Exploring the Role of Interactive Methane in Earth System Models used for Climate Projections

Methane plays a crucial role in the Earth System as a greenhouse gas and a tropospheric ozone precursor. However, in Phase 6 of the Coupled Model Intercomparison Project (CMIP6), Earth System Models predominantly relied on prescribed surface methane concentrations derived from historical observations or predefined future pathways. This study uses novel Earth System Model capability to investigate the impact of an emissions-driven methane cycle, including interactive wetland emissions. Specifically, we explore the influence of interactive methane on the effective radiative forcing of carbon dioxide and the model’s transient and equilibrium climate responses to changes in carbon dioxide. The response of the climate to external forcings is intricately linked to climate feedbacks. With the inclusion of an interactive methane cycle in Earth System Models, understanding how changes in carbon dioxide and climate affect the methane cycle becomes imperative. This work critically re-evaluates the CMIP6 assessment of methane feedbacks and, for the first time, disentangles both the biophysical and radiative effects of carbon dioxide on wetland emissions and methane lifetime.  By enabling the interaction of the biophysical and radiative effects of carbon dioxide with natural methane emissions, concentrations, and climate responses, this presentation highlights the necessity of incorporating interactive methane components in Earth System Models. Notably, this approach provides scientists with the means to assess the direct implications of methane emission reduction policies and climate feedbacks on meeting global climate and air quality targets.