The Belt and Road Initiative (BRI) stands as the most ambitious infrastructure project in history, marked by its scale of investment, extensive geographical reach across continents and countries, and a diverse array of projects from roads to digital networks. While the BRI's environmental sustainability has raised concerns, the impacts of construction materials used in these projects have been overlooked, especially in developing countries. Here, we map and account for the materials embodied in the BRI by integrating, for the first time, official governmental project reports, geographical information, and material flow analysis. We pinpoint and analyze the BRI material stocks in each individual project by material types, countries, regions, and sectors. Between 2008 and 2023, 328 million tons of construction materials have accumulated in 540 BRI projects around the world, mostly in Asia and Africa. Aggregates (sand and gravel) constitute the largest share (82%), followed by cement, steel, and other materials. Most of the materials are used in transportation infrastructure. Our work further highlights some limitations in terms of data quality for such sustainability assessments. By shedding light on the significant impact of BRI projects on raw material usage across the globe, this study sets the stage for further investigations into environmental impacts of BRI and material stock-flow-nexus from perspective of an initiative.

Climate change, caused by carbon dioxide (CO₂) emissions, has become increasingly severe and is a serious constraint on the sustainable development of the global economy. Economists are aware of the close relationship between export trade and the growth of CO₂ emissions, especially for the Belt and Road Initiative countries that are experiencing economic growth and transformation. Extant literature also agrees that the composition of the export basket is one of the crucial factors influencing CO₂ emissions, but the mechanisms by which changes in the export basket affect carbon emissions from a sustainable production perspective remain unexplored. Based on international trade theory, this study examines how shifts in production patterns affect subsequent CO₂ emissions through the lens of exogenously driven changes in the composition of a country's exports, with the consideration of the mediating role of industrial structure upgrading and the moderating role of intellectual property protection simultaneously. The results reveal that export composition improvement contributes to carbon reduction, and industrial structure upgrading plays a significant mediating role in the export composition improvement for carbon reduction. Intellectual property protection moderates the relationship between export composition improvement and industrial structure upgrading. The mediating effect of export composition improvement affecting carbon emissions reduction through industrial structure upgrading is also moderated by intellectual property protection.