The above diagram is supposed to capture the essence of the science of CO2 global warming alarmism. We see massive "Back Radiation" of 324 W/m2 hitting the Earth's surface from the "Greenhouse Gases" below the Top of Atmosphere TOA, while the net radiative transfer from the surface to TOA is 26 W/m2, about 10 times as small.
The main "greenhouse gas" is water vapor with CO2 contributing maybe 10% to the total "greenhouse effect" of 33 C as the difference between the surface temperature and that of TOA.
To estimate the effect of a doubling of CO2, one can argue as follows: The total "back radiation" from "greenhouse gases" is about 300 W/m2 and so the total effect of CO2 can be estimated to 30 W/m2, which according to Stefan-Boltzmann may correspond to a global warming of 7 C, which is the upper limit of CO2 alarmism, without taking any saturation reduction effect into account.
On the other hand, using instead of a nominal 300 W/m2, a net of 30 W/m2, we end up with 0.7 C as the upper limit, without saturation effect.
We thus have the following two estimates for global warming upon doubled CO2 to compare:
- With "back radiation": 7 C
- Without "back radiation": 0.7 C
Of all scientific bluffs through the history of science, "back radiation" will be described as the biggest, as the bluff with potentially biggest effects for human civilization.
For a deeper analysis of "back radiation" see earlier posts in categories "radiative heat transfer" and "myth of back radiation".