Not only does CO2 lag the temperature changes in the ice age, but the CO2 feedback is only capable of explaining 20 % to 40 % of the total temperature change and, in many timelines, the temperature trends and the CO2 trends are going in the opposite direction. (realclimate.org)
By dividing the total temperature change (as indicated by the best - fit linear trend) by the observed rise in atmospheric carbon dioxide content, and then applying that relationship to a doubling of the carbon dioxide content, Loehle arrives at an estimate of the earth's transient climate sensitivity — transient, in the sense that at the time of CO2 doubling, the earth has yet to reach a state of equilibrium and some warming is still to come. (cato.org)