Abstract:  After decades of rapid economic growth, societies around the world are facing severe challenges with environmental pollution. In some developing countries, environmental issues are threatening their sustainable development and people’s health. In economic and psychological literatures, environmental problems are usually recognized as social dilemmas because natural resources are public goods, which imply conflicts between individual and collective benefits. Empirical studies found that social distance had an effect on cooperative behavior in social dilemmas. Meanwhile, the phenomenon of social discounting on monetary outcomes was also revealed by many studies. However, the impact of social distance on environmental decisions remains unknown. The purpose of this study was to explore the phenomenon of social discounting of environmental outcomes, fit the behavioral data of social discounting, and investigate the effect of altruism on social discounting under gain and loss frames. The experiment was designed as a 4 (social distance level: a family member, friend, mere acquaintance, and stranger) × 2 (task frame: environmental gain, environmental loss) study in which social distance was manipulated within the subject, but task frames were assigned between subjects. The choice titration procedure was used to measure the social discounting rate of environmental outcomes. Participants were asked to make a series of choices between “I live in high (or poor in environmental loss frame) quality air for X days” and “Another person (in different social distances) lives in high (or poor) quality air for 110 days.” The value of “X” in the choice series varied from 10 days to 100 days with an interval of 10 days. In addition, participants’ altruism was measured by the Self-report Altruism Scale. The results showed that: (1) in both environmental gain and loss frames, exponential models could fit social discounting of environmental outcomes better than hyperbolic model; (2) the interaction between social distance and task frame could influence the social discounting rate. As social distance increased, the discounting rate increased more rapidly for environmental gain than for environmental loss; (3) altruism had moderate effect on the relationship between social distance and social discounting. For participants with high level of altruism, social distance had less impact on social discounting. In conclusion, this study suggests that social distance, altruism, and task frame may play important roles in people's environmental decision-making. These findings enlighten us that decision makers may become more pro-environmental if some measures are taken to enhance their altruistic tendencies and reduce their psychological distance with others.

Key words:  environmental outcome, social distance, social discounting, task frame, altruism