The paper rigorously defines sustainable decisions from first principles. A decision is sustainable if its performance (e.g., utility) constitutes at least a fair game. From a probabilistic point of view, this idea can be formalized by applying the concept of submartingales. Our approach allows us to establish the novel concept of sustainable optimization and leads to novel sustainable optimization and equilibrium problems. It requires an extension of the classical dynamic-programming paradigm including a formal derivation of a sustainable Bellman principle. Our approach can be applied to a huge number of decision problems where potentially heterogeneous decision makers optimize some form of ”well-being” (e.g., utility or costs). We demonstrate its usefulness by studying various problems from economics, finance, marketing, or engineering. We derive sustainable consumption-investment strategies with habit formation or recursive utility, sustainable advertising strategies, sustainable compensation contracts in a principal-agent framework, or a sustainable equilibrium in a two-agent endowment economy.
This paper analyzes sustainable climate policy in the presence of disaster risk using a sustainability concept derived from first principles. The climate–economy system is modeled with Epstein–Zin preferences, and sustainability is defined as a submartingale condition on the social planner’s value function, ensuring that future welfare is not expected to decline. The paper makes two main contributions. First, it embeds the sustainability condition into a recursive climate policy framework and derives implications for optimal mitigation and investment. Second, it evaluates the role of the sustainability condition across three disaster risk scenarios—no disaster risk, constant disaster risk, and state- dependent disaster risk—and under two institutional regimes: one in which the social planner is continuously required to act sustainably, and another in which sustainability is only enforced once a critical global temperature threshold of 1.5°C is exceeded. Results show that disaster risk alone induces some precau- tionary behavior, but a binding sustainability condition substantially amplifies mitigation and investment. Under the conditional regime, anticipation of future policy constraints further strengthens early abatement. These findings highlight how ethical constraints and climate risks jointly shape dynamic climate policy.
I review the literature on the conceptual distinction between sustainability and ESG frameworks. While both aim to guide responsible decision-making, they differ in scope, temporal focus, and normative foundations. Sustainability is associated with intergenerational fairness and long-term well-being, whereas ESG emphasizes three specific pillars tied to short- and medium-term corporate performance. Sustainability reflects a holistic perspective on societal and environmental well-being, while ESG is primarily applied at the business and investment level.