Magnitude of biome shifts over the last 21,000 years reveals the impact of seasonality and intense warming on future vegetation

Ongoing global warming and intensified human disturbance are projected to substantially alter future biome dynamics. However, robust prediction of such shifts requires long-term, spatially extensive datasets to evaluate model performance. Here, we integrate pollen-based biome reconstructions from a global compilation of 3,420 fossil records with simulations from the Max Planck Institute Earth System Model (MPI-ESM) to detect and attribute biome shifts over the past 21,000 years. Our results show that currently non-forested regions and ecotones have undergone more frequent biome shifts than forested and intra-biome areas since the Last Glacial Maximum (LGM). In the Northern Hemisphere, biome changes were particularly pronounced during the LGM–Lateglacial period, characterized by elevated compositional turnover and frequent biome-type transitions, driven by rapid growing season warming and enhanced seasonality. In contrast, anthropogenic-driven compositional turnover over the past 2,000 years surpassed that induced by LGM–Lateglacial climate change, but did not result in biome-type shifts. Future projections based on MPI-ESM simulations under a high-emission scenario (RCP 8.5) suggest that ecotones and non-forested regions—particularly those subject to increasing seasonality and warming—are likely to experience the most substantial biome shifts over the next 300 years.