**4. Conclusions**

Despite a growing empirical literature, the income-pollution nexus remains a controversial topic. The puzzling results of previous studies incite to investigate it indepth to better assess this issue. I examine the EKC curve in the case of OECD countries and tested the nonlinearity of the income-pollution nexus. To this end, I used the PSTR model of González et al. [36] to capture the heterogeneous effect of income across 34 advanced economies by using yearly data from the World Bank between 1997 and 2015. The overall impact of income on environmental degradation is slightly positive for the 34 OECD countries. This means that technological and structural effects do not exceed the scale effect regarding this relationship. Based on these results, I suggest that policymakers should consider supporting the development of this new energy sector by improving the quality of the existing clean technologies, by financing R&D investments in other promising renewable technologies and related infrastructure network to make renewable energy sources more competitive than fossil fuels and, to reduce, in this way, CO2 emissions and enhance the energy security. Promoting regional cooperation and developing clean energy technologies will improve the environmental quality of countries, too.
