Explore the relationship between trade openness and green total factor productivity: evidence from countries along the Belt and Road

The rise of trade protectionism has introduced instability into the global economy and environment, prompting a re-examination of the trade–environment nexus. This study uses panel data from 35 countries along the Belt and Road during 2007–2019 and employs super-efficiency SBM-GML, panel threshold models, and machine learning models to investigate how trade openness affects green total factor productivity. The statistical results for the 35 countries show that economic growth can weaken the negative correlation between trade openness and green total factor productivity, while infrastructure development first intensifies and then weakens the negative relationship between trade openness and green productivity. The trade impacts vary across income groups. The green total factor productivity of non-high-income countries is more vulnerable to the adverse effects under trade openness. These findings highlight unequal developmental challenges and demonstrate how trade affects countries at different income levels. Three policy recommendations are proposed: (1) Provide non-high-income countries with targeted clean technology transfer programs and tariff reductions on green goods to offset the environmental costs of trade openness. (2) Conduct environmental impact assessments for infrastructure projects and increase investment in renewable energy and low-carbon infrastructure. (3) Establish a transnational cooperation platform for countries along the Belt and Road to share environmental monitoring data, harmonize environmental standards, and jointly develop cross-border green projects. By examining these heterogeneous effects, this study contributes to broader discussions on achieving environmental sustainability.