With recent U.S. government efforts to develop policy procedures for addressing climate change, public understanding of basic aspects of climate change is imperative in order for people to understand such policy. However, widespread misconceptions of basic atmospheric principles exist among the public. In this study, we document levels of misunderstanding that undergraduate students at a large U.S. research institution have with respect to atmospheric carbon budgets and factors that may account for variability in their understanding. Students enrolled in an introductory geology course (n = 947) completed a survey on atmospheric carbon budgets in two sequential semesters. Results indicated that most students did not have a basic understanding of mass-balance problems and that their misunderstanding varied according to gender and their interest in science but not according to factors, such as students' opinions of the seriousness of climate change. Students also tended to exhibit poor graphical interpretation skills when examining mass-balance graphs.