Is normalization in Life Cycle Assessment sustainable? Alternative approach based on natural constraints

Life cycle assessment, a widely used methodology of environmental impact assessment, employs the step called normalization to allow comparison and contextualization of the multiple environmental impacts driven by human activities. However, the currently used normalization references based on total human impacts do not reflect any sustainability limits. This leads to a paradox where the more humanity causes an impact, the less important it appears in the results. We propose that normalization references be based on natural constraints, values that delimit the level of impact which can be expected to cause no significant harm. Such approach can be applied to most characterization methodologies, as we demonstrate on the case of Environmental Footprint methodology with 16 impact categories. In this work we quantify such normalization references, we compare them to the currently used values and we statistically test the difference on the case of 60 processes from common LCA databases. The results show that the proposed normalization method significantly changes the relative ranking of most of the impact categories. According to our findings, the proposed method may alter the ranking of assessed scenarios and change the conclusions and recommendations of LCA studies. This shift in the rationale for normalization can provide a different perspective on results interpretation and thus offer more robust policy guidance.