What do you think of the correlations between the length of the solar cycle and climate, such as that presented in the journal Science by Friis-Christensen and Larsen (Science 254, 698-700, 1991)? When this article was published I thought it effectively ended the greenhouse gas argument. But you can't kill Dracula that easily (or scientists feeding at the funding trough).
A plot from the 1991 article made it to this Stanford site: http://solar-center.stanford.edu/sun-on-earth/glob-warm.html
Others have extended this plot farther back in time, and the agreement with the reconstructed temperature record is fairly good. At the ends of some upswing cycles the observed temperature sometimes exceeds that predicted by the correlation for a few years before rejoining the correlation line. I think we may be in such a period now.
Solar variations can predict the ups and downs of the global temperature record, like the cooling observed in the 50s and 60s. A steadily increasing CO2 would just drive the temperature higher.
I don't think the paleo record(or the current record) bears that statement out, because most of the CO2 in fossil fuels was deposited during the Cretaceous period, and the temp then was only slightly higher than it is now. More CO2 means more plant and animal growth as they thrive in higher levels.
Now if you were to alter the water vapor(H20) somehow, that would cause a more direct effect on temperature. CO2, and all others are a minor GHG compared to water vapor.