Re: Old News?
So the key CO2 one is sensitivity. That's generally X degrees per doubling of CO2. If X is high, more warming, low, less. And it's generally assumed the response is logarithmic.The response to additional CO2 on infra-red light absorption by Earth's atmosphere was characterised by Svante Arrhenius in the 19th C.
It is not "assumed" to be logarithmic. It is logarithmic on theoretical and empirical grounds. As an analogy, think of CO2's infra-red absorption to be characterised as a sheet of glass between a light source and light absorber. To keep it simple, our sheet of glass absorbs 50% of the light passing through. Adding a second sheet of glass blocks 50% of the remaining light thus total absorption is now 75%. Rinse and repeat.
Calculating the absorption of infra-red emitted by Earth's surface for entails dividing the atmosphere into an arbitrary number of layers and summing the result for each layer. This would be tedious except for MODTRAN:
The MODTRAN® (MODerate resolution atmospheric TRANsmission) computer code is used worldwide by research scientists in government agencies, commercial organizations, and educational institutions for the prediction and analysis of optical measurements through the atmosphere. MODTRAN was developed and continues to be maintained through a longstanding collaboration between Spectral Sciences, Inc. (SSI) and the Air Force Research Laboratory (AFRL).
The high sensitivity to CO2 claimed by warmists is the result of an assumption. To wit, the so-called Enhanced Greenhouse Effect. This entails the belief that the slight increase in temperature caused by increased CO2 necessarily increases the amount of water vapour in the atmosphere. As Paltridge, Rking and Pook revealed in their paper Trends in middle- and upper-level tropospheric humidity from NCEP reanalysis data there is no empirical evidence for this.