I think you're right about the global warming thing, it would be a bigger factor than people would like admit.

But really I'm sure it's choice. Having a child is like having a pet now. You can either choose to have one or not. You don't need kids for survival and contraception is cheap and effective at preventing pregnancy.

What aged care will look like when most people are old is a different story, I guess they'll except my kids to wipe their ass but that's a deferred problem for young people with money and a bunch of entertainment and no incentive to have kids.