Thermal baselines and climate‐space geometry mediate systematic terrestrial biodiversity responses to warming

Global warming is rapidly restructuring biological communities, yet terrestrial ecosystems often appear to lack the systematic climate‐driven signatures observed in marine realms. We hypothesise that this apparent idiosyncrasy arises from neglecting the geographic structure of climate. Using 1161 terrestrial community time series, we transitioned from geographic grids to a multidimensional climate space defined by temperature and precipitation. This framework allows climatic associations to be evaluated while accounting for climate‐space geometry by quantifying two key components: climate area and climate isolation. Using Bayesian hierarchical models, we evaluated how baseline climate and climate‐space geometry jointly shape temporal trends in richness, abundance, and evenness. While the average effect of warming on biodiversity appeared non‐significant, we found that terrestrial biodiversity responses varied systematically with baseline climate and climate‐space geometry. Species richness increased with warming in cooler climates but declined in the warmest regions. Furthermore, richness responses to warming became more positive in climatic regimes occupying larger areas, while the evenness response to warming depended on the interaction between climate area and isolation. Our findings identify the geography of climate as a critical link for understanding terrestrial biodiversity shifts. By treating climate as both an environmental condition and a spatial structure, we reveal coherent community responses to warming that were previously obscured in geographic space. These results suggest that conservation strategies benefit from looking beyond local temperature rates to consider the extent and connectivity of the climatic regimes being reshaped by climate change.