Econometric analysis of the impact of the urban population size on carbon dioxide (CO2) emissions in China

In China, urbanization has been rapidly developing since the country began its economic reform in 1978. With the expansion of the urban population size and the corresponding urbanization and industrialization, the rapid increase in CO2 emissions has become a major restraint on China’s economic growth. However, current studies have not paid sufficient attention to the impact of the urban population size on CO2 emissions in China due to poor data availability. In this paper, we apply index decomposition analysis (IDA) to decompose CO2 emissions into five elements, and we investigate both the direct and indirect impacts of the urban population size on total CO2 emissions and per capita CO2 emissions in China. Additionally, we empirically study the impact on 175 Chinese cities at the prefecture level and above for the first time. The results show that the urban population size significantly promotes total CO2 emissions but curbs per capita CO2 emissions in cities in China. A 1% increase in the urban population size will lead to a nearly 1% increase in total CO2 emissions and a 0.3% decrease in per capita CO2 emissions. Regarding heterogeneity, the expansion of the urban population size in the large city group drives a greater increase in CO2 emissions than the expansion of the urban population size in other city groups. The main transmission pathways are through population density, economic agglomeration and energy intensity. Regarding the mechanism variables, high economic agglomeration leads to more CO2 emissions, while an increase in population density and energy efficiency results in carbon mitigation. Moreover, public green areas, foreign direct investment (FDI) and technology innovation are conducive to reducing CO2 emissions.