Without CO2 in the atmosphere the earth would be an uninhabitable ice planet. As in many substances in many systems, small concentrations can make a big difference. A few berries of nightshade can kill you, as can nearly trace amounts of fentanyl. If you’ve ever kept a fish tank you’ll know that a tiny imbalance in ph or other factors can kill all the fish. So it goes.
The point is: this is not guesswork. It is trivial, in the laboratory, to create atmospheres with varying concentrations of CO2, expose them to infrared radiation, and map the response with great precision. The results never vary. If they did vary, the basics of physics would be wrong. Thus when scientists say “this much CO2 is likely to get us this result,” it carries more weight than what feels right to some guy on the internet.
I would suggest starting with Six Degrees by Mark Lynas for a summary, then proceed to the more fundamental science if you still don
The book /r/tinylittlesocks quoted:
Also, it's been 16 years since the book was published. Have temperatures risen? Have the predictions come to pass?