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

Abstract

Increasing atmospheric methane (CH _4 ) concentrations have contributed to approximately 20% of anthropogenic climate change. Despite the importance of CH _4 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 _4 emissions from wetlands, the largest natural global CH _4 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 _4 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 CH _4 emissions. Despite uncertainties in wetland area mapping, our study shows that global wetland CH _4 emissions have not contributed significantly to the period of renewed atmospheric CH _4 growth, and is consistent with findings from studies that indicate some combination of increasing fossil fuel and agriculture-related CH _4 emissions, and a decrease in the atmospheric oxidative sink.

Keywords

• methanogenesis
• wetlands
• methane