Embodied Transboundary Greenhouse Gas Emissions and Mitigation Opportunities of over 700 Belt and Road Initiative Projects.

The Belt and Road Initiative (BRI), the world's largest ongoing infrastructure endeavor, tackles urgent development needs in underserved regions. However, its construction phase, especially material extraction and processing, may have far-reaching climate implications that remain poorly known. Here, we present the first global, project-level assessment of greenhouse gas (GHG) emissions embodied in the construction of over 700 individual BRI projects (2008-2024) across 105 countries. By integrating a detailed project data set with a physically grounded global supply chain model that captures material-specific sourcing patterns, we estimate 134 Mt of CO2 equiv emissions, around half of which occur outside the project host countries. This reveals the previously unquantified global supply chain reach of the BRI. Depending on operational performance, BRI renewable energy projects may achieve emission reductions comparable in scale to the construction-phase emissions within 2 years. Our results underscore the need and opportunity to embed cleaner material sourcing and sustainability assessment into BRI and other transnational infrastructure efforts.