Simulating Miocene warmth: insights from an opportunistic Multi-Model ensemble (MioMIP1) and efforts towards a coordinated intercomparison (MioMIP2)

The Miocene epoch, spanning 23.03-5.33Ma, was a dynamic climate of sustained, polar-amplified warmth that peaked during the Miocene Climatic Optimum (16.75-14.5Ma). Miocene atmospheric CO₂ concentrations are typically reconstructed between 300-600 ppmv with estimates as high as 800-1100 ppmv during the MCO. With surface temperature reconstructions pointing to substantial midlatitude and polar warmth, it is unclear what processes maintained the much weaker-than-modern equator-to-pole temperature gradient. Emanating from community discussions at MioMeet (hosted by the Bolin Centre for Climate Research in 2019), Burls et al. (2021) synthesize several Miocene climate modeling efforts, together with available terrestrial and ocean surface temperature reconstructions. The range of model-data agreement was evaluated, highlighting robust mechanisms operating across the Miocene modelling efforts, as well as the regions where the differences across models (coming from a combination of model differences in imposed non-CO₂ Miocene boundary conditions and model feedback strengths) result in a large spread in warming responses. This MioMIP1 effort was an ensemble of opportunity: the models, boundary conditions, and reference datasets were state-of-the-art, but also inhomogeneous and not ideal for a formal intermodel comparison effort. Building on MioMIP1, the Miocene community is currently drafting the experimental design for a coordinated set of MioMIP2 simulations wherein participating modelling groups will use common boundary conditions. This talk will review the take-home findings from MioMIP1 and the status of the community’s MioMIP2 effort.