[B.O. Plenty]

"So how did the leading environmentalists get it so wrong in the 1970s?"

It's easy, they didn't have computers to make their predictions. If they had computers they most likely would have been wrong-er.

[KC_for_Freedom]

The reason for bad predictions from the environmental crowd is most likely corruption and a political agenda. For a scholarly treatment of these issues, suggest you look into "The Skeptical Environmentalist" by Bjorn Lomborg. Its a phone book size book with several thousand footnoted references. He uses the actual data used by the environmentalists and shows how they skew it with worst case assumptions when worst case assumptions are not justified. Well worth the $25.