I suspect that more than a few readers of Climatic Change shared with me the burden of responding to scores of press, politician, and business group inquiries about the hypothesized connections among the heat, drought, and fires in the United States this summer and the long-anticipated greenhouse effect. I am one who has long argued for the plausibility of the belief that human emissions of carbon dioxide and other trace greenhouse gases could lead to significant, probably unprecedented climatic change by the middle of the next century. Thus, it was with some pleasure that I observed this viewpoint passing from the ivy-covered halls of academe and the concrete and glass of government offices into the popular consciousness. But at the same time, the way it happened, in the United States at least, allowed only a small (and perhaps only fleeting) measure of pleasure.
By July, 1988, there were cover stories in news weeklies, lead articles on broadcast news programs, and hundreds of newspaper and magazine writeups appearing on the presumed connection between the heat wave and the greenhouse effect. With a few exceptions, there was very little scientific content in most of the stories. Instead, dramatic visuals of damaged crops, dried up rivers, sweltering cities, record hurricane pressures, or burning forests dominated the coverage. The greenhouse effect was, typically, explained by a 10-second colorful visual showing downward yellow arrows of sunlight reaching the Earth's surface but fewer upward red arrows escaping to space. Better stories pointed out that there was some debate as to whether anyone could ascribe the weather events of one year to a global trend. After all, the drought in May and June was a result of an out-ofposition jet stream, which diverted storms up into Canada rather than across the mid-United States. (My NCAR colleague, Kevin Trenberth, believes this circulation anomaly may have been forced by the unusually cold sea surface temperature anomalies in the equatorial Pacific -a 'reverse E1 Nino', in effect.) Some reporters even questioned whether the approximately 0.7 ~ trend over the past century reported by groups at a climatic research unit in East Anglia and Goddard Institute for Space Studies in New York represented 'proof' that the 25% increase in CO 2 over the same period had finally been detected in the climatic record. But most coverage, especially on television, had little discussion that reflected the consensus of views on what is well accepted and what is deemed speculative by most researchers. Mostly, the association of local extreme heat and drought with global warming took on a growing credibility simply from its repeated assertion. Therefore, my excitement at the long-overdue public attention the greenhouse affect was finally receiving was tempered substantially by a fear that should next summer be anomalously cold and wet -by no means a remote possibility -not only could we lose the momentum of public interest, but some of our credibility as well.
How then, should we scientists approach public discussion of a complicated issue such as the detection of a greenhouse effect signal in a noisy climatic record? In essence, we face what I like to characterize as a 'double ethical bind'. While we do not have a formal Hippocratic path, most scientists feel a loyalty to the scientific method: test and retest ideas, constantly being vigilant for false hypotheses. This loyalty translates into public comments filled with caveats, if's, and's, and but's, and other clear statements of the nature of technical uncertainties. On the other hand (there always is one, of course), most