If that is your proposition it seems to me that we are certain that "natural" factors affect climate. That's a 100 percenter.
Though increased concentrations of CO2 in the atmosphere should, theoretically, increase retained heat how significant that factor is in a highly complex earth climate system, in significantly changing climate is a different kettle of fish.
What alerted some of us to be wary of the alarmist approach of the IPCC report is that some of its highly qualified scientists like John Christy (and he is not a lone climatologist with this slant on AGW) advised us to take its predictions and alarmist approach with a grain of salt. (on the grounds that we (the best science) don't yet understand fully how climate works.
Some will remember Ian Plimer the geologist who got into a bit of defaming trouble with the "Answers in Genesis" crowd. He is no less scathing in his claim that AGW is not played by the "rules" of science. Reading his panoramic view of climate through the geological ages was influential in making me a sceptic.
From a scientific point of view that seems to me to be a most useful stance in terms of prompting more compelling evidence for things like AGW.
