Conceptual frameworks in the realm of climate-related policy, attitudes and behavior frequently argue that moral emotions play a crucial role in mobilizing pro-environmental action. Yet, little is known about the direct impact of moral emotions on environmental attitudes and behavior. Drawing on emotion research in the context of intergroup relations, the current paper investigates the role of guilty conscience (guilt and shame) as well as other emotions (anger, sadness, pride, and emotional coldness) in motivating pro-environmental behavior intentions and actual behavior as a specific form of reparative action. When confronted with human-caused (vs. seemingly natural) environmental damages, participants (N=114) reported significantly more guilty conscience. Importantly, participants in the humancaused condition were significantly more likely to spontaneously display actual proenvironmental behavior (sign a petition addressing environmental issues). Highlighting its psychological significance in motivating pro-environmental behavior, a guilty conscience mediated the experimental manipulation's effect on behavioral intentions as well as on actual behavior. We conclude by discussing the potential of moral emotions in developing timely and sustainable climate policies and interventions.