The importance of uncertainty sources in LCA for the reliability of environmental comparisons: A case study on public bus fleet electrification

Abstract

Life Cycle Assessment (LCA) is widely used to externally compare environmental indicators across different systems. Although uncertainty analysis is required by standards, it is often neglected, which threatens the reliability of the comparisons. The authors highlights how different assumptions and uncertainty sources can shape LCA outcomes. A case study on public bus fleet electrification was conducted, involving 20 bus models with various modeling assumptions. The impact of following factors on LCA uncertainty was analyzed: LCI database, LCIA method, modeling approach, energy carrier consumption and lifetime. The most significant discrepancies, comparing with baseline models of diesel and electric bus, occurred when different LCIA methods were applied, with results varying by up to 649.0%. The use of alternate LCI caused changes of up to 99.4%. The maximum discrepancies due to modeling approach, energy carrier consumption, and lifetime were 33.0%, 35.7%, and 20.9%, respectively. The paper recommends that comprehensive LCA studies should include multiple indicators, and clearly explained uncertainty sources, assumptions and limitations. Modeling approaches, databases, and LCIA methods should align with the analysis goals. Standardization of LCA methodologies by EPD program operators are suggested to reduce variability. When comparing studies with different assumptions, recalculating results to harmonize assumptions is advised. Transparency and understanding of model uncertainties are essential for drawing reliable conclusions. The study demonstrated that comparing deterministic LCA results undermines reliability. As LCA gains importance in environmental and sustainability communications, increasing awareness of LCA uncertainty and applying the novel findings of this paper is essential for informed decision-making.