Sunday, March 22, 2009

The mystical planet problem

(As part of Rabett Run's Gerlich and Tscheuschner project, Eli has started drafting parts of a response, which we will gift wrap in Bozo paper and send to some unsuspecting journal, but certainly arXiv. This second part comes from Duae Quartunciae. The Editorial Board expresses its thanks=:> [Rabett Run has an exceedingly small Editorial Board] Suggestions for changes and additions are welcome. Below is what was sent with minor formatting changes. It certainly needs a lead in that sets forth the issue and summarizes the result. The organization of the section should make clear why and how G&T are gone astray. Although this mostly covers Section 3.7 I think it should logically go after the part we just worked on which covered section 3.9 BTW, that is a good model for what I think we want. I'll come back to this tomorrow with some suggestions, but will leave it up as is for comments until then - Eli)

UPDATE: Eli has added a bit in Green) anything further


FW?IW the idiocy du jour is that thermal energy is not heat. Thermal energy is heat. Joule showed that about 150 years ago



On page 65 of their paper, Gerlich and Tscheuschner contrast two methods of calculating a temperature for a hypothetical planet, which they call Teff and Tphys.

The basis for both numbers is a consideration of solar energy reaching the globe of the planet. This is described in section 3.7.4. The sun's emission can be treated as a 5780K blackbody. Scaling for the distance between the Sun and Earth the solar insolation is 1369 W/m2 above the atmosphere.

1. Temperatures for a globe exposed to solar radiation.

Gerlich and Tscheuschner consider the amount of energy reaching each point of the Earth's sphere. This is zero on the night side, and on the day side it is scaled by a cosine to account for the angle at which light reaches different regions. The energy is also scaled by 0.7, to account for the amount of energy is reflected away rather than absorbed. (The Earth has an albedo of about 0.3.). At the surface, on average the solar flux is ~340 W/m2.

Teff is the temperature you must to give to every point on the globe in order to radiate all this energy away, again as a blackbody.

Gerlich and Tscheuschner prefer a model which assumes every point on the globe is in equilibrium with the local solar radiation at that point. This corresponds to a planet with no rotation, and with no heat transport over the surface, and uniform albedo. This model is absurd, especially because it neglects the heat capacity of the surface, the atmosphere (about which they have made a great fuss at the beginning of their paper) and most especially the oceans. All of these do not cool anwhere near night temperatures implied by a local radiative equilibrium even at the poles during their long nights.

They then take an average of the temperature for this hypothetical and unphysical planet; ironically calling it the physical average temperature, Tphys.

Teff and Tphys correspond to the two extremes of having uniform temperatures over the globe, and having temperatures at each point depending only on the instantaneous solar input.

Comparing equations 81 and 83, it can be seen that Teff = 1.25*sqrt(2)*Tphys = ((1-α)S/4/σ)0.25, where S is the solar constant (1369) and α is the albedo (0.3). Plugging in the numbers, one gets Tphys = 144K (-129C) and Teff = 255K (-18C). These values are shown by Gerlich and Tscheuschner in their table 12.

In practice, of course, the distribution of temperature over a planet will be between these two extremes. If the conventional average temperature is taken by integrating real temperatures over the globe, the value Tmean should be between Tphys and Teff.

From the first law, the energy emitted has to be the same, no matter how temperatures are distributed. It follows that the fourth power of temperature, integrated over the globe, should be an invariant, since this is proportional to energy. This is why Teff is a more useful quantity in practice than Tphys. In any case, Tphys must be less than Teff .

The effect of an atmosphere

These values can only be associated with the surface if there is no atmosphere, and no greenhouse effect, so that the surface radiation is equal to the planet's radiation. If there is an atmosphere that absorbs surface radiation, then this atmosphere will be heated from the surface, and will be cooler than the surface as shown in the previous section. Most of the radiation escaping to space will be emitted from the atmosphere, and this is what must match solar input. The surface must be warmer than the atmosphere, by the second law, because the surface is heating the atmosphere.

Tmean corresponds to a level in the upper atmosphere where most of the energy escapes into space, and the average surface temperature Tsurf must be somewhat warmer than this.

In practice, when you integrate temperatures over the surface of the Earth, you get about 15 C. This is indeed much greater than the -18 C of Teff, and this is called the greenhouse effect; the difference between surface temperatures below the atmosphere, and the effective temperature for radiation escaping into space. Arthur Smith (arXiv) has provided a more sophisticated, and thus mathematically complex, consideration of this issue, reaching the same conclusion as here.

Gerlich and Tscheuschner show how to integrate temperatures over the globe's surface, and they correctly note that the value obtained by such integration should be less than Teff to balance the solar input. They completely fail to note that if you actually do integrate over the surface, you get a value substantially greater than Teff. The reason for this difference is the greenhouse effect.

This is a bit like having a blanket on a cold night. You end up warmer than you would be without a blanket, but not because the blanket is a source of energy to heat you up. In fact, you are the source of energy heating the blanket, and this means you have to be warmer than the blanket.

Gerlich and Tscheuschner make this elementary mistake in their section 3.9, when they describe the greenhouse as a violation of the second law. In fact, the second law is what requires the surface of a planet to have a higher temperature when there is an atmosphere that is being heated from the surface.

3. The example of the Moon

The Moon is a good example to contrast with the Earth. It rotates much more slowly, and therefore has a temperature distribution that approaches what is used by Gerlich and Tscheuschner to derive their "Tphys". Each point on the Moon's surface is tolerably close to radiative balance with the solar input at that point.

The Moon has an albedo of about 0.12. It therefore absorbs more of the incoming solar energy than Earth. Using the solar constant of 1369 W/m2, the absorbed radiation for the surface facing the Sun is about 1205 W/m2. Hence Teff for the Moon is (1205/4/σ)0.25 = 270K, or -3C. This is the temperature that would radiate back the solar energy, if evenly distributed over the moon. But directly facing the Sun, the temperature will be more like (1205/σ)0.25 = 382K, or 109 C. Albedo is not uniform. In any particularly dark patches, the temperature could even get up to (1369/σ)^0.25 = 394K, or 121C. On the night side, however, temperatures will fall toward absolute zero. Bear in mind that as temperatures fall, so too does the rate of emission of energy. Hence it takes a long time to fall all the way to zero. Say rather that temperatures should fall far enough for the emission of energy to be small.

Now consider data on the Moon from http://www.solarviews.com/eng/moon.htm

Average day temperature is 107 C. Maximum day temperature is 123 C. These are close to theoretical expectation, to within a couple of percent.

The mean night temperature is -153C. This about 120K, and radiates a bit less than 12 W/m2. That's less than 1/100 of the solar constant, so the temperature has indeed fallen close to zero, using radiated energy as the basis for comparison.

There's no average temperature given, but the mid point of mean day and mean night temperatures is in the ballpark. This is -23C. And, just as should be expected, it is somewhere between Tphys (-120C) and Teff (-3C). But it is closer to Teff, because it is the cool side of the moon that is most different, in absolute temperature, from the unphysical extreme that is the basis of Gerlich and Tscheuschner's Tphys

On Earth, fortunately, we have an atmosphere that has to be heated from the surface. By basic thermodynamics, the Earth's average surface temperature is therefore substantially warmer than our airless moon. where surface radiation escapes directly to space.


Comments.

10 comments:

Chris Colose said...

Do G&T bring back the "IPCC vs. housewife" example with the pot of boiling water? I don't have access to this version so I'm working off of the Arxiv version...not sure of any major differences I should be aware of

Anonymous said...

In fact, the second law is what requires the surface of a planet to have a higher temperature when there is an atmosphere that is being heated from the surface."

Wouldn't that really be the "First law"? (ie, energy conservation)

What do all these energy flux arrows represent if not energy conservation?

At it's most basic, it seems to me that by arguing that for the earth NOT to be heated by the atmospheric greenhouse, there would have to be a violation of energy conservation.

In other words, G&T's whole argument violates the first law of thermodynamics. That would appear to be a rather serious matter -- FAR more serious than any hypothetical violation of the second law, in my opinion.

Chris Colose said...

I'm probably wrong but wouldn't you use the hemispheric surface area (2 pi r^2) for a body like the moon or mercury with large diurnal temperature gradients?

Hank Roberts said...

We need more transparency:

http://graphics8.nytimes.com/images/2009/03/23/science/24scan_600.JPG

Arthur Smith said...

Eli, of course this is very much the subject of my arXiv paper here - http://arxiv.org/abs/0802.4324, "Proof of the Atmospheric Greenhouse Effect" - but it doesn't hurt to rephrase the argument. Anyway, I won't comment a lot on this version, it seems ok.

One point though. The G&T T_phys actually could apply to a rotating planet if it (also unphysically) had zero heat capacity. Their requirement is instantaneous local radiative equilibrium, so all other heat flows are ignored.

It always amuses me when you have one group of "skeptics" arguing loudly that the problem with models is they ignore non-radiative stuff, and then they vociferously support papers like Miscolzi or G&T's that *only* deal with radiative effects! I wish I had a greater ability to highlight that for the full level of mockery it deserves :-)

Chris Colose said...

Arthur, it's probably worthwhile to put together a proper rebuttal piece which is a bit more accessible to laymen than your paper was (yours was great though). After all, this must have been the target audience of G&T.

To be honest, I'm not too sure how many people you would have convinced-- those people who had the physics and math background to go through your paper are not the sort that would have bought into G&T in the first place.

Duae Quartunciae said...

I'm having second thoughts about this project. I've been directed to another supposed German physicist (apparently a retired power generation engineer?) who has been making these same claims for years. He's cited in G&T, and crops up somewhat in the denialist merry-go-rounds.

See: Greenhouse Gas Hypothesis Violates Fundamentals of Physics by Dipl.-Ing. Heinz Thieme (a private webpage). There are several more essays by this author. Here's a beauty: On the Phenomenon of Atmospheric Backradiation. He "proves" it can't exist.

It's all the same nonsense as G&T, but being more concise the errors stand out better.

We obviously can't hope to persuade committed cranks. The message should be that this is not a scientific debate, but crank pseudoscience that somehow got into a journal; as does happen from time to time. The real reason for giving technical refutations, IMO, is to underline that the paper is pseudoscience on its own intrinsic merits, and is not being rejected just because we dislike the conclusions. So I guess the response is worthwhile. But oh boy.

EliRabett said...

Nick and Eli already went through a Thieme page in the Climate Audit forum, but if you think it is bad now take a look at this

CapitalClimate said...

And IceCrap is run by a Fellow of the American Meteorological Society. Makes you wonder what's the point of having any accreditation process if this kind of wingnuttery can get through.

Anonymous said...

what's the point of having any accreditation process if this kind of wingnuttery can get through.

I think it diminishes the amount of "wingnuttery".

It's impossible to eliminate entirely. As we all know, sometimes scientists who are quite sane (and competent) in their early years become quite incoherent in their twilight ( emeritus) years.

Then there are those who were never sane OR competent to begin with....