Partisans appear to hold very different information about climate change, with Republicans more likely to respond to knowledge questions incorrectly than Democrats or Independents. As polarization undermines the ability of science to inform policy, clarifying why partisans report different science knowledge is vital. This study uses novel measurement to differentiate among knowledge, misinformation, guessing, and rejection while identifying covariates of these cognitions. First, we find that Republicans’ incorrect beliefs about climate change stem from a mix of guessing, misperceptions, and rejection. Second, multiple cognitions appear closely linked to partisanship, suggesting politically motivated reasoning as likely driving knowledge differences. Finally, partisan knowledge differences about climate change do not reflect broader polarization of science knowledge but are limited to select issues.