A Dynamic Model for International Environmental Agreements

In this paper we develop a model that uses a dynamic framework to analyze the process through which countries join international environmental agreements (IEAs). In the model, while all countries suffer from the same environmental damage as a result of total global emissions, non-signatory countries decide on their emission levels by maximizing their own welfare, whereas signatory countries decide on their emission levels by maximizing the aggregate welfare of all signatory countries. It is assumed that signatory countries will be able to punish non-signatories, at some cost to themselves. When countries decide on their pollution emissions, they account for the evolution of the stock of pollution over time. Moreover, we propose a mechanism to describe how countries reach a stable IEA. The model is able to capture situations characterized by partial cooperation within an IEA that is stable over time. It also captures situations where all countries participate in a stable agreement, and situations where no stable agreement is feasible. Where more than one possibility coexist, the long-term outcome of the game depends on the initial conditions (i.e., the initial number of signatory countries and pollution level).