Saunois, et al., report that unlike CO2, atmospheric methane concentrations are rising faster than at any time in the past two decades and, since 2014, are now approaching the most greenhouse-gas-intensive scenarios. The reasons for this renewed growth are still unclear, primarily because of uncertainties in the global methane budget. New analysis suggests that the recent rapid rise in global methane concentrations is predominantly biogenic, most likely from agriculture, with smaller contributions from fossil fuel use and possibly wetlands.
Additional attention is urgently needed to quantify and reduce methane emissions. Methane mitigation offers rapid climate benefits and economic, health and agricultural co-benefits that are highly complementary to CO2 mitigation.
Atmospheric methane (CH4) has experienced puzzling dynamics over the past 15 years. After a period of relative stagnation in the early 2000s (plus 0.5 plus-minus 3.1 ppb yr−1 increase on average for 2000–2006), atmospheric methane concentrations have increased rapidly since 2007 at more than ten times this rate (plus 6.9 plus-minus 2.7 ppb yr−1 for 2007–2015). The atmospheric growth rate of methane accelerated to plus 12.5 ppb in 2014 and plus 9.9 ppb in 2015, reaching an annual average concentration of 1,834 ppb in 2015.
Because of this acceleration, the evolution of atmospheric methane over the last three years is inconsistent with the mitigation required in the Representative Concentration Pathways (RCP) of 2.5, 4 and 6 W m−2 and now most closely aligns with the RCP 8.5 W m−2. This emerging dynamic highlights the methane growing contribution to global warming relative to the observed slower growth rates of CO2 over the past three years and a relatively constant growth rate of nitrous oxide (N2O).
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