Chris Ho-Stuart
I did answer the question but I will break it down further if you are still wondering.
1. Do I believe in a two way radiative transfer process …….yes
2. What does a thermopile sensor in a pyrgeometer measure …….net flux
3. In thermodynamics what name is usually given to net flux …..heat or heat transfer
4. What do naive users of pyrgeometers think they are measuring ……backradiation, more correctly termed DLW.
5. Why is this an unwise assumption …..because the value displayed follows from a long series of assumptions any one mistake could possibly render the reading meaningless.
For instance is the SB law being applied properly and appropriately in all links of the instrument and source.
A. The source may contain solar contributions
B . The air may contain more or less water vapour
C . For a gas the SB law does not hold
D. Have the correct values of emissivities been use in the calculation
E . Circular reasoning is an acknowledged problem
F Does the calibration formula accurately respond to temperature change effects
…..and so on.
A careful read of the error reports show that if a number of pyrgeometers were at the same time and place pointed at the same object they would get an unacceptable range of readings.
To try to solve this problem a users group was set up.
They departed from the manufacturers calibration formula and devised their own(Nicks paper from about 2000)
6. What is the current situation…….. my link (above, 2006) say that the instrument can have errors of up to 17W/m2
7. Are you sure that this last report gives the upper limit for uncertainty …no.
8. I understand that the CO2 alarm figure is 1W/m2, would readings from the pyrgeometers be a basis for firm policy decisions on how much CO2 in air should be permitted…….no