To be fair, I think both sides blow it out of proportion and that can stifle discussion. It won’t be the “end of the world” where everyone will die, but we will have the “end of the world” as we know it.
I think one of the main points that need to be stressed to the kind of people in your example would be droughts.
Droughts will continue to get worse and will affect everyone. With a bad enough drought, we won’t be able to feed entire cities. And that’s when things really start to fall apart.