The primary data share indicator for supply chain specificity in product carbon footprinting

• First analysis of the primary data share (PDS) as an indicator for product carbon footprint specificity. • Consistent PDS calculation of PCFs involving negative emission require further definitions. • Further definition required regarding multi-output processes and market-based chain of custody models. • Potential double counting challenges of primary and secondary data require further investigation. Ongoing industry initiatives like Pathfinder / Partnership for Carbon Transparency from the World Business Council for Sustainable Development, Catena-X from the automotive industry, and Together for Sustainability from the chemical industry advocate for sharing primary product carbon footprint (PCF) data along the supply chain to increase specificity. All three initiatives agree on requesting a primary data share (PDS) alongside the PCF. The PDS as an indicator of PCF specificity has not yet been addressed in scientific literature. To address this gap, this research analyzes the PDS definitions and demonstrates remaining challenges and gaps for further research by means of a hypothetical case study. While the definitions for PDS calculations with exclusively positive PCF contributions are consistent across the three initiatives, the definitions differ regarding negative PCF contributions. Further, the definitions of negative emissions do not explicitly specify the system boundaries for PDS calculations. Different system boundary choices can influence PDS results. In addition, challenges regarding the PDS calculation of multi-output processes as well as products which have been modeled using the mass balance – credit method or book and claim are identified. We provide potential solutions to these challenges which can serve as a basis for further research and specification on the PDS calculation. Primary data potentially reflects “real” emissions in a product-specific supply chain more accurately than secondary data. Thus, the PDS is a relevant indicator for the reporting company. Nevertheless, conflicts of interest can occur between achieving a low PCF and high PDS.