Does population aging reduce environmental pressures from urbanization in 156 countries?

Urbanization and population aging are key indicators of human-related social attributes. With economic progress and urban development, human living conditions and the level of medical and health care have been continuously improved. Population aging has become a global trend, which brings serious challenges to the world. Environmental sustainability is closely linked to both urbanization and aging. Most of the existing studies only focus on the linear relationship between urbanization and the environment, and the effect of aging on the ecological environment is also controversial. It is of great significance to conduct systematic research on urbanization-aging-environment. This paper aims to reconstruct the linear relationship between urbanization and the environment, investigating the nonlinear effect of population aging on the nexus of urbanization-environment in 156 countries. This paper focuses on exploring ways to improve environmental quality from the perspective of population aging. To this end, the panel threshold regression models of urbanization-carbon emissions and urbanization-ecological footprint are developed respectively. In which, urbanization is set as the explanatory variable, carbon emissions and ecological footprint are set as the explained variables, and population aging is set as the threshold variable. This paper divides four income groups according to the income standard of the World Bank, and regresses the panel data of the global and four income groups respectively to reflect the comprehensiveness of this work. The results show that there is a threshold effect of population aging on the nexus of urbanization-carbon emissions/ecological footprint both the global scale and different income groups. On a global scale, urbanization has a positive effect on carbon emissions and ecological footprint. When aging crosses the threshold in turn, the promotion effect of urbanization on carbon emissions gradually becomes smaller, and the influence coefficient of urbanization on the ecological footprint shows an inverted U-shaped change trend. Aging can reduce the environmental pressures related to urbanization. There is heterogeneity in the nonlinear regression results for different income groups. Population aging variable in high income group, upper middle income group helps to improve environmental quality. In lower middle income countries and low income countries, aging slightly increases the coefficients of urbanization and ecological footprint.