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 (CH₄) concentrations, with gross primary productivity (GPP) serving as a key proxy for predicting CH₄ fluxes, yet the efficiency with which photosynthetic carbon is associated with CH₄ fluxes remains poorly quantified at the global scale. Here, we integrated multiple GPP products with CH₄ data sets to evaluate global CH₄/GPP ratios, as an apparent ecosystem-level metric of methane–carbon coupling. We found striking spatial heterogeneity, with the highest CH₄/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 CH₄/GPP, with temperature being the strongest predictor. Future projections under four Shared Socioeconomic Pathway scenarios suggested a relatively stable global mean CH₄/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.