This paper proposes a dynamic game model of the process through which countries join international environmental agreements (IEAs). The model assumes that both the number of signatory countries and the stock of accumulated pollution evolve over time, as a result of countries' emission and membership decisions. The evolution of the number of signatory countries is described by a discrete-time replicator dynamics, while that of the stock of pollution results from feedback emission strategies. We show that evolutionary farsightedness, that is, the capacity of players to account for the impact of their decisions on the evolution of the number of signatory countries, is beneficial to the formation and stability of self-enforcing IEAs.