Tracing CO2 emissions across megacity landscapes: beyond citywide totals to structural heterogeneity and mitigation

Cities are central to global climate change mitigation efforts due to their substantial carbon emissions. Effective, evidence-based climate policy requires a detailed understanding of urban carbon metabolism, allowing for targeted mitigation pathways and the accurate evaluation of sustainability. However, a persistent lack of clarity on how carbon flows are distributed spatially and sectorally within cities has hindered tailored climate action, particularly in rapidly developing megacities. Here we map the shifting landscape of carbon emissions in Chinese megacities and show that accountability for these emissions has undergone a profound spatial and sectoral transformation. We found that the primary burden of emission responsibility has moved from production-focused sectors, such as industry and energy generation, to consumption-based end-users, including residential and commercial buildings. This transition is driven by a structural shift in accounting boundaries from direct fossil fuel combustion (Scope 1) to indirect emissions from electricity consumption (Scope 2), fundamentally redistributing carbon liability across urban districts. Our landscape-level framework reveals the hidden carbon dependencies of end-use sectors and provides a model for equitable and effective accounting, enabling the design of region-specific strategies to address the complexities of urban carbon emissions.