A widely-held explanation involves politically motivated reasoning: Rather than helping uncover truth, people use their reasoning abilities to protect their partisan identities and reject beliefs that threaten those identities. Despite the popularity of this account, the evidence supporting it (i) does not account for the fact that partisanship is confounded with prior beliefs about the world, and (ii) is entirely correlational with respect to the effect of reasoning. Here, we address these shortcomings by (i) measuring prior beliefs and (ii) experimentally manipulating participants’ extent of reasoning using cognitive load and time pressure while they evaluate arguments for or against anthropogenic global warming. The results challenge the politically motivated system 2 reasoning account: engaging in more reasoning led people to have greater coherence between judgments and their prior beliefs about climate change - a process that can be consistent with Bayesian reasoning.