söndag 6 januari 2013

GHE: Elephant Discovered by Microscope

Let me sum up the two previous posts to make the argument clear. The crucial observations come from an infrared satellite thermometer in radiative contact with the Earth + atmosphere, which selectively can measure the temperature of different frequencies. Reading of the infrared thermometer shows the following temperatures:
  1. 220 K for wave numbers 600 - 800 (attributed to the trace gas CO2 at the tropopause)
  2. 288 K for wave numbers 800 - 1200 (attributed to the Earth surface)
  3. 255 K for wave numbers below 600 (attributed to water vapor at 5km altitude). 
From these temperature reading the above radiance spectrum is constructed using Planck's law
  • R(n) ~ T n^2
where R(n) is the radiance in W/m2 per unit of frequency, n is the frequency (~ wave number) and T the temperature (common for all frequencies).

The GHE is supposed to be the ditch in the radiance curve for wave numbers 600 - 800, which results from the drop in temperature from the reading of 288 K attributed to the Earth surface with a transparent atmosphere in the range 800 - 1200 of the atmospheric window, to the 220 K attributed to CO2 at the tropopause in the range 600 - 800 of absorption/emission of CO2.

Visibly, the drop in temperature from 288 to 220 K and the ditch in the spectrum in the range 600 - 800, is most substantial and hence the GHE must be most substantial, even if it is the effect of a trace gas. Right?

The key to the GHE is thus the reading by the infrared thermometer of a temperature of 220 K of the trace gas CO2. The thermometer could be the Nimbus 4 michelson interferometer first flown in 1970.

The thermometer reads the temperature of a radiating body from radiative equilibrium in the frequency range of the radiation of the body, and the thermometer can be designed to have a very narrow range allowing the selective reading of a specific frequency. The absorption/emission spectrum of CO2 has a very narrow spike at a wave number of 666 (wave length 15 micrometer) as seen in the following absorption spectrum:

Now, tuning the thermometer to the frequency of the CO2 spike makes it possible to read a temperature of atmospheric CO2 even if the concentration is very small, and increasing the sensitivity of the thermometer may compensate for any decrease of CO2.

In other words, even with a vanishingly small presence of CO2 in the atmosphere, a sufficiently sensitive thermometer would be able to report a temperature of 220 K in the range 600 - 800, as the evidence of a powerful GHE.

Evidently the Nimbus 4 thermometer was sensitive enough to report in 1970 the temperature of the atmospheric trace gas CO2 (390 ppm = 0.039%) to be 220 K in the troposphere.

This opened to the CO2 global warming alarm based on the argument that even if CO2 is a trace gas, it has the power of changing the climate of the Earth, with the evidence being the visible ditch in the radiance spectrum documented by the reading of the Nimbus 4 thermometer.

But the ditch in the radiance spectrum is constructed from a selective reading of the temperature of CO2 and may not represent reality, only the reading of a vanishingly small effect by a very sensitive thermometer.

The discovery of the GHE is thus directly connected to the use of the sensitive Nimbus 4 thermometer:
  • The major effect of atmospheric CO2 is evidenced by a very sensitive instrument, as if an elephant is discovered by a microscope!    
PS Notice the connection with How to Fool Yourself with a Pyrgeometer. In both cases, it is the temperature which is measured and the radiance is computed. Recall that using an ideal blackbody as thermometer, allows the determination of the temperature of a body at distance without knowing the emissivity (=absorptivity) of the body: If the thermometer heats up then the body has a higher temperature, and if the thermometer cools then the body has a lower temperature. In other words, temperature can be measured at distance, but determining radiance requires emissivity which in general is unknown.

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