Tol and Yohe point out that, in their reply [Vol. 8, No. 1] to Tol and Yohe’s review [Vol. 7, No. 4], the Stern team demonstrates the fragility of the numerical findings of the cost–benefit analysis in the Stern Review. At the same time, the Stern team puts less weight on cost–benefit analysis as a guide to policy making on climate change. Tol and Yohe show that the Stern Review allows several, mutually contradictory interpretations of the model that underlies the cost estimates; and argue that each interpretation implies that Stern’s cost estimates have a severe downward bias.

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.