Hidden heterogeneity in low-carbon cities via demand-sensitive carbon intensity

Urban decarbonization is commonly assessed using the carbon intensity (CI) of electricity consumption, yet this average indicator does not capture how emissions respond to changes in demand. Consequently, cities that appear low-carbon may exhibit structural vulnerabilities to demand growth. Here, we introduce demand-sensitive carbon intensity (sensitivity in CI; SCI) as a complementary diagnostic indicator that characterizes observed emission responses to incremental changes in electricity demand under existing system conditions. Using high-resolution smart meter data covering approximately 22.2 million demand contracts and 0.94 million photovoltaic (PV) generation contracts across 424 Japanese municipalities, we jointly evaluate CI and SCI at the municipal scale, accounting for voltage-level differences between residential and commercial–industrial sectors. The analysis reveals substantial hidden heterogeneity among cities with similar CI values, with some low-CI cities exhibiting high SCI. By distinguishing low-carbon states from low-carbon sustaining structures, the CI–SCI framework provides a basis for targeted urban decarbonization strategies.