. emitted to the atmosphere having a global warming potential (GWP) 23 times greater than that of a kg. of carbon dioxide over a 100-year time horizon. Since the pre-industrial era, the concentration of methane in the atmosphere has more than doubled, rising from around 715 parts per billion (ppb) in 1800, to more than 1,770 ppb today—higher than at any time in the preceding 650,000 years. Methane emissions resulting from human activities now exceed those from natural sources, comprising around 60 percent of the 600 million metric tons of methane emitted globally ...