Defining sustainability objectives

Two of the challenges of thinking sustainability are how to deal with potentially conicting issues and how to ensure intergenerational equity. In practice, policymakers define sustainability objectives by setting thresholds that act as constraints on indicators. When defining a specific objective, they usually do not take into account either potential conflicts with other objectives or the diffculty to achieve all of them over time. In this paper, we propose an approach that defines sustainability objectives represented by a set of constraints on indicators and their associated thresholds. This approach meets the challenges of sustainability because objectives are defined such that all the constraints can be satisfied at all times. The thresholds are interpreted as minimal rights to be guaranteed to all generations, in a Rawlsian equity perspective. To define them, we have developed a criterion, which is, from a mathematical point of view, a "generalized" maximin. Applying the criterion is a two-step process. Firstly, the set of achievable objectives, given the endowment of the economy, is defined, revealing the necessary trade-offs between them. Secondly, a static optimization of sustainability preferences on that set results in the proposed definition of sustainability objectives. We illustrate this approach by applying it to a canonical model often used to investigate sustainability issues (Dasgupta-Heal-Solow model; Review of Economic Studies 1974). We emphasize the relevance of this approach because it rationalizes the practice of using indicators to deal with sustainability in terms of the given challenge. We also discuss how to apply our approach to real sustainability issues.