Income, human capital and pollution: a multi-emission approach to the EKC hypothesis

This article reexamines the relationship between per capita income and environmental quality, with a particular emphasis on the role of education. Using a panel of 154 countries classified by income level (high, lower middle, upper middle and low), and covering the period 1998–2022, the study extends the traditional Environmental Kuznets Curve (EKC) framework by incorporating multiple greenhouse gases – carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). The empirical analysis relies on both static and dynamic regression models. The findings confirm the existence of an EKC and reveal a nonlinear relationship between GDP per capita and emissions. Education emerges as a critical determinant of environmental performance, though its direct impact varies across income groups: it substantially reduces emissions in high-income countries, has a moderate effect in middle-income countries and only a limited effect in low-income economies. Furthermore, the interaction term between GDP and education is significantly negative, indicating that education mitigates the environmental impact of economic growth – particularly in more developed nations. Overall, the results underscore the importance of integrated policies that simultaneously foster education and strengthen environmental regulation as a pathway to reconciling economic development with environmental sustainability.