Popular Science, May 1969. Page 76.
It was a pretty good article for the 60's. It mentioned carbon dioxide as a warming influence and particulate matter as a cooling influence. That hasn't changed. What has changed is that we now have a better understanding of the quantitative impact of each. I don't have the link at my fingertips, but there was a literature search of actual scientific climate papers in that time period, and a majority favored the warming hypothesis, but a significant minority favored the cooling hypothesis. You can probably find it in skeptical science or Coby Beck's blog.
I was arguing about that with a chemtrailer last night. I said the Clinton administration wouldn't have done it because the scientific consensus on global warming was not rock solid until the 2001 IPCC report, and the next commander in chief, along with most of his party, thought global warming was nonsense. He mentioned a '60s paper by Carl Sagan as evidence everybody knew about global warming back then.
In the thirty years leading up to the 1970s, available temperature recordings suggested that there was a cooling trend. As a result some scientists suggested that the current inter-glacial period could rapidly draw to a close, which might result in the Earth plunging into a new ice age over the next few centuries. This idea could have been reinforced by the knowledge that the smog that climatologists call ‘aerosols’ – emitted by human activities into the atmosphere – also caused cooling. In fact, as temperature recording has improved in coverage, it’s become apparent that the cooling trend was most pronounced in northern land areas and that global temperature trends were in fact relatively steady during the period prior to 1970.
At the same time as some scientists were suggesting we might be facing another ice age, a greater number published contradicting studies. Their papers showed that the growing amount of greenhouse gasses that humans were putting into the atmosphere would cause much greater warming – warming that would a much greater influence on global temperature than any possible natural or human-caused cooling effects.
By 1980 the predictions about ice ages had ceased, due to the overwhelming evidence contained in an increasing number of reports that warned of global warming. Unfortunately, the small number of predictions of an ice age appeared to be much more interesting than those of global warming, so it was those sensational 'Ice Age' stories in the press that so many people tend to remember.
The fact is that around 1970 there were 6 times as many scientists predicting a warming rather than a cooling planet. Today, with 30+years more data to analyse, we've reached a clear scientific consensus: 97% of working climate scientists agree with the view that human beings are causing global warming.