How methodological choices affect LCA climate impact results: the case of structural timber
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Life cycle assessment (LCA) is broadly applied to assess the environmental impact of products through their life cycle. LCA of bio-based products is particularly challenging due to the uncertainties in modeling the natural biomass production process. While uncertainties related to inventory data are often addressed in LCA by performing sensitivity analyses, the sensitivity of results to LCA methodologies chosen is seldom addressed. This work investigates the influence of common methodological choices on LCA climate impact results of forestry products.
Performing a consequential LCA, the study compares results obtained through different choices concerning four methodological aspects: the modeling of land use change effects, the choice of climate metric for impact assessment, the choice of time horizon applied, and the completeness of the forest carbon stock modeled. Eight scenarios were tested, applied to the same case study to ensure the full comparability of the results. A dynamic life cycle inventory of annual forest biomass production and degradation was obtained through a methodology accounting dynamically for the annual carbon fluxes in a forest plot.
Results and discussion
The results obtained for the eight scenarios showed a great variability of the estimated climate effect, ranging from a net carbon sequestration of 24 kg CO2 equivalents to a net carbon emission of 3220 kg CO2 equivalents, though seven out of eight scenarios resulted in a net carbon emission. The results are particularly sensitive to the choice of time horizon, especially when combined with the choice of static or dynamic climate indicator and different climate metrics as GWP and GTP. The case study showed a lower variability of results to the choice of forest carbon stock compared to the effect of the other tested assumptions.
LCA results of forestry products were highly sensitive to the tested methodological choices. A description and motivation of these choices is required for a clear and critical interpretation of the results. The choice of climate indicator and TH applied depends on the goal and scope of the study and strongly affects the contribution to climate impact results of all LCA processes. Those choices need to be carefully discussed and should be in accordance with the goal of the study, since different climate metric and TH have distinct interpretations. The interpretation of different climate indicators and their time horizons should be linked with the considered endpoints of climate change.
KeywordsCarbon footprint Forest carbon cycle Forestry Indirect land use change Life cycle assessment
This work was funded by the Aarhus University through the project “Environmental and socioeconomic potential of new concepts and business models for increased production and utilization of biomass from agricultural land in Denmark (ECO-ECO).” Massimo Pizzol’s contribution to this work was funded by the research grant no 1305-00030B of the Danish Strategic Research Council. The authors would like to thank the anonymous reviewers for their contribution.
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