Talking about climate change doesn’t come naturally to most people, even those who are worried about it. Roughly two-thirds of Americans report discussing it with family and friends “rarely” or “never,” a survey found last fall. They might be intimidated by the science, nervous about starting an argument, or afraid of being a Debbie Downer. The resulting silence is part of why there’s not more social pressure to reduce fossil fuel emissions: People dramatically underestimate public support for climate policies...