The consequences of global warming are uncertain and possibly irreversible. In this article, I investigate the value of early mitigation action given these uncertainties and irreversibilities. I complement standard economic techniques with a political analysis: in the model, an incumbent government may be replaced through elections or other means by another policymaker with very different preferences. I find that if a green policymaker (very concerned about global warming) is probably replaced by a brown policymaker (mildly concerned about global warming), the case for early mitigation action is even stronger than otherwise. Thus, if environmentally aware governments will gain power in major emitter countries, they have particularly strong incentives to negotiate a global climate treaty when they expect that their successor may be less interested in climate cooperation. Similarly, concerns about the preferences of future policymakers could motivate environmentally aware local policymakers to impose increasingly stringent climate policies.