Does Coordinated Regional Development Reduce Urban Carbon Emissions? Evidence from the Beijing–Tianjin–Hebei Strategy

Coordinated regional development plays an increasingly important role in promoting low-carbon transitions across China’s urban agglomerations. This study examines the effect of the Beijing–Tianjin–Hebei Coordinated Development Strategy, elevated to major national strategic status in 2014, on urban carbon emissions. Using an unbalanced panel of 294 prefecture-level and higher-level cities from 2010 to 2023, we employ a two-way fixed-effects difference-in-differences model to evaluate the strategy’s overall carbon-mitigation effect, potential transmission pathways, and spatial heterogeneity. The baseline DID coefficient is −0.052, corresponding to a 5.0% decline in city-level total CO2 emissions in the 13 treated cities relative to the national comparison group after policy implementation. Within the same comparison framework, further analysis documents significant positive post-policy differentials in both the industrial-structure-upgrading index and green invention-patent applications; the industrial-structure-upgrading results are consistent with a potential emissions-reduction pathway. The heterogeneity analysis indicates a statistically significant relative carbon-mitigation effect for the prefecture-level cities of Hebei compared with the national comparison group, with a larger relative effect in Beijing and Tianjin. This spatial pattern is consistent with differences in industrial structure, innovation capacity, and environmental governance capacity across cities. The findings provide city-level quasi-experimental evidence that coordinated regional development can promote urban carbon mitigation and support differentiated carbon governance, coordinated industrial upgrading, and cross-regional low-carbon policy design.