Comments on “The Energetic Metabolism of the European Union and the United States” by Haberl and Colleagues: Theoretical and Practical Considerations on the Meaning and Usefulness of Traditional Energy Analysis

This commentary responds to the study “The Energetic Metabolism of the European Union and the United States: Decadal Energy Input Time‐Series with an Emphasis on Biomass” by Haberl and colleagues, published in this issue. Their article provides an analysis based on a set of data that could be very useful for discussing the sustainability of economic processes in terms of resource flows and societal relations to nature. The authors' choice to adopt a reductionist analysis of the metabolism of societies in energetic terms—that is, an analysis based on a single‐scale and single‐variable indicator such as “joules of energy input metabolized per year for the whole society”—is a controversial one. Such a choice implies the aggregation of different types of data (referring to nonequivalent categories of energy inputs) into a single overall assessment. That is, in their study the authors are adopting an old and controversial solution for aggregating different types of energy forms: applying a set of flat conversion factors (calorimetric equivalent) to the different types of energy inputs considered. This commentary discusses the trade‐off entailed by any method of aggregation of energy forms of different quality: (i) compression—reducing the number of indices used—versus (ii) relevance—maintaining a diversity of categories needed for the usefulness of the analysis. A brief history of the main strategies adopted, so far, for dealing with the problem of aggregation suggests implications for the approach adopted by Haberl and colleagues.