torsdag 24 november 2022

Global Warming: Measuring Temperature vs Flux of Heat Energy vs Radiative Forcing

OLWR (right) as measured by CERES

The central concept in the prediction of global warming from human emissions of CO2 presented by IPCC, is that of radiative forcing as a warming effect of 3-4 W/m2 upon doubling of atmospheric CO2 from pre-industrial time with corresponding global warming of less than 1 C. From this non-alarming warming is obtained alarming warming by up to 4 C by various positive feed-backs. If the 1 C was instead 0.3 C corresponding radiative forcing of 1 W/m2 instead of 3-4 W/m2, there would be no reason for alarm. And of course not, if feed-backs are smaller (very likely) or even negative. 

Let us now check how IPCC comes up with a radiative forcing of 3-4 W/m2 as the central argument behind alarm.    

The radiative forcing of 3-4 W/m2 is obtained from a radiative perturbation computation starting from measured spectra of Outgoing LongWave Radiation OLWR or radiative flux from the Earth into space by bolometers in CERES satellites as shown above. The computation estimates the radiative forcing as the  change of OLWR from doubled CO2. See lecture by Will Happer.

The advantage of this approach is that knowledge of the complex physics of turbulent convective heat transfer and phase change behind the present measured OLWR is not needed. The radiative computation concerns the change of OLWR from a change of radiative properties of the atmosphere from doubled CO2 everything else being the same. The radiative forcing is thus obtained from a radiative heat transfer computation based on radiative properties.    

A bolometer measures temperature (in degrees Kelvin K) through a temperature dependent resistance which is translated to OLWR (in W/m2) through some form of Planck's Law

That primarily temperature is measured, is seen from the fact that CERES delivers the altitude from where OLWR is coming, because altitude directly connects to temperature, which would not be possible if OLWR was the prime measurement.

The translation from measured temperature in K to OLWR in W/m2 is tricky. To see the difficulty, let us consider heat conduction with heat flux corresponding to radiance and Planck's Law replaced by Fourier's Law taking the following form (in one space dimension): 

  • $Q = C \frac{dT}{dx}$ 

where $T$ is temperature $Q$ heat flux, $x$ a spatial coordinate and $C$ is a coefficient of heat conductivity. Now, temperature can be directly measured by a thermometer corresponding to the bolometer in CERES, while to determine the heat flux Q the coefficient of heat conductivity must be known. Temperature is a primary measured quantity and heat flux is a secondary computed quantity requiring knowledge of a heat conduction coefficient and temperature derivative. 

To measure inside and outside temperature of a wall is direct and precise using a thermometer, while determining the heat flux through the wall requires (i) detailed data on the design of the wall or (ii) experiments with known heat source. 

Measurement of OLWR in CERES carries the same difficulty. What is directly measured by the satellite bolometer are temperatures of different spectral bands as seen from the bolometer, while the translation to OLWR requires detailed knowledge of atmospheric emittance corresponding to heat conductivity of a wall. Measured OLWR is thus subject to large uncertainties as well as the computation of radiative forcing. Experiments corresponding to (ii) cannot be made. 

Total OWLR is about 240 W/m2 and so a radiative forcing of 3-4 W/m2 is a small perturbation which is difficult to assess. It could as well be 2 or 0 or even negative. The central element of the IPCC global warming message to the World thus cannot be viewed to be scientifically settled. If the estimated radiative forcing was 1 W/m2  instead of 3-4 W/m2, then there would be no alarm.  

Radiative forcing of 3-4 W/m2 is by IPCC presented as the basic scientific argument behind the present march in the West into a fossil free society of pre-industrial standard and population.  The theory and observation supporting the argument is highly uncertain and cannot motivate continued march.   

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