Vostok Station is an Antarctic research station dedicated to climate among many other issues. Ice cores have been taken to study the climate going back over 400,000 years. Anthony Watts provides space for a summary of an article showing that there is no correlation in these results between changes in CO2 and changes in temperature; where there is an apparent correlation, the temperature change came first--CO2 changes because there tends to be "equilibrium" between the two. In the recent period of a dramatic increase in man-made CO2, there is no corresponding increase in temperature.
No correlation, no basis to speculate on cause and effect.