Capturing and storing atmospheric CO2: LCA assesses its relevance

Thesis by Sybille Duval-Dachary: « Evaluation du potentiel d'émissions négatives des technologies d'utilisation du CO₂ » (Assessment of the negative emissions potential of CO₂ utilization technologies).

The average global temperature has already risen by more than 1°C. What is to blame? The increase in the concentration of greenhouse gases, including CO₂, in the atmosphere caused by human activities. To limit future increases, technologies known as CCUNET, which combine CO₂ utilization and negative emissions¹ (Figure 1), show great promise: capturing, converting, and then storing CO₂ from the atmosphere would not only reduce atmospheric CO₂ concentrations, but also reduce the extraction of fossil fuels. 

¹ Practices or technologies that enable the permanent removal or storage of CO₂ present in the atmosphere

However, the environmental benefit of CCUNET technologies is not automatically guaranteed and must be verified using life cycle assessement (LCA). Although mature and applicable to many systems, LCA remains a developing method that seeks to achieve increasingly reliable and meaningful results. In particular, three methodological challenges associated with LCA for CCUNET systems were identified and studied in this thesis: 

•    Inventory data availability: A review of recent scientific literature on the LCA of bioenergy with CO₂ capture and storage (35 articles) [1] enabled the compilation of generic inventories for biomass combustion and gasification, CO₂ capture based on amine solvents, pipeline transport, and underground storage, thereby expanding the available generic inventories.

•    The relevance of existing recommendations for assessing negative emissions: via a case study, the various existing recommendations were compared and their applicability was verified. In particular, this study showed that allocation, a method previously identified as reliable for assessing emissions, can lead to negative scores (CO₂ fixation) being assigned to products within systems where, overall, emissions remain positive. This bias can lead to unfavorable decisions in terms of overall carbon footprint, because an increase in the production volume of a product with “pseudo-negative” emissions will not result in a reduction in the amount of CO₂ in the atmosphere, quite the opposite [2].

•    Incorporation of the temporal dimension: in another case study, a dynamic LCA was carried out with the dual purpose of testing and improving the existing tool and assessing the contribution of the temporal dimension to the quality of the results. This exercise showed that, despite the additional effort required to perform a dynamic LCA, it does not necessarily lead to results that are very different from those of a static LCA [3]. A method was thus proposed (illustrated in Figure 2) to enable LCA practitioners to identify, using simplified information, the flows for which the addition of this temporal data is crucial [4]. 
 

In summary, this thesis has made several methodological and practical contributions to improving and facilitating the assessment of CCUNET systems using LCA. Translating the recommendations proposed within the specific framework of carbon accounting would represent a logical next step. 

References:

1. Duval-Dachary S., Beauchet S., Lorne D., Salou T., Helias A., Pastor A. (2023) Life cycle assessment of bioenergy with carbon capture and storage systems: Critical review of life cycle inventories. Renewable and Sustainable Energy Reviews 183:113415. 
   >> DOI :  https://doi.org/10.1016/j.rser.2023.113415
      
2. Duval-Dachary S., Lorne D., Beauchet S., Salou T., Hélias A. (2025) Life cycle assessment of carbon capture and utilisation as a negative emission technology: recommendations and case study. International Journal of Life Cycle Assessment 30, 66-78. 
   >> DOI :  https://doi.org/10.1007/s11367-024-02388-6
         
3. Duval-Dachary S., Lorne D.,  Batôt G., Helias A, (2025) Facilitating dynamic life cycle assessment for climate change mitigation. Sustainable Production and Consumption 51, 159-168. 
   >> DOI : https://doi.org/10.1016/j.spc.2024.09.017
    
4. Duval-Dachary S., Beauchet S., Lorne D., Salou T and Helias A., Result variations due to dynamic life cycle assessment compared to result variations due to sensitivity analysis on static inventory data (2024) SETAC Europe 34th annual meeting (Seville, Spain)
    

Scientific contact : Sibylle Duval-Dachary

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