The conversation on global warming started in 1896, when a physical chemist estimated that the mean global temperature would rise several degrees if the level of carbon dioxide in the atmosphere was doubled. The topic eventually became one of the most passionate in the history of science. The author points out that climate experts were initially strongly skeptical of the theory of global warming; it took a variety of evidence to gradually convince them that warming due to human emissions was likely. The public, however, was guided away from this conclusion by a professional public relations effort, motivated by industrial and ideological concerns. Deniers of the scientific consensus avoided normal scientific discourse and resorted to ad hominem attacks that cast doubt on the entire scientific community—while disrupting the lives of some researchers. The author points out that scientists have failed to mount a concerted public relations campaign to defend their position. When trust is lost, he asserts, a determined effort is needed to restore it.