Climate Constraints on the Methane‒Carbon Efficiency of Global Wetlands: Spatiotemporal Drivers and Future Projections

Abstract

Wetlands play an important role in the growth rate of atmospheric methane (CH ₄ ) concentrations, with gross primary productivity (GPP) serving as a key proxy for predicting CH ₄ fluxes, yet the efficiency with which photosynthetic carbon is associated with CH ₄ fluxes remains poorly quantified at the global scale. Here, we integrated multiple GPP products with CH ₄ data sets to evaluate global CH ₄ /GPP ratios, as an apparent ecosystem‐level metric of methane–carbon coupling. We found striking spatial heterogeneity, with the highest CH ₄ /GPP ratios in northern high‐latitude and tropical wetlands, and much lower values in some temperate regions. Using a random forest model, all variables explained 81% of the global variance in CH ₄ /GPP, with temperature being the strongest predictor. Future projections under four Shared Socioeconomic Pathway scenarios suggested a relatively stable global mean CH ₄ /GPP ratio, likely reflecting compensating regional changes and intrinsic climatic constraints on methane–carbon coupling. Despite this stability, scenario‐dependent differences became apparent, with higher ratios under high‐emission pathways. These results indicate that wetland methane–carbon coupling may be a spatially variable and climate‐sensitive property. Incorporating such relationships into Earth System Models may help reduce uncertainties in projecting wetland carbon–climate feedbacks under future climate change.