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

Abstract

Increasing atmospheric methane (CH₄) concentrations have contributed to approximately 20% of anthropogenic climate change. Despite the importance of CH₄ 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 CH₄ emissions from wetlands, the largest natural global CH₄ 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 CH4 emissions increased by 1.2 Tg yr⁻¹ (−0.2–3.5 Tg yr⁻¹), tropical emissions decreased by 0.9 Tg yr⁻¹ (−3.2−1.1 Tg yr⁻¹), yet globally, emissions remained unchanged at 184 ± 22 Tg yr⁻¹. 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 CH₄ emissions. Despite uncertainties in wetland area mapping, our study shows that global wetland CH₄ emissions have not contributed significantly to the period of renewed atmospheric CH₄ growth, and is consistent with findings from studies that indicate some combination of increasing fossil fuel and agriculture-related CH₄ emissions, and a decrease in the atmospheric oxidative sink.