Three Decades of Wetland Methane Surface Flux Modeling by Earth System Models‐Advances, Applications, and Challenges.

Earth System Models (ESMs) simulate the exchange of mass and energy between the land surface and the atmosphere, with a key focus on modeling natural greenhouse gas feedbacks. Methane is the second most important greenhouse gas after carbon dioxide. There are growing concerns over the rapidly increasing methane concentration in the atmosphere, underscoring the need for accurate global modeling of its emissions using ESMs. Of the multitude of sources of methane globally, wetlands are the largest natural emitters for methane, leading to significant efforts targeting their representation in ESMs with a special focus on their methane emissions. In this review, we first provide a historical overview of including wetland‐methane components in ESMs and how methane modeling approaches have evolved over time. Second, we discuss recent modeling advancements that show promise for improvements in methane emissions predictions, namely the coupling of surface and atmospheric modules of ESMs, the representation of microtopography and transport mechanisms, the resolution of microbial processes at different spatial‐temporal scales, and the improved mapping of wetland area extent across the different wetland types. Third, we shed light on the different challenges hindering accurate estimations of wetland‐methane emissions, as shown by the consistent discrepancy between bottom‐up and top‐down models' predictions. Finally, we emphasize that more detailed representation of biogeochemistry and dynamic hydrology while resolving the within‐wetland vegetation heterogeneity should improve model predictions, especially when coupled with expanding ground‐based measurement networks and high‐resolution remote sensing mapping of methane‐relevant variables, such as water elevation, water table depth, and methane concentration. Plain Language Summary: Earth system models (ESMs) are computer‐based tools to study and predict the complex relationships between the climate and ecosystem. One key aspect ESMs are used to study is the ecosystem role in emissions and uptake of greenhouse gases. Methane is the second most important greenhouse gas, and wetlands are the largest natural emitters for methane. In this review, we first provide a historical overview of including wetland‐methane components in ESMs and how methane modeling approaches have evolved over time. Second, we discuss recent modeling advancements that show promise for improvements in methane emissions predictions. Third, we shed light on the different challenges hindering accurate estimations of wetland‐methane emissions. Finally, we explore the knowledge gaps and point out some areas where models of wetland methane flux can improve. Key Points: Recent decades have seen significant improvements in simulating wetland‐methane dynamics in ESMs at both local and global scalesChallenges lie in discrepancies in model predictions and global mapping of different wetland typesImproving transport and microbial mechanisms coupled with expanding high‐resolution data sets should improve wetland‐methane estimations [ABSTRACT FROM AUTHOR]

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