Comparing End-of-Life carbon accounting methodologies reveals the need for standardization

Abstract

Abstract This study provides a comparative assessment of existing methodologies and allocation approaches for quantifying End-of-Life (EoL) Greenhouse Gas (GHG) emissions in product life cycles, emphasizing the importance of harmonization and standardization in carbon accounting. Using single-use Polyethylene Terephthalate (PET) bottles in Germany as a case study, this study demonstrates how different EoL allocation methods influence emission results, circularity incentives, and comparability across approaches. The analysis demonstrates that methodological choices, such as formula structure, system boundary definitions, and allocation methods, significantly affect outcomes, yet no single approach fully aligns with the objectives of circular economy. Simplified formulas do not necessarily enhance transparency or robustness, and inconsistencies in process definitions and unit handling remain major sources of uncertainty. The findings highlight the critical relevance of standardized assessment procedures, which are essential to improve consistency, reliability, and credibility across industrial and regulatory applications. While existing standards, such as the International Organization for Standardization (ISO) 14,067, Circular Footprint Formula (CFF) and Publicly Available Specification (PAS) 2050, provide a foundation, they require adaptation to reflect real-world recycling systems and diverse EoL pathways. This work applies well-known methodologies from the guidelines mentioned before in combination with cut-off, reverse cut-off and 50:50 allocation methods to the case study of PET bottles. By doing so, insights are provided on both, methodologies and allocation methods, and their impact on the final Product Carbon Footprint (PCF) results as well as on their impact on incentivizing circular value chains by allocating emissions and burdens between waste producers and recycled material users, supporting more transparent, comparable, and circularity-aligned EoL emission accounting.