I don't think it's a matter of what Trump believes or doesn't believe. He may say he doesn't believe in the proven science of global warming, but as we all know he's a serial liar so nothing he says about anything can be taken at face value. I think he actually does believe it but says otherwise so he can justify deregulating the coal and fossil fuel industries, thereby lining his buddies' pockets. He can't come right out and say as much because that would be too crass, even for him. So instead he lies. Par for the course.