Estimating global natural wetland methane emissions using process modelling: spatio-temporal patterns and contributions to atmospheric methane fluctuations

The fluctuations of atmospheric methane (CH₄) that have occurred in recent decades are not fully understood, particularly with regard to the contribution from wetlands. The application of spatially explicit parameters has been suggested as an effective method for reducing uncertainties in bottom-up approaches to wetland CH₄ emissions, but has not been included in recent studies. Our goal was to estimate spatio-temporal patterns of global wetland CH₄ emissions using a process model and then to identify the contribution of wetland emissions to atmospheric CH₄fluctuations.

Global.

A process-based model integrated with full descriptions of methanogenesis (TRIPLEX-GHG) was used to simulate global wetland CH₄emissions.

Global annual wetland CH₄ emissions ranged from 209 to 245 Tg CH₄ year⁻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 0.48 Tg CH₄ year⁻¹, which was largely caused by emissions from tropical wetlands showing a decreasing trend of 0.44 Tg CH₄ year⁻¹ since the 1970s. Emissions from tropical, temperate and high-latitude wetlands comprised 59, 26 and 15% of global emissions, respectively.

Global wetland CH₄ emissions, the interannual variability of which was primary controlled by tropical wetlands, partially drive the atmosphericCH₄ burden. The stable to decreasing trend in wetland CH₄ emissions, a result of a balance of emissions from tropical and extratropical wetlands, was a particular factor in slowing the atmospheric CH₄ growth rate during the 1990s. The rapid decrease in tropical wetland CH₄emissions that began in 2000 was supposed to offset the increase in anthropogenic emissions and resulted in a relatively stable level of atmospheric CH₄ from 2000 to 2006. Increasing wetland CH₄ emissions, particularly after 2010, should be an important contributor to the growth in atmospheric CH₄ seen since 2007.