Re-examining the environmental Kuznets curve through environmental efficiency

This paper re-examines the Environmental Kuznets Curve (EKC) from the perspective of environmental efficiency. Using panel data for 41 countries over 1990–2023, we estimate environmental efficiency with an SBM–DEA model and then analyze its nonlinear relationship with GDP per capita. The results indicate an inverted N-shaped pattern for the full sample and OECD countries, while non-OECD countries show an inverted U-shaped pattern. These findings imply that income growth alone does not ensure sustained improvements in environmental efficiency and that structural and institutional conditions remain important for green growth.