A common misconception about the status of climate science in the 70s is that many scientists believed that global temperatures were cooling. Here’s an article from the excellent climate blog RealClimate.org:
And there’s also this paper from the American Meteorological Society.
The basic storyline is familiar: some scientists published papers about the topic. The papers were picked up in the general news media, and so, a new–and quite persistent–myth was born.
It should be noted that at the time, as I understand it, the data for global warming was very spotty and scientific consensus was nowhere near where we are at today.