A Dynamic Analysis of International Environmental Agreements under Partial Cooperation

We study the dynamics of equilibrium membership of an international environmental agreement aimed at increasing the stock of a global public good such as climate change mitigation.In contrast with previous studies, we assume partial cooperation among signatories, and showthat the coalition size can be large, and increasing over time, even when the initial coalitionsize is small. We highlight a novel trade-o§ between agreements that are narrow-but-deep-andlong-lived vs. those that are broad-but-shallow-and-short-lived. We show that loose cooperativeagreements, which are broad-but-shallow-and-short-lived, are both welfare- and Pareto-superiorto tight cooperative agreements, which are narrow-but-deep-and-long-lived. We also show thatconditions exist under which the equilibrium coalition size is e¢ cient