While the science and values literature has seen recurrent concerns about wishful thinking, there have been few efforts to characterize this phenomenon. Based on a review of varieties of wishful thinking involved in climate skepticism, we argue that instances of wishful thinking can be fruitfully characterized in terms of the mechanisms that generate them and the problems associated with them. We highlight the array of mechanisms associated with wishful thinking, as well as the fact that it can be evaluated both from epistemic and ethical perspectives. We argue that it is doubtful that a single unified definition of wishful thinking can be developed. Moreover, the concept of wishful thinking can problematically focus excessive attention on individual and epistemic problems in science, to the exclusion of social and ethical problems.