Increasingly, public understanding of issues vital to humanity’s well-being and future – climate change, health policy, international relations – is informed by debate that pits specious prejudice, masquerading as opinion, against expertise. Communicating with a lay audience, experts on complex yet politically charged subjects confront twin challenges: they must present evidence that is multifaceted and can provide no perfect or certain solution, while simultaneously dismantling arguments, founded in denialism, that endorse simple strategies and offer comforting but false hope. Experts and those who wish to construct evidence-based policy are struggling to meet these challenges.