Fair point. How about animals? It seems that many modern mammals, including primates, evolved and thrived during the Eocene. Most of the world today is too cold

Fair point. How about animals? It seems that many modern mammals, including primates, evolved and thrived during the Eocene. Most of the world today is too cold for humans living without protection, so I'm not completely buying that it would be worse than today. It might require moving around a bit, but not a total catastrophe.