Under the leadership of the C40 Cities Climate Leadership Group (C40), approximately 1,100 global cities have signed to reach net-zero emissions by 2050. Accurate greenhouse gas emission calculations at the city-scale have become critical. This study forms a bridge between the two emission calculation methods: 1) the city-scale accounting used by C40 cities —the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories (GPC) and 2) the global-scale gridded datasets used by the research community —the Emission Database for Global Atmospheric Research (EDGAR) and Open‐Source Data Inventory for Anthropogenic CO2 (ODIAC). For the emission magnitudes of 78 C40 cities, we find good correlations between the GPC and EDGAR (R2 = 0.80) and the GPC and ODIAC (R2 = 0.72). Regionally, African cities show the largest variability in the three emission estimates. For the emission trends, the standard deviation of the differences is ±4.7 %/year for EDGAR vs. GPC and is ±3.9 %/year for ODIAC vs. GPC: a factor of ~2 larger than the trends that many C40 cities pledged (net-zero by 2050 from 2010, or −2.5%/year). To examine the source of discrepancies in the emission datasets, we assess the impact of spatial resolutions of EDGAR (0.1°) and ODIAC (1km) on estimating varying-sized cities’ emissions. Our analysis shows that the coarser resolution of EDGAR can artificially decrease emissions by 13% for cities smaller than 1,000 km2. We find that data quality of emission factors used in GPC inventories vary regionally: the highest quality for European and North American and the lowest for African and Latin American cities. Our study indicates that the following items should be prioritized to reduce the discrepancies between the two emission calculation methods: 1) implementing local-specific/up-to-date emission factors in GPC inventories, 2) keeping the global power plant database current, and 3) incorporating satellite-derived CO2 datasets (i.e., NASA OCO-3).

Cities emit the majority of greenhouse gas emissions globally and are increasingly committing to aggressive mitigation actions. Cities are also experiencing poor—and in some cases worsening—air quality, contributing to large disease burdens for adults and children. Integrated planning frameworks can help cities leverage and prioritize measures that achieve climate, air quality, and health benefits simultaneously. We developed and applied an integrated climate action planning process that includes air quality, utilizing Pathways-AQ, a new assessment tool, in six pilot cities: Accra, Ghana; Addis Ababa, Ethiopia; Buenos Aires, Argentina; the metropolitan area of Guadalajara, Mexico; Johannesburg, South Africa; and Lima, Peru. Implementing the “ambitious” greenhouse gas reduction scenarios in these cities' climate action plans would reduce in-city contributions to fine particulate matter (PM2.5) concentrations and would avoid 230–1,040 annual premature deaths per city, by 2050. This new integrated climate action planning process revealed the importance of (i) geographic scales of analysis, (ii) data integration across climate and air quality, (iii) local civic engagement, and (iv) nuanced health messaging. Rapidly scaling up and applying this integrated approach can broaden the group of municipal stakeholders involved in climate-related planning goals, potentially leading to greater ambition by integrating climate, air pollution, and health objectives.