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Summary
Methane is, after water vapor and carbon dioxide, the third most important greenhouse gas in the atmosphere. Its concentration in the atmosphere has more than doubled since preindustrial times. Human energy production and use, landfills and waste, cattle raising, rice agriculture, and biomass burning are considered responsible for this increase (1). However, ∼40% of current global methane sources are natural. Most natural emissions come from anaerobic decomposition of organic carbon in wetlands, with poorly known smaller contributions from the ocean, termites, wild animals, wildfires, and geological sources. Two observational studies now shed light on how these natural sources are changing in today's changing climate (2, 3).
