Although there is widespread agreement about the dangers of global warming and the resulting need to cut down emissions, there does not seem to be general agreement about the exact form the policy should take or the timing of its adoption. Failure to adopt and implement policies against global warming reflects the complexity of the problem, the uncertainties of climate change and the cost of policy adoption. Issues associated with the interactions between uncertainties and irreversibilities in determining the timing of policy adoption are analyzed by using the methodology of optimal stopping rules. Optimal policy functions are derived for cooperative and noncooperative solutions, with differential game representation. Issues associated with the empirical application of the optimal policy rules are also considered.