What counts as a Footprint? On the categorization of Footprint indicators

Over the past years a continuously expanding list of indicators termed "Footprint" has been introduced in industrial ecology and related areas of research since the emergence of the very first Footprint indicator — the... [ view full abstract ]

Over the past years a continuously expanding list of indicators termed "Footprint" has been introduced in industrial ecology and related areas of research since the emergence of the very first Footprint indicator — the Ecological Footprint in the 1990s. Nowadays Footprint-style indicators have received considerable popularity throughout the scientific and policy communities, and the sustainability issues addressed have gone far beyond the original scope of the Ecological Footprint. The Footprint discourse, however, has been steeped in controversy. Of particular concern is what actually counts as a Footprint. The primary purpose of the present study is to bring clarity to the ongoing international debate in the Footprint concept. It begins with an overview of the Footprint Family in its current form. By conducting a bibliometric analysis of all Footprint-related publications in the ISI Web of Science, we map the word cloud of existing Footprint indicators and the flow of paper keywords in the literature containing "Footprint". We then provide a brief review of generalized Footprint definitions presented by a large number of studies. It shows that a consensus-based Footprint definition that has won mainstream acceptance of the scientific community remains lacking. Rather than continuing to look for a "universal" definition of Footprints, we propose looking deeper into the categorization of Footprint indicators, which is key to making sense of the Footprint concept while being largely ignored by Footprint practitioners and users. In view of the variations of Footprint indicators in methods, applications and policy relevance, any well-designed classification schemes should avoid creating an overly simplistic view of the Footprint Family that is heterogeneous and expanding. Proceeding with this recognition, the study comes up with a classification scheme that successively divides the Footprint Family at four levels: (1) into two dimensions (object and theme); (2) within the theme dimension into two domains (socio-economic and environmental); (3) within the environmental domain into two groups (resource and emission); and (4) within each group into two categories (inventory and impact). All existing Footprint indicators encompassing the three pillars of sustainability (i.e., environmental, economic and social) fit well within the classification scheme proposed. Within the environmental domain, for instance, four quadrants of Environmental Footprints have been identified, namely, the Inventory-Oriented Emission Footprints, the Impact-Oriented Emission Footprints, the Inventory-Oriented Resource Footprints, and the Impact-Oriented Resource Footprints. The two most widely recognized Footprint indicators — the Carbon and Water Footprints have been employed to verify the four-quadrant categorization. Each of them has two fundamentally different versions which, in aggregate, constitute the four quadrants of Environmental Footprints. As such, the proposed typology represents a good starting point for stimulating a scientific debate on the concept of Footprints. Finally, we call for interdisciplinary research programs devoted to more elaborated or alternative classification schemes that would support the development of Footprint Science — an upcoming field of research that goes beyond current paradigms for Footprinting and develops a suite of harmonized Footprint indicators that can be used to evaluate the three pillars of sustainability for multiple levels of objects and themes.