I review the economic characteristics of the climate problem, focusing on the choice of discount rates in the presence of a stock externality, risk and uncertainty/ambiguity, and the role of integrated assessment models (IAMs) in analyzing policy choices. I suggest that IAMs can play a role in providing qualitative understanding of how complex systems behave, but are not accurate enough to provide quantitative insights. Arguments in favor of action on climate issues have to be based on aversion to risk and ambiguity and the need to avoid a small but positive risk of a disastrous outcome.

The fact that a consumer is frequently uncertain about the quality of a product that he purchases, and is therefore also unsure of the extent to which it will render him the services he might expect of it, is one that is gaining increasing recognition. In an earlier paper [5] I examined in a simple framework the effects of changes in the uncertainty about a product's quality on the consumer's demand, and also touched briefly on the effect of a guarantee. In this paper I want to examine in more detail some of the economic issues posed by the existence of guarantees. There are several useful distinctions that can be drawn as a preliminary to more detailed study. One is a distinction between situations where buyers and sellers have equal access to information, and a situation where sellers have superior access. The first situation is exemplified by a market where trade is in a product whose quality is genuinely random, with the distribution known to both buyers and sellers. Thus if a certain fraction p of the cars from a given factory are generally known to be faulty, then a transaction in which a retailer sells a car to a buyer comes into this category: each knows that the chance of the car being faulty is p, but, because the car is unused, neither knows whether it is actually faulty. Contrast this with a situation where the first owner of the car is reselling it: now there is an important asymmetry, in that the seller is much better informed about the quality of the product than the buyer. This is the case with which Akerlof's very interesting analysis [1] is largely concerned, and which I have also discussed in [4]. My main concern here, however, is with a situation of equal information. Thinking casually about such a situation, it is clear that one can distinguish between the incentive effects and the risk-sharing effects of a guarantee. Incentive effects arise because the existence of a guarantee provides the producer with an incentive to improve the quality of his product, at least to the extent of reducing the chances of its falling below the guaranteed level. If the compensation in the event of failure is less than complete, then the consumer also has an incentive to maintain the product. For example, a used car guarantee, under which the buyer and seller will each pay half of any repair bills, provides both parties with incentives to minimize these bills. Of course, if the guarantee is valid for only a limited period of time, then there is the further effect of providing the buyer with an incentive to ensure that if there is to be a failure, it occurs early in the product's life. This may act in opposition to the other effect, and reduce his eagerness to maintain the product. In addition to creating the incentive effects mentioned, a guarantee also acts as a way of sharing the risk associated with uncertainty about the quality of a product: to be efficient in this sense, it will apportion this risk in accordance with the risk-aversion of the participants. My main concern here is with the risk-sharing aspects of guarantees. This is partly because these seem to be the most tractable aspects of the problem, but also stems from a belief that these are the most important aspects. Casual empiricism suggests that except in rather unique cases, a product is usually designed and produced before any attention is given to the choice of guarantee terms: these are then chosen as part of a marketing package. In such situations, the reliability of the product will clearly be independent of the

I. Introduction, 499.—IL Akerlof's problem and the prisoner's dilemma, 499.

This paper provides a critical review of the literature on choosing social discount rates (SDRs) for public cost-benefit analysis. We discuss two dominant approaches, the first based on market prices and the second based on intertemporal ethics. While both methods have attractive features, neither is immune to criticism. The market-based approach is not entirely persuasive even if markets are perfect, and faces further headwinds once the implications of market imperfections are recognised. By contrast, the ‘ethical’ approach—which relates SDRs to marginal rates of substitution implicit in a single planner’s intertemporal welfare function—does not rely exclusively on markets, but raises difficult questions about what that welfare function should be. There is considerable disagreement on this matter, which translates into enormous variation in the evaluation of long-run payoffs. We discuss the origins of these disagreements, and suggest that they are difficult to resolve unequivocally. This leads us to propose a third approach that recognises the immutable nature of some normative disagreements, and proposes methods for aggregating diverse theories of intertemporal social welfare. We illustrate the application of these methods to social discounting, and suggest that they may help us to move beyond long-standing debates that have bedevilled this field.

Partha Dasgupta, Geoffrey Heal; The Optimal Depletion of Exhaustible Resources12, The Review of Economic Studies, Volume 41, Issue 5, 1 December 1974, Page

Harl E. Ryder, Jr, Geoffrey M. Heal; Optimal Growth with Intertemporally Dependent Preferences12, The Review of Economic Studies, Volume 40, Issue 1, 1 Jan

I. Introduction, 297.—II. The model, 298.—III. Variable return on foreign investment, 303.—IV. Uncertain future demand, 303.—V. Conclusions, 305.

Geoffrey Heal, Michael Barrow; The Relationship between Interest Rates and Metal Price Movements, The Review of Economic Studies, Volume 47, Issue 1, 1 January

Journal Article Equity, Efficiency and Increasing Returns Get access Donald J. Brown, Donald J. Brown Cowles Foundation for Research in Economics at Yale University Search for other works by this author on: Oxford Academic Google Scholar Geoffrey Heal Geoffrey Heal University of Sussex Search for other works by this author on: Oxford Academic Google Scholar The Review of Economic Studies, Volume 46, Issue 4, October 1979, Pages 571–585, https://doi.org/10.2307/2297028 Published: 01 October 1979 Article history Received: 01 July 1978 Accepted: 01 January 1979 Published: 01 October 1979