Supply Chain Factors Contributing to Improved Material Flow Indicators but Increased Carbon Footprint.

Improvements in four material flow indicators (MFIs) have helped facilitate Japan's transition to a sound material-cycle society. However, the economic and technological factors that have affected these MFIs have not been identified previously. Moreover, it is unclear whether the improvements in the MFIs have contributed to Japan's progress toward carbon mitigation. In this study, we quantified the contribution of the factors in the capital-embodied supply chain to changes in the MFIs at the national and sector levels. We also examined the consistency of MFI improvements with carbon footprint reduction. Our results show that, in many sectors, structural changes in the supply chain improved two of the MFIs (resource productivity and material circularity) but increased the carbon footprint of the sector. To address this conflict, producers need to manage their supply chains based on an understanding of the nexus between material consumption and carbon emissions, paying particular attention to supply chains associated with capital formation.

Efficient use of cement and concrete to reduce reliance on supply-side technologies for net-zero emissions.

Decarbonization strategies for the cement and concrete sector have relied heavily on supply-side technologies, including carbon capture and storage (CCS), masking opportunities for demand-side intervention. Here we show that cross-cutting strategies involving both the supply and demand sides can achieve net-zero emissions by 2050 across the entire Japanese cement and concrete cycle without resorting to mass deployment of CCS. Our analysis shows that a series of mitigation efforts on the supply side can reduce 2050 CO2 emissions by up to 80% from baseline levels and that the remaining 20% mitigation gap can be fully bridged by the efficient use of cement and concrete in the built environment. However, this decarbonization pathway is dependent on how CO2 uptake by carbonation and carbon capture and utilization is accounted for in the inventory. Our analysis underscores the importance of including demand-side interventions at the heart of decarbonization strategies and highlights the urgent need to discuss how to account for CO2 uptake in national inventories under the Paris Agreement.