Materials Availability, Working paper III: Comparison of material criticality studies - methodologies and results.

Policy makers and industry are increasingly concerned over the availability of certain materials key to the manufacture of low carbon technologies. The literature addressing this topic includes reports termed criticality assessment that aim to quantify the relative criticality of a range of materials. In this study we examine the methodologies underpinning these criticality assessments, and attempt to normalise and compare their results. This process identified a list of 10 metals or metal groups for which average normalised scores are presented, along with maximum and minimum scores to indicate the range of uncertainty. We find that criticality assessment methodologies diverge significantly, making comparison difficult. This leads to apparently wide uncertainty in results. We also find that in order to achieve comparability within studies, authors typically rely on simple metrics for which data is available for all metals considered. This leads to some compromises which affect results. Finally we suggest that, given these uncertainties and methodological difficulties, criticality assessments are best used to highlight materials or technologies of particular interest, which should then be further examined in isolation, to improve insight and accuracy.