Effects of a new supply chain decomposition framework on the material life cycle greenhouse gas emissions—the Japanese case

Abstract

This research extends the methodology proposed in a previous study to assess the life cycle greenhouse gases (GHGs) of 64 target materials. In the earlier paper, GHG emissions associated with the production of materials (i.e., upstream emissions) were calculated considering the standard Leontief/supply chain framework. As a consequence, the process emissions of any material were distributed to many other materials as part of their supply chain emissions. In this paper, we developed a new decomposition of the supply chain allowing the redistribution of one target material supply chain emissions to the other target materials in a clear and consistent way. The application of this new framework is found to lead to subsequent changes in the emission patterns of target materials. The emissions of 33 and 13 target materials are indeed found to respectively decrease and increase by more than 10%. However, refinery petroleum products and crude steels (converters) represent more than 40% of the 569 MtCO2e associated with the production and use of the 64 studied target materials for both allocations demonstrating the strong concentration of CO2e emissions in the Japanese economy. We nonetheless still recommend to use the standard Leontief framework for reporting the life cycle emission of materials and to reserve the new decomposition framework for conducting relevant analysis of the relationships between target materials.