Urban morphology, not scale, dominates building-operational carbon emissions across 520 million buildings in China

Building are responsible for 37% of global energy-related CO₂ emissions, yet the operational carbon of building stocks is still predominantly assessed at aggregated statistical scales or for small, non-representative samples. This obscures how the physical configuration of cities shapes their emission profiles. Here, we construct a spatially explicit, bottom-up inventory of building operational carbon emissions(BOCE) for China that couples city-level energy statistics with morphological and functional data for more than 520 million individual buildings across 330 prefecture and 2,633 counties. In 2021, Chinese buildings emitted 2,767 Mt CO₂, with pronounced spatial clustering that aligns with major urban agglomerations but exhibits far stronger variation in carbon intensity than in total emissions. We show that urban form—not city size or economic scale—is the primary determinant of BOCE intensity. A systematic morphological paradox emerges: districts with low building density but high floor area ratio host vertically concentrated high-rise clusters dispersed over large areas and become carbon hotspots, frequently exceeding 15 kg CO₂ m⁻²—a level higher than that observed in 71% of all districts—whereas compact, morphologically coherent developments sustain much lower intensities. Case studies of five representative cities spanning distinct climates and urban forms reveal a nearly three-fold range in intensity (10.27–28.82 kg CO₂ m⁻²) despite comparable total emissions, arising from interactions among climate, building typology and energy infrastructure. Our multi-scale framework demonstrates that redesigning spatial configuration and power systems can decouple urban development from emissions, providing actionable pathways for context-specific decarbonization in rapidly urbanizing regions.