Qiuan Zhu^1,2, Changhui Peng^2,1, Jinxun Liu³, Hong Jiang⁴

　　1. Laboratory for Ecological Forecasting and Global Change, College of Forestry, Northwest A&F University, Yangling, Shaanxi 712100, China; 2. Centre CEF/ESCER, University of Quebec at Montreal, QC, Canada; 3. Western Geographic Science Center, U.S. Geological Survey, Menlo Park, CA 94025, USA; 4. International Institute for Earth System Science, Nanjing University, Hankou Road 22, Nanjing 210093, China

　　The fluctuations of atmospheric methane (CH₄) in recent decades are not fully understood, particularly regarding contributions by wetlands. A newly developed process-based model integrated with full descriptions of methanogenesis (TRIPLEX-GHG) was applied to simulate global wetland CH₄ emissions and to estimate spatiotemporal patterns of global wetland CH₄ emissions and identify the contribution of wetland emissions to atmospheric CH₄ fluctuations. The simulation results showed that: Global annual wetland CH₄ emissions ranged from 155 Tg C yr^-1 to 185 Tg C yr^-1 between 1901 and 2012, with peaks occurring in 1991 and 2012. There is a decreasing trend between 1990 and 2010 with a rate of approximately 0.36 Tg C yr^-1, which was largely caused by tropical wetlands emissions that have a decreasing trend of 0.33 Tg C yr^-1 since the 1970s. Tropical wetlands are the primary contributors to the inter-annual variability of global wetland CH₄ emissions and atmospheric CH₄. The stable-to-decreasing trend in wetland CH₄ emissions, which resulted from a balance of emissions from tropical and extratropical wetlands, was a factor particularly for the slow-down in the atmospheric CH₄ growth rate during the 1990s. Model simulations also showed that CH₄ emissions from tropical wetlands respond strongly to repeated ENSO events, with negative anomalies occurring during El Niño years and positive anomalies during La Niña years.