Future Generations and the Social Rate of Discount

This paper reexamines the case for discounting for time in public investment appraisal where long-term or irreversible effects on future generations are involved. It is concluded that—while, in the short-term, considerations of equity reinforce the commonly advocated case for discounting for time—in evaluating long-term or irreversible effects, current discounting procedures require the doubtful assumption of perpetual exponential growth of real income. However, if discounting were abandoned, use of the standard cost—benefit-analysis framework would require the forecasting of shadow prices for all future dates, unless an arbitrary time horizon is adopted. Thus cost—benefit analysis does not appear to be a satisfactory method for evaluating effects on future generations.