My position is that I don't know.
I understand that CO2 levels have some historical correlation with surface temperature but here is a graph that shows a major problem with CO2 being the currently controlling factor.
Look at the data from 1945 to 1976. The temperature is basically flat with random fluctuations and yet this was a time of great industrialization and CO2 increase.
http://www.tigtail.org/L_View/TIG/TVM/E/PreHistory/Europe/prehistory-europe.html
About a 1000 centuries ago they must have had some real gas guzzlers.