I review the complex welfare economic issues that arise in environmental decision-making over very long periods, as in cases relating to climate change and biodiversity loss. I also consider the issues that arise in choosing a discount rate to apply to very long-run projects and indicate how...

A group of agents disagree about the appropriate inter temporal preferences to use when exploiting a common productive resource. They thus delegate decision making to a social planner who allocates consumption efficiently across heterogeneous individuals and over time. We define `policy...