What is a footprint? A conceptual analysis of environmental footprint indicators

To describe and measure the apparent pressures humanity poses to functioning of the crucial Earth systems, scientists have long strived to develop comprehensive indicators, of which environmental footprints are probably the most popularly recognized and employed. Since the inception of environmental footprint accounting in the 1990s, the concept has evolved to comprise, next to the ecological footprint, many other environmental and socio-economic issues. However, there is not yet a generally accepted definition of what (environmental) footprints are and how should they be calculated. Thus, most people have only a vague idea of what the footprint results entail, which seems to hold for the scientific community as well. This paper sets to critically overview the various methodological approaches to the most eminent footprinting methodologies, and to conceptually analyze the, often opposing, views on what footprint indicators are or should be; thus providing a key to current footprint research literature and debates. Starting with the ecological footprint, it is shown how footprints started and evolved, but also how the original concept is heavily criticized. The carbon footprint is the most well-known indicator; however, it is also the one where the chaos is most apparent, with a multitude of differing definitions and approaches. The evolution, as well as the debate of the opposing views and methodologies are described regarding water footprint. Also, other evolving concepts, such as land or material footprints are analyzed, as well as how environmental footprints are grouped to a Footprint Family. Then, the general environmental footprint concept is analyzed, regarding the most eminent debates and opposition to life cycle assessment. Finally, the relationship of footprints to the planetary boundaries concept is analyzed. (C) 2020 Elsevier Ltd. All rights reserved.