The greenhouse effect is not the effect that warms greenhouses

Every now and again, people get a little bit confused when they realise that the thing we all call the “greenhouse effect” is not the mechanism that warms greenhouses. This is nothing new; R. W. Wood: Note on the Theory of the Greenhouse pointed it out in 1909. The wikipedia [[Greenhouse effect]] page states this explicitly (because I added it. I had a very long edit war with some bozo who didn’t believe it). Sometimes septics – or simply the badly confused – get very excited, because they think it tells you something useful about the actual greenhouse effect – usually, they think it proves it doesn’t exist. Of course, it tells you nothing useful about the physics of the greenhouse effect – this is simply a nomenclature issue. To re-use some old text: this is like asserting that the US political party called the “Democrats” must be, um, democratic; and their opponents anti-demoncrats, smimply based on names.

The latest froth around this is BREAKING NEWS: Greenhouse Gas Theory Trashed in Groundbreaking Lab Experiment by John O’Sullivan, guest post at Climate Realists which claims that “Nahle Nails Shut Climate Scare Coffin”. The poor old climate-scare-coffin has had so many “last nails” put into it over the years (if you believe folks like these) that you’d think there was no Wood left.

The source of the froth appears to be Experiment on the Cause of Real Greenhouses’ Effect – Repeatability of Prof. Robert W. Wood’s experiment who confirms that – err, yes, exactly what we knew already. Wood’s experiment is repeatable. Nahle himself makes none of the frothy claims, as far as I can tell [I’m wrong: see below]: all he says is, I reproduced Wood’s exp, and it worked. His failure, I think, is in not doing his back ground reading; perhaps this post will help him.

I wonder if any of the usual-suspect septic folk will be dump enough to fall for this?

[Update: I gave Nahle too much credit. He doesn’t claim that the (atmospheric) GHE doesn’t exist in the initial page or abstract, but he does claim it in his “sixth experiment” in the detailed PDF. This is fairly wacky: if you’re going to discover something as exciting as this, you’d put it into your abstract (unless you were hoping to sneak your paper past inattentive reviewers, that is).

So, he says:

The Greenhouse Effect hypothesis is founded in the argument that the atmosphere inhibits the direct outcome of longwave infrared radiation from the surface to the outer space… The hypothesis says that a great part of the solar shortwave radiation incoming from the Sun penetrates the Earth’s atmosphere and strikes on the surface -land and oceans- heating it up. As the solar shortwave and longwave infrared radiation is absorbed by the surface, the latter starts radiating longwave infrared radiation that is effectively absorbed by the greenhouse gases in the atmosphere, stored by them and reradiated towards the surface heating it up more and more.

The principle adduced by the greenhouse effect promoters is based on the idea that, in a real greenhouse, the glass panels permit the solar shortwave irradiance to penetrate into the enclosure but does not permit the longwave emitted by the inner surfaces of the enclosed space to go out.

Note the total non-sequitur in the second paragraph. The (atmospheric) GHE does not depend in any way on what happens in a glass greenhouse. Nahle is just one of the many people confused by names. Hopefully he’ll read this post, and be enlightened (he has already commented on, but clearly not read, this post).

R. W. Wood: Note on the Theory of the Greenhouse

This has been on my website for some time now; but websites are so tedious to update. So I think I’ll copy it here; more may follow. And it will distract the squabbling children. Note that as of now, this is the maintained copy; the version on my website is now longer “live”.

R. W. Wood: Note on the Theory of the Greenhouse

The following text is from the Philosophical magazine (more properly the London, Edinburgh and Dublin Philosophical Magazine (and Journal of Science?); its name has morphed since), 1909, vol 17, p319-320. Cambridge UL shelfmark p340.1.c.95, if you’re interested.

I found this reference by reading “History of the greenhouse effect”, M. D. H. Jones and A. Henderson-Sellers, Progress in physical geography, 14, 1 (1990), 1-18. This, in its turn, I found from Jan Schloerer’s FAQ: Climate change: some basics.

I present the full text, although the second-to-last paragraph is (in my opinion) regrettable and wrong. See after the text for why I think its wrong.

XXIV. Note on the Theory of the Greenhouse

By Professor R. W. Wood (Communicated by the Author)

THERE appears to be a widespread belief that the comparatively high temperature produced within a closed space covered with glass, and exposed to solar radiation,
results from a transformation of wave-length, that is, that the heat waves from the sun, which are able to penetrate the glass, fall upon the walls of the enclosure and raise its temperature: the heat energy is re-emitted by the walls in the form of much longer waves, which are unable to penetrate the glass, the greenhouse acting as a radiation trap.

I have always felt some doubt as to whether this action played any very large part in the elevation of temperature. It appeared much more probable that the part played by the glass was the prevention of the escape of the warm air heated by the ground within the enclosure. If we open the doors of a greenhouse on a cold and windy day, the trapping of radiation appears to lose much of its efficacy. As a matter of fact I am of the opinion that a greenhouse made of a glass transparent to waves of every possible length would show a temperature nearly, if not quite, as high as that observed in a glass house. The transparent screen allows the solar radiation to warm the ground, and the ground in turn warms the air, but only the limited amount within the enclosure. In the “open,” the ground is continually brought into contact with cold air by convection currents.

To test the matter I constructed two enclosures of dead black cardboard, one covered with a glass plate, the other with a plate of rock-salt of equal thickness. The bulb of a themometer was inserted in each enclosure and the whole packed in cotton, with the exception of the transparent plates which were exposed. When exposed to sunlight the temperature rose gradually to 65 oC., the enclosure covered with the salt plate keeping a little ahead of the other, owing to the fact that it transmitted the longer waves from the sun, which were stopped by the glass. In order to eliminate this action the sunlight was first passed through a glass plate.

There was now scarcely a difference of one degree between the temperatures of the two enclosures. The maximum temperature reached was about 55 oC. From what we know about the distribution of energy in the spectrum of the radiation emitted by a body at 55 o, it is clear that the rock-salt plate is capable of transmitting practically all of it, while the glass plate stops it entirely. This shows us that the loss of temperature of the ground by radiation is very small in comparison to the loss by convection, in other words that we gain very little from the circumstance that the radiation is trapped.

Is it therefore necessary to pay attention to trapped radiation in deducing the temperature of a planet as affected by its atmosphere? The solar rays penetrate the atmosphere, warm the ground which in turn warms the atmosphere by contact and by convection currents. The heat received is thus stored up in the atmosphere, remaining there on account of the very low radiating power of a gas. It seems to me very doubtful if the atmosphere is warmed to any great extent by absorbing the radiation from the ground, even under the most favourable conditions.

I do not pretend to have gone very deeply into the matter, and publish this note merely to draw attention to the fact that trapped radiation appears to play but a very small part in the actual cases with which we are familiar.

Why is his second to last paragraph wrong?

Firstly, note that unlike the earlier paragraphs which describe the results of experiments, this paragraph merely expresses his opinion.

Second, although the troposphere is subject to convection, the stratosphere is not.

Third, in contradiction to his assertion about “the very low radiating power of a gas”, the troposphere is largely opaque to infra-red radiation, which is why convection is so important in moving heat up from the surface. Only in the higher (colder) atmosphere where there is less water vapour is the atmosphere simultaneously somewhat, but not totally, transparent to infra-red and thus permits radiation to play a part.


* Note sur la th̩orie de la serre, par R.W. Wood РFrench translation, refers back to my web page.
* Someone really really dumb wrote a paper saying that because the greenhouse effect is a misnomer, it couldn’t possibly warm the earth. Mercifully I’ve forgot who. Can someone remind me?
* What appears to be the journal website