GOOD NEWS. Doubling and quadrupling CO2 has minimal impact on temperatures.
The CO2 doubling debate is the last hope for the alarmists who claim that the troposphere, mesosphere, and stratosphere trap heat due to CO2, thus defeating the argument that doubling reaches saturation. This slight of hand is a desperate attempt to cloud the issue and keep the money for CO2 reduction flowing.
I have applied the University of Chicago online MODTRAN analysis tool to study the problem. The model uses the entire atmosphere to any altitude one desires. I chose to look down from 70km. Using multiple runs of MODTRAN, I was able to determine conclusively that there is a saturation effect which minimizes the impact of doubling and quadrupling CO2.
The tool is here: MODTRAN
Examine the plot below:
Taken from the chart:
CO2 ppm Temperature rise
400-800 0.7ºC
400-1600 1.48ºC
400-1800 1.61ºC
Bottom line: CO2 is not a problem because it's effect lessens as its concentration increases. Good news for the world. We can get on with our energy lives and forget about carbon taxes and credits.