No, pressure alone does not define surface temperatures!

Eli’s already covered this but I thought I would present a slightly different argument. The topic is a recent paper by Ned Nikolov and Karl Zeller called new insights on the physical nature of the atmospheric greenhouse effect deduced from an empirical planetary temperature model, an earlier version of which was retracted because they had published under pseudonyms (reversing the letters in their names).

The basic argument is that surface pressure sets surface temperatures. The idea being that for a planet like the Earth, we can get the pressure from the weight of the atmosphere and the surface area of the Earth, and that this then sets the surface temperature. This is patently nonsense, and a fairly simple way to see this is via the ideal gas law. The ideal gas law is that the pressure, $P$, is given by

$PV = NkT,$

where $V$ is the volume being considered, $N$ is the number of molecules in that volume, $k$ is Boltzmann’s constant, and $T$ is the temperature of the gas. If the gas has mass $m$ and the mean mass per molecule is $\mu m_u$ ($m_u$ being some reference mass, and $\mu$ a constant) then $N = m/(\mu m_u)$ and we can write

$P V = \dfrac{m}{\mu m_u} k T \Rightarrow P = \dfrac{m}{\mu m_u V} k T \Rightarrow P = \dfrac{\rho}{\mu m_u} k T,$

where $\rho$ is now the mass density.

As should be obvious from the above, the pressure alone cannot tell you what the temperature should be; it depends also on the density. For a given pressure, we could have a hot surface with a low density, or a cool surface with a higher density.

Update (09/08): As per Tom’s comment, their model does include a dependence on solar insolation and albedo and then indicates that the enhanced temperature depends on surface pressure. So, their model is not simply pressure, but it is still the case that surface pressure alone does not determine how the surface temperature is enhanced.

So, what actually sets the temperature?

Let’s imagine we have the Earth, but without an atmosphere (or with an atmosphere that is completely transparent). In such a scenario, the surface must radiate back into space – on average – as much energy as it recieves from the Sun. If it didn’t, it would either heat up, or cool down, until it did so.

If we assume this imaginary Earth has the same albedo as today’s Earth, and orbits today’s Sun, then it would reflect 30% of the incoming sunlight, and would absorb – on average – 240 W m-2. It would also, therefore, radiate 240 Wm-2 and would have an effective surface temperature of 255K. The exact distribution of temperatures on the surface, however, would depend on its rotation and the heat capacity of the surface (as discussed in this paper by Arthur Smith) but, in the absence of an atmospheric greenhouse effect, the surface has to have the same effective temperature as a blackbody that radiates – on average – 240 Wm-2.

Okay, so what about the actual Earth. Well, the surface of the Earth radiates almost 400 Wm-2. This is considerably more than the energy that we receive from the Sun. In the absence of an atmospheric greenhouse effect, the surface would be cooling rapidly, but it obviously does not.

How does this work? Well, there are many ways to explain this, but let’s go back to our imaginary Earth that does not have an atmospheric greenhouse effect. Now add an atmosphere with radiatively active gases. The surface would no longer be able to radiate directly to space. The atmosphere would act to block some of the outgoing longwavelength radiation coming from the surface. The atmosphere would then emit some of this energy back into space and some back down to the surface. However, initially, the amount escaping to space would be less than the amount being received from the Sun. The surface would then warm and emit more energy back into the atmosphere. The atmosphere would also warm, and emit more energy into space, and transfer more down to the surface. This would continue until the system (surface and atmosphere) had warmed until the amount of energy being radiated into space matched the amount of energy being received from the Sun.

A key point is that the amount of energy – on average – being radiated into space has to match the amount of energy being received from the Sun. In the absence of an atmospheric greenhouse effect, this comes directly from the surface. In the presence of an atmospheric greenhouse effect, this comes mostly from within the atmosphere and requires that the surface be warmer than it would be in the absence of the atmospheric greenhouse effect.

So, we can be very confident that Nikolov and Zeller’s argument that planetary surface temperature is set by pressure alone is wrong. Not only does pressure alone not define temperature, in the absence of a planetary greenhouse effect the surface should radiate as much energy as it receives from the Sun, which is clearly not the case for the Earth. The only way to explain why the surface radiates more energy than it gets from the Sun is because of the atmospheric greenhouse effect (to be clear, the surface radiates more than it gets from the Sun, but the planet radiates – into space – the same, on average, as it gets from the Sun). Also, if we add additional greenhouse gases to the atmosphere – as we are currently doing – then we’ll cause the surface to warm even more, as is currently happening.

Attribution – a post that tries to explain the energy balance.

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64 Responses to No, pressure alone does not define surface temperatures!

1. dikranmarsupial says:

Caveat lector: I am not a physcist (as I suspect I am about to demonstrate).

As I understand it, gas pressure is caused by the force exerted by gas molecules bouncing of the surface that experiences the pressure. The higher the kinetic energy of the molecules, the greater the pressure. This kinetic energy has to come from somewhere, in this case, largely energy radiated/convected from the surface, so isn’t the causal link more in the other direction?

I wonder if any of this is a misunderstanding of the Kelvin-Helmholz mechansim by which potential energy of the atmosphere is converted into thermal energy (which happens on Jupiter, but not here), but that requires the atmosphere to be contracting and you only use up the potential energy once.

I think I’ll stop there and go back to statistics ;o)

2. Dikran,
Indeed, gas pressure does come from the kinetic energy of the molecules, but it depends on their energy (temperature) and the number of molecules (density). You can’t get temperature (or density) from pressure alone.

I don’t know if it is related to a misunderstanding of the Kelvin-Helmholz mechanism (which we have had a discussion about here before) but you’re correct, that if an atmosphere contracts it converts potential into thermal energy, but can only do that once, so you can’t sustain a constant atmospheric temperature using Kelvin-Helmholz.

3. Geoff,

4. dikranmarsupial says:

Yes, I wasn’t suggesting that you could work out temperature from pressure alone, more that it is the surface temperature that keeps the atmosphere up, so while the two things are related, you can’t say that pressure sets/controls/governs surface temperatures (which I suspect is the thing that interests climate skeptics). In other words, pressure is the dependent variable and surface temperature is the independent variable (the mass of the atmosphere being held constant)?

5. Dikran,
At the base of the atmosphere, pressure is determined by the mass of the atmosphere (mass of atmosphere x g)/(surface area of Earth). Temperature is then set by energy balance, which determines the scale height (or vertical pressure profile).

6. dikranmarsupial says:

Ah, I see, of course, so it is “effective volume” that is the dependent variable (“surface temperature that keeps the atmosphere up)? I did say I wasn’t a physicist! ;o)

7. Ed Davies says:

I think the simplest explanation is to skip all the complexity of radiation between layers in the lower atmosphere and just point out that with extra CO₂ its density at altitude will be higher therefore the effective height at which radiation to space happens will be greater. The adiabatic lapse rates (dry or saturated as appropriate) then have more height to work over so the surface finishes up warmer.

I understand that this way of looking at it was first published by Nils Ekholm in the QJRMS in 1901 but I don’t have library access to get a copy of the original article in full; I’ve only seen excerpts.

After all, if some odd bit of chemistry meant that the extra greenhouse effect only happened in the upper atmosphere (e.g., if CO₂ needed to be exposed to UV radiation to make it act as a greenhouse gas or something) then we’d still get much the same warming.

The effect of extra greenhouse gasses in the lower atmosphere is only to change the proportion of energy transfer done by radiation and that done by conduction/evaporation/convection. The temperature profile (and the emissivities) sets the amount of energy transferred by radiation; convection and co then deal with the rest [¹]. While I expect that’s interesting I think it would have, at most, a second order effect on the surface temperature.

[¹] When the atmosphere is sufficiently transparent that radiation alone is enough to transfer the energy required then convection stops happening. We call that the stratosphere.

8. Ed,

I think the simplest explanation is to skip all the complexity of radiation between layers in the lower atmosphere and just point out that with extra CO₂ its density at altitude will be higher therefore the effective height at which radiation to space happens will be greater. The adiabatic lapse rates (dry or saturated as appropriate) then have more height to work over so the surface finishes up warmer.

Indeed, and I do like this explanation. I’ve used it before. Was really just trying something different in this post.

9. There’s also this post that addresses the it’s saturated argument.

10. What’s interesting to me is how hard it is to argue with people advancing arguments like this. What I’ve realized is that most arguments between scientists are at the margin — scientists agree on almost everything and only disagree on this turbulent interface between what we know and don’t know. If you run into someone who doesn’t agree with you on anything, it becomes essentially impossible to resolve disagreements because there’s no shared basis of knowledge to use.

11. Andrew,

What’s interesting to me is how hard it is to argue with people advancing arguments like this.

Indeed. I keep thinking “okay, here’s something obviously wroong – all I need to do is point it out” and then being surprised by how hard it is. I think you’re right that situations like this are when there isn’t even a shared knowledge about the basics, and so there is virtually no chance of agreement.

12. Phil says:

In your thought experiment, could you not modify the composition of the atmosphere of your hypothetical Earth so that the surface pressure (i.e. total mass of the atmosphere) remains unchanged, but the concentration of GHG changes ?

This would change the amount of back radiation received by the surface. Unless Nikolov and Zeller have problems with the Planck-Einstein relation, its difficult to see how they could not understand this would result in differing surface temperatures for the same surface pressure ?

13. Phil,

could you not modify the composition of the atmosphere of your hypothetical Earth so that the surface pressure (i.e. total mass of the atmosphere) remains unchanged, but the concentration of GHG changes ?

That is essentially what I was assuming. The surface pressure depends only on the mass of the atmosphere. The greenhouse effect – as you suggest – depends on the composition.

Unless Nikolov and Zeller have problems with the Planck-Einstein relation, its difficult to see how they could not understand this would result in differing surface temperatures for the same surface pressure ?

What I should have mentioned in the post is that there was a very lengthy Twitter exchange with Ned Nikolov involving Scott Denning, and myself, and others. Things that you would imagine would convince him that he was wrong, very obviously did not.

If you run into someone who doesn’t agree with you on anything, it becomes essentially impossible to resolve disagreements because there’s no shared basis of knowledge to use.

The most frustrating to me are the ones who think they know what science is, despite not being able to take the first step toward understanding AGW. Where do they get that idea? Who filled their heads with nonsense? It’s as if they attended a madrasa for AGW-deniers instead of high school.

15. Eli Rabett says:

About all you can do is try and inform third parties. Mary Beard and Mike Stuchberry have done a great job with different tactics on the issue of who the Romans in Britain were. One thing for sure, you need your own style

16. Tom Curtis says:

ATTP, from Nikolov and Zeller’s “functional model” 12, T(s) is proportional to T(na) x P(s)/P(r). In turn, T(na) is a function of a specified albedo and insolation. That is, it is not given by pressure alone, so quoting the Ideal Gas Law does not constitute a rebuttal.

A more direct rebuttal is to note that functional models 1, 5, 7, and 12 all have R^2 greater than 0.98, and adjusted r^2 greater than 0.9. All but the last of these are purportedly attempts to model a greenhouse effect. Given that all of those models rely on an assumption that the volumetric concentration of CO2 equals the volumetric concentration of CH4 equals the volumetric concentration of H2O, and that the volumetric concentration of all other greenhouse gases equals zero (equation 7), it is clear that Nikolov and Zeller cannot argue that the deficiency in models 1, 5, and 7 is due to deficiencies in the theory rather than the unphysical assumptions in his model.

What is worse, the theory of the greenhouse effect, properly understood, predicts that the greater the mass (and hence pressure) of all gases, the stronger the greenhouse effect provided that some GHG are present. As I understand it, if the Earth had an atmosphere of 100% CO2, but no more CO2 in the atmosphere than currently exists, it would have a much weaker greenhouse effect than an Earth whose only GHG was CO2, but the composition of whose atmosophere was otherwise unchanged. That the partial pressure of CO2 would fall more rapidly in the former case than in the latter. Therefore the mean altitude of radiation to space by the CO2 would be closer to the ground, and because of the relationship between mean altitude of radiation to space and tropospheric lapse rate to ground temperature, consequently the ground temperature would be lower. Arguably, therefore, the theory of the GHE predicts all of the successful models in Nikolov and Zeller’s paper. That is hardly justification for rejecting that theory in favour of the one model with no explicit GH component.

17. Tom,

ATTP, from Nikolov and Zeller’s “functional model” 12, T(s) is proportional to T(na) x P(s)/P(r). In turn, T(na) is a function of a specified albedo and insolation. That is, it is not given by pressure alone, so quoting the Ideal Gas Law does not constitute a rebuttal.

Indeed, but I think the same basic problem exists. The enhanced surface temperature cannot be determined by the surface pressure alone. Okay, I guess I wasn’t quite clear that I meant the enhancement in surface temperature cannot be determined by pressure alone – I realise that he does have an insolation and albedo dependence.

18. dikranmarsupial says:

“What’s interesting to me is how hard it is to argue with people advancing arguments like this.”

Indeed, this has been my experience with the “rise in atmospheric CO2 is not man made” arguments. They are obviously wrong, but no amount of engaging on the science will convince them, but hopefully it will mean that the other readers won’t be misled by them.

19. Andrew Dodds says:

I think that the very first statement in the paper:

A recent study has revealed that the Earth’s natural atmospheric greenhouse effect is around 90 K or about 2.7 times stronger than assumed for the past 40 years.

This is something of a warning sign, IMO.

20. Andrew,
Indeed. That is based (as I understand it) on a calculation of the average temperature of the surface of the Earth in the absence of an atmosphere, and in the absence of an ocean (i.e., the night side very quickly becomes very cold). The calculation may even be correct, but it simply illustrates a massive confusion about what we mean when we say the greenhouse effect increases the surface temperature by 33K – this is based on effective radiative temperatures (i.e., what would be the temperature of a blackbody that emits the same energy per square metre per second as the surface) not on the actual average of the temperature on the surface.

21. David B. Benson says:

A correction: the interior of Terra contains uranium which continues to decay and give off a sensible amount of heat. This needs to be added to the surface IR flux.

22. David,
Technically true. In practice, though, this is small and has probably been constant over the timescale of interest.

23. David B. Benson says:

Yes, according to Wikipedia only 0.027% of the surface heat budget is from internal heating.

24. I must say that for a lay audience, it is difficult to beat this 1873 explanation of (what we now call) the Greenhouse Effect, by Tyndall:

“As a dam built across a river causes a local deepening of the stream, so our atmosphere, thrown as a barrier across the terrestrial rays, produces a local heightening of the temperature at the earth’s surface. This, of course, does not imply indefinite accumulation, any more than the river dam does, the quantity lost by terrestrial radiation being, finally, equal to the quantity received from the sun.”
John Tyndall, “Contributions to Molecular Physics on the Domain of Radiant Heat”, Chapter II, Section 23, Published 1873
Available on The Internet Archive here
https://archive.org/details/contributionsto00tyndgoog

So, adding CO2 to the atmosphere would be equivalent to having a dam, holding back water (energy). If more CO2 is added, then it is equivalent to raising the height of dam, with more energy held back, and thereby, a higher temperature.

25. Noting that Tyndall understood the importance of the ‘top of atmosphere’, as did Arrhenius. Pierrehumber & Archer (The Warming Papers) discuss how this understanding got lost somehow, even as late as Plass (1955), before it was finally reinstated in mid 1960s. But of course, some folk like to fight old battles from the 1860s, not just the 1960s!

26. Richard,

Noting that Tyndall understood the importance of the ‘top of atmosphere’, as did Arrhenius. Pierrehumber & Archer (The Warming Papers) discuss how this understanding got lost somehow, even as late as Plass (1955), before it was finally reinstated in mid 1960s.

Indeed. This post has focussed a bit on the surface energy budget, but it’s worth highlighting Ray P’s comment, where he says

The surface energy budget is mostly a sideshow. For the most part, the surface budget (which consists of radiation plus turbulent latent heat and sensible heat transfers) just acts to drag the surface temperature along with the low-level air temperature. Even so far as the downwelling IR goes, the main reason for the increase of downwelling IR is the increase of lower tropospheric temperature (mandated by combination of convection and top-of-atmosphere budget), not the direct effect of increased low-level opacity due to CO2. As the planet warms you do get a significant boost in lower level opacity from increasing boundary layer water vapor, but given that in most places the surface temperature is already close to the low level air temperature, this is not a major player, especially not over the oceans.

27. Magma says:

@ David B., average geothermal heat flow is estimated at ~80 mW/m² but it is not all that accurately known due to the technical difficulties of carrying out representative heat flow measurements across the highly varied surface geology/geography of the Earth, and the less complex but also less accessible sea floor.

For comparison, solar variability corresponds to about 0.1% of the 340 W/m² top of atmosphere insolation, and mostly averages out over the main 11-year solar cycle. Tidal energy dissipation is ~8 mW/m² (mostly in the oceans, but some lost as solid-Earth inelastic deformation and heating. And nobody ever seems to mention the 8 or 9 mW/m² top of atmosphere irradiance from the Moon (inlunation?) consisting of reflected sunlight and blackbody radiation — sad!

28. raypierre says:

Many thanks to Ed Davies for the Ekholm reference. I haven’t been able to get hold of the 1899 Swedish original, but did download the QJRMS translation (which also evidently extends the original version). I’m reading through it now — it has a whole lot more in it than just the radiating level formulation of the greenhouse effect. For a long time I’ve been looking for the first published statement of this formulation, which is the most correct simplified way of looking at the phenomenon. If I had known about this paper earlier, David and I might have included at least an excerpt in The Warming Papers.

I’m no longer inclined to write blog posts, having broken the addiction a few years back, but a discussion of the Ekholm paper would make a terrific historical post. I don’t know if it’s under copyright, so I can’t just post the article publicly, but I think it would be within fair use for me to email to one or two folks who might be interested in writing a piece on it.

29. Willard says:

> I don’t know if it’s under copyright

Ekholm died in 1926, so it’s fair ball.

30. dikranmarsupial says:

@raypierre The Ekholm paper was discussed a bit by Steve Easterbrook here. I was surprised to see how old the “modern” mechanism of the greenhouse effect was! Prof. Easterbrook seems to have a book in preparation (which sounds very interesting – “computing the climate”), so he might be interested.

31. Steven Mosher says:

More history of science.
And more rayp.

32. Phil says:

ATTP:

That is essentially what I was assuming. The surface pressure depends only on the mass of the atmosphere. The greenhouse effect – as you suggest – depends on the composition.

Sorry, I think in part my comment was me working out your OP for myself. So what I was suggesting was not a change to the physics of your explanation, but merely a different way of presenting it that made it easier to see how N&Z’s model was flawed (to me, at least).

In my case one has two situations where the surface pressure is equal but the energy flux at the surface is different. You could also conceive of many other situations (by altering the balance of IR active and inactive gases) where the surface pressure is the same but the energy flux is different. The N&Z model suggests that these should all have the same temperature, despite the differing energy flux – which seems highly implausible.

33. Ed Davies says:

@raypierre I’d be grateful for a copy of the Ekholm paper if you email some out.

https://edavies.me.uk/contact.html

I think that Steve Easterbrook page that dikranmarsupial referenced was one of the places I saw an excerpt. There was another elsewhere but I really can’t remember where.

34. Ed Davies says:

If we’re going to be pedantic about 8 mW/m² of tidal dissipation then I’ll also point out that it’s the weight of the atmosphere which sets the surface pressure, not the mass, as gravity reduces with height.

For the early versions of the software for these gliding flight date recorders http://ewavionics.com/ I did not take this into account in the software which did the conversion of pressure readings to height with the consequence that the calibration curves had a small but noticeable bias.

If the atmosphere warms it will expand upwards so, even if its mass remains constant, its weight will decrease slightly so the surface pressure will also decrease, though not by much.

35. Ed,

it’s the weight of the atmosphere which sets the surface pressure, not the mass, as gravity reduces with height.

Indeed 🙂

36. Eli Rabett says:

Tyndall was a pretty fair hand at Twitter too:

The atmosphere admits of the entrance of the solar heat, but checks its exit; and the result is a tendency to accumulate heat at the surface of the planet.

37. Marco says:

Ed, maybe you were referring to Doc Snow’s article here?
https://hubpages.com/education/Global-warming-science-press-and-storms
If not, at the very least it is a very interesting piece of history that the Doc relates in that article 🙂

38. angech says:

“The basic argument is that surface pressure sets surface temperatures. The idea being that for a planet like the Earth, we can get the pressure from the weight of the atmosphere and the surface area of the Earth, and that this then sets the surface temperature. This is patently nonsense, and a fairly simple way to see this is via the ideal gas law.”

Something I am not clear on is the temperature at the bottom of the sea. Not a gas, sure.
But having the interesting property that it’s solid form is lighter than the liquid so must rise to the warmer surface. Surely what keeps the water liquid at the massive pressures is that the pressures do affect the temperature preventing the water from freezing and rising?

Relevance?

39. angech,
The temperature at the bottom of the ocean is a few oC. Water remains liquid to very high pressures at that temperature.

40. angech says:

“So, we can be very confident that Nikolov and Zeller’s argument that planetary surface temperature is set by pressure alone is wrong.”

Good to see we are both on the same page re the model of radiation into space even if we disagree as to the effects that GHG leads to.

I would essay that there may be some indirect truth in the statement in that there is a correlation between temperature and pressure as evinced by your ( their) formula hence knowing the pressure could lead to knowing the temp and vice versa. Does this mean one can state that the pressure sets the temp or that the temp sets the pressure or that both are correct?
I would argue that once you introduce a GHG you have changed not only your mass density but your mass density response to pressure and temperature changes.
In other words a gas containing a GHG fraction behaves differently to a gas that does not even if of equal initial density the the density changes of the different gas atmospheres would respond differently.
I would not take it that they are totally wrong, only a flip side of your argument that has some merit if you look at the whole picture. The pressure at a surface is dependent on the actual atmosphere composition that exists.
Eli savages them for using water as a basic reference. Fair enough. One does have to have some substance to use as a reference point to get their idea across.
If we all could go that next step to what is the actual reference atmosphere composition then the two ideas are actually scientifically logical and not disproving each other.

41. angech,
See, Tom’s comment. There is a dependence on pressure, even in the standard greenhouse effect. The greenhouse effect is stronger if the pressure in the atmosphere is higher.

42. angech says:

“, The temperature at the bottom of the ocean is a few oC. Water remains liquid to very high pressures at that temperature.”

Realised but the deeper it goes the less the heat from the sun can get to it by currents or convection so it should keep getting colder. That it doesn’t is due to the effect of pressure which as it increases must raise the temperature .
There are no large bodies of earth size or greater that can have an ice core. I would imagine a world sized mass of water could be frozen on the outside but would be hot at its centre due to he pressure from its mass.

43. angech,
I’m not an expert at this, but I think water has this property that the density actually decreases if you go from 4oC to 0oC. As you get deeper, the water cools. However, any water that cools below 4oC starts to get less dense, and then rises. Hence, the bottom of the ocean can’t cool much below this and so doesn’t freeze.

44. angech says:

dikranmarsupial says:
“August 8, 2017 at 7:23 pm
Yes, I wasn’t suggesting that you could work out temperature from pressure alone, more that it is the surface temperature that keeps the atmosphere up, so while the two things are related, you can’t say that pressure sets/controls/governs surface temperatures (which I suspect is the thing that interests climate skeptics).”

Some climate skeptics.
Quite correct.
There are people who do not want the GHG effect to be true by any way and means and this seems to be one of those lines.
The point is still the composition of earth’s atmosphere along with its size and weight is such that changing the atmospheric composition will introduce a temperature change precisely by the pressure method specified hence it does not obviate the CO2 argument at all.

My take, which you disagree strongly with, is that the CO2 introduction results in a large number of poorly quantified feedbacks and distributions that might mean ECS is a lot lower than we think. Another story.
As said most skeptics know that CO2 raises temperature, some still want to buy an easy fix that does not exist.

45. angech says:

ATTP thanks it is very vexed that temperature of deep water. Maybe one of the oceanographers here can help. Certainly ice has a lower density (8/9ths) that of water whether at 4, 0, -2.8 (salty) degrees C. I doubt that the water at the bottom of the Mariambad trench is as warm as 4 C. I think it can be colder if the density is higher due to greater depth even if the pressure is stopping it getting colder and freezing.
In other words what you say is true at the surface, must help the ice form at the surface, but at depths the temperature and density issues must have a different way of sorting out.
Could even be like a lava lamp at the bottom !

46. Scptical Wombat says:

Eli aptly describes this paper as a word salad. When reading papers like this I tend to read them quickly and look for statements that are clearly wrong and show either a wish to be misleading or a profound ignorance of the field. For me the following extract fits this criterion beautifully.

If gases of high LW absorptivity/emissivity such as CO2, methane and water vapor were indeed capable of trapping radiant heat, they could be used as insulators. However, practical experience has taught us that thermal radiation losses can only be reduced by using materials of very low IR absorptivity/emissivity and correspondingly high thermal reflectivity such as aluminum foil. These materials are known among engineers at NASA and in the construction industry as radiant barriers [129]. It is also known that high-emissivity materials promote radiative cooling. Yet, all climate models proposed since 1800s were built on the premise that the atmosphere warms Earth by limiting radiant heat losses of the surface through to the action of IR absorbing gases aloft.

47. angech,
Water is essentially incompressible (the density is not strongly influenced by pressure). What determines the density (as I understand it) is the temperature and salinity.

48. dikranmarsupial says:

Interesting question about pressure dependence of the freezing point of water, so I did a bit of googling, which led (via the physics StackExchange) to this phase diagram

which AFAICS seems to suggest that, freezing temperature is essentially independent of pressure until about a few hundred bar, which I think would cover most of the oceans, but not trenches etc.

ATTPs suggestion about the density of water near freezing point sounds familiar/reasonable – doesn’t that imply it would be possible to have a “convection current” where the cold water is rising and the warmer water is falling!?

“I would imagine a world sized mass of water could be frozen on the outside but would be hot at its centre due to he pressure from its mass.”

now imagine it transported outside the solar system (so the amount of radiation falling on it is negligible). It will radiate heat away according to the Stefan-Botlzmann law and grow colder and colder. AFAICS, if mass/pressure alone kept the center warm we would have an inexhaustible source of energy (and have broken the first law of thermodynamics) as that heat would be continuously transferred to the outer layers of the planet and radiated away.

49. doesn’t that imply it would be possible to have a “convection current” where the cold water is rising and the warmer water is falling!?

I probably does, but maybe the timescale is long enough that it’s not all that relevant (I don’t know, though).

50. raypierre says:

Regarding the temperature of the deep ocean:

There is no reason the deep ocean would keep getting colder and colder. Liquid water is so opaque in the infrared, it really has no way of losing heat. Vertical heat transport is fairly small, but insofar as it’s there, the vertical heat transport is downward. And (small though the effect is), heat is coming OUT of the hot interior of the earth into the ocean, not going the other way.

Since the densest water sinks, the temperature of the deep ocean is set by the temperature of the water at the surface that becomes dense enough to sink. This is not a columnwise 1D process (unlike the tropical atmosphere, which really does behave in a sort of 1D way). The temperature of the deep ocean pretty much follows the polar temperatures, with some allowance for salinity effects.

As others have noted, the equation of state for water does not come close to the liquid/solid transition even at the large pressures of the bottom of the ocean. On a very water-rich exoplanet, however, with a much deeper ocean, you can actually form Ice VI, which unlike Ice 1, stays at the bottom of the ocean. Very interesting oceanography. But Earth is nowhere near that regime.

Fourier noted that the temperature goes down with depth in the ocean, opposite to the behavior in the atmosphere. He had some attempt at explaining that, but was pretty much off the mark, as he was for the atmosphere as well (though his atmospheric idea would be sort of on the right track for an atmosphere with a radiative-equilibrium rather than convective troposphere). Right about lotsa stuff, tho’

51. dikranmarsupial says:

Yes, I suspect the salinity changes (due to formation/melting of sea ice) would be more important in the Arctic, but it would make a cool lab experiment.

52. raypierre says:

Forgot to mention that in order to close the ocean circulation, you need to have a mixing process that allows cold water at the bottom to reach the surface. This generally takes some input of mechanical energy in order to mix against a stable density gradient. Without such stirring, the whole ocean fills up with the densest surface water made on the planet, and the circulation then becomes stagnant except for a thin frictional layer at the top. Cf “Sandström’s Theorem”

53. Ray,
Thanks, I thought someone who knew more would comment to clarify 🙂

54. JCH says:

This dance between upwelling and downwelling is interesting. I keep watching the behavior of OHC and SST: going into the 14-16 El Niño, during it, and after it. I don’t see how it can be squared with low climate sensitivity.

It’s great to see raypierre commenting here. That should reinvigorate aTTP.

55. Maybe I’m mistaken but what are the implications of this paper testing literally a dozen different statistical models with 15 variables with only 6 data points? This in itself seems rather dubious.

56. angech says:

“Water is essentially incompressible (the density is not strongly influenced by pressure).”

What I also believed as well until reading about the expansion of solids as they come from the pressure of the depths.
Different to a liquid at the surface (depths) but if one goes 40 kilometres down say a metal cannonball might conceivably be half the volume for the same mass.
Water and iron are incompressible on the surface but the greater he depth the more compressible they become.
Happy to be proved wrong.

Dikran the larger the mass the more it generates its own heat from the pressure. A mass of water the size of the sun is near impossible but in the temporary time it existed would generate immense heat very quickly presumably leading to its dispersal.
Meteorite size in absolute space cold
Moon size. Some energy heat always at the core
Earth size more so
Jupiter size type more so but would contract in size
Super Jupiter say 100 times a quasi sun.
Sun size always a sun
I would be interested to hear if astrophysicists have identified large cold bodies Jupiter size or above in space.
Accumulating enough mass always leads to heat formation.

57. Ragnaar says:

Lucia and Curry had threads related to this. Ned Nikolov and Karl Zeller on this subject, sky dragons.

58. Marco says:

Ragnaar, did Curry really have a thread about this? I haven’t been at her place for a very long time, so I only remember the time she rapidly withdrew from any discussions with the sky dragons, because somehow they were not to be reasoned with. Which was quite hilarious at the time, considering her demand that climate scientists engage with skeptics.

59. Ed Davies says:

Marco: “Ed, maybe you were referring to Doc Snow’s article here?
https://hubpages.com/education/Global-warming-science-press-and-storms”

Yes, that was one of them. There’s also some interesting coverage of those attempted polar balloon flights in Richard Holmes’s book _Falling Upwards – How we took to the air_ though obviously with somewhat less about GHGs.

I think I found the Doc Snow article as a result of searching while reading Spencer Weart’s _The Discovery of Global Warming_ pages, specifically this bit:

https://history.aip.org/climate/simple.htm#S1C2

Amusingly, that has a sidebox link just above to an article by raypierre. If only web links were bi-directional.

60. Ragnaar says:

https://judithcurry.com/2011/01/31/slaying-a-greenhouse-dragon/
“I only remember the time she rapidly withdrew from any discussions with the sky dragons, because somehow they were not to be reasoned with.”
I’ve found skydragons on youtube, and found myself appealing to authority. Finding discussions by Spencer addressing the subject too. And I saw the irony in that. Let’s see if I can offend everyone. WUWT should cut the skydragons loose. Then there’s the ocean skin layer sky dragons. I don’t see that you have to endorse everyone that’s on your side.

61. MarkR says:

@ dikranmarsupial, ATTP,

You established this: pressure comes from air mass + planetary gravity and temperature is set by the energy balance, including the greenhouse effect, so it must be the atmospheric volume that increases or shrinks in response to T (V = nRT/P).

Now think of Venus. It’s so hot that its surface radiates ~16.5 kW/m2, but it only gets ~0.1 kW/m2 in sunlight. Nikolov and Zeller should be able to explain how that ~16.5 kW/m2 is replaced. There was chat at Tallbloke’s where they and their fans refused to answer, except one person who suggested the greenhouse effect of dust based on a decades-old Hansen paper, which we now know is not the major factor. Nikolov refused to answer.

You could release the gravitational potential by collapsing the atmosphere of course: Venus’ atmosphere has enough gravitational potential for a few months of those temperatures. That’s obviously not happening. With N&Z if they engaged and talk about the physics it could be useful. For example, if they stated that they reject conservation of energy or the Stefan-Boltzmann law, we could see specifically why their opinion is different from the results of physics. If they accept the laws of physics, then that raises other questions and real scientists would typically be interested in answering questions that come from their ideas.