Objective biome classification across global vegetation models reveals consistent biome shifts under future climate change

Abstract. Climate change is altering ecosystems and will reshape the global distribution of biomes. These shifts can significantly influence ecosystem functions and services that are essential for human livelihoods. Robust assessments of future biome dynamics are therefore urgently needed. Here, we employed random forest models and 31 observation-based biome maps representing current land cover to classify outputs from five global vegetation models (GVMs) into biomes, and evaluated potential biome shifts under three climate change scenarios (RCP2.6, RCP6.0, RCP8.5). Model-derived biome maps showed strong agreement with observation-based maps (average κ = 0.77), with higher agreement for biomes with well-known temperature constraints. Across all scenarios, GVMs projected biome shifts until the end of the century, where the likelihood of change increased with the level of climate change in RCP scenarios. Between 4 % and 56 % of the land surface were projected to undergo biome transitions in different combinations of GVMs, RCP and observation-based biome maps used to create biome maps. Broad spatial patterns of biome change were consistent across models. Poleward shifts of boreal and temperate forests dominated, as biomes follow temperature change. Equatorial rainforests remained largely stable, while other studies found forest dieback. These findings highlight regions and biomes most susceptible to future climate change, even under the low-emission scenario RCP2.6. Our transparent and objective biome classification approach can be applied to any vegetation model and provides critical insights for targeted climate mitigation and adaptation strategies and conservation of the remaining natural vegetation.