Ecological Footprint Convergence in Hydrocarbon-Based Economies: Quantile and Fourier Evidence from GCC Countries

Over the past seven decades, rapid economic growth has been accompanied by a substantial increase in environmental degradation worldwide. Given the magnitude and transboundary nature of environmental externalities, country-specific policies may be insufficient, and regionally coordinated environmental strategies are likely to be more effective. For such frameworks to succeed, convergence in levels of environmental pressure among member countries is essential. In this study, convergence is examined using the ecological footprint (EFP), a comprehensive indicator of environmental pressure. The analysis covers the six member states of the Gulf Cooperation Council (GCC)—Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and the United Arab Emirates—over 1971–2024 and tests for the stochastic convergence of per-capita footprints relative to the year-t regional average. Conventional ADF tests indicate convergence for Kuwait and Qatar—with Saudi Arabia at the 10% level—and Phillips–Perron results point in the same direction. Quantile ADF and Fourier quantile KSS tests with bootstrap inference show that adjustment is regime-dependent and country-specific: mean reversion is confined to below-average states in Bahrain, to above-average states in Kuwait and Saudi Arabia, and to both extremes in Qatar, while the United Arab Emirates and Oman revert to almost no quantile. The Phillips–Sul log-t procedure does not reject full-panel convergence: all six countries form a single convergence club, the result survives leave-one-country-out and cross-sectional-dependence checks, and subsample estimates date the convergence process mainly to the post-1990 period. Component-level analysis shows that aggregate convergence is carried by the carbon component (84–99% of the GCC footprint), whereas cropland, grazing, forest, and built-up components diverge. The findings support regionally coordinated energy–carbon policy combined with nationally tailored land-use policy.