Methane–Climate Interactions over Phanerozoic Timescales in an Earth System Modelling Framework

Methane is a powerful greenhouse gas that plays an important role in Earth’s climate. However, its long-term evolution over deep-time remains poorly constrained. Consequently, methane is rarely treated as an explicit, dynamically evolving component in Earth system models, and its potential contribution to long-term climate variability has not been systematically explored.

Here we present a modelling framework coupled to the Earth System Model HadCM3, designed to investigate methane–climate interactions over multi-million-year timescales. The model represents major methane sources, with a particular focus on wetland emissions, and simulates methane sinks through an explicit atmospheric chemistry scheme, enabling a process-based calculation of atmospheric methane concentrations. Methane radiative forcing is subsequently derived from the simulated concentrations to evaluate its long-term climatic impact.

Our preliminary simulations indicate that methane variations exhibit nonlinear and systematic dependencies on background climate state and carbon cycle conditions. The persistent co-variation between CO₂ forcing and global temperature over the Phanerozoic, despite the gradual increase in solar luminosity, implies the presence of additional compensating forcings or feedback mechanisms. Our results indicate that methane radiative forcing alone is insufficient to provide this compensating influence, pointing to the involvement of additional long-term climate factors that are not yet fully understood.