LBJ, fresh from winning the ’64 election and playing escalatio with the Vietnamese (Gulf of Tonkin and all that), gave a “special message” to congress on conservation and restoration of natural beauty.” It includes the sentences-
Air pollution is no longer confined to isolated places. This generation has altered the composition of the atmosphere on a global scale through radioactive materials and a steady increase in carbon dioxide from the burning of fossil fuels.
This in the immediate aftermath too of Rachel Carson’s seminal book Silent Spring and general unease about the costs of “progress”. Roger Revelle was, I think, involved in drafting the bit on climate