The EU and the United States disagree deeply about the need for more stringent climate policies. Increased climate change concern in 2006-2008 created new opportunities for convergence, but ended in sharp policy differences. We explore two related explanations. First, scientific input was used to frame joint gains among stakeholders differently in the EU and US. Framing was different concerning the consequences of the problem, and particularly in the impact assessments of proposed policy. Second, different governance systems enabled distinctive responses to new opportunities in the EU and United States. Differences in how new policies were initiated and negotiated caused divergent climate policies. The paper tentatively concludes that the relationship and interaction between scientific input and governance systems resulted in distinctively different policy-making processes. This relationship reinforced a cooperative attitude to identify joint gains among EU decision- makers. In contrast, the framing of scientific knowledge reinforced a competitive attitude among US lawmakers, fueled by different stakeholder interests. Scientific knowledge was used and applied to reinforce differences in governance systems. The main lesson from this case is that the framing and application of scientific knowledge in the debate matters, but differences in governance systems are more instrumental for policy outcome.