The Single Score indicator refers to several things, depending on the audience, and the context. In the context of LCAs, the Single Score attempts to indicate the total environmental impact of your LCA through one overarching score - typically based on other environmental impact categories.

Distinct (midpoint) environmental impact categories quantify the impact of your LCA on one part of the environment. For example, the value of the Climate Change indicator describes the amount of kilograms CO2-eq emitted in your LCA, and how much it contributes to global warming. Similarly, the result of the Ozone depletion indicator tells the reader how many chlorofluorocarbons equivalents (kg CFC11-eq) are emitted and to what extent it depletes the ozone layer. However, none of these distinct midpoint environmental impact categories inform about the LCA’s total impact on the environment.

So, how do you estimate the total impact of an LCA on the environment in one number? Keeping things simple, in essence, one can argue that the total environmental impact of an LCA is ‘just’ the sum of all separately quantified environmental impact categories. This is easier said than done because each midpoint environmental indicator is measured in its own unit. In the examples given above - Climate Change is measured in kg CO2-eq, while Ozone Depletion is measured in kg CFC11-eq. Items measured in different units can’t be simply added up together.

This is where the concept of the Single Score comes into play. Single Score is an end-point indicator that normalizes and weights midpoint indicators to a total score.

The remainder of this article explains the concept of the Single Score indicator from the perspective of two methodologies:

The Single Score indicator is an end-point indicator that aggregates the main impact categories listed below in Table 1. The Single Score is obtained by using the Environmental Footprint 3.1 (EF3.1) LCA calculation method. Each unique, individual impact category is measured in its own, respective unit. For example, Climate change is measured in ‘kg CO2 eq.’, while Photochemical ozone formation is denoted in ‘kg NMVOC eq.’. Since each impact category has its own measurement unit, it is impossible to simply add all the individual, original results to a total score. Instead, it is necessary to apply a normalization and weighting factor to make the unique impact categories compatible.

The Single Score indicator provides a comprehensive way to assess and communicate the total environmental impact of an LCA by aggregating multiple impact categories into a single, meaningful result. Both the EF and MKI methods apply distinct normalization and weighting factors to achieve this. Understanding how the Single Score functions is essential for effectively analyzing and reporting on environmental performance within Mobius and beyond.