There are so many candidates for causes here. Thinking about and watching climate change can't be good for, say, a teenager imagining their future. Of course, that teenager is also watching the world not coming together to solve this problem so you could say the situation is connected to "loss of community" in a way.
Worrying about nuclear war was probably worse for mental health since you'd die quite quickly (if you were lucky), rather than some nebulous future were something's going to happen.
I don't know about the kids these days; I'm not one of them, but I'm personally rather terrified of the future that we are careening into in regards to climate change.