Some climate change deniers are convinced that global warming is a massive conspiracy. Ironically, there is a sort of conspiracy – but one that downplays how serious the consequences could be and exaggerates the impact of action to limit them. It involves everyone from scientists and politicians to activists and journalists.

At the research level, there is what renowned climate scientist James Hansen calls the John Mercer effect. In the 1970s, Mercer published the first paper that suggested the West Antarctic ice sheet could collapse in response to warming. Afterwards, he struggled to get funding, and those who criticised his work …