Conversion factors for linking life cycle assessment with the planetary boundaries framework for improved representation of biodiversity impacts in the building sector and beyond

The intersection of climate change and biodiversity loss poses a significant threat to the well-being of current and future generations. Existing regulations dictate methods for measuring the greenhouse gas (GHG) emissions from buildings, including specific performance thresholds. Such a narrow focus on reducing GHG emissions neglects impacts on other key planetary boundaries (PB), such as biosphere integrity, and could even lead to an increase in these non-climate impacts. Existing environmental indicators for biosphere integrity, such as the Biodiversity Intactness Index (BII), are not directly operational in LCA, making it difficult to define regulations on environmental disclosures for actors in the building sector and related threshold values. Current LCIA methods used in other sectors aggregate midpoint indicators, such as climate change and land use, into damage to the endpoint indicator ecosystem quality. This endpoint indicator is for example measured in the unit potentially disappeared fraction of species integrated over time (PDF.yr). While this only captures some aspects of biosphere integrity, this paper argues that endpoint damage indicators can be used as a proxy. This study aims to bridge the gap between the PB for biosphere integrity and current LCIA methods by developing a set of conversion factors for three common LCIA methods: ReCiPe 2016, Impact World+ (IW+) and LC-IMPACT, and comparing to one LCIA method with an existing PB link: PB-LCIA. This is accomplished by defining a relationship between the units BII and PDF, based on different land use types defined in the original GLOBIO model underlying the PB. The conversion factors were used to translate the BII boundary value (90 %) to a corresponding boundary value for the respective PDF-based endpoint units of the LCIA indicators of the three methods. Through case studies of five Danish buildings, the results show that the impact on biosphere integrity through the proposed conversion factors highly depends on the chosen LCIA method, with LC-IMPACT systematically estimating the highest impacts. ReCiPe and IW+ show similar results, with ReCiPe estimating 48–63 % and IW+ 55–74 % of LC-IMPACT impacts. Using PB-LCIA results in the lowest level of transgressions of the allocated PB compared to the three other methods, and it demonstrates a greater distinction in results between materials in wood and concrete, indicating higher sensitivity to material choice. In some cases, the disagreement between LCIA methods led to uncertainty on whether the ecosystem damage impacts were below or above the allocated thresholds. Further, a contribution analysis of the life cycle impacts showed that the LCIA methods even identify different hotspots within the case studies. This highlights the need for future research to better understand the reasons for these disagreements across LCIA methods for the development of consistent and robust conversion factors. Still, our study represents an initial step in linking the LCA and planetary boundaries framework. Ultimately, this may help the building sector quantify its life cycle impacts on biodiversity following indicators from the planetary boundaries framework. This could, in turn, inform new regulations mandating actors to account for these impacts and set science-based targets for their reduction.