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Climate change is a lot of things, but it's not news.  I remember reading about it in 1988 - this cover story in Newsweek magazine, in fact.   I haven't looked at the article since then but from what I remember it was pretty much on point.
Once something makes the front page of Newsweek magazine, it's not a secret any more.  I was 15 when I read that article and thought "wow, I hope somebody does something about this."  The fact that no one did is not Exxon's fault.  Their business was digging the stuff out of the ground so it could be cracked and burnt; no one was paying them to prevent a climate crisis, and no one was regulating them either.  Though they could have been regulated, had there been the will to do so.
EDIT:  Wow, 1912.  I guess we had every opportunity as a species to nip this in the bud, didn't we?
Iirc the Eisenhower Administration did a military study regarding the effects of Climate change so everyone knew.