UC Berkeley

Wetland methane (CH4) emissions (FCH4$${F}_{{{CH}}_{4}}$$) are important in global carbon budgets and climate change assessments. Currently, FCH4$${F}_{{{CH}}_{4}}$$ projections rely on prescribed static temperature sensitivity that varies among biogeochemical models. Meta-analyses have proposed a consistent FCH4$${F}_{{{CH}}_{4}}$$ temperature dependence across spatial scales for use in models; however, site-level studies demonstrate that FCH4$${F}_{{{CH}}_{4}}$$ are often controlled by factors beyond temperature. Here, we evaluate the relationship between FCH4$${F}_{{{CH}}_{4}}$$ and temperature using observations from the FLUXNET-CH4 database. Measurements collected across the globe show substantial seasonal hysteresis between FCH4$${F}_{{{CH}}_{4}}$$ and temperature, suggesting larger FCH4$${F}_{{{CH}}_{4}}$$ sensitivity to temperature later in the frost-free season (about 77% of site-years). Results derived from a machine-learning model and several regression models highlight the importance of representing the large spatial and temporal variability within site-years and ecosystem types. Mechanistic advancements in biogeochemical model parameterization and detailed measurements in factors modulating CH4 production are thus needed to improve global CH4 budget assessments.