MioVeg1: A Global Middle Miocene Vegetation Reconstruction for Climate Modeling

Climate models require boundary condition information, such as vegetation and soil distributions because they influence the mean state climate, and feedbacks can significantly influence regional climate and climate sensitivity to CO₂ forcing. Information about past distributions comes primarily from the paleobotanical record, which is often supplemented by a vegetation model to fill data gaps. For recent past periods such as the Pliocene, a quantitative suitability assessment of these vegetation model simulations is sufficient. However, the Miocene Climate Optimum spanning 16.9–14.7 Ma was the warmest period on Earth over the last ∼25 million years and models struggle to reproduce those conditions for the range of paleogeographies and CO₂ concentrations tested, particularly at high latitudes. Here we bring together the Miocene modeling and data communities to update previous vegetation reconstructions used for climate modeling with a new regional approach that relaxes the requirement for a single model simulation to be used, blending instead simulations forced by different paleogeographies and CO₂ concentrations. This ensures the simulated vegetation is first, and foremost, consistent with the paleorecord and provides a baseline for future comparisons. The reconstruction shows global increases in forest cover at all latitudes as compared to today and extensive C₃ grasslands across the high northern latitudes. Data gaps at high latitudes are filled with vegetation models forced by higher CO₂ concentrations than were required at lower latitudes consistent with the inability of current models to simulate Miocene high latitude warmth.