EcoTime—An intuitive quantitative sustainability indicator utilizing a time metric

Sustainability indicators strive to convey the impacts of human activities on natural resource utilization, yet many fail to express these impacts in a simple relatable manner. We introduce a new sustainability indicator, EcoTime, which recasts an environmental burden of a process or item (e.g., the emission of 10 kg CO2 associated with a car trip) in time units (seconds, days, etc.). The EcoTime units represent the burden's share of a benchmark quota calculated according to location or context. For example, a developed country's average yearly CO2 emissions of 11 ton per capita would translate to 365 EcoTime days in which case the 10 kg CO2 mentioned above would equal ≈8 EcoTime hours. Since time units are commonly used the EcoTime indicator is easy to communicate to a varying audience alleviating challenges often associated with existing sustainability indicators. It leverages our innate ability to easily grasp contrasting time units over several orders of magnitude, ranging from seconds to years. Another key advantage of EcoTime is that its value shifts attention from the absolute environmental impact, which may not be meaningful to most people, to impact magnitude relative to world resource availability or usage, thus giving the burden an intuitive, intrinsic context. In addition, EcoTimes of different impact types can be conveniently and succinctly grouped as a vector (e.g., GHG emissions, water, or land footprints), or, because of the similar units, as a composite scalar. We provide several case study examples of the methodology.