A historical oddity is how the U.S. government and Exxon “knew” about the ‘greenhouse signal’ and perilous anthropogenic climate change when climate scientists did not. But such is the state of the debate where PR and lawsuits overwhelm a rational view of knowledge. (below)
“In my expert opinion, in the period shortly after President Carter took office in 1977,” states James Gustave Speth, “there was a growing sense of concern and indeed urgency within the federal government that fossil fuel burning was heating the planet and causing the climate to change in many ways that could be catastrophic….” 
“Exxon was aware of climate change, as early as 1977, 11 years before it became a public issue,” stated an article in Scientific American. “This knowledge did not prevent the company … from spending decades refusing to publicly acknowledge climate change and even promoting climate misinformation.”
But the Science . . .
How did the U.S. government and Exxon know about the “greenhouse signal” and perilous anthropogenic climate change when climate science did not? But such is the state of the debate where PR and lawsuits overwhelm a rational view of knowledge.
In the real world, global cooling was the fear. “Certainly the threat of another ice age was the topic of much scientific and popular discussion in the 1970s,” stated Harold Bernard, Jr., in The Greenhouse Effect.
Books and articles entitled ‘The Cooling,’ ‘Blizzard,’ ‘Ice,’ and ‘A Mini Ice Age Could Begin in a Decade,’ abounded. The ‘snow blitz’ theory was popularized on the public television presentation of ‘The Weather Machine’ in 1975. And certainly the winters of the late 1970s were enough to send shivers through our imaginations. 
And in the late 1980s and early 1990s (and even today), evidence about the positive and negative effects of carbon dioxide on global climate was (is) controversial. 
Enter Richard Kerr, longtime global-warming writer at Science, the flagship publication of the American Association for the Advancement of Science. He chronicled how the mainstream of climate science disputed James Hansen’s assertions of the arrival of global warming and the enhanced greenhouse effect as opinion rather than science.
Kerr wrote in mid-1989:
If many of Hansen’s colleagues find his first point about the warming trend regrettable, they view his second–that the warming could, with “high confidence,” be linked to the greenhouse effect–as unforgivable. None of the select greenhouse researchers at the meeting could agree with him. ‘Taken together, his statements have given people the feeling the greenhouse effect has been detected with certitude,” says Michael Schlesinger, himself a modeler at Oregon State University. “Our current understanding does not support that. Confidence in detection is now down near zero.”
There was no settled science about a climate crisis well after James Hansen lit the fires in 1988. In 1998, William K. Stevens, global warming scribe at the New York Times, quoted “a leading expert on the issue of detecting the greenhouse signal, climatologist Thomas Wigley of the National Center for Atmospheric Research in Boulder:
”They’re making progress, and there is a lot of hard work involved, and I hold them in the highest regard,” Dr. Tom Wigley … said of Dr. Mann and his colleagues. ”But I think there’s a limit to how far you can ever go.” As for using proxy data to detect a man-made greenhouse effect, he said, ”I don’t think we’re ever going to get to the point where we’re going to be totally convincing.”
So again, what did Exxon or the U.S. government (or anyone else) know about the strength of the enhanced greenhouse effect, much as a doom-and-gloom answer to increasing concentrations of CO2 and other man-made greenhouse gases in the atmosphere?
 Speth, They Knew: The US Federal Government’s Fifty-Year Role in Causing the Climate Crisis (MIT Press: 2021), p. 11.
 Harold Bernard, Jr., The Greenhouse Effect (Cambridge, MA: Ballinger Publishing, 1980), p. 20.
 Given anthropogenic global warming, the qualitative begs the quantitative question of good, benign, and not benign. Lower-range warming is generally thought by climate economists as net beneficial, while higher warming scenarios are neutral-to-negative. (Climate models can be calibrated to tell you just about anything).