Circular, avoided, or captured carbon (dioxide)? - A taxonomy approach for life cycle assessment and CO2 accounting

Individuals utilizing Life Cycle Assessment within the emerging field of circular carbon might phrase and understand matters differently, causing ambiguity, due to different educational backgrounds and lacking definitions of central terms. Our research addresses the question, whether misleading or ambiguous terms exist, which impair transparency and scientific accuracy in carbon (dioxide) accounting in LCA. A structured literature research was performed to screen LCA standards, ISO standards, and the European legal database EUR-Lex. Nine terms with potential ambiguity in meaning or usage in LCA were identified: Avoided burden, avoided carbon, avoided CO2, carbon capture, carbon credit, circular carbon, circular CO2, negative emission, and net zero emission. A workflow was introduced to either obtain a consensus-based definition from standard literature or from peer-reviewed publications. For all terms, except avoided carbon, a recommended definition was found and showcased within case studies on the topic of mechanical recycling of plastics to produce a taxonomy suggestion for precise descriptions of different carbon dioxide (equivalent) accounting methods in LCA.