Environmental rating ecolabels: Considerations for establishing a rating scale with categorical performance classes

The award of environmental rating ecolabels (ERE) to products involves the definition of a common rating scale on which products can be placed and compared. This process is essential to translate Life Cycle Assessment (LCA) results into relative performance ratings that can effectively orient consumers towards more sustainable consumption choices. Yet, limited evidence currently exists regarding the choices available to scheme developers within this process, and their implications for final ratings. Using the food sector as a case study, we explored the significance of various rating scale parameters for ERE schemes. Potential product ratings were established for 2253 products based on cradle-to-shelf environmental single scores derived from the Agribalyse 3.1 database. We investigated the effects of three distinct ‘thresholding’ scenarios for establishing the placement of products in five environmental performance classes (A-E) along the rating scale; these were the class width, the number of products per class, and a hybrid of the two. The effect of other methodological choices made prior to the rating stage (e.g., functional unit and data linearity) on final ratings were also considered and assessed. The choice of thresholding approach was a critical determining factor in the distribution of products across the A-E rating classes. Nearly 90 % of products experienced a shift of one class or more depending on the scenario chosen to define the class boundaries, with 50 % of products obtaining a different rating across the three scenarios investigated. The distribution curve of the single scores from which ratings were established was another major factor and was influenced by choices in the functional unit definition, the linearity of the data, as well as the sample dataset used to establish the rating scale. Overall, we demonstrate the rating approach to be a fundamental component of an environmental rating scheme's methodology, necessitating clear consideration from the earliest stages of methodological development and transparent, thorough documentation regarding its definition. • LCA results are translated into product environmental ratings (A-E) via the definition of a rating scale. • We establish the significance of various rating scale parameters based on a food sector example. • Rating ecolabels need clear and transparent documentation of their rating methodology. • Scheme developers are encouraged to develop rating approaches early, and guidance is provided.