One of the challenges in managing the Earth's common pool resources, such as a livable climate or the supply of safe drinking water, is to motivate successive generations to make the costly effort not to deplete them. In the context of sequential contributions, intergenerational reciprocity dynamically amplifies low past efforts by decreasing successors' rates of contribution. Unfortunately, the behavioral literature provides few interventions to motivate intergenerational beneficence. We identify a simple intervention that motivates decision makers who receive a low endowment. In a large online experiment with 1378 subjects, we show that asking decision makers to forecast future generations' actions considerably increases their rate of contribution (from 46% to over 60%). By shifting decision makers' attention from the immediate past to the future, the intervention is most effective in enhancing intergenerational beneficence of subjects who did not receive a contribution from their predecessors, effectively neutralizing negative intergenerational reciprocity effects. We provide suggestive evidence that the attentional channel is the main channel at work.