Hyperbolic Discounting with Environmental Outcomes across Time, Space, and Probability

Environmental discounting is a potentially important research area for climate change mitigation. We aimed to replicate and extend earlier work on the discounting of a negative environmental outcome. We measured ratings of concern, and willingness to act to mitigate, an outcome involving air pollution that would hypothetically affect the garden and drinking water of the participants over psychological distance represented by temporal (1 month, 6 months, and 1, 3, 5, 10, and 80 years), spatial (5, 20, 50, 100, 1000, and 5000 km), and probabilistic (95%, 90%, 50%, 30%, 10%, and 5% likelihood) dimensions. For our data from 224 first-year psychology students, of four potential models (an exponential, simple hyperbolic, and two hyperboloid functions), the Rachlin hyperboloid was the best-fitting model describing ratings of concern and action across all three dimensions. Willingness to act was discounted more steeply than concern across all dimensions. There was little difference in discounting for outcomes described as human-caused rather than natural, except that willingness to act was discounted more steeply than concern for human-caused environmental outcomes compared to natural outcomes across spatial (and, less conclusively, temporal) distance. Presenting values of the three dimensions in random or progressive order had little effect on the results. Our results reflect the often-reported attitude-behavior gap whereby people maintain concern about a negative event over dimensions of psychological distance, but their willingness to act to mitigate the event is lower and more steeply discounted.