<p>The present study examined the impact of risk and ambiguity on environmental donations. Using a dictator game, the research investigated the behavior of student donors in a laboratory experiment in which the recipient was an environmental agency financing sustainable projects. The findings showed that participants used objective risk as a justification to avoid donating, particularly when the risks associated with the donation’s outcome were explicit. This implicitly suggests that, under conditions of uncertainty, individuals tend to prioritize private consumption over collective environmental concerns. Risk- and ambiguity-averse participants tended to place greater weight on the potential benefits of pro-environmental actions over their uncertain drawbacks. Additionally, participants’ perceived level of ambiguity—and the general difficulty they faced in assessing objective probabilities—tended to increase selfish behavior. Finally, regarding the timing of decisions, contributions seemed to be driven by instantaneous and intuitive decisions.</p>