Dr. John Bockstoce, arctic historian and archaeologist, was doing an archaeological study at Cape Nome in 1972.  I was in Nome and spent many evenings listening to John talk about his work.  I remember is his description of the last major Eskimo migration across the Arctic about 800 AD during the Medieval warming period.  According to John the Eskimos could do this because at the time there was very little ice in the Arctic Ocean.  
We all know that the “green house” gases, predominately water vapor block certain energy spectrums from radiating from the dark side of the earth. This has been calculated to  add 19 C to the temperature of the earth.
The question of the effect of CO2 is the same question as does the crowing of roosters cause the sun to rise or does the sun’s rising induce the roosters to crow?  Will anyone that can show the method that a change of 100 parts per million of CO2 “pushes” a significant change of the earth’s temperature please answer.