Large Methane Emission Fluxes Observed from Tropical Wetlands in Zambia

Methane (CH4) is a potent greenhouse gas with a warming potential 84 times that of carbon dioxide (CO2) over a 20-year period. Atmospheric CH4 concentrations have been rising since the 19th century but the cause of large increases post-2007 are disputed. Tropical wetlands are thought to account for ∼20% of global CH4 emissions, but African tropical wetlands are understudied and their contribution is uncertain. In this work, we use the first airborne measurements of CH4 sampled over three wetland areas in Zambia to derive emission fluxes. Three independent approaches to flux quantification from airborne measurements were used: airborne mass balance, airborne eddy-covariance, and an atmospheric inversion. Measured emissions (ranging from 5–28 mg m-2 hr-1) were found to be an order of magnitude greater than those simulated by land surface models (ranging from 0.6–3.9 mg m-2 hr-1), suggesting much greater emissions from tropical wetlands than currently accounted for. The prevalence of such underestimated CH4 sources may necessitate additional reductions in anthropogenic greenhouse gas emissions to keep global warming below a threshold of 2 °C above pre-industrial levels.