1421
It's that easy!
(lemmy.ml)
https://climatejustice.social/@breadandcircuses/112303357717712825 Scroll down inside that link for a slightly more extreme version (NSFW).
Could have happened as soon as the 1950s when they first began seeing substantial proof of how harmful fossil fuels are.
But of course, the ones with all the money got to decide what the public gets to know. Just like it's been ever since 🤬