I don't know for sure but...
I don't know anything about planetary climatology, how the weather works, or anything like that. So I also have genuinely no idea whether "global warming caused by humans" is true or not true.
However - the idea seemed to come from nowhere and provided the perfect excuse for the introduction of yet another tax ("carbon tax") by people I don't trust. This does tend to colour my judgement quite a lot. Follow the money.