There were scientists then proposing "global cooling" as a result of aerosol pollution blocking the sun (a problem that is now much reduced and which rich countries have now largely exported to poor countries).

The "new ice age" was a popular media scare story at the time which may have helped boost the apparent credibility of this narrative. However, at the time theories about cooling were not published anywhere near as often as theories about warming and were based on over-estimating the cooling effect of aerosols and under-estimating the warming effect of CO2.

Who sparked the global cooling myth? is a useful short article from the New Scientist which links to a number of relevant academic sources including the literature survey which initially debunked the myth by counting the number of papers falling on either side of the debate.