Assessment of climate change policies requires aggregation of costs and benefits over time and across generations, a process ordinarily done through discounting. Choosing the correct discount rate has proved controversial and highly consequential. To clarify past analysis and guide future work,...

The choice of the proper discount rate is important in the analysis of projects whose costs and benefits extend into the future, a particularly striking feature of policies directed at climate change. Much of the literature, including prominent work by Arrow et al. (1996), Stern (2007, 2008),...