The GHE Decoded

The GreenHouse Effect GHE is supposedly captured in the above radiance spectra showing the radiance in W/ m2 per wavenumber as function of wavenumber/frequence looking down from a satellite (top) and looking up from the Earth surface (bottom), with the radiance supposedly being measured by an instrument sensitive to infrared radiation, like a pyrometer, bolometer or infrared camera.

The ditch in the outgoing long wave radiation OLR (top) around 15 mikrons is supposed to show the major impact of atmospheric CO2 by "blocking radiation" with a warming effect.  The big hump to the right in the downwelling long wave radiation DLR (bottom) is supposed to show massive "back radiation" to the Earth surface from the atmosphere, with an even more impressive warming effect.

Having seen the big ditch and massive hump, how could you ever doubt that that the atmosphere has a warming effect by blocking outgoing radiation and by backradiation? This argument has convinced many scientists into believing in CO2 global warming, with the evidence being the reading of an instrument supposedly recording a radiance spectrum.

But to properly understand the relevance of the reading of the instrument, it is necessary to understand the functioning of the instrument used. In the last sequence of posts I have shown that an instrument like pyrometer or bolometer does not measure radiance, but instead temperature, and then computes  radiance from Planck's law assuming emissivity = 1. The correct scale of the instrument is thus in Kelvin and not W/m2, which makes a difference if the emissivity is not known, which is the case in general.

The instrument should be viewed as an infrared thermometer capable of measuring the temperature of a distant radiating object by radiative equilibrium between object and detector, for different wave numbers.

The measured (total) emissivities of the Earth atmosphere recorded in

• Effective Atmospheric Emissivity under Clear Skies
• Parametrization of Atmospheric Longwave Emissivity...

are thus fictional emissivities computed from temperature measurements of different parts of the atmosphere depending of the presence of clouds, with low clouds of temperature close to the surface temperature giving emissivities close to 1, while high colder clouds and clear sky gives emissivities down to 0.5.

Similarly, the ditch in OLR around 15 mikrons represents measurement of the temperature of the radiating trace CO2 in the tropopause, and not radiance.

Having understood that the radiance spectra are not true measured spectra, but fictional spectra computed from temperature measurements assuming emissivity = 1, it is natural to search for data concerning true spectra in particular for true OLR spectra. 

But you find nothing of this sort, because there are no such instruments. There are many infrared thermometers but no infrared radiance-meters. At least as far as I have found. Data from such true radiance-meter would be very interesting to view.

In particular, a true radiance-meter would allow determining true emissivities. But there is no radiance-meter at the disposal by climate scientists to determine in particular the effect of CO2 on the emissivity of the atmosphere, which has opened to speculation. Global warming alarm is based on a GHE as a substantial effect of CO2 on the emissivity of the atmosphere. The ditch in the OLR spectrum is the evidence of GHE put forward, but the ditch is based on an assumption that emissivity = 1.

What effect on the (total) emissivity of the atmosphere could then 0.036% CO2 have? GHE is based on the idea that the effect is substantial, which could be a 1-10% change (decrease) of the emissivity. 

But data by Hottel and Leckner indicate an effect smaller than 0.2% resulting from the fact that the partial pressure of CO2 as a trace gas is very small, also supported by a simple model.

Summary: GHE is based on fictional radiance spectra obtained from temperature measurements assuming emissivity =1, suggesting that the trace gas CO2 has an effect on the emissivity of the atmosphere in the range 1-10%,  while realistic estimates indicate an effect smaller than 0.2% of a Non-GHE.