Politics caused the split. The change in course where it slowly creeped up is two fold. First, the warming became completely obvious. People could see in their

Politics caused the split. The change in course where it slowly creeped up is two fold. First, the warming became completely obvious. People could see in their own living memory very dramatic changes between their childhood and modern day. That just took time. Second, as the left became more and more radicalized toward actions to fight the threat, the right wing could take a less radical position and still claim to be holding the line against radicals. The left shifted the Overton Window left enough that the right could have a politically viable platform that included climate change.