In the 1970s, people were dealing with things like Acid Rain and large hole in the ozone layer. Things probably were much more dire looking at that point.
More to the point, we acted decisively as a society to remediate these conditions and those efforts succeeded. To look back now and ridicule those predictions without considering the actions taken to prevent them is folly.
Some were, yes, but they were in the minority. Curiously, folks are still predicting global cooling, but the proportion of such papers continues to dwindle.
If you look at a temperature graph all would become clear. It's not like the data they had was fake or misrepresented, it's just that the trend is noisy and became clearer later. Now that it is clear, it makes no sense to say "we could still be wrong". It's like a stock market graph; you don't know if a few days ago was the peak, but in a year you do. Or in case of climate, 30-40 years.