Nudging Cooperation in Environmental Social Dilemmas: Moral versus Social Appeals in Waste Sorting

Pro-environmental behaviours are often social dilemmas in which cooperation depends on what others do. When others seem not to do their part, effort tends to decline. We examined whether social and moral nudges can counter this tendency, and whether their effect depends on how much others recycle. In a 3 × 2 between-subjects experiment, 123 US adults completed an eight-round waste-sorting task in which recycling took time, whereas discarding waste was immediate. After each round, they saw that the other members of their group had recycled either about 80% or 20% of their waste (high vs. low cooperation). Bayesian mixed models showed that participants recycled far more when the rest of their group did. The moral nudge increased recycling only under low cooperation, especially among those reporting stronger personal norms, whereas the social nudge did not. Moral appeals may sustain pro-environmental effort where others’ behaviour would otherwise discourage it.