Global wetland contribution to 2000–2012 atmospheric methane growth rate dynamics

<jats:title>Abstract</jats:title>                <jats:p>Increasing atmospheric methane (CH<jats:sub>4</jats:sub>) concentrations have contributed to approximately 20% of anthropogenic climate change. Despite the importance of CH<jats:sub>4</jats:sub> as a greenhouse gas, its atmospheric growth rate and dynamics over the past two decades, which include a stabilization period (1999–2006), followed by renewed growth starting in 2007, remain poorly understood. We provide an updated estimate of CH<jats:sub>4</jats:sub> emissions from wetlands, the largest natural global CH<jats:sub>4</jats:sub> source, for 2000–2012 using an ensemble of biogeochemical models constrained with remote sensing surface inundation and inventory-based wetland area data. Between 2000–2012, boreal wetland CH<jats:sub>4</jats:sub> emissions increased by 1.2 Tg yr<jats:sup>−1</jats:sup> (−0.2–3.5 Tg yr<jats:sup>−1</jats:sup>), tropical emissions decreased by 0.9 Tg yr<jats:sup>−1</jats:sup> (−3.2−1.1 Tg yr<jats:sup>−1</jats:sup>), yet globally, emissions remained unchanged at 184 ± 22 Tg yr<jats:sup>−1</jats:sup>. Changing air temperature was responsible for increasing high-latitude emissions whereas declines in low-latitude wetland area decreased tropical emissions; both dynamics are consistent with features of predicted centennial-scale climate change impacts on wetland CH<jats:sub>4</jats:sub> emissions. Despite uncertainties in wetland area mapping, our study shows that global wetland CH<jats:sub>4</jats:sub> emissions have not contributed significantly to the period of renewed atmospheric CH<jats:sub>4</jats:sub> growth, and is consistent with findings from studies that indicate some combination of increasing fossil fuel and agriculture-related CH<jats:sub>4</jats:sub> emissions, and a decrease in the atmospheric oxidative sink.</jats:p>

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