That CO2 is a greenhouse gas is about as solidly KNOWN as anything in science. Now, one can question climate models, I do myself, as climate is extremelly complex.
The more I read about all this the more I get confused, really, the topic is basically beyond my efforts. So, what politicians have done is get a group of folks together to prepare a broad summary, we call this the IPCC Report, which anyone can read, the summary thereof is not very complex nor long. Whether they are right or not is a valid question, but certainly is beyond my pay grade. All models are wrong, some models are useful.