Satellite-Based Analysis of CO2 Emissions From Global Cities: Regional, Economic, and Demographic Attributes

Abstract

Cities play a crucial role in reducing global greenhouse gas emissions. While activity-based (“bottom up”) emission estimates are widely used for global cities, they often lack independent verification. In this study, we use remotely-sensed CO₂ observations from the Orbiting Carbon Observatory-3 (OCO-3) to “top-down” estimate CO₂ emissions for 54 global cities. This global-scale analysis is enabled by a computationally efficient cross-sectional flux approach, which uses NO₂ observations from TROPOMI and trajectory simulations from HYSPLIT to identify OCO-3 pixels influenced by urban plumes. Our satellite-based emission estimates for 54 global cities agree within 7% to two widely used bottom-up data sets but reveal regional discrepancies. Bottom-up estimates tend to overestimate emissions for cities in Central East Asia and South and West Asia, while underestimating emissions in Africa, East and Southeast Asia & Oceania, Europe, and North America. Additionally, our satellite-based socioeconomic analysis shows that (a) high-income cities tend to have less carbon-intensive economies: North American cities emit 0.1 kg CO₂ per USD of economic output, while African cities emit 0.5 kg CO₂ per USD, and (b) per capita emissions decrease with increasing population size, from 7.7 tCO₂/person for cities under 5 million residents to 1.8 tCO₂/person for cities over 20 million residents. This study highlights the potential of satellite data to bridge gaps between top-down and bottom-up emission estimates, enhancing the robustness and transparency of emissions monitoring. Our findings emphasize the growing role of satellite data in verifying urban CO₂ emissions and supporting efforts to mitigate emissions for global cities.