which shows the spectrum of the outgoing longwave radiation OLR from the Earth with atmosphere as computed by the software Modtran on the basis of certain satellite measurements.
The idea is that the ditch in the spectrum in the wave number interval 600 - 800 can be attributed to the main absorption line at 667 of CO2. The total effect is then supposed to be the area between the Planck curves for 288 K and 220 K in the interval 600 - 800, which comes out to be about 40 W/m2. The total "radiative forcing" of atmospheric CO2 is thus supposed to be about 40 W/m2 (disregarding overlap with H2O), which by Stefan-Boltzann's Law can be connected to a temperature rise of about 10 C. The total effect of CO2 as the main cause of the ditch, would thus be global warming of 10 C. (With half the ditch attributed to CO2, the effect would be 5 C, which by Lindzen is cut down to 2.5 C without disclosing the reason). PS With 20 instead of 40, and half of 20 attributed to CO2 one would get 10 W/m2 and thus Lindzen's 2.5 C.
If CO2 was complemented by other trace gases together covering the whole spectrum, the warming effect would be 288 - 220, that is a whopping 68 K, from the mere presence of trace gases.
Is this reasonable? Is it possible that trace gases, making the atmosphere opaque for certain wave numbers, can make the full atmosphere opaque over the entire spectrum?
No, it does not seem to be reasonable, as detailed in an earlier discussion, which means that the above spectrum computed by Modtran does not seem to describe reality.
Yet the Modtran spectrum is the very basis of CO2 alarmism as the core evidence that the presence of of a trace gas can cause substantial global warming.
So there is the question: Can the presence of trace gases make the atmosphere fully opaque?
From where does the value of 40 W/m2?
SvaraRaderaA black body at 255 °K emits approximately 8% of the total power in the range 13.5-16.5 microns, that’s about 20 W/m2.
The CO2 produces a very strong effect even in small concentrations because it is nothing more than an electromagnetic capacitor. You can then consider the atmosphere as a parallel RC circuit in which the ratio Ic/Ir is ωRC.
In this case 15 microns mean a frequency ω = 2000GHz. Then Ic/Ir suddenly becomes very high also with a very small capacity.
Michael
OK, let us say 20 W/m2 then. The question is if the trace gas is capable to fill the entire interval 13.5 - 16.5 mikron or if it is active in only a small interval around 15.
SvaraRaderaThe frequency 15 microns is the bending resonance, all the others are a plethora of rotational frequencies induced as a side effect but they are still due to CO2. Of course, with reference to the pure CO2 spectrum.
SvaraRaderaMichael
Do you mean this to be an answer to my question at the end?
SvaraRadera