Other than reporting anonymously or being reincarnated with powers, those kinda warnings would either send you to an asylum or on a terrorist list , he's prolly not thinking about that compared to being busy as a teen lol
Plus, what kind of warning can he make?
He'd also have to know (and remember) enough of the details to be able to make a good warning.
And then somehow be convincing enough that they'd care.
Fukushima problems were about pride and prejudice (lost of things were poorly planned to save money, and everyone knew it was poorly planned to save money but were guessing it would be "good enough" - but to then rebuild it at even greater expense because some rando says something.. won't happen)
And terrorist attacks with nerve gas - if you suggest that before it happens, you'd be accused of being part of the culprits (or at least of having inspired them).