This paper begins with the "knowledge-ignorance paradox" - the process by which the growth of specialized knowledge results in a simultaneous increase in ignorance. It then outlines the roles of personal and social motivations, institutional decisions, the public culture, and technology in establishing consensual guidelines for ignorance. The upshot is a sociological model of how the "knowledge society" militates against the acquisition of scientific knowledge. Given the assumption of widespread scientific illiteracy, the paper tries to show why the ozone hole was capable of engendering some public understanding and concern, while climate change failed to do so. The ozone threat encouraged the acquisition of knowledge because it was allied and resonated with easy-to-understand bridging metaphors derived from the popular culture. It also engendered a "hot crisis." That is, it provided a sense of immediate and concrete risk with everyday relevance. Climate change fails at both of these criteria and remains in a public limbo.