From Dr Roy Spencer’s Global Warming Blog
by Roy W. Spencer, Ph. D.
There was a recent weeks-long exchange of emails between many climate people — professional and amateur — regarding the idea that air pressure (in combination with absorbed solar energy) is what causes temperature. There were insults launched at those who refused to believe what a certain physics-trained person says should be a revolution in our understanding of planetary temperatures. That person even managed to get a paper published in a journal that (in my opinion) used reviewers who were in over their heads on the subject.
The whole ordeal makes me think of the Dunning-Kruger Effect, which is the tendency for people who start to understand a complex subject to overestimate their level of understanding. This then leads to a point of peak overconfidence (climbing “Mount Stupid”), which then gradually relaxes as more is learned and the person increasingly realizes that the subject is more complicated and nuanced than they originally thought.
I claim that the person in question who thinks [pressure + absorbed solar energy = temperature] is still stuck on Mount Stupid.
The reason I bring this up again (I’ve preached on it before) is that many have been misled into believing the “theory”. As a result, I have spent many years responding to questions from the public (including science-savvy citizens) regarding the issue. Many have been convinced by the “theory”, and have joined the proponent of the theory on Mount Stupid.
After lurking in the weeks-long email discussion, I finally responded with the following summary of the issue. I have removed the person’s name to protect the not-so-innocent.
SUBJECT: Where <NAME REDACTED> Is Right… and Where <PRONOUN REDACTED> Is Wrong
All:
After working in meteorology and then climate during my 40+ year career, I think I can offer some insight into the issues being discussed in these emails. Like <NAME REDACTED>, I have always been skeptical of what I have been told until I could fully understand an issue for myself.
I’m sure the following explanations will be of help to many of you. (I suspect <NAME REDACTED> is too invested in theories to change <PRONOUN REDACTED> mind.) Many of the concepts are not trivial, and I will admit it wasn’t until many years after all of my education (PhD Meteorology) that I finally understood a few of them, because they were not taught in school. Dick Lindzen helped me in this in the early climate research years.
Most of what follows is fundamental atmospheric thermodynamics, and I question whether <NAME REDACTED> really did take a university-level Atmospheric Thermodynamics course. If he did, I’d like to know where.
And if <PRONOUN REDACTED> shows me <PRONOUN REDACTED> grades, I’ll show <PRONOUN REDACTED> mine.
A THOUGHT EXPERIMENT
Imagine you could suddenly dump an extra 1 atmosphere of air on top of the existing atmosphere, what would happen to air temperature in the 1 ATM below? Just as <NAME REDACTED> would predict, the temperature of the original atmosphere below would increase greatly through adiabatic compression.
But what would happen NEXT?….
The high [hot] atmospheric temperatures in the lower atmosphere would then be far out of energy balance compared to what existed before. The result would be cooling of all of that air that was heated through adiabatic (or nearly so) compression (work done on the lower atmosphere) until a new state of energy equilibrium was reached. The energy loss would be through infrared radiation of the hotter air.
In fact is it always ENERGY BALANCE that determines temperature, through the 1st Law of Thermodynamics. A change in temperature is proportional to the rate of energy input minus the energy output (which includes any work done in the process).
In contrast, the Ideal Gas Law (PV=nRT) cannot tell you what the temperature “should be”. It only says how the variables P, V, and T are interrelated during the process of re-equilibration and in the final equilibrium state. What <NAME REDACTED> misses in <PRONOUN REDACTED> theory is the “n” part of the equation (the number of moles, or mass… which is in the density form of the equation, P = rho RT). In my hypothetical 2-atmosphere thought experiment, as the lower atmosphere cools to reach a new state of energy equilibrium with the solar input, the decreasing temperature causes an increase in the air density (“shrinkage”), and the pressure remains the same… even while the temperature is changing.
Specifically, following the 1st Law, the internal temperature of a volume of atmosphere exposed to an energy INPUT will increase until the temperature-dependent energy OUTPUT processes equal the rate of energy gain. This is true of every physical system… the atmosphere, a pot of water on the stove, a car’s engine, the human body, the interior of the sun, etc. That energy equilibrium is what determines the final temperature. (In the real atmosphere, there are constant energy imbalances and thus changes in temperature; Trenberth’s global-average energy balance diagram is only useful to gain a conceptual understanding of the relative role of the major energy flows in the global-average climate system.)
THE IDEAL GAS LAW
Again, the Ideal Gas Law equation (PV=nRT) cannot tell you what the temperature of a gas should be, only energy flows in and out can do that. The gas law just tells you how the P, n, and T are interrelated for a given volume (V) of air. Yes, <NAME REDACTED>, on short time scales, ascending air cools and descending air warms, but if all of that motion was to stop, energy flow processes would then determine what the final temperature would be… not what the air pressure is.
For a given surface air pressure, a huge range of temperatures is possible, and that huge range is all due to energy flow processes. Again, if the near-surface air temperature over the whole planet is much higher than local energy flow processes can support, the temperature falls, and the air’s volume shrinks (or density, rho, increases, according to the equivalent Ideal Gas Law equation, P=rhoRT). The surface air pressure remains the same because the total mass of the atmosphere is unchanged.
SO WHY MIGHT THERE BE A CLOSE RELATIONSHIP BETWEEN DIFFERENT PLANET’S LOWER ATMOSPHERIC TEMPERATURE AND PRESSURE?
I haven’t studied the atmospheres of other planets, because I don’t care. Even if those other planets did not exist, they are not necessary for understanding our own atmosphere. But if indeed <NAME REDACTED> is correct about a close statistical relationship between different planets’ surface air pressure and temperature, after adjusting for solar input, then I suspect it’s because the more atmosphere there is, the more greenhouse gases there are.
On the subject of GHGs, I’ve forgotten… does <NAME REDACTED> believe that air absorbs and emits IR energy? Because the greenhouse effect is a necessary consequence of that absorption/emission. Energetically, the GHE is a radiative insulator. It’s analogous to adding insulation to a heated building’s walls in winter. For a given energy input into the building, the air temperature inside will rise, and the outside of the walls will experience a temperature fall. This is exactly what the GHE does to the atmospheric temperature profile (in an energetic sense.. clearly involving radiation rather than conduction as a heat transfer mechanism).
If <NAME REDACTED> doesn’t believe air absorbs IR energy, how does <PRONOUN REDACTED> explain all of the thousands of spectroscopic measurements of CO2, water vapor, and methane as a function of temperature and pressure? And if <PRONOUN REDACTED> does believe the atmosphere absorbs and emits IR energy, then <PRONOUN REDACTED> must also believe in a greenhouse effect, because it is a necessary consequence…. the greenhouse effect in planetary atmospheres always causes warming of the lower atmosphere and cooling of the upper atmosphere.
(BTW, it is a common misconception that air which absorbs IR energy immediately loses that energy through emission of IR. Not true. Look up the “kinetic theory of gases” and related concepts. When CO2 or H2O vapor molecules absorb IR photons they extremely rapidly lose their extra energy to other air molecules through collisions. This happens much faster [by a factor of ~50,000] than the time it takes to re-emit energy through IR photons. This is how IR absorption immediately leads to “thermalization” [a term I hate].
Furthermore, it is crucial to understand that since IR absorption is largely independent of temperature, but IR loss is VERY dependent upon temperature, almost all air in the atmosphere is in a continual state of IR energy imbalance. Much of that imbalance is what [is balanced by] convective overturning.
WHAT IS THE ROLE OF THE ADIABATIC LAPSE RATE?
The adiabatic lapse rate in the troposphere (9.8 deg C per km without moisture condensation) is the RESULT OF convective overturning. If condensation of moisture is involved in updrafts, then the lapse rate is lower. Like the Ideal Gas Law, it doesn’t tell you what the temperature “should” be. It just tells you how the temperature of an air parcel changes during ascent or descent, if there is no energy gain or loss (“a-diabatic”). [But there are energy gains and losses occurring everywhere, all the time, and those determine what the absolute temperature will be — not pressure.]
HOW DOES THE GREENHOUSE EFFECT PLAY INTO THE LAPSE RATE?
This is a very interesting subject. It is something that even many atmospheric scientists and climate researchers don’t really understand. The combination of solar heating of the surface and IR absorption and emission by the surface and atmosphere ALONE, WITHOUT ANY CONVECTIVE OVERTURNING would result in an extremely steep tropospheric lapse rate, with very high surface temperatures and exceedingly cold upper tropospheric temperatures. This was first demonstrated by Manabe & Strickler (1964), and it’s called the “pure radiative equilibrium” case. It is sort of what makes the term “greenhouse effect” technically correct; like a real greenhouse inhibiting convective heat loss [because it has a roof], the greenhouse effect is, by definition, what happens WITHOUT the resulting convective overturning.
But in the real world, convective overturning is the RESPONSE to this GHE destabilization! So, that 33 deg. GHE warming people talk about? That’s not the GHE. It’s the GHE + CONVECTION. Without convection, that 33 deg. C figure would be more like 65 or 75 deg. C. Which then leads to another fascinating question…
WHAT WOULD HAPPEN IF THE ATMOSPHERE DID NOT ABSORB AND EMIT IR ENERGY?
Imagine a cold planetary atmosphere with no energy input. Then, turn on the sun. Solar heating of the surface would warm the atmosphere through convective overturning. But the [deep] atmosphere would have no way to shed that energy to cool in the presence of all of that energy input. The temperature of the [deep] atmosphere would then continue to rise until it had the same temperature as the surface, through its entire depth. Long before that process finished convective overturning would have stopped, because the atmosphere would be too stable to support convection. The atmosphere would eventually become isothermal (or nearly so, since there might be some planetary scale overturning between the tropics and the poles, due to their different rates of solar input), with the same temperature as the surface. Interestingly, as a result all weather activity would cease. All clouds would probably disappear, resulting in higher temperatures. Any [remaining] circulation systems would have a planetary scale, because the horizontal scale of those systems are related to the lapse rate (through the “Rossby radius of deformation”), which is also why the stratosphere only has planetary-scale circulations.
-Roy
Apparently <NAME REDACTED> doesn’t fully understand the difference between the thermodynamics of a closed system and an open system. The former is used a lot in teaching thermodynamics as it makes the problems much easier. The latter is reality.
I was a bit surprised when reading Roy’s essay about what skeptics often get wrong about CO2’s IR absorption and emission process, especially the delayed emission. This started a though process about the physics of the CO2 emission involving antennas and quantum mechanics – the CO2 molecule makes for a lousy transmitting antenna and emissions are in the form of photons and not a continuum, which meant that an emission from an excited CO2 molecule would follow the same laws as radioactive decay unless there is a flux of photons of the same energy that would stimulate emission of radiation. With that I finally understood what was going on with lasers.
Having this understanding made it a lot easier to understand the various papers written by van Wingaarten and Happer, such as explanation why the rotation of the CO2 molecule broadens the line width (think modulation).
Mark Twain observed, “The trouble with most of us is that we know too much that ain’t so.”
Adding to the “Δ33C without an atmosphere” (see other article) that completely ain’t so is the example of Venus.
Venus, we are told, has an atmosphere that is almost pure carbon dioxide and an extremely high surface temperature, 750 K, and this is allegedly due to the radiative greenhouse effect, RGHE. But the only apparent defense is, “Well, WHAT else could it BE?!” (besides/also molten core volcanism)
Well, what follows is the else it could be: (Q = U * A * ΔT) aka a contiguous participating media.
Venus is 70% of the Earth’s distance to the sun, its average solar constant/irradiance is about twice as intense as that of earth, 2,602 W/m^2 as opposed to 1,361 W/m^2.
But the albedo of Venus is 0.77 compared to 0.31 for the Earth – or – Venus 601.5 W/m^2 net ASR (absorbed solar radiation) compared to Earth 943.9 W/m^2 net ASR.
The Venusian atmosphere is 250 km thick as opposed to Earth’s at 100 km. Picture how hot you would get stacking 1.5 more blankets on your bed. RGHE’s got jack to do with it, it’s all Q = U * A * ΔT.
The thermal conductivity of carbon dioxide is about half that of air, 0.0146 W/m-K as opposed to 0.0240 W/m-K so it takes twice the ΔT/m to move the same kJ from surface to ToA.
Put the higher irradiance & albedo (lower Q = lower ΔT), thickness (greater thickness increases ΔT) and conductivity (lower conductivity raises ΔT) all together: 601.5/943.9 * 250/100 * 0.0240/0.0146 = 2.61.
So, Q = U * A * ΔT suggests that the Venusian ΔT would be 2.61 times greater than that of Earth. If the surface of the Earth is 15C/288K and ToA is effectively 0K then Earth ΔT = 288C. Venus ΔT would be 2.61 * 288 C = 748.8 K surface temperature.
All explained, no need for any S-B BB LWIR RGHE hocus pocus.
Simplest explanation for the observation.
(NASA planetary data sheet, engr tool box, first principles & math)
In Science when someone puts a new idea or theory forward for discussion and we disagree. The correct words would be “You are free to think this, but I don’t agree with you because of “this” and “that” etc…” Using words like idiot or dumb does not promote dialogue or Science?
I know Dr. Spencer has opened on this in the past, but Hallelujah for this post.
I have taught Engineering thermodynamics at least a dozen times and maybe more, and the most common misconception of students is that they view the Ideal Gas Law as the be all of thermodynamics. I think this comes from the presentation of this law in introductory physics and chemistry. Student’s will attempt to apply it even to problems involving liquids and solids.
Many folks on this website merely repeat this same mistake.
As Dr. Spencer notes what determines the temperature of any substance is the first law of thermodynamics — heat in minus work out — plus some residual temperature resulting from the substance possibly not being in equilibrium with its current surroundings.
And then there’s gravity …
I previously PROVED, not just claimed but PROVED, that not only NAME REDACTED’s claim is false but that ALL claims that a GHG-free atmosphere plus gravity can permanently raise the surface temperature are false.
I’m actually quite proud of my proof, as things in climate science are often claimed or indicated or supported, but very rarely proved.
The proof is in my post “A Matter Of Some Gravity”
Read it. Nobody’s ever found a single fault in it. If you think you have, QUOTE what you think is wrong, and SHOW us why.
w.
In that “proof” you wrote “radiating energy”. You subsequently, in another comment, defined “Radiation is energy”, and also in yet another posting used the phrase “the energy associated with radiation”. You finally told us that “energy is the capability to do work”. These are all correct statements. But then, back in the “proof” article, you wrote “radiation (measured in watts per square metre, “W/m2”)”.
But do we measure “energy”, i.e. the “capability to do work”, in “W/m^2”, Willis?
“Nobody’s ever found a single fault in it.”
Liar.
How in the world does someone get 5 downvotes for this? I had a look at Willis’s proof and it looks pretty solid to me. I do note it accumulated 1.2k comments. Where those the good old days?
I looked through a few comments and note that many commenters make the mistake of thinking that if their are no GHGs, then there are no means of any kind to transfer heat between the surface and the atmosphere. Yet, there is always conduction between the ground surface and the atmosphere which will lead to some stirring of the atmosphere…it’s how a near surface temperature inversion develops overnight in desert or high altitude regions.
You’re not a physicist either, are you, Kevin? No, Willis’s “proof” is not “solid”. It is full of hallucinations. Such as this one: “radiation … W/m^2”
“in over their heads on the subject”
For someone who doesn’t know what a Watt is, that’s a pretty bold claim, don’t you think, Dr. Spencer?
We have to agree to disagree.
(BTW, it is a common misconception that air which absorbs IR energy immediately loses that energy through emission of IR. Not true. Look up the “kinetic theory of gases” and related concepts. When CO2 or H2O vapor molecules absorb IR photons they extremely rapidly lose their extra energy to other air molecules through collisions. This happens much faster [by a factor of ~50,000] than the time it takes to re-emit energy through IR photons. This is how IR absorption immediately leads to “thermalization” [a term I hate].
There are two phenomena at work.
The part you allude to is EM wave pressure. It is minute.
The second part you skip past is valence absorbtion and emission.
The oversimplification of kinetic interactions in your explanation needs to be addressed.
First, CO2 is a linear molecule, which means it has an infinite number (spherical) or orientations relative to the EM wave front. Second, CO2 has an infinite number (spherical) of kinetic energy (aka motion) vectors.
The wave pressure is akin to gravity in that it induces an acceleration. This falls into the realm of kinetic interactions.
There are recent papers that conclude IR quantum emissions (CO2) occur more frequently via kinetic interactions, but there are other papers that quantify the quantum probability of EM emissions in the range of picoseconds to nanoseconds.
Based on molecular density and mass in the atmosphere, it is estimated that air molecules travel at an average of 171 m/s. Speed of light is 299 792 458 m/s. Molecular mean free path is 60-70 nm.
1n 1 second, the potential is 2.85E9 collisions. In 1 second, 15 um IR goes through 2E13 cycles. Simple statistics calculates for each molecular collision, the molecule receives ~ 10,000 cycles of EM valence energy. Such a build up of valence energy will certainly result in an equivalent create of emissions or the molecule will dissociate.
CO2 does not have a molecular dipole moment. H2O does due to its bond angle (104.5 degrees between H-O bonds) geometry, which means it interacts with the electric field resulting in kinetic motion. This is the bases for microwave ovens. This is not quantum absorption/emission. This is electric field interaction.
Correct. Thermalization is a hijacked, repurposed word, that does not relate to EM waves.
Also, it is more than IR at play.
Once must consider how science has been corrupted to introduce new definitions and new concepts to “prove” CO2 “traps heat” and that is what warms the air (aka “GHE”). Without these inventions, a “runaway greenhouse effect” cannot be defined.
I’ve read several papers that model vibration modes. The first stated assumption is the electro-static valence bonds are modelled as springs. No need to go into how wrong that is. Second, it assumes photons are particle and a single photon can hit the center of one atom’s nucleus setting off the vibration. It ignores that EM is continuous waves.
Other than the 1 paragraph we agree to disagree on, your article is an excellent read.
Cheers.
I see the chains of causes this way:
1) sunlight => absorption => enthalpy => conduction => temperature (of air)
2) mass(es) => gravitation => pressure (of air)
… finally the equation for ideal gases: P * V = n * R * T => V = n * R * T / P
… so in combination: temperatrure & pressure of air produces its VOLUME! …
… but not heat!
The day night cycle drives water vapor, the working fluid in a massive atmospheric heat pump. The orifice is gravity, resulting in a hot high pressure region and a cold low pressure region. If rhe planet didn’t rotate day/night there would be minimal gradient.
Roy, Thank you for this clear and thorough explanation. Your emphasis on energy balance as the ultimate determinant of temperature, the limitations of the Ideal Gas Law for setting absolute temperatures, and the role of convection in response to radiative destabilization are well taken. The thought experiment with added atmosphere pressure is particularly helpful.
I agree that pressure alone (plus solar input) does not “cause” temperature in the way some have argued. However, I’ve been exploring a related but distinct idea called the Dew-Point Anchor Hypothesis (DPAH) that tries to address the moisture side of the equation more explicitly.
DPAH proposes that the dew-point lifting condensation level (LCL) acts as a primary thermodynamic anchor in the tropical atmosphere. Rather than treating water vapor (and thus dew-point temperature) strictly as a feedback that follows surface air temperature (as in the conventional Clausius-Clapeyron view), it elevates dew-point temperature to an independent state variable that helps constrain the vertical structure and preferred equilibrium states of the troposphere. In a simple Markov-chain probabilistic model, this anchoring naturally produces two stable regimes — moist ascent (ITCZ-like) and drier descent — that appear consistent with observed tropical circulation.
This framework does not challenge the primacy of energy balance. Instead, it suggests that moisture availability, anchored at the LCL, provides an important additional constraint on how that energy balance is expressed vertically, especially in the deep tropics where moist convection dominates.
Early documentation and modelling results are available here:
• DPAH Markov Model – Proposal #1: Dew-Point Lifting Condensation Level (LCL) as a Thermal Anchor in a Markov Chain Atmospheric Model
• DPAH Markovian Matrix: A Probabilistic Two-Regime Model of Tropical Atmospheric Circulation – Interim Report
I’d be genuinely interested in your thoughts on whether an explicit LCL/dew-point anchoring concept could usefully complement the moist-adiabatic and convective-adjustment ideas you discuss. I fully acknowledge the importance of precipitation microphysics and energy flows on Earth, which DPAH attempts to incorporate at a simplified level.
Thank you again for taking the time to address these recurring questions so directly.
Best regards,
Philip