January 1988 showed relatively high rates of public concern: 47 percent of respondents judged ozone layer destruction to be very serious, 36 percent saw acid rain as very serious, and 33 percent viewed the greenhouse effect as very serious. Despite this, the greenhouse effect still ranked twenty-fourth out of twenty-eight environmental hazards viewed as very serious. Also noteworthy is the fact that public responses showed unusually high rates of "don't knows," even for acid rain, which has been extensively publicized. Although the data suggest increased public concern, potential climate change scored well down on the public's list of top environmental concerns, which continued to be dominated by issues associated with hazardous wastes, toxic materials, nuclear accidents, pesticides, and air and water pollution.
In 1987 and 1989, Cambridge Reports conducted national polls in the United States assessing the degree of threat to (1) personal health and safety and (2) the overall quality of the environment. The results showed dramatic increases in the perceived degree of threat associated with global environmental problems. Indeed, the largest increase in perceived "large threat" was for the greenhouse effect. These changes in opinion, however, must be placed in the context of the poll's finding that between 1987 and 1989, "Americans were not only growing vastly more concerned about environmental problems of all kinds, they were also increasingly likely to feel those problems posed a direct risk to their personal health and safety" (Cambridge Reports, 1990). It is also instructive that public perceptions of threats from climate change in the United States continued to follow well behind hazardous waste disposal, pollution, and pesticides.
Neither the public nor policymakers like large uncertainties. In our daily lives, we seek to remove them if the stakes involved matter greatly to us; or, finding this impossible, we either decide to forego the activity or make our uneasy peace. Which will it be for human-induced climate change? One possibility is that public responses to these problems will over time come to resemble those to nuclear war and nuclear power. Both conjure up futures of vast destruction and uncontrollability in the public mind (Slovic, Lichtenstein, and Fischhoff, 1979). Some, like Robert Lifton (1976), see the sources of public concern in a state of denial—what Lifton calls "psychic numbing"—in which, however uncertain, the catastrophic threatening of the earth itself is at stake. Others, such as Paul Slovic (1987) attribute it not only to the vast destructiveness and dread that it brings to mind but to a series of other qualitative properties—newness, involuntary nature, uncon-