This conversation just doesn't seem promising. Your initial wildly-off claim got me worried I might misunderstand the world by that much (I remember the 70s, fuzzily). I wasted time checking it, wondering if the actual peak might be in a year not mentioned, trying to find the paper Wikipedia cited: it was a non-open-access paper with at least four links to check; one of them did show the first page, which at least gave the figure in question, if not the ultimate source.