This article explores the cognitive dimension of climate change policy making in Brazil and the United States as both countries prepare for the Conference of the Parties to the United Nations Framework Convention on Climate Change or COP15 in Copenhagen. The comparative policy analysis is framed by Putnam (1988) and informed by Bazerman (2009), but adapted to explore the cognitive expressions of policymaking through investigation of public opinion, newspaper coverage, and policymaker statements. The analysis reveals key differences in the ways that Brazilian and U.S. citizens, journalists, and policymakers understand global warming and climate change and think through the policy alternatives for addressing this global challenge through national policy and international negotiations. Brazil's cognitive dimension provides its negotiators with a wide range of strategic positions, allowing this country to play the role of dealmaker. The U.S. administration arrives at Copenhagen with a narrow win-set, limited by the discordant and divisive cognitive expressions that surround policymaking. These differences limit bilateral cooperation and complicate the COP15 negotiations.