There has been much discussion lately about the selection of an appropriate discount rate in the cost-benefit analysis of climate change. This is the rate at which the value of future stuff—commodities, harms, benefits—is weighed against the value of present stuff. To ‘discount’in cost-benefit analysis is to select a positive discount rate, thereby devaluing future stuff. A number of factors determine what rate is appropriate, and theorizing about these factors has led eminent economists to select very different discount rates for the cost-benefit analysis of climate change. This seemingly small matter is of great practical importance. Nicholas Stern and William Nordhaus are two economists who make sharply divergent recommendations for action based on the results of their respective analyses; the divergence is due primarily to differences in the discount rate used. 1

Philosophers appear to stand largely against the practice of discounting, which is also called ‘discounting the future.’They oppose it on ethical grounds. Different philosophers oppose the practice in different ways. Most commonly, philosophers tend to oppose the incorporation of what is called a ‘pure time discount rate’or a ‘rate of pure time preference’into the overall discount rate. This is discounting future stuff simply because it comes in the future.