I remember being in grade three (1988) and being told about what was then called 'the greenhouse effect' - some apparently respected scientists informed us alarmingly of how whole parts of the world would be underwater by 2000.
I also remember similar predictions from the late 1980s. I think the bottom line is that prognostications of doom sell much better than more conservative predictions with caveats and margins of error added. Scaremongering is more likely to result in increases in funding, career promotion, magazine/journal articles, impassioned speeches by celebrities, etc.
I'm a bit older (was in third grade in '69-70, right after watching Apollo 11 in real time) and the climate science consensus in the '70s and I think before was that we were headed for very bad global cooling, a new Ice Age that would put a mile of ice on top of much of the continental US. Read rather a lot of topical science fiction based on this "science".
Of course it was all man's fault (ignore that we're due for another Ice Age anytime now, see e.g. Fallen Angels: http://www.baen.com/library/ -> The Authors -> Larry Niven) due to sulfur dioxide increasing the reflectivity of clouds.
The "greenhouse effect" has a long history in scientific writings, though not necessarily always in the context it is now. The oldest example I can think of is its appearance in Fourier's writings. Of course, it was in French so it was like "effet de serre"
