Dissertation

Repenser l’évaluation des impacts du cycle du vie à travers le prisme des services écosystémiques : Enjeux, cadre méthodologique et applications

Debarre, Laura

2025

Overview

Life Cycle Assessment (LCA) is a key tool for sustainable management. This standardized methodology is structured into four main steps. The third step, called Life Cycle Impact Assessment (LCIA), aims to translate inventory data (e.g., emissions of toxic substances) into potential environmental impacts. This translation relies on characterization factors, which are derived from characterization models representing the involved environmental mechanisms. Characterization models are structured within an “LCIA framework”, which is a coherent and comprehensive conceptual structure that identifies and organizes pathways of potential impact and relevant indicators for decision-making.Over time, the LCIA framework and its associated characterization models have evolved. However, the current framework still insufficiently addresses the pathways by which human activities affect the benefits provided by nature, known as ecosystem services. Such services are essential to human well-being, and their omission from LCA impact profiles represents a significant blind spot for decision-making. Bridging this gap requires the development of appropriate impact models and characterization factors assessing pathways of impacts on ecosystem services. Yet, such developments must remain consistent with existing LCIA models, which typically address other impact categories such as human health or ecosystem quality. Many of these existing models implicitly integrate concepts closely related to ecosystem services, such as ecosystem functions. Therefore, to ensure conceptual coherence and avoid double counting, it is important to identify and make explicit the interactions between ecosystem services concepts and traditional LCIA pathways. In this context, the present article-based thesis proposes a revision of the LCIA framework through the lens of ecosystem services. Building on the revised framework, models and characterization factors are developed for two specific impact pathways.The first article presents a critical literature review, combining two research works: a review of the fundamental concepts relating to ecosystem services and an analysis of attempts to integrate ecosystem services into LCIA. The review highlights both the relevance and the challenges of incorporating ecosystem services into LCIA. It identifies inconsistencies and a lack of conceptual clarity in several existing proposals and advocates for a more suitable LCIA framework for ecosystem services integration.In response, the second article introduces a revised LCIA framework built on the “cascade model” developed by the ecosystem services research community. This new framework reveals strong conceptual linkages between ES-related concepts and most existing LCIA models. To illustrate its comprehensiveness and applicability, all characterization models from the IMPACT World+ methodology are mapped onto this revised framework.On the basis of this new structure, models and CFs are being developed for two impact pathways. The third study of this thesis develops a model and associated characterization factors to assess the impacts of sea-level rise and the intensification of extreme events on coastal ES. The characterization factors are calculated as the ratio between (1) the loss of ecosystem service supply potential in coastal zones projected to be flooded between 2015 and 2100, and (2) the cumulative greenhouse gas emissions over the same period. Depending on the scenario, characterization factors values range from 16.7 to 66.1 $/tCO2,eq, aligning with the social cost of carbon (estimated at 185$ /tCO2,eq), thus validating their order of magnitude. Nevertheless, limitations are acknowledged, including the challenges of modeling the capacity of coastal ecosystems to adapt to flooding and of quantifying global ecosystem services demand.A second impact pathway of the revised framework explored in this thesis addresses the potential human health impacts from freshwater use and deprivation, expressed in DALYs/m3 consumed. Two articles are dedicated to this topic. The fourth article of this thesis revisits and consolidates a characterization model developed in 2011, updating its fate, exposure, and effect factors to produce a new set of characterization factors. However, the work reveals a significant limitation of the effect factor, which estimates health impacts due to water deprivation. Being global in scope, the effect factor does not account for disparities in water access within populations.To address this shortcoming, the fifth article proposes a new effect factor calculation method, based on the premise that health consequences of losing 1 m3 of water depend on the user’s typical daily consumption. By distinguishing user classes, new country-scale effect factors are developed and integrated with the updated characterization factors components, yielding a consolidated set of characterization factors. Despite these improvements, the empirical demonstration of the causal chain from water deprivation to health outcomes remains a key research need. The application of the revised LCIA framework across these two impact pathways demonstrates both its relevance and practical utility. However, the case study on sea-level rise also highlights a key limitation in operationalizing the framework: the complexity of modeling demand for ecosystem services.The proposed framework is designed to be flexible and adaptable to different cause-effect chains. Rather than offering strict guidelines, this work aims to provide a coherent and comprehensive structure for methodological developments, ultimately enabling the creation of meaningful indicators for decision support. However, it is important to emphasize that the selection of relevant impacts is inherently subjective; differing value systems can lead to the development of alternative frameworks.The revised LCIA framework proposed in this thesis serves as a conceptual tool for LCA modelers, supporting consistency and completeness in characterization models development. The characterization factors derived from it are intended for LCA practitioners, helping to generate more comprehensive and robust information for decision-making. More broadly, this work contributes to advancing and consolidating the field of LCIA.

• Publisher: ProQuest Dissertations & Theses
• Subject: Decision making / Ecology / Ecosystems / Emissions / Environmental management / Natural Resource Management / Sustainability / Water
• ISBN: 9798277489192