Harmonizing LCIA of mineral resource use - guidance from the UN Environment Life Cycle Initiative task force

The environmental impacts caused by mining and refining processes producing usable materials are considered in relatively well established impact categories (e.g., climate change, acidification, and eco-toxicity). However, the assessment of impacts of resource use as such is still controversial – even though a wide range of methods are available. Therefore, the task force primary mineral resources of the global guidance for LCIA indicators project (a central project of the Life Cycle Initiative hosted by UN Environment) works towards consensual guidance for assessing resource use in LCA.
In a comprehensive literature review, 29 methods assessing impacts of resource use in LCA have been identified. Depending on the impact pathways described, these methods have been clustered into four categories: methods assessing depletion of stocks, methods assessing “future efforts” resulting from ore grade decline as an (assumed) consequence of current extraction, methods using thermodynamic accounting (exergy and emergy approaches), and methods assessing the supply risk of raw materials based on socio-economic aspects (like country concentration, political stability, barriers of trade, etc.).
Within the four clusters of methods, key axioms and methodological choices, like the resource stocks used in depletion methods, the reference environment used in exergy methods, or the socioeconomic aspects considered in methods addressing supply risk are discussed. All methods are analyzed and compared by means of a comprehensive evaluation scheme comprising criteria like scientific robustness, documentation, applicability, and acceptance. Moreover, all methods are applied to analyze the life cycle inventory of an electric vehicle and to discuss the different findings resulting from methodological differences.
Finally, relevant impact pathways leading to the agreed on area of protection “availability of resources for humans in the technosphere” are recommended and clear guidance for selecting methods depending on the question to be answered, as well as future research needs is given.