We've known about the greenhouse effect and it's threat potential for nearly 2 centuries. Exxon just helped add to a growing body of evidence that we ignore.
Nowadays the predictions are much higher, because scientists started asking “if the oceans get warmer, what changes will that cause, and how will those changes affect the temperature?” In 1970, Exxon wasn’t suppressing research on whether warmer oceans mean more water vapor in the air, more carbon dioxide outgassing from the oceans, etc. They were only asking “should we really make drastic changes to head off a 1°-2°C temperature change that may not happen for a century? Is there a reason to believe that nothing will change in that time to make the prediction irrelevant?”
Did you mean decades?
From the linked wikipedia article on Greenhouse effect
https://medium.com/@cimuir/we-ve-been-talking-about-climate-...
has a picture of a newspaper commenting on the possibility, dated July 17th, 1912.