When predictions of what was then called the greenhouse effect first came to the public consciousness in the 1970s, they were pretty handwavy. So most people over 60 today would have dismissed those early predictions as yet another science fiction doomsday scenario when they first heard about it. That wasn't an unreasonable conclusion based on how reliable the science was in the 70s. They should, of course, update their beliefs based on 2018 science, but a lot of people stop doing that as they get older.