Until now, every USA president since 1965 has warned about global warming. Even oil companies did so until the early 90s. Here are some videos documenting that we’ve known about global warming since the 1950s:
1984 Documentary “The Greenhouse Effect and Planet Earth” (31 minutes):
https://www.cbc.ca/archives/entry/the-greenhouse-effect-and-planet-earth
Shell Oil's Stark Climate Change Warning from 1991 (28 minutes):
https://youtu.be/vTlYYlRN0LY
Climate Science 1956: A Blast from the Past (10 minutes):
https://youtu.be/sdALFnlwV_o
1980: Walter Cronkite on Climate Change (2 minutes):
https://youtu.be/MU9s0XyEctI
Climate Change 1958 (2 minutes)
https://youtu.be/m-AXBbuDxRY
If you enjoyed the above, then consider a look at Earth’s Climate History —
“Richard Alley: "The Biggest Control Knob: Carbon Dioxide in Earth's Climate History" (56 minutes):
https://youtu.be/RffPSrRpq_g