Hybrid multi-stage steel footprinting unveils a more interdependent material foundation of the global economy

Steel is foundational to modern society, yet tracking its socio-economic metabolism is challenging due to the complex global trade networks. Traditional indicators, such as domestic material consumption (DMC) and consumption-based material footprints (MF), typically focus on metal ore extraction, overlooking the multiple stages of steel production and consumption. To address this, we integrate multi-national anthropogenic steel cycles and international trade networks of steel-containing products into a global monetary multi-regional input-output (MRIO) model. We construct material efficiency indicators based on footprints of iron ores, crude steel, castings, finished steel, and fabricated steel products, comparing them with conventional economy-wide material flow indicators like domestic material production (DMP) and DMC. Our findings reveal that per capita multi-stage MF indicators exhibit more robust log-linear relationships with per capita GDP with an average R2 value of 0.72 compared to 0.10 and 0.18 for DMP and DMC. Shares of Embodied trade in total global production exceed direct trade by 24 percentage points on average, emphasizing the significance of international embodied metal transfers. Using multi-stage MF indicators also reduces disparities in material efficiency between developed and developing countries. This study unravels the intricacies of global steel supply chains and the true interdependencies of steel-containing products among countries.