This research aimed to investigate the nature of cognitive processes when college students reason about evidence on global climate change (GCC). Twenty-six undergraduate students participated in this qualitative study, where they were interviewed to evaluate competing arguments on key issues related to GCC and discuss their own perspectives. Constant comparative analysis of data from think-aloud protocols and semi-structured interviews revealed three patterns of reasoning: minimum reasoning, constrained reasoning, and deliberative reasoning. Minimum reasoning demonstrated that participants predominantly favoured arguments which supported their own beliefs, with limited reasoning about the relative correctness of opposing arguments. Constrained reasoning showed participants' emphasis on surface features of evidence on GCC rather than its scientific underpinnings. In contrast, deliberative reasoning involved more sophisticated cognitive efforts in coordinating evidence and claims, and a key characteristic of this pattern was in-depth statistical and causal reasoning. The current findings added to our understanding of college students' reasoning processes when they are faced with controversial issues like GCC. This work contributed to current efforts in using cognitive research to inform science and environmental education, and laid a foundation for future endeavours in promoting scientific reasoning and argumentation in climate change education.