I also remember something about global warming being more than
   CO2 level, although I think that might be more related to school
   in the 1980s, where we went over earth's possible futures and
   one of those was that of Venus, followed with a study of the
   Venusian atmosphere. I'm not even sure if it was called
   Greenhouse effect then but it was presented with a list of a few
   possible earth futures, which had included mini ice-ages and
   such. I think a lot of those other ideas have since been
   discarded though.