Global vegetation zonation and terrestrial climate of the warm Early Eocene

The early Eocene is a key geological time interval to further our understanding of climate change and biosphere variability under high atmospheric CO2 concentrations of more than 800 ppmv that could potentially be reached by the end of this century under very high emission scenarios. Vegetation plays a crucial role in the global carbon cycle and climate, and future warming associated with high atmospheric CO2 will alter modern vegetation patterns and biome distribution, consequently affecting vegetation-climate feedbacks. Here we present the most comprehensive global synthesis of vegetation and quantitative terrestrial climate estimates to date, compiled for 193 palaeobotanical locations, covering the early Eocene (Ypresian; 56.0-47.8 Ma). The floristic components of these palaeofloras are translated into 41 Plant Functional Types (PFT) and statistically grouped into palaeo-biomes. In addition, we used leaf phenology and PFT percentage of shrubs and xerophytes to assess vegetation openness. Our global biome reconstruction and quantitative climate estimates show a warmer and overall wetter world with reduced latitudinal temperature gradients and highlight the importance of climate seasonality as environmental controls of early Eocene biome distribution. A comparison of proxy-based reconstructions with outputs of the vegetation model BIOME4, driven by climate models of the Deep-Time Model Intercomparison Project (DeepMIP), show general good agreement at low intertropical and high polar latitudes. However, widespread discrepancies between proxy reconstructed forests and woodlands and modelled dry shrublands and deserts, covering most of the subtropics and mid latitudes, reveal fundamental gaps in our understanding of the early Eocene hydrological cycle and/or vegetation-climate interaction.