Global patterns of urban heat shaped by climate and morphology

Urban morphology and background climate are evolving drivers of the urban heat island (UHI) effect, yet the thermal influence of surrounding urban structure and its coupling with climate remain elusive. Here, we show that climate and morphology jointly shape global urban heat. Using a six-class urban typology, long-term climatology, and machine learning, we quantify the thermal influence of surrounding urban structure and project future urban heat across 2,213 cities. We define a city-level thermal impact of the surrounding built environment (T_BE) as the area-weighting UHI change induced by specific built-up types. Climatically, cold regions most frequently exhibit high daytime T_BE, while arid regions dominate high nighttime T_BE. Structurally, a universal pattern persists; high T_BE corresponds to denser and taller forms, whereas sparser and lower types dominate low T_BE during day and night. Future projections indicate that climate change dominates T_BE change in 69% of cities, whereas the Global South exhibits stronger tendencies toward morphology-driven and synergistic intensification than the Global North. Our results highlight the need for locally tailored adaptation strategies that target the dominant drivers-climatic, morphological, or both.