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|  |  | | (This debate is closed and is a read-only archive) | | An open letter to Dr Viner
[18-Dec-2001]
| Dear Dr Viner,
| As I sit here in my pillory, being ignored and slowly dwindling, I think back to my first encounter with planetary temperatures, many years ago when I was learning to become a non-genuine scientist. I was told that Venus receives about twice the radiation from the Sun as does the Earth. However it reflects more and only absorbs about half as much as the Earth. Since half as much of twice as much is the same as much, the surface temperature of Venus should be similar to that of the Earth. At the time, I didn't realise that the argument is a fallacy. Curiously, the argument has been repeated recently by those advocating the snowball Earth theory. More snow cover means more reflection means less absorption means colder temperatures means more snow cover means...and so on.
| My second encounter with planetary temperatures was in the 1960s, when I was a fully fledged non-genuine scientist, cunningly disguised as a genuine scientist to earn my daily bread. In VA Firsoff's book 'Exploring the Planets', he first calculated the temperatures for planets assuming them to be black. Then he allowed for the albedo, describing the planets as greyspheres. All of his greysphere temperatures were lower than the blacksphere temperatures. He didn't seem to be aware that his calculations were wrong and that he was merely repeating the fallacy mentioned above. Curiously, the argument is repeated in, for example, the NSSDC website pages giving data for the planets. In fact, this fallacious argument has been repeated over and over, and it is at the heart of discussions on global warming.
| We are repeatedly told that the Earth is around 33 or 34 centigrade degrees warmer than it would be if there were no greenhouse effect. I'm sorry, sir, but, to non-genuine scientists like myself, that is nonsense. I have long been baffled by this repetition of a nonsense argument. Perhaps you could explain it to me. The first argument, for Venus, takes account of the changes of input conditions - but makes no mention of the change in output conditions. The snowball Earth argument does likewise. Firsoff changes the input condition from black to grey, but treats the output as if from a black surface for both his blackspheres and greyspheres.
| The NSSDC effectively repeats Firsoff's mistake, but gives a different description. They define something they call 'the equivalent black body temperature' as the surface temperature the planet would have if it had no atmosphere but with the same albedo. The NSSDC seems to think that a planet without an atmosphere is perfectly black in the infra-red, and that it is the atmosphere alone that limits the output of radiation. To the NSSDC, the White Cliffs of Dover are blacker than coal in the infra-red, as is the snow on Antarctica and Greenland. The NSSDC has also re-invented the wheel; its 'equivalent black body temperature' is actually the well-known 'apparent temperature'. Apparent temperature, as its name implies is not a real temperature. It is a bit of an oddity, being the only precisely defined deliberately wrong number in the whole of science. Its use is strictly limited, and it must be used with care. It is not appropriate to discussions of planetary surface temperatures.
| The equation used by Firsoff and the NSSDC is A(I)E(I) = E(O), where A(I) is the absorptivity, E(I) is the input energy flux, and E(O) is given by the Stefan-Boltzmann relation. The Stefan-Boltzmann relation, in its pure form, applies quite strictly only to radiation from a black body. The equation that should be used is A(I)E(I) = e(O)E(O), where e(O) is the output emissivity. The emissivity cannot be ignored. Removing the atmosphere may change the value, but it does not change to unity. In point of fact, circumstances may arise in which removal of the atmosphere could decrease the value rather than increase it. For example, a low emissivity surface, such as snow, coated with a high absorptivity/high emissivity medium, such as carbon dioxide, would emit more with the coating than without.
| The misbegotten number that the NSSDC calculates is 254.3K. That's the number that global warmists, and even sceptics, say is the temperature the Earth would have if there were no greenhouse effect. No, it is not. In fact, it is merely the 'apparent temperature' of the Earth right now, greenhouse effect or no greenhouse effect. The equation A(I)E(I) = e(O)E(O) applies to simple surfaces (where there can be no greenhouse effect). It can also apply to compound surfaces where there is neither a positive nor a negative greenhouse effect. Planets are not strongly coloured. The most likely value for e(O) is a value similar to that of A(I). It may be a bit higher or lower, but its most likely value is equal to that of A(I). That is the value for a neutral-coloured body, and we may refer to the neutral body temperature as T(N). For the Earth, T(N) is about 279K. That is the only sensible value to take as a starting point. It is the most likely temperature the Earth would have if there were no greenhouse effect.
| Furthermore, it should be noted that colour alone could raise or lower that value, still without need to invoke any greenhouse effect. For example, the extra snow cover in winter tends to reduce e(O), but has little or no effect on A(I), because the extra snow is mainly on the night side of the Earth. Snow in winter helps to keep the Earth warm. The important thing to note is that a change of snow cover in winter is not a greenhouse effect. It is just a colour effect, but it changes the equilibrium temperature of the Earth. Colour effects and alleged greenhouse effects can both produce temperature changes, but their effects must to separated out. Currently, this is not being done. Everything is being attributed to a greenhouse effect, and we have the invalid claim that there is 33 or 34 centigrade degrees worth of greenhouse effect. The NSSDC device of removing the atmosphere, but only in the infra-red, is effectively a means of eliminating the possibility of a greenhouse effect. The remaining bare surface, however, is not black. Therefore, the temperature would not be 254.3K. It would be significantly higher - in the region of 279K, or even 288K perhaps, the exact value being dependent upon the emissivity of that bare surface.
| Do you see my problem, Dr Viner ? I have no wish to denigrate you , your colleagues, or your work, yet I cannot accept your conclusions. I cannot even agree with other so-called sceptics. They, like you, start from a point that my 50 years of experience with such thermodynamic problems tells me is wrong. All that I have learnt tells me that 279K must be the starting point. This is a fundamental objection, which is independent of any actual measurements or claims relating thereto, but it means that I just cannot accept any of those claims. I'm sorry, Dr Viner, I don't want to say it, but I have to: your claims are invalid.
| Yours sincerely,
| Peter Warlow, UK
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