## 5 Conclusions  
This study's findings reveal significant quantitative impacts of renewable energy consumption and environmental taxes on CO2 emissions within OECD countries. Specifically, the long-run analysis demonstrates that a 1% increase in renewable energy consumption leads to a 0.258% reduction in CO2 emissions, while a 1% increase in environmental tax revenues corresponds to a 0.175% decrease in emissions. These results are statistically significant and align with the broader literature on the efficacy of green policies. Furthermore, the short-run analysis corroborates these findings, with a 1% rise in renewable energy consumption and environmental taxes resulting in reductions of 0.292% and 0.169% in CO2 emissions, respectively. This study also highlights the contrasting effects of industrialization and urbanization, which are associated with increases in CO2 emissions both in the short and long run, underscoring the challenges faced by OECD countries in balancing economic growth with environmental sustainability. These numerical findings not only validate the theoretical framework but also provide concrete evidence to inform policymakers about the potential impacts of renewable energy and environmental taxes on reducing carbon emissions. This study underscores the necessity of continued investment in renewable energy infrastructure and the implementation of well-designed environmental tax policies to achieve long-term sustainability goals. Based on this study's conclusions, several policy implications are proposed to enhance environmental sustainability in OECD countries. First, the significant negative impact of renewable energy consumption on CO2 emissions underscores the necessity for policies that foster the adoption and expansion of renewable energy sources. Governments should bolster subsidies, tax incentives, and grants for renewable energy projects. Increasing investment in research and development for renewable technologies is crucial for enhancing efficiency and reducing costs. Additionally, the establishment of clear regulatory frameworks can stimulate private sector investment in renewable energy. Second, the negative correlation between environmental taxes and CO2 emissions indicates that environmental tax policies are effective instruments for emission reduction. Policymakers should design and implement comprehensive carbon tax schemes that accurately reflect the social cost of carbon emissions. The revenue generated from these taxes should be reinvested into sustainable initiatives, such as green infrastructure, public transportation, and energy efficiency programs. Regular assessments and adjustments of tax rates are essential to maintain their effectiveness in achieving emission reduction targets. Third, the positive effects of industrialization and urbanization on emissions highlight the challenges associated with sustainable growth. Urban planning policies should prioritize green building standards, the development of sustainable public transportation systems, and the preservation of green spaces. Industrial policies should promote the adoption of cleaner production technologies and practices. Implementing stringent environmental regulations and providing incentives for businesses to adopt green technologies can mitigate the adverse environmental impacts of industrialization and urbanization. Finally, the negative impact of foreign direct investment on emissions suggests that international investments play a vital role in facilitating the transfer of green technologies. Countries should create favorable conditions for attracting foreign direct investment in sectors that promote environmental sustainability. This includes developing clear and stable regulatory environments, offering incentives for foreign companies that introduce clean technologies, and fostering international partnerships for technology transfer and innovation. Strengthening intellectual property rights can also encourage foreign investors to share their advanced green technologies.