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Data Papers on Discounting

Ethics of the Discount Rate in the Stern Review on the Economics of Climate Change
Wilfred Beckerman & Cameron Hepburn, World Economics, March 2007
Any comparison of the costs and benefits of climate change is dominated by the chosen discount rate. But, although the Stern Review emphasises the ethical nature of the parameters entering into its choice of a relatively low discount rate, its discussion of the ‘pure time preference’ parameter is unbalanced. In particular, no consideration is given to the role of ‘agent-relative ethics’, which (i) has a wellestablished philosophical pedigree going back to David Hume; (ii) is likely to correspond closely to world-wide public attitudes towards intergenerational welfare; and (iii) would entail discounting a unit of welfare accruing to future generations compared to an equal unit accruing to people alive today at a positive rate. The authors also discuss the other ethical parameter upon which the discount rate depends, namely the elasticity of marginal utility with respect to consumption. In the conventional model, this simultaneously reflects different aspects of inequality aversion as well as risk aversion, which complicates its interpretation. Finally, they discuss the divergence between market rates of discount and the low rate chosen in the Review, and the limitations—on the one hand—on the normative significance of market rates, as well as the danger—on the other hand—of relying on rates chosen by elites or philosopher kings.
A Review of the Stern Review
Richard S. J. Tol & Gary W. Yohe, World Economics, December 2006
The Stern Review on the Economics of Climate Change was published on 30 October 2006. In this article Richard Tol and Gary Yohe, while agreeing with some of the Review’s conclusions, disagree with some other points raised in the Review and they address six issues in particular: First, the Stern Review does not present new estimates of either the impacts of climate change or the costs of greenhouse gas emission reduction. Rather, the Stern Review reviews existing material. It is therefore surprising that the Stern Review produced numbers that are so far outside the range of the previous published literature. Second, the high valuation of climate change impacts reported in the Review can be explained by a very low discount rate, risk that is double-counted, and vulnerability that is assumed to be constant over very long periods of time (two or more centuries). The latter two sources of exaggeration are products of substandard analysis. The use of a very low discount rate is debatable. Third, the low estimates for the cost of climate change policy can be explained by the Review’s truncating time horizon over which they are calculated, omitting the economic repercussions of dearer energy, and ignoring the capital invested in the energy sector. The first assumption is simply wrong, especially since the very low discount rates puts enormous weight on the other side of the calculus on impacts that might be felt after the year 2050. The latter two are misleading. Fourth, the cost and benefit estimates reported in the Stern Review do not match its policy conclusions. If the impacts of climate change are as dramatic as the Stern Review suggests, and if the costs of emission reduction are as small as reported, then a concentration target that is far more stringent than the one recommended in the Review should have been proposed. The Review, in fact, does not conduct a proper optimization exercise. Fifth, a strong case for emission reduction even in the near term can nonetheless be made without relying on suspect valuations and inappropriate summing across the multiple sources of climate risk. A corollary of this observation is that doing nothing in the short term is not advisable even on economic grounds. Sixth, alarmism supported by dubious economics born of the Stern Review may further polarize the climate policy debate. It will certainly allow opponents of near-term climate policy to focus the world’s attention on the estimation errors and away from its more important messages: that climate risks are approaching more quickly than previously anticipated, that some sort of policy response will be required to diminish the likelihoods of the most serious of those risks, and that beginning now can be justified by economic arguments anchored on more reliable analysis. These six points are discussed in separate sections before the authors reach their conclusion.
Valuing the Future: Recent advances in social discounting
David Pearce, Ben Groom, Cameron Hepburn & Phoebe Koundouri, World Economics, June 2003
One of the most controversial areas of economics is the practice of discounting: attaching a lower weight to future costs and benefits than present costs and benefits. Discounting appears to offend notions of sustainable development and the interests of future generations. Recent advances in the theory of discounting hold out strong hope that the ‘tyranny of discounting’ can be avoided through the use of time varying discount rates (TVDRs). This paper reviews the recent rationales for TVDRs and applies the results to issues such as nuclear power and global warming control.