La conférence international de la SETAC (Society of Environmental Toxicology and Chemistry) est le lieu où sont présentées et discutées les dernières avancées méthodologiques en ACV. Cette année, en raison du coronavirus, la conférence qui devait avoir lieu à Dublin, a été réalisée en visio-conférence, et a malgré cela réuni plusieurs milliers de participants des 5 continents. En ce qui concerne l’ACV, le prix du jeune chercheur a été décerné à Nadia Mirabella (KU Leuven) pour ses travaux sur l’empreinte environnementale des villes, dans la lignée des travaux portés par Eléonore Loiseau au sein de ITAP-ELSA sur les ACV territoriales. La Chaire ELSA-PACT et le pôle de recherche ELSA ont été très bien représentés avec des travaux inédits présentés par Arnaud Hélias, Philippe Roux et Angel Avadi.
Ces travaux concernent :
- la dynamique du Carbone dans les filières biomasse-bioenergie*
- une nouvelle approche de l’épuisement des ressources biotiques appliqué à la pêche**
- une proposition pour améliorer l’empreinte eau du modèle AWARE ***
Résumés en anglais:
* Framework for dynamic carbon accounting: development of complete carbon balances in LCA: Renewable energy carriers and biomaterials originating from dedicated and residual forestry and agricultural biomass (e.g. energy crops, woody residues, and perennial grasses) are promoted as carbon neutral options to displace/offset fossil carbon and mitigate climate change. The exclusion of the temporal variability of biogenic carbon (Cbio) flows justifies carbon neutrality, and thus zero net CO2 emissions. The objective of this study is to incorporate the time dimension in the LCA of biomass supply chains to account for biogenic-sourced flows within dynamic LCA framework. A proposed framework, building on dynamic life cycle inventories, considers: a) upstream models for non-linear biomass growth, above- and belowground Cbio sequestration, soil organic carbon (SOC) dynamic associated to land uses, including management practices and yields; and b) downstream models for case-specific end-of-life pathways, eventually delaying emissions due to carbon storage. The dynamic models are designed to be coupled with outputs from any demand model (i.e. technical flows specifying the amount of biomass supply/use in a studied system or bioproduct) to develop complete dynamic carbon inventories (fossil + biogenic) and estimate the consequences of decision-induced changes (i.e. energy transition). The framework was tested with case studies on French energy policy, which propose alternative pathways of biomass-based (i.e. from forestry and agriculture) energy and transport. The overall results demonstrated that both Cbio sequestration and SOC dynamic vary according to the biomass-type and management practice in place (e.g. rotations, residue removal rates). Annual crops have no growth dynamic; however the residual proportion of the plant is an input to the soil relevant for SOC modelling. The mitigation results are sensitive to the model parameters (e.g. temperature), as well as to the modelling approaches undertaken, concerning the setting of the temporal boundaries (future or historic time perspective for forest carbon sequestration), shortening the rotation length, and variations in the residue removal rates. Coupling with demand models is useful for prospective evaluations and incorporation of socio-economic indicators in the assessment. Accounting for dynamic carbon flows is non-negligible as it reduces uncertainty and bias in defining actions to mitigate climate change.
Ariane Albers, Pierre Collet, Anthony Benoist, Arnaud Helias
** Biodiversity impact of fisheries: Fisheries modified all the marine ecosystems. If Life Cycle Assessment (LCA) successes to quantify the land use its consequences on the environment (the ecosystem quality area of protection (AoP)) the impact of sea use on ecosystems appears poorly assessed by LCA community. To our knowledge, there is no approach assessing ecosystem impact of fisheries (the withdrawal of fish) which would be compliant with the current guideline. This lack of indicators is highlighted for comparison between sea- and agricultural-based products: the impacts are not expressed in the same unit and are not comparable. With the current LCIA possibilities, the causal effect on ecosystem quality of fishing cannot be represented, that means its impact equals zero. The aim of the present work is to solve this situation proposing operational CFs for global fisheries. The impacts leading to ecosystem quality are often addressed with CF = FF ×EF. For a given intervention, the characterization factor (CF) is the product of the fate factor (FF) with the effect factor (EF). FF allows the representation of the time period during which the effect occurs and the second gives the associated effect. In a recent work, we defined CFs for biotic resources (natural resource AoP) based on population dynamic model and marginal approach. This approach is based on the disappeared fraction of the stock (the given species in its habitat) and is used here as EF. Most impacts leading to ecosystem quality result from substance emissions. In this context the FF represents the persistence of the involved substance in the media. For a given compartment, it can be assimilated to the inverse of the sum of the removal rates or to a residence time. The FF for an impact on the ecosystem of fisheries is reversed since it results from a resource withdrawal, but the principle remains the same. By analogy, we defined the fate factor as the inverse of the growth rate of the fish stock. We have calculated CFs for almost 5000 fish stocks identified by FAO, using both marginal and average approaches and considering vulnerability scores to convert regional PDF to global PDF. CFs are spread over ten orders of magnitude but with the interquartile over less than two. The global CFs vary over 13 orders of magnitude but here again the interquartile is much more compact with two orders of magnitude. As illustration, four contrasted fisheries are presented and compared to livestock production.
Arnaud Helias, Vanessa Bach
*** Improvement of the water footprint AWARE model: The Available WAter REmaining (AWARE) model highlights the importance of considering consumption rather than withdrawal and takes into account spatial variability. It results from a massive and collective effort on behalf of the Water Use in LCA (WULCA) working group. The AWARE model provides a consensual, operational and recommended indicator for addressing and comparing water impacts, and fully succeeds in this purpose.The present work discusses the shape of the model, as well as associated limitations on its range of validity, which do not distinguish between regions that are more degraded than fair. A subsequent improvement is then proposed. This improvement is based on the ratio of the demand (requested by the ecosystem) to availability (minus the effective human appropriation), more simply named the Demand-To-Remaining (DTR). It provides useful and straightforward information representing the current state. follows the common practice in LCIA by (1) the definition of a relationship modelling the impact according to human intervention and (2) the use of marginal approach for determining the characterisation factor (CF). The significance of the approach is addressed by the sensitivity of the CFs according to the components of the model. As expected, the CFs of the AWARE and DTR models increase linearly with the area, in the same manner. In both situations, an increase in CH (the human water consumption) produces the same result as a decrease in A (availability). The increase grows faster when the AWARE model upper boundary is being reached, and when the complete human appropriation of water (CH = A) is being attained for the DTR model. This implies that the relationships present similar features but at different intervals, without any discontinuities for DTR.AWARE consensus model brings a major benefit to the community by proposing a shared standard. However, AWARE relationship is only defined when human consumption has spared sufficient water for an ecosystem in fair condition and loses its validity for more severe situations. By defining impact as the fraction of ecosystem demand on what is left by human activity, the DTR model proposed in the present work makes it possible to overcome this limitation. This improvement is mathematically sound, all the while satisfying the same expectations as the AWARE model.
Arnaud Hélias, Philippe Roux