The simple fact is that CO2 has been warming the planet since the beginning of time and we know for certain that adding a lot more to the atmosphere will increase that warming. Radiative physics 101. The 100 trillion $ question is how much warming. Enviro-nazi kooks will tell us that it will warm 5-8C by 2200 and waves of water will cover NYC. Heartland kooks will tell us "no worries, no warming at all." They are both likely very wrong. Even the estimates made in IPCC AR4 (2-6C) are highly speculative and have little or no supporting evidence.
If you are seriously interested in a frank discussion on the big question of "how much warming?" by mostly scientists and engineers around the world I recommend this website:
http://rankexploits.com/musings/
These are mostly number crunchers who put observable evidence and known properties far above wild eyed speculation and don't have a political dog in the fight. It's worth a look.