How population migration affects carbon emissions in China: Factual and counterfactual scenario analysis

China's large-scale inter-provincial population migration has a vast impact on social changes, and significantly altered the energy consumption demand of various provinces, and further affected the spatial distribution of carbon emissions. Nevertheless, less attention has been paid to the impact of population migration on carbon emissions. To make up for the niche, this paper develops an innovative framework by integrating a geographically weighted regression model, a population migration matrix, and an environmentally extended multi-regional input-output model to assess the impact quantitatively based on factual and counterfactual scenarios. The results show that the carbon emissions increased by 78.16 million tonnes (Mt) in 2017 due to population migration, of which direct carbon emissions increased by 6.91 Mt. and indirect carbon emissions increased by 71.25 Mt. It must be emphasized that population migration increases indirect carbon emissions driven by urban consumption and investment in the provinces with net in-migrants. But these provinces transfer more carbon emissions to the regions with net out-migrants, which implies that population migration exacerbates carbon emissions inequality. This especially increases the carbon emission reduction barrier of provinces with net out-migrants. Overall, these empirical discoveries shed light on making regionally coordinated carbon reduction policies.