Temporal Inconsistencies in LCA : A New Tool for Calculating Dynamic Climate Change Characterization Factors
Abstract
Achieving Net Zero by 2050 will notably induce delayed emissions, for instance due to carbon capture and utilization (CCU), e.g. emissions optimization through temporary storage in materials. The effects of temporary storage on climate change could be worse than doing nothing [1]. That is why impacts should be carefully assessed using dynamic life cycle assessment (D-LCA). In such a rapidly evolving context, considering temporality in LCA is becoming more and more crucial.
Dynamic modelling in LCA relies on three different temporal aspects: (i) dynamic foreground inventory, (ii) prospective background inventory, and (iii) dynamic impact assessment (e.g. dynamic Global Warming Potential (GWP) indicator [2,3]). While the first two aspects are mainly determined by the amount of data available, the dynamic impact assessment requires in addition carefully derived methodology and indicator.
The purpose of this paper is to review the dynamic GWP indicator based on the "time corrected" approach initially proposed by Levasseur [2], and recently revised by Ventura with the "fixed horizon of impact" method [3]. Even though the latter are useful and provide a clear improvement compared to the basic use of a static indicator in D-LCA, both solutions may not seem entirely satisfactory and a modified version is suggested in order to keep what seems relevant in each of these two approaches.
These different dynamic versions of the GWP/GTP indicator are compared in regard to the static indicator. Following [3], three temporal parameters are therefore used: the time horizon of the study, indicating the total time over which impacts are effectively assessed; the life cycle duration, which is the period of time between the first and the last inventory flow; and the time horizon of the impact, defined by the practitioner (e.g. usually 100 years for the GWP). The “time corrected” approach and the “fixed horizon of impact” method give similar values and trends for the GWP and GTP when the time horizon of impact is more than 20 years. The modification introduced in this work leads to opposite trends and in particular gives higher importance to a future increase in global temperature – that will actually be felt by the next generations.
The choice of the temporal method for calculating a "dynamic" impact is not neutral and should be considered and discussed depending on the stakes at hand. In particular, adopting a cost-benefit viewpoint allows interpreting the trends as the weight given to future generation in regard to the actual one: a more than central issue today.
[1] Shimako AH et al. 2017. Sci Total Environ 624:1250-1262.
[2] Levasseur A. et al. 2010. Environ Sci Technol 2010, 44, 8:3169–3174.
[3] Ventura A. 2022. Int J Life Cyle Assess (2022). https://doi.org/10.1007/s11367-022-02028-x