Global Wetland Methane Emissions From 2001 to 2020: Magnitude, Dynamics and Controls

The large uncertainties in estimating CH₄ emissions from wetland ecosystems, the leading natural source to the atmosphere, substantially hinder the quantification of the global CH₄ budget. This study used the IBIS-CH₄ (Integrated BIosphere Simulator-Methane) model, a process-based model integrating microbial mechanisms associated with CH₄ production and oxidation processes, to simulate global wetland CH₄ emissions from 2001 to 2020. Initially, we employed the IBIS-CH₄ model to evaluate its performance across 26 diverse wetland sites worldwide. The results showed that the magnitude and seasonality of observed CH₄ fluxes over various wetland sites were well reproduced. We then used this model to estimate the annual global wetland CH₄ emissions from 2001 to 2020, averaging 152.67 Tg CH₄ yr⁻¹, with a range of 135.72–167.57 Tg CH₄ yr⁻¹. The estimated global wetland CH₄ emissions are generally in agreement with the current bottom-up estimates (117–256 Tg CH₄ yr⁻¹) and closely overlap with independent top-down estimates (139–183 Tg CH₄ yr⁻¹). During 2001–2020, the estimated global wetland CH₄ emissions initially showed an increasing trend, followed by a decline. The peak of CH₄ emissions reached in 2010, coinciding with the peak of wetland area. The majority of global wetland CH₄ emissions were concentrated in tropical regions, which exhibited a clear seasonality and had a peak in July. The impact of meteorological factors on wetland CH₄ emissions was greater than that of leaf area index, indicating the importance of soil hydrothermal conditions on wetland CH₄ emissions.