WTF? Why are you engaging in AGW discussion if this is the strawman you're attacking? Only complete noobs use CO2 vs temperature to prove or disprove AGW, and they just wind up hurting their case as a result.
No, that has very little to do with how we know what CO2 does to climate. GW theory is based on measuring the physical properties of all gases in the atmosphere, and throwing in bulletproof physics about absorption and emission to make a computer model for an experiment that we cannot possibly conduct in a lab. Even skeptics with half a brain accept that CO2 causes warming. CO2 vs. time just confirms that humans are pumping out enormous amounts of CO2 capable of changing the atmosphere's composition. Model temperature vs. time and proxy temperature vs. time is merely a sanity check to see if the models are plausible. Nobody in the scientific community is using temperature vs CO2 to predict anything, whether directly or indirectly.
The real debate is over the degree and certainty of warming attributable to CO2, as some physical processes (especially cloud formation) are arguably too chaotic and poorly understood to correctly model with our current understanding, and even when we do have hypotheses, they're next to impossible to verify.