Stephan Lewandowsky was deep in denial. About six years ago the cognitive scientist had thrown himself into a study of why some people refuse to accept the overwhelming evidence that the planet is warming and humans are responsible. As he delved into this climate change denialism, Lewandowsky, then at the University of Western Australia, discovered that many of the naysayers also believed in outlandish plots, such as the idea that the Apollo moon landing was a hoax created by the American government. “A lot of the discourse these people were engaging in on the Internet was totally conspiratorial,” he recalls.