Protected Areas Reduce Heat Exposure in Squamates Globally

Protected areas (PAs) are central to biodiversity conservation, yet their capacity to buffer species from climate-driven heat exposure, that is, the duration and frequency of exposure to temperatures exceeding species' critical thermal limits, remains poorly quantified at global scales. Here, we assessed whether squamate reptiles inside PAs experience lower heat exposure than conspecifics in unprotected, human-modified landscapes, and how this buffering effect varies across latitudes, biomes, and evolutionary lineages. Using biophysical modelling of operative temperatures across 248 species, we show that PAs consistently reduced both annual hours above critical thermal maximum (CT_max) and the frequency of critical days under current and future climatic scenarios (+2°C and + 4°C). We found that under current climate, protected sites had 51 fewer hours above CT_max and 3.5 fewer critical days than unprotected sites, and the proportional reduction persisted under +2°C and + 4°C warming scenarios. The buffering effect was most pronounced at low latitudes and tropical biomes, where species already operate close to their thermal limits. Deserts and xeric shrublands, together with tropical grasslands and savannas, emerged as biomes with elevated heat exposure, reinforcing growing concern for arid-zone reptiles under climate change. Substantial phylogenetic signal in heat exposure indicated that evolutionary history shapes thermal vulnerability beyond geography and biome alone, with the magnitude of PA buffering varying considerably across squamate lineages. Our findings demonstrate that PAs can provide refugia from heat exposure, and that their conservation value under climate change depends on the retention of structurally complex habitats and thermally heterogeneous microhabitats.