Global vegetation of the warm Early Eocene: insights from a model - data comparison

The Early Eocene, with CO₂ levels exceeding 800 ppm, is a well-suited period for studying the effects of elevated atmospheric CO₂ concentrations on climate, vegetation and their interplay. Here, we present insights from a model – data comparison using simulations with a dynamic global vegetation model (LPJ-GUESS) and a comprehensive global paleobotanical data set. The vegetation model is driven by climate input from four climate models of the Deep-Time Model Intercomparison Project Phase 1 (DeepMIP 1) under varying CO₂ concentrations. Using climate input from two models with CO₂ concentrations between three to six times pre-industrial CO₂, we successfully replicate the extension of tropical, sub-tropical and temperate forests into higher latitudes, consistent with the paleobotanical record. Notably, tropical forest extent as suggested by paleobotanical data is also captured at CO₂ concentrations exceeding four times pre-industrial CO₂, contrasting with previous modeling results. However, input from the other two climate models produce excessively dry conditions in subtropical regions, misaligning with the paleobotanical evidence. Our vegetation distribution results will inform the next phase of the DeepMIP (DeepMIP 2). In addition, our comparison provides insights into the performance of climate and vegetation models under high CO₂ concentrations, with implications for simulating future climate change and its impacts.