Simulating the terrestrial biosphere in the high CO2 world of the early Eocene

The early Eocene is a warm period suitable for studying the influence of high atmospheric CO₂ concentrations on climate, the terrestrial biosphere, and their interaction. Here, we simulated the terrestrial biosphere of the early Eocene with a dynamic global vegetation model (LPJ-GUESS), driven by climate input from the Deep-Time Model Intercomparison Project (DeepMIP). We find a strong expansion of tropical and temperate forests to higher latitudes, which is more pronounced when assuming CO₂ concentrations at the high end of plausible values. The modeled vegetation distribution is compared to a recently compiled extensive early Eocene paleobotanical global dataset. Simulated and reconstructed vegetation show good agreement, which improves with higher CO₂ concentrations. In contrast to earlier vegetation modeling studies our simulations are able to accurately simulate the expansion of tropical forests under CO₂ concentrations larger than 4-times pre-industrial CO₂. Given the good agreement between modeled vegetation and paleobotanical data our simulations allow us to gain a more comprehensive understanding of the early Eocene terrestrial biosphere, including the global carbon cycle and the role of wildfires. In addition, our comparison of modeled vegetation and paleobotanical data is an important test of the performance of the climate and vegetation models used, which are also used to simulate future impacts of climate change.