Revisiting the EKC hypothesis in high-income EU countries: The role of technological innovation, green energy, and transport energy in shaping ecological footprints

This study revisits the Environmental Kuznets Curve (EKC) hypothesis by analyzing how technological innovation, green energy use, transport energy consumption, and population density shape ecological footprints in 11 high-income EU countries from 1990 to 2022. Using a pooled mean group-autoregressive distributed lag (PMG-ARDL) model and multiple robustness checks we confirm a long-term inverted U-shaped relationship between economic growth and ecological degradation, validating the EKC hypothesis. Innovation and green energy adoption significantly curb ecological degradation, whereas higher transport energy consumption and population density intensify it. Causality tests and quantile-regression checks corroborate these directions and reveal that innovation is most effective in lower-impact countries. These results highlight the importance of policies that foster innovation, expand green energy, and promote sustainable transport to advance ecological sustainability in high-income EU economies.