The author analyzes the optimal investment in environmental protection in a model of non-overlapping hyperbolically discounting agents. He shows that, in the long run and in the absence of a commitment device, society is stuck in a situation where all agents prefer further investments, yet no agent invests. This holds no matter whether agents are aware of the time inconsistency of their preferences. As a consequence, awareness of the time-inconsistency problem poses at best a short run remedy. Moreover, such an outcome may be Pareto inefficient and may explain the weak performance of long-run environmental policies.