Stéphane Zuber

Suppose that, for whatever reason, it is decided that inequalities within countries are more offensive than inequalities between countries, and that inequalities between populations living together are more offensive than inequalities between generations living in different times. Can a social welfare function express that preference? We show that it is actually difficult to incorporate such a localist preference into a social welfare function, except in a limited way (i.e., from a situation of specific similarity between countries). We also show that in order to obtain such preferences, the relative size of inequality aversion within and between countries may be counter-intuitive in some relevant cases, in the sense that a greater inequality aversion may happen to be required across countries than within countries. This research highlights new social welfare functions that aggregate the outcomes of evaluations over pairs of agents.

We examine utilitarian criteria for evaluating profiles of well-being among infinitely many individuals. Motivated by the non-existence of a natural 1-to-1 correspondence between people when alternatives have different population structures, with a different number of people in each generation, we impose equal treatment in the form of Strong Anonymity. We demonstrate how a novel criterion, Strongly Anonymous Utilitarianism, can be applied in the Ramsey model, leading to an efficient and sustainable stream. We show how the criterion is the result of combining Strong Anonymity with other regularity axioms (Monotonicity, Finite Completeness, and continuity axioms) as well as axioms of equity, population ethics, sensitivity, and separability. We relate it to other strongly anonymous utilitarian criteria.

Climate policy is often described by economists as an intertemporal consumption trade-off: consume all you want today and face climate damages in the future, or sacrifice consumption today to implement costly climate policies that will bring future benefits through avoided climate damages. If one assumes enduring technological progress, a society that is more averse to intertemporal inequalities should postpone climate policies and let future, richer generations pay more. Growing evidence however suggests that the trade-off is more complex: abrupt, extreme, irreversible changes to the climate may cause discontinuities to socio-economic systems, possibly leading to a sharp decline of human population and consumption per capita. In this paper, we show that, when accounting for a very small risk of catastrophic climate change, it is optimal to pursue stringent climate policies to postpone the catastrophe. Our results conform with the well-known conclusion that tight carbon budgets are preferred when aversion towards inequalities between generations is low. However, by contrast with previous studies, we show that stringent policies are also optimal when inequality aversion is high. The non-monotonicity of the influence of inequality aversion is due to the fact that, for a given investment in abatement, a higher inequality aversion gives a smaller weight to avoided future non-catastrophic damages, but a larger weight to the catastrophic outcome. We also explore the role of population ethics, and show that the size of the optimal carbon budget decreases with the social preference for large populations, although this parameter plays almost no role at extreme levels of inequality aversion. Our result demonstrates that views from opposite sides of the ethical spectrum in terms of inequality aversion converge in terms of climate policy recommendations, warranting immediate climate action.

Utilitarianism is the most prominent social welfare function in economics. We present three new axiomatic characterizations of utilitarian (that is, additively-separable) social welfare functions in a setting where there is risk over both population size and individuals’ welfares. We first show that, given uncontroversial basic axioms, Blackorby et al.’s (1998) Expected Critical-Level Generalized Utilitarianism is equivalent to a new axiom holding that it is better to allocate higher utility-conditional-on-existence to possible people who have a higher probability of existence. The other two characterizations extend and clarify classic axiomatizations of utilitarianism from settings with either social risk or variable-population, considered alone.

When evaluating well-being distributions in an anonymous (and replication invariant) manner, one faces a dilemma between (i) assigning dictatorship to a single worst-off person, thus succumbing to a tyranny of non-aggregation and (ii) assigning dictatorship to (unboundedly) many better-off persons, thus succumbing to a tyranny of aggregation. We show how this corresponds to a population-ethical dilemma in the variable population setting between, on the one hand, a reversed repugnant conclusion (preferring a very small population with high well-being) and, on the other hand, a repugnant conclusion (preferring a sufficiently large population with lives barely worth living to a population with good lives) or very sadistic conclusion (not preferring a large population with lives worth living to a population with terrible lives). The dilemma can be resolved by relaxing replication invariance and thus allowing that evaluation in the fixed population setting might change with population size even though the relative distributions of well-being remain unchanged. Rank-dependent criteria are evaluation criteria that resolve this dilemma but fails replication invariance. We provide conditions under which rank-dependent criteria are the only way out of the dilemma. Furthermore, we discuss the following consequence of relaxing replication invariance: It becomes essential to take into account the existence and well-being of non-affected people when evaluating population policies with limited scope.

While little agreement exists regarding the taxation of bequests in general, there is a widely held view that accidental bequests should be subjected to a confiscatory tax. We reexamine the optimal taxation of accidental bequests by introducing a concern for compensating individuals for a premature death. Assuming that individuals care about what they leave to their offspring, we show that, whereas the 100 % tax view holds under the utilitarian criterion, the ex post egalitarian criterion (giving priority to the worst-off ex post) implies subsidizing accidental bequests so as to compensate the short-lived. In a second-best setting, compensating the short-lived justifies taxing total bequests at a rate increasing with the age of the deceased. Finally, when the model is extended to an intergenerational setting, accidental bequests cannot be used as a redistributive tool anymore, so that ex post egalitarianism rejoins the 100 % tax view.

We highlight a new paradox for the social evaluation of risk that bears on the evaluation of individual well-being rather than social welfare, but has serious implications for social evaluation. The paradox consists in a tension between rationality, respect for individual preferences, and a principle of informational parsimony that excludes individual risk attitudes from the assessment of riskless situations. No evaluation criterion can satisfy these three principles. This impossibility result has implications for the evaluation of social welfare under risk, especially when the preferences of some individuals are not known. It generalizes existing impossibility results, while relying on very weak principles of social rationality and respect for individual preferences. We explore the possibilities opened by weakening each of our three principles and discuss the advantages and drawbacks of these different routes.