CO2 is only one of the greenhouses gases that are affecting climate change. Methane is more devastating than CO2 for affecting climate change.
One thing that we tend to forget is that measurements of any greenhouse gas is a fairly modern invention. Ironically, better measurement tools are a result of the industrial revolution.
Often when we look at CO2 in the atmosphere, we are comparing ice core samples from the poles to actual air reading taken from near the equator from the 1950's on.
I find that sometimes the methods of scientific studies have certain flaws. I don't mean to say that they are wrong, I'm just pointing out that methods of analysis are improving over what may have been report 100 or 200 years ago.
Bottom line...the earth has warmed and cooled many times over millions of years. This occurred before mankind was here, and I'm sure that it will happen again after mankind is gone.