Thursday, February 18, 2016

On Competing Mechanisms for the Observed Temperature Gradients Between Surface and Upper Air

... or in other words, is it the purported longwave radiative gradient due to water vapour, CO2, methane, and other so-called greenhouse gasses?  Or something else?  Is the "greenhouse" effect real, but presently saturated at present levels of GHG atmospheric concentrations?  Or is the planet self-regulating to an extent that climate sensitivity to increased CO2 concentration is smaller than the present IPCC-published range of 1.5-4.5 K/2xCO2?

I promise only strong and (sometimes) well-argued opinions, no definitive answers.



Background

This post derives from the culmination of many discussions I've been having with a fellow name of Chic Bowdrie across several WUWT threads which started, I think, with our mutual intent to compare reliability and uncertainty of the surface temperature anomaly with bulk upper air temperature anomaly obtained by orbiting (advanced) microwave sounding units a la RSS and UAH.

As these things so often do, that discussion sprawled into other areas such as ocean heat content, energy imbalance estimates, the pros and cons of atmosphere/ocean general circulation models, confirmation bias in science when policy is on the line and "bias bias" -- that all too common malaise which occurs when one's interlocutor is such a stubborn git that surely he's the one who can't see the forest through the trees.  Not to mention some wrangling over Popper-style falsification, Fisher-esque null hypothesis testing and the Three C's of "normal science" as generally seen in practise, Consistency, Consilience and Consensus.

"Damn your assertions, show me your evidence!" has been a common refrain.

"That is utterly inconclusive (you ignorant clod)!" has been a common response upon delivery of same.

And no small amount if wondering whether the other guy is burden of proof shifting, or really IS open to accepting the others' view if a mechanism could only be convincingly articulated, backed up with solid maths and reliable-looking empirical data.  I have also openly held forth on my distaste for the word "proof" when inductive inference is a dominant logic.

I exaggerate with the tone and parenthetic unspoken thoughts; at least for Chic's part he is far more polite in his responses than my inner dialogue often is when I read them.  For the very reason that I enjoy discussing these things with him and because it has gotten logistically hairy for our conversations to have sprawled out over several threads (and now other blogs, namely ATTP's joint) I have invited him here to discuss what we have mutually agreed upon is the most interesting and central premise of AGW: the radiative theoretical model of climate forcing vs. various alternative mechanisms he thinks have merit sufficient to explore in earnest.

My premise in support of that agreement is that all the evidence in the world for a given physical phenomenon does not a strong argument make unless it is backed by consistent, robust, well-tested theory.  That, and I'm just plain weary of discussing (in)credible error estimates.

Pretty Pictures and Other Reference Materials

If there's any one thing which has dominated our discussions, it is the energy budget cartoon found in Trenberth, Fasullo and Kiehl (2009), Earth's Global Energy Budget:


I believe it is fair for me to say that we both provisionally accept the indicated fluxes, if not as a reasonable approximation of current global diurnal averages, at least as a faithful representation of the IPCC-approved model of radiative forcing and energy imbalance for sake of argument.  We both have noted that net fluxes at all of the three layers of this model (surface, mid-troposphere and top of atmosphere) net to roughly zero, which is state we would both expect in the system at a steady state thermodynamic equilibrium.  We also both recognize that the planet is never truly at equilibrium, only ever "seeking" it. However we have agreed to accept steady state (pseudo-)equilibrium as a useful illustrative and conceptual model.

Chic does have at least two issues with this schematic that I can recall:
  1. He thinks the stated 0.9 W/m^2 downward flux imbalance should be closer to zero.
  2. The 333 W/m^2 Back Radiation flux drawn from mid-troposphere to surface is unrealistic because extinction path length for 15 micron longwave radiation is variously cited as being between 3 and 10 meters at sea level pressure.
To (2) I would add that water vapour being a potent absorber outside the 15 micron band and present near the surface up to 4% by volume as opposed to CO2's 0.04% relatively well-mixed ratio should not be neglected either.

As to (1), he has previously cited Stephens et al. (2012), An update on Earth’s energy balance in light of the latest global observations, which gives the TOA imbalance as 0.6 +/- 0.4 W/m^2 at TOA and 0.6 +/- 17 W/m^2 at the surface:


He is of the mind that 0.6 W/m^2 is still too non-zero to be a credible estimate, especially given the magnitude of the stated uncertainties in the paper and the budget diagram.  In light of that objection, I took it upon myself to appeal to published ocean heat content estimates to see if I could get into the ballpark on that basis alone.  The data were from KNMI Climate Explorer which more or less conform to this plot from NOAA/NESDIS/NODC:


In this post I use the KNMI plots for the visuals which come sans error bars.  The moral of the story is that I calculate an energy imbalance from 1957-present of 0.34 W/m^2 for the upper 2,000 m of oceans, compared to 0.004 W/m^2 for the whole atmosphere over the same interval according to HADCRUT4.  I then note that my OHC estimate falls within the stated uncertainty of Stephens (2012), and that I think it is plausible that the difference between my estimate and Stephens could be found deeper than 2 km as ARGO is upgraded to go deeper.

One final citation and graphic from Wu and Liu (2010), A new one-dimensional radiative equilibrium model for investigating atmospheric radiation entropy flux:


The above plot encapsulates the main theses of my argument to date, namely:
  1. The radiative gradient as a function of altitude (both solar SW and LW emission/absorbtion by/from the surface and atmosphere) is primarily responsible for the temperature gradient in the troposphere between tropopause and surface (i.e., the lapse rate).
  2. Convective transport of latent and sensible heat from the surface to (roughly) the tropopause must be considered by more complex models to explain observation.  As well, this convective transport has the tendency to reduce the temperature gradient (i.e., reduce lapse rate).
  3. (1) is not saturated, and thus increasing CO2 atmospheric concentration by way of anthropogenic emission will tend to reduce net LW loss from the surface as well as proportionally at higher altitudes as suggested by the curves shown by (b) in the above figure.  The implication also being that where both the downwelling (blue) and upwelling (red) LW curves intersect at the surface will move to the right (increase) by way of response to any conceivable increase in CO2 levels.
  4. (2) is not expected to compensate for (3) due to any mechanism, including albedo feedback due to increased cloudiness as a result of increasing specific humidity near the surface due to increased surface evaporation.  IOW, if cloud feedback is negative, it is only weakly negative with respect to the increased radiative forcing due to CO2 and the secondary radiative feedback due to higher atmospheric water vapour content.
  5. Whatever the final steady equilibrium state of the system thus perturbed by rising CO2, the NET of ALL fluxes at ALL levels is expected to be zero in any proposed model which reasonably represents actual physical processes taking place in the entire climate system.  Until that equilibrium is reached, I expect there to be a net downward energy flux present at TOA and the surface when averaged over a climatically representative interval ... on the order of three decades or greater.

Invitation to Comment

Although this post is intended mainly for Chic and me to check our own understandings and assumptions against alternative models, I welcome contributions from others who may (improbably) happen by.  I have never formally established posting policies for this blog.  However, my intent for this particular post wants some rules, which are as follows:
  1. Burden to substantiate claims is on the one making them.  Citations to primary literature, observational data obtained from same, appeals to well-established physical theory, detailed calculations (show your work) and/or independently developed statistical/physical models are acceptable.  Be prepared to defend all of the above on the merits of the arguments made themselves, not by who said them where.
  2. Converse to (1), bickering about politics, making sweepingly generalized statements about the obvious biases and blind spots of one's interlocutor and other red herrings are strongly discouraged.  I get it we all have preconceived notions and cognitive biases; this thread takes that as a given and I wish to rule it out as subject of "debate" herein.
  3. Unilateral self-declarations of victory will be considered an immediate loss.  Forward progress is obtained by at least understanding someone else's position, if not accepting some or all of their evidence and reasoned arguments.  Unqualified victory here is being challenged and learning something from it.
  4. Bluntly pointing out that someone else's argument is crappy is acceptable if one also explains why.  Bluntly pointing out that one's own argument is crap is encouraged, especially if one also explains why.
  5. Reminding me that I wrote the latter part of (4) may be necessary.  The former, not so much.
First violations will stand, but with warning.  Second violations will be redacted with explanation, with any surrounding non-offending comments left intact.  Subsequent posts containing offences will be deleted in toto with explanation.

With that all said (it was supposed to be short, dammit) I yield the floor to Chic.  I would suggest to him that he also write a summary of his own position to date first, which I'll add to the head post, before taking up point-by-point arguments in comments.

Update 2/29/2016 - Chic's Opening Statement

Brandon,
I accept your invitation to continue our debate on various climate change issues.  Our chance meeting on another blog and many subsequent discussions attests to the degree we both seek the truth regarding climate science.  I liken my quest to the Holy Grail of climate change, a search for definitive evidence that any further increase in atmospheric CO2 will cause a corresponding and discernable effect on global temperatures.  Failing to see sufficient evidence, I am suspect of the radiative theoretical model of climate forcing which I agree is the central premise of anthropogenic global warming (AGW), but not the only one.  In addition to the claim that CO2 warms the atmosphere, another aspect of the theory is that the increase in CO2 is primarily, if not totally, due to man. That is also a debatable subject.  I will only address the potential for CO2 to cause further warming, regardless of where the CO2 comes from.  This presumes I acknowledge some global warming, but consider natural causes more likely to be the predominant contributing factors.
I dislike using the term greenhouse effect and avoid its use as an analogy for the atmosphere.  A greenhouse is warm, because it is enclosed.  The atmosphere has no lid and convection and wind contribute considerably to energy transfer.  For this reason I do not consider CO2 and water vapor as greenhouse gases, but rather IR active gases because of their ability to absorb and emit SW and LW radiation.  I also make a distinction between a greenhouse effect evidenced by a planet with an atmosphere compared to one without vs. the enhanced greenhouse effect which raises the issue of whether or not increasing amounts of CO2 in the atmosphere will cause any further increase in global temperatures.  
Brandon notes our agreement on the basic virtues and flaws of the energy budget diagrams.  In a response to his opening statement, I stated my disagreements with the main elements of the position encapsulated in his summary of the Wu and Liu paper.  In the following paragraphs, I summarize my position generally and then follow that up with a more detailed explanation.
Aside from the inherent problem of oversimplification, the energy diagrams suffer from their inability to account for the effects of a rotating Earth.  The Sun heats the surface only part of the day at any one location. This obviates any equilibrium being established and complicates energy budget estimates.  The SW radiation is absorbed in land and ocean surfaces which eventually lose that energy to the atmosphere through several processes described in the diagrams.  The three main phenomena, conduction, evaporation, and radiation, all have the same consequence which is causing the air above the surface to rise.  Evaporation does it by making the air less dense.  Conduction warms directly and radiation warms through absorption of LW radiation by IR active gases and subsequent thermalization by collisions with the more predominant atmospheric gases.  Convection and advection bring this energy, originally from the Sun, up into the troposphere. This energy warms the troposphere mostly during the day, before being radiated back to space, mostly at night.  On average, all the energy that enters the troposphere, either LW from the surface below or direct SW from the Sun, exits at the end of each diurnal cycle.  If not, then global warming or cooling will occur in the long run.

The upward and downward radiative energy flows illustrated in the Wu and Liu (2010) diagram are unreal, because convection is ignored.  While including mathematical equations that account for convection is currently beyond my ability, I diagrammed conceptually in the Figure above what the energy fluxes would be if my understanding of the atmosphere is correct.  The curve labelled ULWR is similar to Wu and Liu’s upward LW radiation.  It was plotted using the equation
Z = A * ln [197/(ULWR -239)]
Z is the altitude and A is a constant used to shape the curve.  The DLWR curve was plotted using an equation similar to the ULWR curve, but at low altitude values there is a 40 W/m2 difference in consideration of the atmospheric window.  At higher altitudes, I shaped the curve to reduce the downward LW as would be expected from the less dense upper troposphere.
The equation for the solar input is also conceptual and reflects the 78 W/m2 of SW gradually absorbed by the atmosphere that doesn’t reach the surface.  
Solar = 161 + 78*F*EXP(B*(F-1))
F is Z/ZTOA and ZTOA is an arbitrary value for the altitude of the TOA at 13 km.  B is another shape factor that favors most of the SW being absorbed at higher rather than lower altitudes.  When Z = ZTOA , the solar radiation is the 239 W/m2 portion of the total 341 W/m2 solar insolation that isn’t reflected.  The solar input goes to 161 W/m2 when Z = 0.
The convection curve is simply the remainder calculated from the assumption that the energy flux at any altitude is net zero.  Therefore, Convection =  Solar – ULWR + DLWR.  Thus the contribution of convection to atmospheric fluxes is the predominant factor in moving energy from the surface to the upper troposphere where the burden is passed to radiation.  It is only at high altitudes where the density is thin that molecular collisions no longer dominate over emissions.  Although there is a 50:50 chance that an emission will go up or down, there will be a net flux up because upward will exceed the downward absorptions.  This is well represented in the Wu and Liu diagram.  But at altitudes close to the surface, the greater density means that upward and downward absorptions will be essentially equal.  
The lapse rate in my Figure was calculated using the Stephan-Boltzmann constant to convert the temperature at each altitude to a W/m2 value.  A lapse rate of 6.5 K/km was assumed.  I used the shaping factors to bring the DLWR curve close the lapse rate curve.  I justified this on the basis of the spectra of the atmosphere showing that temperatures of the atmosphere correspond to temperatures calculated from Planck’s equation.
While a certain critical mass of IR active gases are required to maintain an atmosphere with a moderate range of temperatures, I contend that further increases in CO2 will not increase global temperatures substantially.  Any actual effect cannot be detected amidst the myriad of natural factors also in play.  If anything, additional CO2 is more likely to increase the ratio of ULWR to DLWR at the high altitudes.
I suspect that discrepancies between climate models and satellite temperature observations may be due to the models attributing too much influence from CO2, water vapor, and other IR active gases.  This blog post addresses this possibility for model error:
Quotes from this article: “One of the striking features in GCM-predicted climate change due to the increase of greenhouse gases is the much enhanced warming in the tropical upper troposphere. Here we examine this feature by using satellite MSU/AMSU derived deep-layer temperatures in the tropical upper- (T24) and lower- (T2LT) middle troposphere for 1979-2010. It is shown that T24- T2LT trends from both RSS and UAH are significantly smaller than those from AR4 GCMs. This indicates possible common errors among GCMs although we cannot exclude the possibility that the discrepancy between models and observations is partly caused by biases in satellite data.”
IPCC AR4 GCMs overestimate the warming in the tropics for 1979-2010, which is partly responsible for the larger T24-T2LT trends in GCMs. It is found that the discrepancy between model and observations is also caused by the trend ratio of T24 to T2LT, which is ~1.2 from models but ~1.1 from observations. While strong observational evidence indicates that tropical deep-layer troposphere warms faster than surface, this study suggests that the AR4 GCMs may exaggerate the increase in static stability between tropical middle and upper troposphere in the last three decades. In view of the importance of the enhanced tropical upper tropospheric warming to the climate sensitivity and to the change of atmospheric circulations, it is critically important to understand the causes responsible for the discrepancy between the models and observations.”
IMO, the main reason for the discrepancy is too much dependence on the amount of radiative forcing attributed to CO2.  One has to keep in mind the time between absorption and emission relative to the time between collisions.  At the surface, molecular density is so great that collisions result in essentially all LW being absorbed within a few meters.  This situation is reversed in the upper troposphere where every collision involving the excitation of a CO2 molecule is more likely to result in emission of radiation rather than another collision transferring energy back to an IR inactive molecule.  Although the emission is equally likely to go up or down, the net radiation will be up because more radiation comes up from the denser atmosphere below than comes down from above.  So there is no justification for a tropospheric hot spot.  The more CO2, the greater difference between upward vs. downward radiation.
Chic Bowdrie
February 24, 2016

Update 3/1/2016

Using output from an online version of the MODTRAN radiative transfer code, I ginned up a plot of radiative fluxes from the surface up to 30 km:


The light blue curve is the Stefan-Boltzmann prediction taken from the temperature profile for the standard tropical atmosphere used in these particular model runs.  The atmospheric emissivity value of 0.84 is my own parameter which I selected to make the difference between the DWLR and the graybody flux = 40 W/m^2, which is the value shown in the K&T energy budget cartoon as the upwelling radiation from the surface which goes out through the so-called atmospheric window.  I've no idea if that's kosher, but it seemed reasonable as 0.84 is in line with other published approximations for emissivity in a "gray" atmosphere.

Compare the shape and values of the longwave curves to Wu & Liu (2010).  Further compare this image from Grant Petty (2006) courtesy of Science of Doom:


Clearly, a pure radiative model which does not take convective/advective, latent and sensible heat transfers into account would not approximate observed temperature profiles with reasonable fidelity.  A simple 1D model which does a better job of it presently eludes me, but I'm chipping away at it.

Update 3/5/2016

I used the following image in a reply to Chic in the comments below.  Since Venus/Earth comparisons have become a main theme of the discussion, I thought it appropriate to elevate this image and some discussion to the main article.


Temperature profiles for Mars, Earth and Venus taken from Astronomy Notes by Nick Strobel.
As I dig into it, it seems appropriate to elevate this discussion to its own article.

133 comments:

  1. Brandon,

    Nice work. Good start to pick up where we left off.

    I have some issues with your summary of the Wu and Liu paper.

    1. The paper ignores convection, so the profiles just represent a hypothetical radiation only situation. The real lapse rate is a perturbation from a thermodynamically derived value equal to –g/Cp. This is about 10K/km for a dry atmosphere. With evaporation and humidity it’s more like 6.5K/km.
    2. The theoretical value is controversial because its derivation doesn’t rely on any radiative influence.
    3. The perturbation of the lapse rate is dynamic and affected by variable amounts of daily SW radiation and evaporation. Any change in the amount of CO2 in the atmosphere has little chance to affect long term energy transport through the atmosphere, because the daily amounts of incoming radiation are completely absorbed and thermalized within a few meters of the surface. Therefore no shift in the temperature profile due to increased CO2 is necessary.
    4. There is no need for compensation because all the available radiation is absorbed near the surface where the warmed air expands. The resulting advection, a combination of convection and wind, is sufficient to transfer all the thermalized energy to higher elevations and latitudes. Increased radiative forcing is hypothetical and unmeasurable.
    5. Observed changes in OLR and incoming SW are within the tolerances indicated in the Trenberth and Stephens it al. cartoons. No change in those measured values can attributed solely to CO2 in any time frame due to the conflating influence of natural factors. Climate models are said to account for both the radiative and convective effects. However, the fact that climate models overestimate actual warming suggests that the underlying mathematical models may not characterize the physical phenomena properly.

    This is just my opening statement. I will provide more in depth arguments as time permits.

    ReplyDelete
    Replies
    1. Thank-you Chic. If you would like to write more of a general overview of your arguments and e-mail it to me I would like to insert that into the head post. Otherwise I can use your above points for that purpose. After that, I suggest it might be good to pick one point to focus on at first; you can choose which one to develop into a fuller argument.

      Delete
    2. Chic B

      Climate models are said to account for both the radiative and convective effects. However, the fact that climate models overestimate actual warming suggests that the underlying mathematical models may not characterize the physical phenomena properly.

      This is a standard contrarian claim that probably lacks merit.

      If it is incorrect, then a great deal of the contrarian argument that rests on this claim fails automatically.

      The claim that the models 'overestimate' warming is based on the misnomered 'pause' or 'hiatus' that should correctly be described as a recent slowing in the rate of surface (tropospheric) warming.

      The suggested mechanisms behind the slowdown in the rate of surface warming include:


      – increase in the rate of ocean heat uptake (England et al 2014)

      – increased aerosol negative forcing (Ridley et al. 2014)

      – predominance of ENSO LN state (Banholzer & Donner 2014)

      – exceptional reduction in solar output during SC24 (SSN index)

      There is evidence that when the CMIP5 forcing estimates used for AR5 are updated to bring them into line with real-world forcing history, then modelled global average temperature comes into much closer agreement with observations (Schmidt et al. 2014). This would suggest that model physics and so emergent behaviours like model sensitivity are reasonably accurate.

      Models are, of course, only a secondary source of knowledge. Palaeoclimate behaviour provides ample evidence that GHGs are indeed efficacious climate forcings and that the most likely fast feedbacks equilibrium sensitivity to a doubling of CO2 is close to 3C.



      Delete
    3. BBD,

      Nice to see you here, thanks for stopping in.

      This is a standard contrarian claim that probably lacks merit.

      I both agree and disagree for reasons which prompted me to elevate this topic to its own article:

      http://climateconsensarian.blogspot.com/2016/02/yes-most-models-run-hot.html

      Delete
  2. Brandon

    Here are some links and references for the PETM. Sorry to dump them here, but I assume you can delete the comment. I didn't want to fill up the thread at ATTP's too much - and besides, he has a four link per comment limit.

    This is all a bit random, sorry ;-)

    A primer and background and interesting issues:

    https://sites.google.com/site/thepaleoceneeocenethermalmaxim/

    A general discussion of the PETM by Phil Jardine:

    http://www.palaeontologyonline.com/articles/2011/the-paleocene-eocene-thermal-maximum/

    SKS: The perplexing PETM

    http://www.skepticalscience.com/the-perplexing-PETM.html

    RC: PETM weirdness

    http://www.realclimate.org/index.php/archives/2009/08/petm-weirdness/

    * * *

    Some (IMO) key studies:

    CIE evidence: (Original discovery:)

    Kennett & Stott (1991) Abrupt deep-sea warming, palaeoceanographic changes and benthic extinctions at the end of the Palaeocene

    http://www.nature.com/nature/journal/v353/n6341/abs/353225a0.html

    (NOTE: K&S dating of ~57.33Ma subsequently revised to ~55.5Ma see Cronin p101)

    See also:

    Koch et al. (1992) Correlation between isotope records in marine and continental carbon reservoirs near the Palaeocene/Eocene boundary

    Svensen et al. (2004) Release of methane from a volcanic basin as a mechanism for initial Eocene global warming
    (This link *includes* Dickens G. R. Nature comment Hydrocarbon-driven warming on Svensen et al. (2004) )

    http://folk.uio.no/hensven/nature/svensen_etal_nature04.pdf


    http://www.nature.com/nature/journal/v358/n6384/abs/358319a0.html

    Zachos et al. (2008) An early Cenozoic perspective on greenhouse warming and carbon cycle dynamics

    http://www.es.ucsc.edu/~jzachos/pubs/Zachos_Dickens_Zeebe_08.pdf

    Bowen et al. (2015) Two massive, rapid releases of carbon during the onset of the Palaeocene–Eocene thermal maximum

    http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2316.html

    Some discussion of Bowen et al.:

    http://www.sciencedaily.com/releases/2014/12/141215113949.htm

    Ze very latest at SkS:

    http://www.skepticalscience.com/news.php?n=3276

    * * *

    As I said, a bit of a random scatter, but hope at least some of this helps...

    ReplyDelete
    Replies
    1. Random scatter is my glory. Your helpful contributions added to the newly-minted Data Sources, Literature References, Et Cetera page.

      Delete
  3. Chic,

    Response to your opening arguments Part I:

    I dislike using the term greenhouse effect and avoid its use as an analogy for the atmosphere. A greenhouse is warm, because it is enclosed.

    True according to my understanding, and I have a similar dislike. The analogy is entrenched, however, and its usage should not necessarily imply that the user misunderstands the actual mechanism described in literature. I'm content to refer to "GHGs" as "IR-active gasses" and the "greenhouse effect" as "radiative forcing", both of which are common in literature and IPCC publications.

    I also make a distinction between a greenhouse effect evidenced by a planet with an atmosphere compared to one without vs. the enhanced greenhouse effect which raises the issue of whether or not increasing amounts of CO2 in the atmosphere will cause any further increase in global temperatures.

    It would be nice if there were an Earth-like planet in this system with an N2-only atmosphere at comparable surface pressure, rotation, insolation and albedo for direct empirical comparison as such might settle many arguments along these lines. Unfortunately there is no such body. I'm also dubious it would resolve our differences as we do have examples in the form of three other terrestrial planets (Mercury, Venus and Mars) plus our own Moon. As I've mentioned before, Venus suggests that the concept of radiative saturation is not operative for any conceivable survivable CO2 concentration on Earth with its far less dense atmosphere.

    ReplyDelete
    Replies
    1. Brandon,

      Radiative forcing is not synonymous with any greenhouse effect. There is no greenhouse atmosphere. The effect we are discussing is whatever makes the Earth’s surface warmer than 1) a similar planet with no atmosphere, 2) a similar planet with an atmosphere without IR active gases, and 3) a similar planet with greater concentrations of IR active gases than Earth.

      I don’t understand how “Venus suggests that the concept of radiative saturation is not operative for any conceivable survivable CO2 concentration on Earth with its far less dense atmosphere.” The surface of Venus is 740K. The temperature is 310K at 53 km. That makes the lapse rate 8.2 K/km. This is pretty close to a value of 7.4 K/km calculated from g/Cp using 8.87 g/sec2 for the gravity on Venus and 1.2 J/g-K for the heat capacity of CO2. Radiative forcing is not required to explain the temperature profile of Venus.

      Delete
    2. Chic,

      There is no greenhouse atmosphere.

      Yes, I agree. Use whatever term for the effect you like.

      I don’t understand how “Venus suggests that the concept of radiative saturation is not operative for any conceivable survivable CO2 concentration on Earth with its far less dense atmosphere.” The surface of Venus is 740K. The temperature is 310K at 53 km.

      For reference, here are temperature profiles for Venus, Earth and Mars taken from this webpage.

      Let's look at some numbers from NASA's Planetary Fact Sheet for Venus:

      Bond albedo 0.90
      Solar irradiance (W/m2) 2601.3
      Black-body temperature (K) 184.0

      On that basis alone, Venus' atmosphere has no business being 310 K at 53 km, which is below the upper sulphuric acid cloud deck responsible for its high albedo.

      That makes the lapse rate 8.2 K/km. This is pretty close to a value of 7.4 K/km calculated from g/Cp using 8.87 g/sec2 for the gravity on Venus and 1.2 J/g-K for the heat capacity of CO2. Radiative forcing is not required to explain the temperature profile of Venus.

      The ideal gas law only predicts temperature change for a given change in pressure, not absolute temperature itself. Noting that 8.2 = 7.4 = 1.0, a parcel of Venusian atmosphere compressed from 52 km to the surface is picking up 53 K in temperature you have not accounted for.

      Radiative forcing is not required to explain the temperature profile of Venus.

      Pressure gradient explains much of the lapse rate, but not all. The absolute temperatures involved are quite independent of gravity. Relative proximity to the Sun doesn't do it either. Assuming for a moment that Venus had a more terrestrial albedo of 0.3, Venus' blackbody temperature would be 299.3 K instead of 184.0 K, compared to 254.0 K for Earth, a difference of about 45 K.

      Delete
    3. "On that basis alone, Venus' atmosphere has no business being 310 K at 53 km, which is below the upper sulphuric acid cloud deck responsible for its high albedo."

      I don't follow. What should Venus' temperature be at 53 km?

      The ideal gas law applies to ideal gases and predicts temperature as a function of pressure and density. Their change with respect to altitude determines the temperature profile of the atmosphere. Compared to the theoretical difference on Earth, the 53 K is not so bad. It is true that a lapse rate doesn't provide enough info to predict a surface temperature. You need the radiation at a certain height. What temperature profile would a purely radiative calculation come up with based on the actual albedo, not your assumed 0.3?

      Delete
    4. I don't follow. What should Venus' temperature be at 53 km?

      On the order of the 184.0 K blackbody temperature cited above -- which is estimated from the S-B equation assuming albedo of 0.9, solar constant of 2601.3/4 and emissivity at unity. Strictly a zeroth-order approximation.

      The ideal gas law applies to ideal gases and predicts temperature as a function of pressure and density.

      No, it predicts change in temperature as a function of change in pressure. When you inflate a tire, its temperature surely rises. When you stop pumping, its temperature returns to ambient over time as the heat imparted by the work done by compressor dissipates.

      Delete
    5. No, it predicts change in temperature as a function of change in pressure. When you inflate a tire, its temperature surely rises. When you stop pumping, its temperature returns to ambient over time as the heat imparted by the work done by compressor dissipates.

      Indeed it does. But Chic - like 'Steven Goddard' does not appear to understand this.

      IMO, Chic is actually a Sky Dragon.

      For this subthread:

      http://scienceofdoom.com/2010/06/12/venusian-mysteries/

      And:

      http://scienceofdoom.com/2010/06/22/venusian-mysteries-part-two/

      Delete
    6. BBD,

      The one "Slayerish" thing he's written recently is pointing out that LW flux is typically a net loss at any locale and level of atmosphere. Obviously net LW could not be positive (toward the surface) for any extended period of time, as that would imply that it's an energy source. I think he understands the argument that adding CO2 (or any other LW-active species) impedes rate of loss until absorbed solar energy warms things up to restore radiative equilibrium, but he just doesn't believe it's a non-negligible effect because ... saturation, lapse rate dominance, etc.

      Just when I think he's about to see the light, he ... lapses ... back into some view or other he toted into this discussion. It can be very frustrating.

      I've been cribbing from SoD posts in my latest efforts, I should probably throw him some credit for his excellent work.

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    7. “I think he understands the argument that adding CO2 (or any other LW-active species) impedes rate of loss until absorbed solar energy warms things up to restore radiative equilibrium, but he just doesn't believe it's a non-negligible effect because ... saturation, lapse rate dominance, etc.”

      That’s a chicken vs. egg which came first way of saying it, although I have no idea what you mean by a non-negligible effect.

      “Just when I think he's about to see the light, he ... lapses ... back into some view or other he toted into this discussion. It can be very frustrating.”

      A bit patronizing, but I’ll overlook it.

      From above: I made a mistake with my calculation of the lapse rate for Venus based on –g/Cp. The 8.86 for g is correct, but Cp is not 1.2 other than at the surface. Cp varies with pressure. At 50 km, Cp for CO2 is only 0.9. At 25 km, the heat capacity of Venus is 1.05 and that makes the theoretically calculated value of the lapse rate, 8.4 K/km, exactly equal to its measured value at the same altitude. Unlike Earth, there isn’t much diurnal temperature variation or water evaporation to cause the lapse rate to deviate much from the theoretical value due to convection.

      “What should Venus' temperature be at 53 km?”
      “On the order of the 184.0 K blackbody temperature cited above.”

      The black body temperature doesn’t determine the effective altitude for balancing radiation flux. I think you just made that up, Brandon. The altitude that corresponds to 184K on Venus is between 70 and 84 km depending on whether your black body temperature comes from SOD, ATTP, or NASA.

      I have more to say on this below.

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    8. Chic,

      That’s a chicken vs. egg which came first way of saying it, although I have no idea what you mean by a non-negligible effect.

      Huh. Seems pretty direct to me. Sun is the main energy input. All else being equal (which it never is, but go with it), impede the rate of loss and the only possible response is accumulation of solar energy until radiative balance is restored. That IS how the "greenhouse" analogy is apt even though the loss rate mechanism differs.

      A bit patronizing, but I’ll overlook it.

      Wasn't meant to be, but it is the truth as I see it. I come from a long line of arrogant know-it-alls, you'd not be the first to bristle at it.

      At 25 km, the heat capacity of Venus is 1.05 and that makes the theoretically calculated value of the lapse rate, 8.4 K/km, exactly equal to its measured value at the same altitude.

      I'll add that to my list of things to read up on. I believe that you are correct.

      Unlike Earth, there isn’t much diurnal temperature variation or water evaporation to cause the lapse rate to deviate much from the theoretical value due to convection.

      That makes quite a bit of sense.

      The black body temperature doesn’t determine the effective altitude for balancing radiation flux. I think you just made that up, Brandon. The altitude that corresponds to 184K on Venus is between 70 and 84 km depending on whether your black body temperature comes from SOD, ATTP, or NASA.

      Perhaps you misunderstood the argument, but I didn't make it up. It comes from a RealClimate post which ATTP also covered:

      "The depth in the atmosphere from which the earth’s heat loss to space takes place is often referred to as the emission height. For simplicity, we can assume that the emission height is where the temperature is 254K in order for the associated black body radiation to match the incoming flow of energy from the sun."

      I have more to say on this below.

      Ok, I'll hold short here.

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  4. Part II:

    Aside from the inherent problem of oversimplification, the energy diagrams suffer from their inability to account for the effects of a rotating Earth.

    The diagrams don't depict the diurnal cycle, however the analyses behind the calculated means consider it. For example, the supplemental for Stephens et al. (2012) notes that several of the gridded observational datasets used were at 6-hr or better (e.g., 3-hr) temporal resolution. Same goes for the radiative transfer model and AOGCM integrations considered for comparison. Intuitively, observational data at hourly or sub-hourly temporal resolution seems optimal; however, it's not clear to me that such high resolution data would overcome the high uncertainty inherent in the measurements themselves.

    I don't consider it a flaw in the analysis that the pretty pictures given in these studies summarize the results at such a high-level -- certainly not a fatal one.

    On average, all the energy that enters the troposphere, either LW from the surface below or direct SW from the Sun, exits at the end of each diurnal cycle. If not, then global warming or cooling will occur in the long run.

    Emphasis mine. Yes, the budget cartoons show the average fluxes over a decade (or longer). This fits my understanding of what climatologists mean when they invoke the concept of a steady-state equilibrium state. On an instantaneous basis, the real system is never in equilibrium and never will be -- fluxes vary by latitude, season and hour of day. A robust analysis should take all those things into consideration, and my reading of literature is that these efforts have improved since, say, Kiehl and Trenberth (1997), Earth’s Annual Global Mean Energy Budget.

    In sum, I believe that energy budgets are estimated to the best of our present capabilities using multiple observational data sources combined with multiple physical models, with ongoing efforts to improve both observation and modelling.

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    1. I don’t object to energy budget diagrams per se, only that there is so much they don’t say.

      “On an instantaneous basis, the real system is never in equilibrium and never will be -- fluxes vary by latitude, season and hour of day.”

      The climate will never be in equilibrium on any time frame. That suggests that energy budget variability may never improve no matter how good observation and modeling become. In any case, energy budget analysis doesn’t explain what causes the changes in the planet’s temperatures.

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    2. Sufficiently accurate observation over long periods of time should be able to establish trends. Climate always comes down to multi-decadal trends.

      Delete
  5. Part III:

    The upward and downward radiative energy flows illustrated in the Wu and Liu (2010) diagram are unreal, because convection is ignored.

    Agreed. I only refer to that paper as a way to visualize the principle of atmospheric radiative forcing as a function of optical depth and altitude. The authors themselves justify the simplification thus: The philosophy for choosing such an idealized Earth system is that it retains enough physics and can still be described by a simple one-dimensional vertical climate model to allow analytical evaluation of the vertical profiles of temperature, radiation energy and entropy fluxes.

    It's beyond my limited understanding to further describe the utility their simplified 1D model has for evaluating more complex models which do take other relevant fluxes into account.

    While including mathematical equations that account for convection is currently beyond my ability, I diagrammed conceptually in the Figure above what the energy fluxes would be if my understanding of the atmosphere is correct.

    That is a very interesting plot, I thank you for sharing it and the formulae used to generate it. I have been chipping away at my own 1D model with the aim of reproducing more realistic temperature profiles as shown in various "standard atmospheres" with limited success, your contribution here may be helpful in getting me unstuck. I'll review it and let you know what shakes out.

    But at altitudes close to the surface, the greater density means that upward and downward absorptions will be essentially equal.

    I don't think that net up/down absorption is strictly, or even mainly, a function of density gradient, but rather a function of:

    1) Relative proximity to the surface/TOA.
    2) Tropospheric lapse rate (layers below are generally warmer than layers above).
    3) Pressure broadening (absorption bands get wider as pressure increases).

    I have fiddled with a free version of the MODTRAN radiative transfer code available from U. of Chicago, which is a line-by-line method that takes pressure broadening into account for a number of IR-active species in addition to CO2. In addition to a single integrated flux value, detailed output by frequency/wavelength/wavenumber is available at any altitude, looking up or down, as one wishes.

    I think it's a very accessible and powerful investigative tool for we lay hobbyists and researchers. If you were not already aware of it, I urge you to spend some time playing with it and comparing its results against your own calculations.

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    1. “I don't think that net up/down absorption is strictly, or even mainly, a function of density gradient…”

      I don’t see what the lapse rate has to do with it, but pressure broadening could be. Density decreasing with altitude means the ratio of photons absorbed to emitted is much greater at the surface than higher up. Good idea to use MODTRAN.

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    2. I may be confused about what you meant by "upward and downward absorptions will be essentially equal". More photons are going to be coming from the direction where things are warmer.

      I'm about to update the head post with a plot of MODTRAN flux profiles up to 30 km for clear sky tropics with CO2 at 400 ppmv.

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    3. "More photons are going to be coming from the direction where things are warmer."

      That's another way to look at it. Close to the surface, the mean path length for a photon to get reabsorbed is way short compared to farther up in the atmosphere. The temperature difference is likewise small between those distances at the surface compared to higher up.

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    4. That ever shorter path length as density of absorbing species increases is why the effect does not saturate.

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    5. That's backwards. Transmittance is 100% at infinite dilution and practically zero at the surface.

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    6. Wellllll .... since transmittance is how radiation ultimately escapes the system ....

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  6. Part IV:

    The lapse rate in my Figure was calculated using the Stephan-Boltzmann constant to convert the temperature at each altitude to a W/m2 value.

    I've used a similar approach in my own simple modelling exercises and think it's a sound approach to get reasonable ballpark estimates for purposes of this discussion. Again, comparison to something like MODTRAN output might be an illustrative comparison because black/gray body calcs are one simplification that introduce non-negligible divergence from calculations using wavelength-specific emissivies.

    While a certain critical mass of IR active gases are required to maintain an atmosphere with a moderate range of temperatures, I contend that further increases in CO2 will not increase global temperatures substantially. Any actual effect cannot be detected amidst the myriad of natural factors also in play.

    Difficult does not mean impossible, uncertain does not mean completely wrong. Appealing to either of these tends to undercut your own assertions for what actually occurs in the real system.

    I suspect that discrepancies between climate models and satellite temperature observations may be due to the models attributing too much influence from CO2, water vapor, and other IR active gases. This blog post addresses this possibility for model error:

    Pielke's post is rather short; as I read it his main argument is that Fu (2011) "refutes" Thorne (2010) and "ignores" Christy (2010) (in which he is a co-author) and Randall (2008) -- in sum, the CMIP3 AOGCMs used in AR4 exhibit "a fundamental disagreement between the model predictions and the real world observations." He offers essentially zero explanation for why. It's basically model-bashing of the sort that I don't think constitutes interesting or useful criticism.

    Although the emission is equally likely to go up or down, the net radiation will be up because more radiation comes up from the denser atmosphere below than comes down from above. So there is no justification for a tropospheric hot spot.

    You're invoking the wrong mechanism used to predict the tropospheric hot spot. This SkS post is a useful primer.

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  7. “Difficult does not mean impossible, uncertain does not mean completely wrong. Appealing to either of these tends to undercut your own assertions for what actually occurs in the real system.”

    I’m not appealing to either. In fact, I’m pursuing evidence for my position despite the difficulty and uncertainty you seem willing to accept.

    “He offers essentially zero explanation for why. It's basically model-bashing of the sort that I don't think constitutes interesting or useful criticism.”

    I didn’t quote Pielke intending for there to be an explanation. I provided the explanation. In these ongoing discussions I plan to explore why the discrepancy that Pielke refers to exists. I was thinking you would be interested in the same goal.

    I don’t know why I invoked any mechanism for a hotspot, as I don’t understand it even after reading the SkS post. It basically says there IS an expectation of a tropospheric hotspot and then rationalizes why it’s not evident. Furthermore, I don’t see how the realization of a tropospheric hotspot could not be caused completely by natural causes, i.e. increased humidity due to a warmer planet.

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    1. I don't think of uncertainty as a reason to NOT act. In my mind, uncertainty is what bites us trying to predict what might happen for a given future emissions scenario -- it could be not as bad as the central estimate, it could be worse.

      Your approach is apparently different -- uncertainty means to you the effect "not definitively established". Not for the first time, I suggest that raises the question how it is you can be certain of your own beliefs, e.g., CO2's radiative effects being saturated, etc.

      I hold Pielke, Sr. to a standard based on his peer-reviewed primary literature. He has the training and intelligence to make better arguments than a boilerplate thrashing of GCMs.

      I understand that you provided an explanation. I'm not opposed to exploring it with you further, but I'd rather have that be a separate conversation which is why created another post dedicated to hot-running models. I'd like to keep this thread focused on working through theory.

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    2. Chic,

      I don’t know why I invoked any mechanism for a hotspot, as I don’t understand it even after reading the SkS post.

      Here's what you wrote: Although the emission is equally likely to go up or down, the net radiation will be up because more radiation comes up from the denser atmosphere below than comes down from above. So there is no justification for a tropospheric hot spot.

      The bolded bit is what I'm interpreting as the mechanism.

      It basically says there IS an expectation of a tropospheric hotspot and then rationalizes why it’s not evident.

      Yes, expectation is due to an increase to moist adiabatic lapse rate as you allude below.

      This image, far from "rationalizing" why it isn't evident has no fewer than six different observational series demonstrating its evolution over the interval 1979–2005.

      Furthermore, I don’t see how the realization of a tropospheric hotspot could not be caused completely by natural causes, i.e. increased humidity due to a warmer planet.

      For good reason: natural causes, e.g. an increase in solar output, would also be expected to cause an increase in tropical tropospheric warming in excess of warming rates at higher latitudes and lower altitudes. It's a myth that the tropospheric hotspot is an AGW "fingerprint". It isn't, and the IPCC are very clear that it is not. Those who perpetuate this strawman are apparently immune to correction on this point ... something I find more than tiresome so I hope you will forgive me if I become somewhat grouchy "defending" a proposition which climate literature doesn't even make.

      This image from the same post shows the predicted changes above 300 mb for a 2% increase in solar output vs. a doubling of CO2. The AGW fingerprint is the pronounced stratospheric cooling above 100 mb which would NOT be expected to occur under an equivalent solar forcing increase.

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    3. The SkS image shows five tropospheric observations showing no warming trend greater than the surface (HadCRUT3). The models all expected greater warming. This is the non-evident hotspot I'm referring to. The fact that the models don't predict stratospheric cooling for a 2% increase in solar output means we can rule out a 2% increase in solar output if we didn't already know that didn't happen. The failure of no greater warming in the troposphere compared to the surface is what the SkS post is rationalizing. There is no AGW fingerprint evidence there. Stratospheric cooling may be a natural response to surface and tropospheric warming whatever the cause.

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    4. This is why I get frustrated appealing to observation in these discussions. Are you sure you're not rationalizing? :)

      It may not be fruitful to continue this line of argument but I'll try one more time. The radiosonde data show greater tropospheric warming and stratospheric cooling relative to themselves, both of which are consistent with elevated CO2 and other IR-active species in the atmosphere. That the indicated rates don't agree with each other or the HADCRUT4 surface trend is unsurprising, we know that structural uncertainties and inhomgenaities exist in all observational datasets, and that what we're measuring is a dynamic, noisy system. That all said, I find the broad agreement in the shapes of those trend profiles compelling evidence that the real system is behaving according to theory which was established well before it was actually seen in empirical data.

      That "the models" run hotter than observation is not in dispute as far as I'm concerned, that's also a topic which has its own article here, I'm be happy to take that up with you there.

      Stratospheric cooling really ought not be controversial in my view -- what else would we expect the system to do when its ability to dump more radiation into space is increased? Appealing to other possibilities isn't satisfying to me without a description of the mechanism. Otherwise, it looks to me like nothing more than a pro forma rejection of the obvious ... otherwise known as rationalization. Just sayin'.

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    5. At ease, Brandon. I'm not accusing you of rationalization and I very well could be rationalizing myself. I admit confirmation bias, the flip-side of which is resistance to alternative points of view. I want to understand the hotspot/fingerprint issues, but I'm not yet familiar enough with it.

      I agree with you that it may not be fruitful to continue discussing the hotspot/fingerprint issue. Until I know what the models are trying to do, I'll be suspicious of any correlation let alone models that run hot. I will organize some tropospheric profile data and comment about it on your "All models run hot" post.

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    6. Thanks Chic, I will enhance my calm. I would also do well to not write posts when I first wake up. I'm playing with MODTRAN at the moment, which is quite enjoyable. By the end of the day I should be able to post some wavelength-specific plots re: your argument below about absorption in the "wings" vs in the stronger 15 micron band.

      Delete
  8. It looks like the difference between ULWR and DLWR is 80 W/m2 on the MODTRAN flux profile plot. Maybe MODTRAN already compensates for the 40 W/m2 atmospheric window?

    "Although the emission is equally likely to go up or down, the net radiation will be up because more radiation comes up from the denser atmosphere below than comes down from above."

    I don't know how to say that any better. It is theoretically true, even at the surface, although the difference is infinitesimal. At the tropopause, almost all the LW radiation is up regardless of CO2 or any other gas concentration. This is indisputable as all these plots are showing. The question is what effect an increase in CO2 will have on the net LW radiation. My view is that CO2 will have no more effect because all the radiation capable of being absorbed by CO2 is absorbed at the surface. You can say there is more absorption available in the wings of the band, but that too will be thermalized by the bulk air. This is due to the greater density which favors absorption over emission. It is a different situation at the tropopause. The air is so thin that emissions predominate. And the emissions from below outnumber those from above making the net Lw radiation almost completely upward. Does a greater CO2 concentration reduce the net radiation? I don't see how. We'll have to see what MODTRAN says.

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    1. My view is that CO2 will have no more effect because all the radiation capable of being absorbed by CO2 is absorbed at the surface.

      Then explain the PETM.

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    2. At this point I can't give you a straight answer. Based on the reported large swings of CO2 and temperatures in the distance past relative to the instrumental record, I suspect alternative explanations for the PETM are possible. I am more confident it would be difficult to convince you of the validity of any alternative explanation. I prefer to concentrate on mathematical and physics-based models that would verify how much of an effect increasing CO2 could have on global temperatures. I'll continue to discuss that here, as long as Brandon reciprocates.

      Delete
    3. Chic,

      It looks like the difference between ULWR and DLWR is 80 W/m2 on the MODTRAN flux profile plot.

      Yes. On par with 63 W/m^2 in the K&T energy budget cartoon.

      Maybe MODTRAN already compensates for the 40 W/m2 atmospheric window?

      Not explicitly, but yes it does account for the fact that those regions have few LW emitters/absorbers in those bands at any level of atmosphere in clear sky conditions. You can throw in clouds and watch the atmospheric windows disappear.

      The apparent 33% error is probably due to me using the tropical standard atmosphere profile in my MODTRAN runs, which is significantly warmer than the global average represented in the various published energy budgets.

      "Although the emission is equally likely to go up or down, the net radiation will be up because more radiation comes up from the denser atmosphere below than comes down from above."

      I don't know how to say that any better. It is theoretically true, even at the surface, although the difference is infinitesimal.


      I've mentioned before that the key thing is how far the average photon goes up or down before being absorbed again and thermalized. At any given layer of atmosphere, the difference IS infintessimally small, but there are effectively an infinite number of layers in the atmosphere. MODTRAN is but one model which integrates those results, which are a non-neglibile difference between net LW flux at the surface and net LW flux at altitude. If lapse rate were the primary mechanism of higher absolute temps, I submit that we wouldn't see that difference.

      At the tropopause, almost all the LW radiation is up regardless of CO2 or any other gas concentration. This is indisputable as all these plots are showing.

      I have never argued otherwise, except maybe in cases of inversions. If I have argued otherwise that you recall, I should be taken out back and shot because me thinking such a thing, writing it and not remembering it is a sure sign that I've lost my last marble.

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    4. Chic part II,

      My view is that CO2 will have no more effect because all the radiation capable of being absorbed by CO2 is absorbed at the surface.

      We've been over this before; I'll try again. I'll go with K&T's energy budget b/c I know those numbers best. Surface emits 396 W/m^2. 40 of it goes out the window. The layer of atmosphere just above the surface gives back 333. 333 / 396 = 0.84. So, at the surface, the atmosphere gives back on the order of 84% of the LW it absorbs to the surface, having irretrievably lost 10% to the atmospheric window. The difference is 6%, which corresponds to a figure I've previously cited: that about 6% of collisions cause CO2 to burp out a photon. That may be coincidence (I didn't realize the sameness until having done the maths just now) but I think that may very well be according to expectation.

      Short story long, that process occurs at EVERY level of atmosphere. Emitters cough up photons and get some portion of them back from all directions. There is no radiative saturation as you argue it because the surface is not the only absorber/emitter to take into account.

      You can say there is more absorption available in the wings of the band, but that too will be thermalized by the bulk air.

      Well yes, thermalization -- especially to non-radiative species by kinetc transfer -- is a BIG part of the mechanism which "traps" the heat.

      This is due to the greater density which favors absorption over emission. It is a different situation at the tropopause. The air is so thin that emissions predominate.

      That makes sense to me, I don't know if it's strictly valid. If true, you seem to be making my case for me: thermalization (warming) dominates at lower altitudes and emission (cooling) dominates at higher altitudes.

      And the emissions from below outnumber those from above making the net Lw radiation almost completely upward.

      Again, nobody I know of that I trust on this stuff would ever say otherwise. CO2 does not add energy to the system. Like anything else, it redistributes it, and half of the time that direction is downward -- which means whatever lower layer catches it has to get rid of it again ... and except for the very near surface, half the time THAT's going to be in the down direction as well.

      Does a greater CO2 concentration reduce the net radiation? I don't see how. We'll have to see what MODTRAN says.

      1) I presume you mean outbound LW. Yes, and this is key, only until a new (higher) equilibrium temperature is reached and outgoing LW once again equals incoming flux (both SW and LW).

      2) Argghhh!!!

      3) After three days of promising some MODTRAN plots, I have finally posted some in a dedicated article. It's a bit long, could stand some editing, but it's finally up. More to come as there are other "experiments" I've done but not written up, and more I want to do. I'll be happy to take requests.

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    5. “I've mentioned before that the key thing is how far the average photon goes up or down before being absorbed again and thermalized. At any given layer of atmosphere, the difference IS infintessimally small, but there are effectively an infinite number of layers in the atmosphere. MODTRAN is but one model which integrates those results, which are a non-neglibile difference between net LW flux at the surface and net LW flux at altitude.”

      Count your marbles. Anywhere near the surface, the average path length travelled by an emitted photon is short before being absorbed again. Also, it is many times more likely that an excited molecule will lose its energy by collision not by emission. Therefore, in those many, but not infinite, layers near the surface the up and down LW difference is extremely small, if you don’t count the LW bands of the atmospheric window. Gradually the average path length before absorption or collision increases and the up/down difference increases with altitude until at the tropopause, nearly all LW is up. This is because of the density difference between the surface and the tropopause. Above the tropopause, the density is too thin for significant absorption and re-emission downward. MODTRAN should demonstrate this nicely for us.

      “If lapse rate were the primary mechanism of higher absolute temps, I submit that we wouldn't see that difference.”

      If you got that from me, forgetaboutit. There is a theoretical lapse rate that would apply in the event the atmosphere was an inert ideal gas. But we have IR absorbing gases that distort from this theoretical value when there is energy input like the sun coming up every day. I suppose you could think of an absolute temperature as being the average surface temperature, if nothing ever changes. But we do have changes, both natural and man-caused. Your mission Brandon, should you decide to accept it, is to prove that CO2 has the potential to affect the average global temperature any more than the present value.

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    6. Your mission Brandon, should you decide to accept it, is to prove that CO2 has the potential to affect the average global temperature any more than the present value.

      Been done. The PETM.

      The problem is that you denied the evidence then tried to make it seem as if it was *me* who was being intransigent:

      I am more confident it would be difficult to convince you of the validity of any alternative explanation.

      I have to say, I did not appreciate that little twisting of the facts, Chic.

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    7. As for all the obfuscation about the GHE, don't see the point of any of it. Additional CO2 raises the altitude of effective emission. It gets colder at altitude, so the whole troposphere needs to warm in order to maintain radiative balance at TOA.

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    8. We cross-posted, is that the right expression?

      “The difference is 6%, which corresponds to a figure I've previously cited: that about 6% of collisions cause CO2 to burp out a photon.”

      I seem to remember you agreeing that 99.9999% of the LW from the surface is absorbed and only the other fractional % emitted. Nevertheless, even if 6% of collisions produced emissions, those photons would go hardly anywhere before being absorbed again. That is what saturation means.

      “Well yes, thermalization -- especially to non-radiative species by kinetc transfer -- is a BIG part of the mechanism which "traps" the heat.”

      Not fond of the trapping-the-heat AGW talking point. Convection moves any absorbed radiation that isn’t emitted. You can say temporarily delayed, but it won’t remain delayed longer than 24 hours.

      1) Yes, I mean outbound, but it applies to all levels of the atmosphere because there is nothing to prevent a day’s energy to escape at night.
      2) ????????????
      3) Good! I'll have a look, but later.

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    9. BBD,

      You seem to have nothing but AGW talking points and PETM.

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    10. but it won’t remain delayed longer than 24 hours.

      Ocean.

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    11. You seem to have nothing but AGW talking points and PETM.

      That CO2 raises the height of effective emission is not an 'AGW talking point', Chic. But your denialism is noted.

      The PETM is evidence that you are wrong and your refusal to accept that this is what it is is denialism and is duly noted.

      You are refusing to accept the reality of this situation which is that you should at this point be saying 'I know I have misunderstood this and I need to work out how'. Not 'CO2 isn't an efficacious forcing and you (everybody) is wrong'.

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    12. Chic, have you ever read this essay by Ray Pierrehumbert on infra red radiation and planetary temperature?

      Might be useful in filling in the gaps.

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    13. There's nothing new there. Troll somewhere else. Oh, and calling people deniers is childish.

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    14. Troll somewhere else. Oh, and calling people deniers is childish.

      In your case, given your absolute resistance to correction*, it is accurate.

      And there is a term 'tone trolling'. Have you come across it? That also applies here.


      * "There's nothing new there"; denial that the PETM invalidates your position; refusal to read SOD links about Venus etc)

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    15. Chic,

      Quick hit and I shall retire for the evening as it is WAAYY past my bedtime:

      You can say temporarily delayed, but it won’t remain delayed longer than 24 hours.

      24 hours is an aeon for photons. It's only 5 light hours to Pluto.

      Look at it another way. If we could prevent 94% of LW photons from exiting the system for 24 hours, it would gain 0.94 * 239 J s-1 m-2 * 86,400 s * 5.10E14 m2 = 9.90E+21 J. Which is enough energy to increase the temperature of the atmosphere 0.52 K. Or, recall from previous discussions that the upper 2 km of oceans have been gaining on the order of 5.47E21 J/yr since the mid-1950s, so a 24 hour delay on all LW photons' exit visas would amount to 2 years of OHC increase down to 2,000 m.

      Around X-mas time I had a third way to go at this -- inspired by something someone said on WUWT last year -- along the lines of how long would we have to delay all exiting photons to generate a 1 W/m^2 flux imbalance. It was crystal clear in my head, but when I tried to run the numbers just now my math blew up. I'll try it tomorrow with a fresher brain ... it's strictly a curiosity number but sort of a fun one.

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    16. BBD,

      Ocean.

      Damn, good answer. The ultimate greenhouse, innit.

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    17. Gents, by 24 hours I meant before the sun rises. Any energy delayed in the air or ocean has plenty of time to leave the system.

      Try this analogy. A capacitor stores electrical charge. When a voltage is applied to a circuit with a capacitor, it gets charged with a certain number of charges analogous to photons. If you increase the size of the capacitor, it will take longer to discharge the capacitor. Doubling the size of a capacitor might increase the discharge time by a few percent. That would be analogous to an hour delay of radiation.

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    18. Conceptually you've lost me there, Chic. The sun is *always* rising (and setting) so the diurnal cycle is averaged out. Atmospheric and ocean heat transport combine with planetary rotation to make it an irrelevance.

      >90% of the energy from DSW ends up in the top 100m of the ocean, from which it cannot immediately escape.

      The (slight) tropospheric warming actually impedes the release of energy from the upper ocean layer and so there it begins to accumulate. This is the 'capacitor' that drives global warming.

      Delete
    19. Thank you for that reasonable retort.

      I’m just saying radiation moves too fast to hang around just because one day gets an extra dose of sunlight. If today is especially hot, that doesn’t mean tomorrow will be hotter. SW is another story, exactly because it can penetrate so deep in the ocean. But that only underscores how unlikely the lower energy LW is responsible for any net accumulative change in global temperatures over long time periods. How do you measure the small fluctuations in daily tropospheric warming and cooling averaged over the whole planet? That is why I am investigating the radiative convective models to justify the potential for CO2 to have any cumulative effect.

      Delete
    20. How about picturing the Earth looking down from space, viewed in IR. It's a slightly fuzzy ball. Zoom in and the fuzziness is the altitude of effective emission. Increase the atmospheric concentration of an IR absorber like CO2 and it gets fuzzier (more opaque) still. It is impossible for this not to raise the altitude of effective emission. Yes?

      But as the altitude of effective emission rises, temperature at altitude falls and this begins to inhibit the radiative transfer of energy to space. Yes?

      So, inevitably, an energy imbalance piles up in the climate system until the troposphere is warm enough for equilibrium with solar flux at TOA to be restored.

      Delete
    21. Chic,

      The capacitor analogy works for me and is relevant to my understanding that nighttime temps rise faster in a warming regime than daytime temps. Additional LW-active species reduce the discharge rate 24/7/365, but more ... effectively ... at night.

      This wants a physical explanation, for which I will need to do some research. IIRC from previous readings, one explanation is that during daytime solar heating raises temperatures such that outbound LW is better able to push against the resistance -- or back pressure if you will -- of downwelling LW from the atmosphere such that more upwelling LW is able to "leak" around the edges of the near-surface absorption bands. It had not previously occurred to me that this is something MODTRAN may be able to illustrate by manually varying surface temperature on a reasonable simulated 24-hour temperature cycle, so I will add it to my list of experiments.

      Another possible explanation -- and here I'm doing more synthesis than recollection -- is that convection is greater (and deeper) during the day than at night, thus more effective at carrying surface heat to altitude where radiative cooling is more efficacious. Contrast nighttime when inversions are more likely to form. I bet you weren't expecting me to come up with that one.

      As MODTRAN doesn't do convection, I won't be able to test it that way.

      I have begun responses to some of your other recent points, but given the amount of homework you have assigned me I think it better for me to focus on reading, thinking and calculating for the next several days. I won't go totally dark. As well, my main priority for today is to write up the second planned post in the MODTRAN series which I hope to push out before I retire tonight.

      Regards.

      Delete
    22. BBD,

      I am enjoying your comments here, especially your more fully developed arguments and references which I'm finding quite helpful. More of that please, as you have time and willingness to do so of course.

      Cheers.

      Delete
    23. BBD,

      “It is impossible for this not to raise the altitude of effective emission. Yes?”

      No. I believe this is all supposition. Are you aware of anyone actually measuring a raise in the altitude of effective emission?

      The atmosphere is not a diagram. It is a dynamic system that obeys the laws of physics, thermodynamics especially. Except that radiation which goes through the atmospheric window, essentially all the rest is absorbed within meters of the surface. Convection takes over and dominates energy through the atmosphere. It’s as likely as not that more CO2 will facilitate emission to space.

      Delete
    24. Brandon,

      “Another possible explanation -- and here I'm doing more synthesis than recollection -- is that convection is greater (and deeper) during the day than at night, thus more effective at carrying surface heat to altitude where radiative cooling is more efficacious.”

      Bingo. I like that explanation much better.

      “I bet you weren't expecting me to come up with that one.”

      A little surprised, but don’t sell yourself short.

      “As MODTRAN doesn't do convection, I won't be able to test it that way.”

      I was wondering about that.

      Delete
    25. No. I believe this is all supposition. Are you aware of anyone actually measuring a raise in the altitude of effective emission?

      Come on, Chic. THINK. How could more CO2 *not* increase the altitude of effective emission (AEE from now on)?

      How?

      Describe the physical mechanism as I did above.

      Delete
    26. It’s as likely as not that more CO2 will facilitate emission to space.

      That is obviously unphysical nonsense.

      Delete
    27. This comment has been removed by the author.

      Delete
    28. “Describe the physical mechanism as I did above.”

      I’ve been doing that throughout this whole thread. If you think it is nonsense, then explain why. Why don’t you try repeating what I’ve been saying in your own words and I’ll tell you if you have it correct or not.

      Meanwhile, have you found where anyone has measured the AEE yet?

      Delete
    29. I’ve been doing that throughout this whole thread. If you think it is nonsense, then explain why.

      I did:

      Imagine the Earth looking down from space, viewed in IR. It's a slightly fuzzy ball. Zoom in and the fuzziness is the altitude of effective emission. Increase the atmospheric concentration of an IR absorber like CO2 and it gets fuzzier (more opaque) still. It is impossible for this not to raise the altitude of effective emission.

      But as the altitude of effective emission rises, temperature at altitude falls and this begins to inhibit the radiative transfer of energy to space.

      You have to explain why this is wrong in order to defend your position.

      Delete
    30. 1, 2, 3, 4…..10.

      I invited you to explain what my position is. You did not. Apparently you can’t. All you seem to be able to do is regurgitate AGW talking points. I’m still working on making my position more coherent, which may or may not explain why the AGW position is flawed. Meanwhile, find the evidence for an increase in the AEE reducing outgoing LW or go piss off somebody else.

      Delete
    31. Meanwhile, find the evidence for an increase in the AEE reducing outgoing LW or go piss off somebody else.

      You are being tedious, not me. Read, please.

      So, how does increasing the concentration of a LW absorber such as CO2 *not* raise the AEE?

      Just explain how and you will have advanced your position. Keep refusing and wriggling and hissing and it is clear that you are in trouble.

      So, explain. Or conceded that you have misunderstood the essence of the GHE.

      No observational evidence is necessary for this discussion. It is a straightforward matter of physics. It would be virtually impossible to provide evidence anyway, which is of course why you are asking for it. Anything to divert away from your failure to answer a simple conceptual question.

      Delete
    32. I invited you to explain what my position is. You did not. Apparently you can’t.

      It's *irrelevant* because you have a flawed conceptual understanding of the physics - which is why we are talking about the AEE. It's fundamental.

      Delete
  9. I suspect alternative explanations for the PETM are possible.

    That's not acceptable Chic.

    At this point the evidence that the PETM was GHG-forced is so strong as to be effectively conclusive. Trying to wave this away as you do is not an option.

    I prefer to concentrate on mathematical and physics-based models that would verify how much of an effect increasing CO2 could have on global temperatures.

    You aren't doing that. You are denying that there will be *any* significant effect:

    My view is that CO2 will have no more effect because all the radiation capable of being absorbed by CO2 is absorbed at the surface.

    And:

    Radiative forcing is not required to explain the temperature profile of Venus.

    And now you are denying the palaeoclimate evidence that shows unequivocally that CO2 is an efficacious climate forcing.

    ReplyDelete
  10. “When you inflate a tire, its temperature surely rises. When you stop pumping, its temperature returns to ambient over time as the heat imparted by the work done by compressor dissipates.”

    What is that supposed to mean? That the temperature of Venus isn’t a result of the pressure and density caused by gravity? IOW, you think that the temperature of the surface of Venus results totally from radiation and the pressure and density just happen to coincidentally satisfy PV=nRT?

    Let’s say the only information you have about the atmosphere and surface of Venus is the solar insolation of 2601 W/m2, albedo of 0.9, black body temperature of 184K at a height of 85 km or reasonable facsimiles. How would you know what the temperature is at any other altitude? Show me how you would calculate temperature profiles with radiative energy transfer equations.

    Using the same information, I could estimate the temperature within about 20%. Give me the temperature at 50 km and I could be within 1%. The papers below support my contention that radiative forcing is not required to explain the temperature profile of Venus. Earth is another story, mainly because convection has so much more influence.

    Nikolov and Zeller: http://wattsupwiththat.com/2011/12/29/unified-theory-of-climate/

    Hans Jelbring: http://ruby.fgcu.edu/courses/twimberley/EnviroPhilo/FunctionOfMass.pdf

    Robinson and Catling (2013) http://faculty.washington.edu/dcatling/Robinson2014_0.1bar_Tropopause.pdf

    William C. Gilbert: http://www.friendsofscience.org/assets/documents/Gilbert-Thermodyn%20surf%20temp%20&%20water%20vapour.pdf

    ReplyDelete
    Replies
    1. Jelbring. Nikolov & Zeller. Gilbert...

      A pattern emerges.

      Delete
    2. Chic

      What is that supposed to mean? That the temperature of Venus isn’t a result of the pressure and density caused by gravity? IOW, you think that the temperature of the surface of Venus results totally from radiation and the pressure and density just happen to coincidentally satisfy PV=nRT?

      You will find this interesting and illuminating.

      Delete
    3. Chic,

      What is that supposed to mean? That the temperature of Venus isn’t a result of the pressure and density caused by gravity?

      Just what it says. I defy you to predict the absolute temperature of a bicycle tyre inflated to 100 psi without knowing anything about ambient conditions or how much time has elapsed since it was inflated. You would have much better luck predicting temperature change as it's being inflated at "normal" rates b/c you could reasonably assume an adiabatic process. But you still wouldn't know the final absolute temperature without knowing the initial absolute temperature.

      IOW, you think that the temperature of the surface of Venus results totally from radiation and the pressure and density just happen to coincidentally satisfy PV=nRT?

      Chicken-egg problem it seems.

      No I don't think its coincidence because a similar thing happens on Earth. Review this plot from MODTRAN results posted above. Note how similar in slope the yellow and light blue curves are until 12 km when the LW gradient all but disappears and that lapse rate continues on until 16 km.

      I submit to you that without the LW gradient, convection would top out at a much lower altitude. As well, absolute temperatures would be much lower. This is something I can't test in MODTRAN because it doesn't do convection. On my long list of stuff to do is look at the R model from Benestad (2016) which we previously discussed over at ATTP's joint.

      I end somewhat randomly on this: I found this last night but haven't had time to dig into it: Stone and Carlson (1979), Atmospheric Lapse Rate Regimes and Their Parameterization. A bit dated, but I often like reading the classics.

      I really mean it this time ... I'm off to do some homework.

      Delete
    4. “I defy you to predict the absolute temperature of a bicycle tyre…”

      The atmosphere is not a tire. I suspect this comes from reading SOD posts. He’s smart, but not infallible. I think he is trying to justify the “CO2 causes global warming hypothesis” by claiming there is no alternative mechanism for a planet’s surface to be warmer than its black body temperature. The alternative mechanism is called the gravito-thermal effect and it naturally causes a temperature gradient when a volume of gases is subject to a pressure gradient.

      “No I don't think its coincidence because a similar thing happens on Earth.”

      What’s similar is that lapse rates can be predicted from thermodynamic principles to be g/Cp. Temperature is the result, not the cause of the gradient.

      Delete
    5. Chic,

      The atmosphere is not a tire. I suspect this comes from reading SOD posts.

      It comes from first-year chem and physics. Granted the atmosphere is a more complex system, but I don't believe that the operative principles are any different.

      The alternative mechanism is called the gravito-thermal effect and it naturally causes a temperature gradient when a volume of gases is subject to a pressure gradient.

      I'm not disputing that temperature changes as a function of pressure.

      What’s similar is that lapse rates can be predicted from thermodynamic principles to be g/Cp. Temperature is the result, not the cause of the gradient.

      Lapse rate is the first derivative of absolute temperature with respect to altitude. It says nothing about what the absolute temperature will be at any given altitude as a function of pressure, only what the change in temperature will be between two different pressure levels.

      Your argument, as stated, implies that the temperature of the surface of Earth, Venus, whatever planet, would be the same if occupied any orbit from Mercury to Oort Cloud.

      Delete
    6. I'm not disputing that temperature changes as a function of pressure.

      This is the nub.

      Now, Chic - address this:

      Your argument, as stated, implies that the temperature of the surface of Earth, Venus, whatever planet, would be the same if occupied any orbit from Mercury to Oort Cloud.

      Delete
    7. “Lapse rate is the first derivative of absolute temperature with respect to altitude. It says nothing about what the absolute temperature will be at any given altitude as a function of pressure, only what the change in temperature will be between two different pressure levels.”

      OK, fine. The lapse rate describes the change in temperature with respect to altitude theoretically. Of course, there are certain deviations, but holds reasonably well with constant composition and sufficient pressure. You are correct, it doesn’t give you the absolute temperature. Do you have an alternative mechanism or hypothesis that does? Let me know.

      “Your argument, as stated, implies that the temperature of the surface of Earth, Venus, whatever planet, would be the same if occupied any orbit from Mercury to Oort Cloud."

      No, where did you get that? Maybe I didn’t express my argument well enough.

      What I’m saying is that when the atmosphere is opaque, upward and downward LW radiation cancels out. The effective temperature of the planet will be at an altitude equivalent to where the opacity thins. This altitude (AAE) depends on how concentrated the IR active gases are. From that altitude down to the surface, the temperature profile will be controlled by the lapse rate, not by radiative factors.

      Here’s where it gets complicated and where I haven’t worked out the details. Increasing the fraction of the LW IR-active gases in an atmosphere affects the density at the AEE. I'm still thinking it through. Who knows, I may come up agreeing with conventional result, albeit a different mechanism.

      Delete
    8. Chic part I,

      The lapse rate describes the change in temperature with respect to altitude theoretically. Of course, there are certain deviations, but holds reasonably well with constant composition and sufficient pressure.

      This is progress. I'm going to go with you on the assumption of constant composition as a conceptual simplification: Cp is determined by the specific heat capacity of the mix of the individual constituent atmospheric components, yes?

      You are correct, it doesn’t give you the absolute temperature.

      And you are correct, I've been putting off fully accepting the obvious: the difference in temperature between surface and tropopause is mainly a function of Cp-determined lapse rate. I'm past due being absolutely clear on that point in this discussion.

      Do you have an alternative mechanism or hypothesis that does? Let me know.

      I do, but it's not fully formed yet as me thinking of the problem in these terms is requiring a not-insignificant reformatting of my brain. I see that as a good thing. I've already laid some of the groundwork if you care to take a peek.

      While I'm summoning the willpower to write the Part 2, I'd like to point out that we're in the same boat: we need to get to absolute temperature somehow before we can predict either or both absolute temperatures at either end of the convection cycle. On that note ...

      “Your argument, as stated, implies that the temperature of the surface of Earth, Venus, whatever planet, would be the same if occupied any orbit from Mercury to Oort Cloud."

      No, where did you get that? Maybe I didn’t express my argument well enough.


      Guilt by association, unfortunately. I've read the gravito-thermal effect argument various places elsewhere, and especially in the context of Venus, invoke that as the primary mechanism for why the surface is so hot.

      We both should now agree that if we were magically able to move Venus to the realm of Pluto's orbit, it would be much much cooler, yes? There's no getting around that one key parameter here is received solar flux, which diminishes as the inverse square of distance from a radiative energy source. It follows that planetary albedo is also a factor. Absolute temperature MUST be related to those factors at the very least. It's a question of where, why and how much.

      Delete
    9. Chic Part II,

      What I’m saying is that when the atmosphere is opaque, upward and downward LW radiation cancels out.

      Okayyy ... what happens in an optically transparent atmosphere? A gradient or no change? Why?

      The effective temperature of the planet will be at an altitude equivalent to where the opacity thins.

      Is this a stepwise function or continuous?

      This altitude (AAE) depends on how concentrated the IR active gases are.

      Well yes, that IS the argument BBD is invoking above, and one with which I am somewhat grudgingly coming around to adopting as an explanatory mechanism, not the emergent property as I've previously seen it.

      From that altitude down to the surface, the temperature profile will be controlled by the lapse rate, not by radiative factors.

      That would be 100% true if net LW was constant. But the fact that your own argument here prevails on AAE being set by opacity implies that it isn't. I'm pretty sure you won't see why; you're still apparently stuck thinking that LW from the surface is absorbed within the first few meters and effectively stays put until opacity at the tropopause is reduced to the point that it can escape.

      I've run out of ways to convince you that no physical mechanism known to me can explain such a thing, and that tried and trusted early 20th century radiative physics vehemently disagrees with it, to wit: Stefan-Boltzmann law of radiant power and Beer-Lambert law of radiative attenuation in an opaque medium.

      Here’s where it gets complicated and where I haven’t worked out the details.

      For me it has this weird quality of being very simple and obvious in my head, but fiendishly difficult to explain, and virtually impossible to "prove".

      Increasing the fraction of the LW IR-active gases in an atmosphere affects the density at the AEE.

      Everywhere. AEE is -- at the very least -- a function of opacity, pressure, AND temperature. Classic chicken-egg if one doesn't pick a suitable entrance point to the problem. About that ...

      I'm still thinking it through. Who knows, I may come up agreeing with conventional result, albeit a different mechanism.

      ... where I'm at right now is assuming the atmosphere is completely transparent to SW, so the only way the atmosphere receives any initial heat is due to contact with the surface.

      Delete
    10. Re: Part I,

      “Cp is determined by the specific heat capacity of the mix of the individual constituent atmospheric components, yes?”

      Yes. The exact value for a mixture would best be measured, but a reasonable estimate would be a proportional average. So increasing CO2 would raise the lapse rate. All things being equal, this should increase surface temperature slightly. The question is does convection let that happen? I don’t think so.

      “…the difference in temperature between surface and tropopause is mainly a function of Cp-determined lapse rate.”

      This is a crucial point. I think the lapse rate is the equilibrium condition that would remain if there were no more incoming sunlight.

      BTW, I read your very interesting post on Venus. You should note that Cp varies with both temperature and pressure, at least according to this website where I got my values: http://www.peacesoftware.de/einigewerte/co2_e.html

      “…we need to get to absolute temperature somehow before we can predict either or both absolute temperatures at either end of the convection cycle.”

      Good luck with that. I’m stuck. I’m one variable short of coming up with a solution. I can calculate the AAE If I know where the surface is, or I can calculate the surface temperature if I know the AAE. I have to have one or the other. Do you know if there is any way to determine the density or pressure of the surface from gravity, the size of the planet, and/or the composition of the atmosphere?

      “Absolute temperature MUST be related to [solar flux and albedo] at the very least. It's a question of where, why and how much.”

      Exactly. That combination gives you the effective temperature of the planet at some unknown altitude, Zeff. If you buy the gravito-thermal (lapse rate = L) principle, then Ts = Teff + L*Zeff.

      Delete
    11. Brandon G

      For me it has this weird quality of being very simple and obvious in my head, but fiendishly difficult to explain, and virtually impossible to "prove".

      Oh, the PETM and other Cenozoic hyperthermals prove that CO2 is an efficacious climate forcing. Which is why CB went directly into evidence denial mode when this was pointed out.

      Delete
    12. Re: Part II,

      “... what happens in an optically transparent atmosphere? A gradient or no change? Why?”

      This is a good question. To me an optically transparent atmosphere means the density of IR-active gases is too low at the surface to maintain a substantial amount of thermalization. The Teff would be at the surface and Ts = Teff, no lapse rate. Take Mars for example. But Mars is mostly CO2. What if Mars was 100 times denser with the same CO2 concentration? There might be a lapse rate, but it may have no effect on energy flux. Just guessing.

      “Is this a stepwise function or continuous?”

      Definitely not stepwise. The outgoing radiation will increase gradually at the altitude where the density gets into the critical range. Integration over the range would be required to be specific. I guess a model fit would accomplish the same thing.

      “Well yes, that IS the argument BBD is invoking above…”

      Very well could be, but he’s making it from an ‘I’m right, you’re wrong’ approach. I just want to get to the facts. Getting the math correct involves integration, not linear stick figure diagrams.

      “That would be 100% true if net LW was constant. But the fact that your own argument here prevails on AAE being set by opacity implies that it isn't."

      Not sure what you mean by the net LW being constant. The average in/out radiation is assumed constant. The AEE is the locus of where 100% control by convection transitions to 0% convection and 100% radiation.

      "I'm pretty sure you won't see why; you're still apparently stuck thinking that LW from the surface is absorbed within the first few meters and effectively stays put until opacity at the tropopause is reduced to the point that it can escape.”

      The LW doesn’t stay put at the surface. It is moved up by convection. Remember pretty much everyone agrees that all LW radiation from surface IS absorbed and thermalized within meters of the surface except the window fraction.

      “I've run out of ways to convince you….”

      I took me to end of second page searching google trying to find a source that you would trust, but gave up. Ed Caryl has an interesting article mentioning 95% absorption of CO2 within one meter. See http://notrickszone.com/2011/02/11/is-co2-warming-a-mirage/#sthash.MelapBED.dpbs . It goes to nearly 100% a few more meters up. MODTRAN should reveal this.

      “‘Increasing the fraction of the LW IR-active gases in an atmosphere affects the density at the AEE.’

      Everywhere.”

      Of course, everywhere. Another misstatement on my part. What I mean is the AEE is a function of the density of the IR-active gases. So if you replace some of the inactive gases with CO2, then the AEE (which is a function of IR-active density) must go up to compensate. However, this doesn’t mean the Teff goes up, because the Teff is constrained by the solar flux. If the AEE goes up, then the calculated Tsurf has to go up (assuming no change in lapse rate). But why? The Teff is still radiating the required LW to balance the incoming solar. The AGW rationale is when Tsurf increases, then the planet warms up. Can you see my dilemma? Won’t a warmer surface over-compensate?

      “AEE is -- at the very least -- a function of opacity, pressure, AND temperature.”

      Pressure broadening applies, but temperature is a result of pressure and density, not the cause of it.

      “... where I'm at right now is assuming the atmosphere is completely transparent to SW, so the only way the atmosphere receives any initial heat is due to contact with the surface.

      Is that so you can look at planets and moons from both opacity extremes? Good idea. Include atmospheres of different composition and mass, too. Great minds think alike, they say.

      Delete
    13. Very well could be, but he’s making it from an ‘I’m right, you’re wrong’ approach.

      Not at all. I invited you to think about the problem by visualising what the Earth's atmosphere looks like from space, viewed in IR. Fuzzy ball etc. Perhaps I didn't make the best job of it, so let me try again.

      If you increase the atmospheric concentration of an IR absorber like CO2, opacity increases and you can 'see' less deeply than before into the atmosphere. This *must* require the AEE to rise.

      As it does, the ambient temperature falls and pressure decreases, both progressively *reducing* the efficiency of radiation to space. So with solar flux constant, energy begins to accumulate in the climate system. When it has warmed up enough to counterbalance the inhibiting effect of the increased AEE, radiative equilibrium is restored.

      Maybe that is a bit clearer.

      Delete
    14. BBD,

      I personally have this pedantic aversion to the word "proof" in ANY non-trivial empirical science. I understand that the PETM is one piece of strong evidence supporting CO2's efficacious radiative forcing. There are others I know and understand better. It's the consilience of multiple line of evidence which I find convincing, but my own personal philosophy of science and belief is such that I don't even say to myself that the sum total of that evidence "proves" my beliefs correct -- my thing is that proof is the purview of deductive logics and maths, not inductive inference.

      I already know that I make little headway with Chic with evidence, and I'm pretty sure he already know it agitates me. Hence our mutual agreement to focus more on trying to walk through theory from first principles.

      Back to the PETM, you've already done me a big favour gathering references. I have skimmed them all and a lot of it has gone "whoosh". I have been wondering if you'd be willing to write an article-length summary for me to post here as a stand-alone article?

      Delete
    15. Brandon

      Well yes, that IS the argument BBD is invoking above, and one with which I am somewhat grudgingly coming around to adopting as an explanatory mechanism, not the emergent property as I've previously seen it.

      YMMV but the only way I can conceptualise the GHE is as described above, with the elevated AEE as the driver, not the consequence, of the GHE.

      A corollary of this was that I understood that all the rabbit-holing about convective processes in the troposphere was irrelevant. It's the troposphere. Stuff happens. Impose a radiative imbalance and it will get warmer.

      Delete
    16. Brandon

      We crossed -

      I personally have this pedantic aversion to the word "proof" in ANY non-trivial empirical science.

      Fair enough, I did hover over it at the time ;-). The thing is, absent *any* alternative explanation and given all the physicsy stuff about the GHE, I do actually think the PETM is dispositive. So sometimes I throw caution to the wind and just say it :-)

      I have been wondering if you'd be willing to write an article-length summary for me to post here as a stand-alone article?

      I'm flattered to be asked, and thank you, but to be honest I think there's enough good material out there already. Nothing I could do would improve on this, just as one example.

      All one needs to do is ask GHE sceptics how their hypotheses accommodate the PETM and point them at the link if they go 'whuh?'. Then ask again ;-)

      Delete
    17. Chic,

      BTW, I read your very interesting post on Venus. You should note that Cp varies with both temperature and pressure, at least according to this website where I got my values: http://www.peacesoftware.de/einigewerte/co2_e.html

      Thanks. I did note that Cp varies, wanted to keep it simple for the first pass at it. I had wondered where your numbers came from, appreciate the reference.

      Good luck with that. I’m stuck. I’m one variable short of coming up with a solution.

      I'm glad you see the problem here somewhat as I do, that's a good basis for mutual investigation. One reason I halted the Venus article where I did is because the next steps require me to dig into how I might reasonably concoct a simple model for convection. It will take some doing.

      I can calculate the AAE If I know where the surface is, or I can calculate the surface temperature if I know the AAE. I have to have one or the other. Do you know if there is any way to determine the density or pressure of the surface from gravity, the size of the planet, and/or the composition of the atmosphere?

      There's got to be one. You might start with the Wikipedia article on the Barometric Formula.

      You make other points above which I will get back to you on later if I don't cover them in Part 2 of the Venus problem, which is my main focus today.

      Delete
    18. BBD,

      We crossed -

      Alas. This is my bush, piss on your own, buddy. :)

      Fair enough, I did hover over it at the time ;-).

      I'm not surprised by that, we seem to share similar views about when it's appropriate to rigorously hold onself to agnosticism (I'm thinking of your response to hexadecimal gibberish the recent thread at the Rabett's spot. It improved my already good impression of how you approach empirically-derived belief.

      The thing is, absent *any* alternative explanation and given all the physicsy stuff about the GHE, I do actually think the PETM is dispositive. So sometimes I throw caution to the wind and just say it :-)

      I surely get that, I just don't share your confidence. But would like to, hence ...

      I'm flattered to be asked, and thank you, but to be honest I think there's enough good material out there already. Nothing I could do would improve on this, just as one example.

      Your first sentence is key to understanding my trepidation about transitioning from blog circuit commenter and shit-stirrer to blog author. I'm not only just aware that thus far I'm simply reinventing the wheel, I have a deep-seated fear that it's square -- nay, an irregular polygon -- instead of round. I'll not pressure you further than to say I wish you would consider it.

      Meanwhile, I'll read the link you provided and mull it over.

      All one needs to do is ask GHE sceptics how their hypotheses accommodate the PETM and point them at the link if they go 'whuh?'. Then ask again ;-)

      You're SUCH a troll.

      That's professional admiration, BTW. :D

      Cheers.

      Delete
    19. I'm not surprised by that, we seem to share similar views about when it's appropriate to rigorously hold onself to agnosticism (I'm thinking of your response to hexadecimal gibberish the recent thread at the Rabett's spot. It improved my already good impression of how you approach empirically-derived belief.

      Ouch.

      You're SUCH a troll.

      You are too kind ;-)

      Delete
    20. BBD,

      Why ouch? (OTOH, ironic juxtaposition noted and appreciated.)

      And whoops, we really did cross:

      YMMV but the only way I can conceptualise the GHE is as described above, with the elevated AEE as the driver, not the consequence, of the GHE.

      My mileage HAS varied. I'm on record elsewhere in fairly recent past opining that AEE as a driver is akin to magic ... words I'm increasingly aware I may need to eat. And gladly, because I (finally) begin to see the elegance of the argument.

      What's been unlocking it for me is thinking about convection in terms of the Carnot cycle. Moving AEE higher increases the distance between hot to cold reservoirs, and the ONLY way convection can lift a given air parcel to the height where efficient radiation to space can occur is if the hot reservoir gets hotter. The cold sink -- outer space -- is too big for Earth's puny contribution to have an effect, yes?

      A corollary of this was that I understood that all the rabbit-holing about convective processes in the troposphere was irrelevant. It's the troposphere. Stuff happens. Impose a radiative imbalance and it will get warmer.

      That's more my former way of seeing it, and I think it's still valid. The monkey-wrench was/IS Benestad (2016) which flatly states in the first sentence of the abstract: The popular picture of the greenhouse effect emphasises the radiation transfer but fails to explain the observed climate change. The bolded bit really pissed me off in a motivational way. The spelunking will continue until the dissonance goes away, irrelevancies and blind alleys be damned. Please do feel free to tell me if you think I'm on a wrong track, just be aware that I can be stubborn to a fault about accepting such assertions until I'm comfortable that the major moving parts add up to the the conclusion.

      As ever, the learning curve is steep, and sometimes slippery. Just how I like it.

      Delete
  11. http://www.nature.com/ngeo/journal/v7/n1/carousel/ngeo2020-f1.jpg

    This is a plot from Robinson and Catling (2013). Notice in addition to all the planets having a tropopause near 0.1 bar, those lapse rates appear to be quite similar. It will be interesting to compare dT/dz profiles.

    One more point before calling it a day. At the black body temperature for Venus, which is either 184K or 230K depending on the source, the atmospheric density is 3.5 g/m3 or 86 g/m3, respectively. Venus is 95% CO2, an almost all IR-active atmosphere. Earth is only 1-4% IR-active depending on humidity. At Earth’s black body temperature, the altitude is about 5km up where the density is about 736 g/m3, if my atmosphere calculator is correct. If you calculate an “effective density of IR-active molecules” in Earth’s atmosphere, at 5km it would contain between 7 and 30 g/m3 depending on humidity. This is right in between the “effective density of IR-active molecules” in Venus’ atmosphere in the 70 to 85 km range. My point is that surface temperature is a function of the lapse rate, the black body temperature, and the corresponding height of the atmosphere where the effective density of IR-active molecules will be in the range of 3 to 100 g/m3. Only large changes in concentrations of the IR active components of the atmosphere will change its temperature profile.

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  12. I just finished reading http://scienceofdoom.com/2010/06/12/venusian-mysteries/ where SOD references Bullock and Grinspoon’s effort to model the Venus atmosphere. I found the following sentence:

    “Convection was treated by taking the radiative equilibrium temperature profile and adjusting the lapse rate to be adiabatic wherever the radiative equilibrium lapse rate exceeded the adiabat (McKay et al. 1989).”

    This was unclear so I went to McKay et al. for an explanation, but it was pay-walled.

    I think they may have done what I did in my opening statement. What I said was “A lapse rate of 6.5 K/km was assumed. I used the shaping factors to bring the DLWR curve close the lapse rate curve. I justified this on the basis of the spectra of the atmosphere showing that temperatures of the atmosphere correspond to temperatures calculated from Planck’s equation.”

    If I am correct, using lapse rates to adjust radiative transfer equation calculations is basically curve fitting.

    BTW, rough calculations on data from Titan result in a calculated lapse rate of 1.35 compared to 1.0 from eye-balled data. The effective black body temperature calculated from 2.45 W/m2 is 81K, which is about what temperature Titan’s atmosphere is at 15 km up. Titan has 4.9% methane in its troposphere which corresponds to an effective IR-active density of 10 g/m3 at 15 km. Using a calculated value of 1.35 for the lapse rate gives Titan’s surface temperature as 101K. The actual lapse rate makes it 96K compared to a reported temperature of 94K.

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    Replies
    1. Chic,

      If I am correct, using lapse rates to adjust radiative transfer equation calculations is basically curve fitting.

      I haven't the bandwidth to dig into this at the moment, but consider the possibility of it being appropriate to constrain models to observation?

      Delete
    2. Tweaking your model with some physical property that correlates well with the lapse rate is one thing. Using the lapse rate to make your model correlate well is a whole other story.

      First, I need to check and make sure that is what they truly did. I may have misunderstood. Then again it might be the standard method. It seems vaguely familiar to what Manabe did in one of those classic radiative convective models.

      Delete
  13. Chic,

    Posting out of sequence b/c the scroll was getting onerous.

    This is a crucial point. I think the lapse rate is the equilibrium condition that would remain if there were no more incoming sunlight.

    That already happens ... only half the planet is sunlit at any given moment. Have we not already agreed that convection reduces at night?

    “Absolute temperature MUST be related to [solar flux and albedo] at the very least. It's a question of where, why and how much.”

    Exactly. That combination gives you the effective temperature of the planet at some unknown altitude, Zeff. If you buy the gravito-thermal (lapse rate = L) principle, then Ts = Teff + L*Zeff.


    I'd like to give Venus a rest for a moment and fill in the values for Earth:

    L = 9.8 K/km
    Teff = 254 K
    Zeff = 6.5 km

    Thus:

    Ts = 254 K + 9.8 K/km * 6.5 km = 317.7 K

    Which is wayyy too hot; the actual mean value is near 288 K. One major reason for the apparent discrepancy is that L = 9.8 K/km is the unsaturated (dry) adiabatic lapse rate. In the real Earth system, we need to consider the effect of water vapour on lapse rate, because the saturated (moist) adiabatic lapse rate can be significantly steeper. Which means (and this consistently breaks my brain) that it tends to reduce temperature change as a function of pressure. It's also much more highly variable with temperature. Around -25 C it has about the same slope as the dry lapse rate. At 15 C it's well here, a picture is worth a thousand words.

    As a consequence, the actual lapse rate tends to fall between the dry and moist adiabats. Once nice thing about Venus is that it's quite dry, and I've been assuming that we can safely ignore the difference. Not so on this planet.

    TL;DR: I don't dispute that lapse rate is important. At the same time, on Earth it's not a slam-dunk predictor of temperature change from tropopause to surface because water vapour is a wildcard that introduces a lot of potential slop into any analysis. Which presents a problem for both of us.

    ReplyDelete
    Replies
    1. “Ts = 254 K + 9.8 K/km * 6.5 km = 317.7 K”

      Here you’ve assumed AEE is 6.5 km. Where do you get that? If you knew 288K was Ts then Zeff would be 3 km. If you start with an observed 6.6 K/km lapse rate and assume Zeff = 5 km, then Ts = 288K exactly. What I’m getting from this is water vapor makes Earth an opaque atmosphere. Without it, the remaining IR-active gas is CO2 and its concentration is below the threshold range of 3 to 86 g/m3 which I calculated from Venus data. As a consequence, the Ts = Teff + Zeff * L calculation is not very useful other than to illustrate the importance of convection. A value of 9.8 for the lapse rate on Earth is useless, but works well for Venus where convection is minimal.

      If you don’t read the gravito-thermal papers, you either have to trust my interpretation or come to the same realization on your own. I suspect the latter based on your agreement that the lapse rate is an equilibrium condition that remains if there were no more incoming sunlight.

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    2. Chic,

      Here you’ve assumed AEE is 6.5 km. Where do you get that?

      Benestad (2016). I include the relevant excerpts in the Venus Part 2 article.

      If you knew 288K was Ts then Zeff would be 3 km.

      Here is how I figure it. Teff is 254 K. Zeff = 6.5 km implies an actual lapse rate of -5.23 K/km.

      If you start with an observed 6.6 K/km lapse rate and assume Zeff = 5 km, then Ts = 288K exactly.

      I get 262 K for 5 km altitude. Teff should be 254 K. 262 K comes from this file, which is the 1981-2010 monthly long term mean from the NCEP/NCAR Reanalysis Monthly Means and Other Derived Variables: Pressure Level web page.

      What I’m getting from this is water vapor makes Earth an opaque atmosphere.

      Yes.

      Without it, the remaining IR-active gas is CO2 and its concentration is below the threshold range of 3 to 86 g/m3 which I calculated from Venus data.

      I don't understand what you mean by threshold.

      As a consequence, the Ts = Teff + Zeff * L calculation is not very useful other than to illustrate the importance of convection.

      I think it's a good starting point from which to add/subtract other effects. I agree that it highlights the importance of convection.

      A value of 9.8 for the lapse rate on Earth is useless, but works well for Venus where convection is minimal.

      -10.4 K/km is more realistic for Venus. Since Cp varies with temperature and pressure as you have pointed out I need my analysis to reflect that, which I'll be doing whenever I get around to writing Part 3 of the Venus series. Tomorrow perhaps.

      Adiabatic lapse rate doesn't happen without convection.

      If you don’t read the gravito-thermal papers, you either have to trust my interpretation or come to the same realization on your own.

      I have read them. They do a good job of explaining lapse rate. If they convincingly explain absolute temperature, I have not seen it and you will need to point that out to me.

      I suspect the latter based on your agreement that the lapse rate is an equilibrium condition that remains if there were no more incoming sunlight.

      Careful. I wrote that convection reduces at night on Earth. So lapse rate still applies, but the implication is that convection isn't as capable of raising air parcels to Zeff, which would explain why nights are expected to warm faster than days in a regime of rising LW-active atmospheric species. I believe it also partially explains temperature inversions at night.

      Delete
    3. "Benestad (2016). I include the relevant excerpts in the Venus Part 2 article."

      I saw that and commented: Benestad's "emission temperature of 254K at around 6.5 km above the ground" translates to 5.2 K/km lapse rate. But they don't call it that. Instead it is a "radiative heating profile" due to convective adjustment. The standard atmosphere vertical temperature profile is 6.5 K/km not 5.2 K/km.

      "I get 262 K for 5 km altitude."

      That's considerably different from the standard atmosphere. Why?


      "I don't understand what you mean by threshold."

      I was referring to my analysis of the density of Venus at the AEE which is the locus of where 100% control by convection transitions to 0% convection and 100% radiation. It is extremely important that we understand what this means. I believe you do, because you spell it out in Venus part II:

      "Which is not to say that emission height is the ONLY altitude at which the Earth loses energy to space. It's the average altitude at which average atmospheric temperature predicts a blackbody flux equal to the average solar energy absorbed by the entire system."

      "-10.4 K/km is more realistic for Venus."

      Nope, you have to get that corrected on your Venus posts. I meant to say the calculated 9.8 K/km for Earth is useless, but a calculated lapse rate works well for Venus (from 7.5 to 10 K/km).

      "Adiabatic lapse rate doesn't happen without convection."

      This simply is wrong. I'll address it in a later comment.

      "If [papers on gravito-thermal effect] convincingly explain absolute temperature, I have not seen it and you will need to point that out to me."

      The gravito-thermal effect does not predict absolute temperature without other info. What it does is explain why the linear temperature profile near the surface is not due to radiation. The additional point that I'm making is that a sufficient density of IR-gases must be present near the surface to establish a linear lapse rate. Mars doesn't have it. Venus overdoes it by plenty. Earth only has it because of water vapor. Take that away and no more linear lapse rate, because there isn't enough CO2 density left to raise the Teff above the surface.

      "Careful. I wrote that convection reduces at night on Earth. So lapse rate still applies, but the implication is that convection isn't as capable of raising air parcels to Zeff, which would explain why nights are expected to warm faster than days in a regime of rising LW-active atmospheric species. I believe it also partially explains temperature inversions at night."

      I don't follow, but will save this too for a later comment.

      Delete
    4. Chic, Part 1:

      I saw that and commented: Benestad's "emission temperature of 254K at around 6.5 km above the ground" translates to 5.2 K/km lapse rate.

      Yup, saw it and thought I replied somewhere in this thread.

      "I get 262 K for 5 km altitude."

      That's considerably different from the standard atmosphere. Why?


      Depends on which standard atmosphere we're talking about. MODTRAN includes something like seven different ones.

      I was referring to my analysis of the density of Venus at the AEE which is the locus of where 100% control by convection transitions to 0% convection and 100% radiation. It is extremely important that we understand what this means. I believe you do, because you spell it out in Venus part II:

      "Which is not to say that emission height is the ONLY altitude at which the Earth loses energy to space. It's the average altitude at which average atmospheric temperature predicts a blackbody flux equal to the average solar energy absorbed by the entire system."


      Ok thanks. I take it on this more than disagree then?

      "-10.4 K/km is more realistic for Venus."

      Nope, you have to get that corrected on your Venus posts.


      I know more now than when I wrote that. I have to research it more now because I'm getting conflicting information and don't understand why.

      "Adiabatic lapse rate doesn't happen without convection."

      This simply is wrong.


      lol. Well, at least it's quite clear that we disagree in this particular point.

      "If [papers on gravito-thermal effect] convincingly explain absolute temperature, I have not seen it and you will need to point that out to me."

      The gravito-thermal effect does not predict absolute temperature without other info.


      I didn't think so, but it's strongly implied. I can dig up specific examples if you'd like. Or you can wait two weeks (at least) for me to do the writeup on them which seems one eventual outcome of the research and modelling doing right now.

      What it does is explain why the linear temperature profile near the surface is not due to radiation.

      That's the argument they're making, and like I said they mostly do a good job as far as I can tell of explaining that. The salient question is why convection is as deep as it is, and they handle that with varying amounts of ... success. IIRC, my ranking of best to worst would be:

      1) Gilbert
      2) Jelbring
      3) Nikolov and Zeller

      (3) is, well, pretty bad IMO. What I like about Gilbert is that he invokes release of latent heat due to wv condensation as a convection booster, which I deem a sound principle, as does Jelbring ... albeit with less maths done to support it. Jelbring wrote something particularly important:

      The greenhouse effect (GE), expressed as temperature lapse rate per meter, in a model atmosphere postulating energetic equilibrium, is constant and independent of the radiative properties of the ideal gases. It is also independent of the density of the atmosphere and of the absolute average temperature of the same.

      My bold. I not only mostly accept the principle, it highlights what I've been saying all along; since -g/Cp is independent of absolute average temperature, it cannot predict absolute average temperature.

      This means that his conclusions do not necessarily follow. In particular:

      The considerations in this paper indicate that effects of the greenhouse gases, other radiative effects, and convection effects all might modulate GE to a minor unknown extent.

      Delete
    5. Chic, Part 2:

      Best paper of the bunch is Robinson and Catling, which states right in the abstract:

      Here we use a simple, physically based model 7 to demonstrate that, at atmospheric pressures lower than 0.1 bar, transparency to thermal radiation allows short-wave heating to dominate, creating a stratosphere. At higher pressures, atmospheres become opaque to thermal radiation, causing temperatures to increase with depth and convection to ensue. A common dependence of infrared opacity on pressure, arising from the shared physics of molecular absorption, sets the 0.1 bar tropopause. We reason that a tropopause at a pressure of approximately 0.1 bar is characteristic of many thick atmospheres, including exoplanets and exomoons in our galaxy and beyond.

      My bold. Read it again, and read Spencer again.

      Otherwise, that's a fascinating paper because the 0.1 bar principle is elegantly argued in my view. And entirely consistent with the consensus position as I understand it, particularly Benestad (2016).

      The additional point that I'm making is that a sufficient density of IR-gases must be present near the surface to establish a linear lapse rate.

      Yes, a thousand times YES, we agree on that for the most part. And they must be present at the top of the cycle for efficient radiative cooling. Without those two things, convection would not be as deep. Temperature profile would then tend to deviate more from the dry adiabatic lapse rate determined by -g/Cp, by which I mean a more isothermal temperature profile.

      This is because dry adiabatic lapse rate is NOT the cause of convection. It's the RESULT of it.

      Not for the first time, think Carnot cycle. If you increase the temperature of the hot reservoir and reduce the temperature of the cold reservoir, a heat engine will be able to do MORE work for the same energy input. IOW, it will be more efficient. Water vapour, CO2 ... any LW-active species can do this for the planet by reducing radiative heat loss at the surface and increasing radiative heat loss at AEE and higher. The system "wants" to do more work -- needs to do more work -- with convection to shed the additional solar energy caused by introducing a LW radiative imbalance.

      Here, water vapour muddies the analysis because of the phase changes at bottom and top of the cycle. And clouds.

      Mars doesn't have it. Venus overdoes it by plenty. Earth only has it because of water vapor. Take that away and no more linear lapse rate, because there isn't enough CO2 density left to raise the Teff above the surface.

      Sure. Clough and Iacono (1995) put CO2's contribution at about 14% of the ~150 W/m^2 total "greenhouse" effect. That doesn't mean that a completely dry atmosphere would only have 86% of that 150 W/m^2 ... due apparently to overlaps between wv and CO2 absorption spectra.

      Delete
    6. response to part 1:

      "Ok thanks. I take it on this more than disagree then?"

      I thought it sounded like on that we did agree. Your sentence is ???

      I'm very impressed that you read all those gravito-thermal papers. Don't you think it helps understand my points of view, if nothing else?

      "This means that his conclusions do not necessarily follow."

      I tend to agree. I don't think he realizes the IR-active gas critical density factor that I'm zeroing in on. If I'm right about that, it will clear up a lot of disagreement on both sides of the issues.

      Delete
    7. "Yes, a thousand times YES, we agree on that for the most part. And IR-active gases must be present at the top of the cycle for efficient radiative cooling. Without those two things, convection would not be as deep."

      Please realize that using phrases like "at the top of the cycle" is not helpful. It is precisely the dilution of the IR-active gases at the locus of the AEE, that allows LW radiation to escape.

      "Temperature profile would then tend to deviate more from the dry adiabatic lapse rate determined by -g/Cp, by which I mean a more isothermal temperature profile."

      Yes, but an isothermal profile will never happen, because an equilibrium profile--a minimum lapse rate--is when the air is saturated with water. That's the closest to isothermal you can get under the influence of gravity.

      "This is because dry adiabatic lapse rate is NOT the cause of convection. It's the RESULT of it."

      This is backwards or a major semantic confusion. Convection reduces the temperature gradient by transering warmed air from the surface to the upper atmosphere. Evaporation also causes convection which also cools the surface and warms the troposphere when the vapor condenses.

      "Sure. Clough and Iacono (1995) put CO2's contribution at about 14% of the ~150 W/m^2 total "greenhouse" effect. That doesn't mean that a completely dry atmosphere would only have 86% of that 150 W/m^2 ... due apparently to overlaps between wv and CO2 absorption spectra."

      Not so sure. Without water vapor, there is an insufficient amount of CO2 to raise the Teff above the surface. Although this thread is mainly about mechanisms, not specifically CO2 concentration, I now think that IR-gases do control surface temperatures, IOW more IR-active gases increase surface temperature. However, there has to be a critical concentration for a linear lapse rate to form. Earth's [CO2] is too low to make much difference relative to the average water vapor levels. A proper model treatment will show this! Keep up the good work.

      Delete
  14. Chic,

    Again posted out of sequence for scroll. Lots of things in there worth discussing, but this is the crux of it:

    What I mean is the AEE is a function of the density of the IR-active gases.

    Yes, we 100% agree on that.

    So if you replace some of the inactive gases with CO2, then the AEE (which is a function of IR-active density) must go up to compensate.

    If you'll excuse the pun, yes, you're getting warmer now.

    However, this doesn’t mean the Teff goes up, because the Teff is constrained by the solar flux.

    Again correct according to my understanding.

    If the AEE goes up, then the calculated Tsurf has to go up (assuming no change in lapse rate).

    BINGO!!!!

    But why?

    Doh! You had the answer in your previous post: Ts = Teff + L*Zeff

    If Zeff increases ..........

    The Teff is still radiating the required LW to balance the incoming solar.

    Yup.

    The AGW rationale is when Tsurf increases, then the planet warms up. Can you see my dilemma?

    Honestly, no I don't. You had the correct math in a prior post, and the correct explanation here that matches the math.

    Won’t a warmer surface over-compensate?

    Nothing you've just walked yourself through leaps out to me as suggesting that. There ARE plenty of proposed negative feeback mechansims, some more plausible than others in my view.

    Pressure broadening applies, but temperature is a result of pressure and density, not the cause of it.

    Tut. After I fill my hypothetical bicycle tire and let it return to ambient temperature, assuming no leaks, won't the pressure in the tire be slightly lower than when I finished pumping it up?

    Wasn't my main point about temperature though. Spectral intensity shifts with temperature according to the Planck distribution, which can have some effect with what gets absorbed and doesn't. Getting into that is something I've been fiddling with in MODTRAN, nothing to show for it thus far.

    Is that so you can look at planets and moons from both opacity extremes? Good idea. Include atmospheres of different composition and mass, too. Great minds think alike, they say.

    The most interesting case for me right now is the atmosphere completely transparent to SW, but a nominal amount of LW opacity, no clouds or water vapour. The aim is to model convection without all the hassles of phase changes, or the funkiness that comes with inbound SW and reflected outbound SW being absorbed. An exercise for another day, I'm afraid. Cheers.

    ReplyDelete
    Replies
    1. “’Won’t a warmer surface over-compensate?’

      Nothing you've just walked yourself through leaps out to me as suggesting that.”

      I think my problem is the lapse rate. A simple linear relationship doesn’t cut it. Humidity varies. There is generally so little CO2 compared to water vapor. Convection is probably the largest confounding factor. I’ll have to let it go for now. I will be interesting to see what you do with your effort to model convection.

      “After I fill my hypothetical bicycle tire and let it return to ambient temperature, assuming no leaks, won't the pressure in the tire be slightly lower than when I finished pumping it up?”

      I still don’t see how tires relate to the atmosphere. The tire is a relatively fixed volume. When you pump it up, the pressure mainly increases because you’re adding air, making it more dense. There might be a small PV difference, but you can’t depressurize a tire much by cooling it down. Much easier to let the air out.

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    2. Chic,

      A simple linear relationship doesn’t cut it. Humidity varies.

      Yup.

      Convection is probably the largest confounding factor.

      It certainly cannot be neglected.

      I will be interesting to see what you do with your effort to model convection.

      I've made some progress today. I'm working on moist adiabatic lapse rate and latent heat flux at the moment.

      I still don’t see how tires relate to the atmosphere. The tire is a relatively fixed volume.

      Fair enough. Instead imagine a cylinder of dry air in equilibrium with its surroundings. Compress it with a piston to 100 psi. Do that quickly enough and we can assume the compressed air does not have enough time to appreciably exchange energy with its surroundings, and we can assume an adiabatic process. Since the piston does work to the gas, the gas heats up. Walk away for a few hours and come back. Assuming no leakage, temperature will have returned to equilibrium with ambient conditions, and pressure inside the cylinder will be ever so slightly less.

      Unless the gas is being constantly compressed (or conversely, is constantly expanding), we cannot assume an adiabatic process.

      How that translates to the real atmosphere is that unless convection is occurring, gravity gradient alone will not create a temperature gradient via adiabatic compression/expansion.

      We need to agree on that previous sentence for there to be any hope of you considering my next steps on this problem valid.

      Delete
    3. BG

      Unless the gas is being constantly compressed (or conversely, is constantly expanding), we cannot assume an adiabatic process.

      Might I suggest a slightly different wording, since CB seems to be missing the key point?

      Unless the gas is subject to continuously increasing compression (or conversely, is continuously expanding), we cannot assume an adiabatic process.

      Now CB might see the reason why atmosphere at eg. 1 bar at *constant pressure* is not warmed by pressure.

      How that translates to the real atmosphere is that unless convection is occurring, gravity gradient alone will not create a temperature gradient via adiabatic compression/expansion.

      That's how I understand it.

      Delete
    4. BBD,

      Your rewording may the more correct way to say it, so sure, let's go with that.

      Doing some reading on Nikolov, I stumbled across this from Roy Spencer:

      Why Atmospheric Pressure Cannot Explain the Elevated Surface Temperature of the Earth:

      Background: The Dry Adiabatic Lapse Rate

      The dry adiabatic lapse rate of temperature is the rate at which the temperature of a parcel of air decreases with altitude (9.8 deg. C per km) if no energy is gained or lost by that parcel to its surroundings (thus the term “a-diabatic”), or though condensation heating by water vapor (thus “dry”).

      It is important to understand that the adiabatic lapse rate deals with temperature *changes* as a result of pressure changes, but it says nothing about what the average temperature will be at any given altitude. It starts with a parcel of air of known temperature, but does not explain why the parcel had that temperature to begin with.


      Which is, like, review of things already written above. THIS is golden because it's the main argument I've been attempting to make from a simple 1D radiative-convective model:

      One of the first things you discover when putting numbers to the problem is the overriding importance of infrared radiative absorption and emission to explaining the atmospheric temperature profile. These IR flows would not occur without the presence of “greenhouse gases”, which simply means gases which absorb and emit IR radiation. Without those gases, there would be no way for the atmosphere to cool to outer space in the presence of continuous convective heat transport from the surface.

      Indeed, it is the “greenhouse effect” which destabilizes the atmosphere, leading to convective overturning. Without it, there would not be weather as we know it. The net effect of greenhouse gases is to warm the lowest layers, and to cool the upper layers.

      The greenhouse effect thus continuously “tries” to produce a lapse rate much steeper than the adiabatic lapse rate, but convective overturning occurs before that can happen, cooling the lower troposphere and warming the upper troposphere through a net convective transport of heat from lower layers to upper layers.


      Or in sum, convective cooling offsets LW-radiative heating (and SW as well), BUT without the LW gradient, convection would not be as active or deep in the first place.

      Delete
    5. "Unless the gas is being constantly compressed (or conversely, is constantly expanding), we cannot assume an adiabatic process.

      How that translates to the real atmosphere is that unless convection is occurring, gravity gradient alone will not create a temperature gradient via adiabatic compression/expansion."

      Let's switch from tires to hot-air balloons. Get in one early in the morning before dawn. Assume no convection which should be negligible if any. As you elevate, ask yourself "Is there any heat being added to the system?" and "Is anybody letting the air out of this planet?" and "BTW, why is the temperature dropping so steadily?"

      The gravito-thermal effect says that the environmental lapse rate is a function of gravity and the heat capacity of the air. Gravity supplies a built-in compression. Convection only tweaks it a bit on Venus, but a lot on Earth.

      "We need to agree on that previous sentence for there to be any hope of you considering my next steps on this problem valid."

      This might be difficult, but very worthwhile IMO.

      Delete
    6. Roy Spencer says: "Without those gases, there would be no way for the atmosphere to cool to outer space in the presence of continuous convective heat transport from the surface."

      Obviously he means without IR-active gases, cooling would occur from a much colder ground/skating rink. Dr. Spencer holds to AGW radiative forcing views, but is a skeptic because he sees sensitivity being a lot less than main-stream AGWers believe. He might even agree with this:

      "Adiabatic lapse rate doesn't happen without convection."

      But I doubt it. It's not clear from the excerpt above. Strange for me to be disagreeing with Dr. Spencer, but here goes.

      The adiabatic lapse rate is the base line condition of an atmosphere without an intermittent energy source. If the same W/m2 was irradiating every m2 of the Earth 24/7, there would be no convection, and a constant lapse rate. The daily sunrise destabilizes the atmosphere and its adiabatic lapse rate by causing convective overturning and weather. [Adiabatic, because the net heat entering and leaving the system would be zero.]

      The daily dose of sunlight warms the surface which in turn warms the lower troposphere. This destabilizes the temperature profile producing a lapse rate greater than the theoretical adiabatic lapse rate. The warmed air near the surface is forced upward by convection, cooling the surface and warming the troposphere. As sunlight subsides, the continual cooling at the TOA/AEE causes the lapse rate to return toward the adiabatic value. The net effect is SW heating of the surface, convective transport of heat through the troposphere, LW radiation of the heat from the AEE. Without intermittent sunlight causing an increased lapse rate, there wouldn't be any convection.

      Delete
    7. Chic,

      Let's switch from tires to hot-air balloons. Get in one early in the morning before dawn. Assume no convection which should be negligible if any. As you elevate, ask yourself "Is there any heat being added to the system?" and "Is anybody letting the air out of this planet?" and "BTW, why is the temperature dropping so steadily?"

      Funny you should bring this up because I keep meaning to bring up the point that an adiabatic process, by definition, means no net change in energy with surroundings. It's actually embedded in Spencer's post in my comment to BBD:

      Background: The Dry Adiabatic Lapse Rate

      The dry adiabatic lapse rate of temperature is the rate at which the temperature of a parcel of air decreases with altitude (9.8 deg. C per km) if no energy is gained or lost by that parcel to its surroundings (thus the term “a-diabatic”), or though condensation heating by water vapor (thus “dry”).


      Three things to think about however:

      1) The real lapse rate differs from the dry adiabat, implying that a rising (or falling) air parcel is either exchanging energy with its surroundings and/or gaining/losing heat due to phase changes of water.

      2) A rising/falling air parcel is gaining/losing potential energy wrt the gravity well.

      3) Both convection and advection imply a change in kinetic energy due to acceleration.

      I don't deem Spencer's statement wrong; it's consistent with every atmospheric text I know of. My understanding is that the dry adiabat is useful because it's the easiest to calculate and the least uncertain to estimate from observation. So it makes the best starting point from which to add/subtract other effects.

      I think I understand completely where you're going with the hot-air balloon example. Effectively no heat is being added to the balloon, that was done by the burner at ground level. For purposes of the analogy, the balloon isn't losing air. Thus, IF the balloon is free to expand as it rises, its temperature must cool.

      In practice, ballooners actually do release some air from the envelope, especially during initial heating. But I think also during altitude gains because the air trapped inside isn't completely free to expand, builds up pressure, becomes more dense than it otherwise would be at that pressure level, thus less buoyant.

      And of course, a real balloon in practice loses heat due to radiative and sensible loss to the cooler surrounds. Hence, time aloft is limited by the amount of fuel aboard to run the burner.

      A very key lesson of the actual practice of ballooning is that if one wishes to go higher than the intial ground-level heating provided, one must add heat to the air inside the envelope to obtain it.

      That's what Spencer is getting at when he wrote:

      Indeed, it is the “greenhouse effect” which destabilizes the atmosphere, leading to convective overturning. Without it, there would not be weather as we know it. The net effect of greenhouse gases is to warm the lowest layers, and to cool the upper layers.

      Another way of putting it is that LW flux in the troposphere makes the actual lapse closer to the dry adiabatic lapse rate than it would otherwise be due to the effects of latent heat exchanges driven by the moist adiabatic lapse rate.

      Delete
    8. Chic, Part 2:

      The gravito-thermal effect says that the environmental lapse rate is a function of gravity and the heat capacity of the air.

      I agree, with the usual caveat that it only predicts delta-T wrt Z, not absolute T. ;)

      Gravity supplies a built-in compression.

      THIS is where nearly every "its gravity, not LW flux" explanation of absolute temperature I've read begins to run off the rails, and one reason why I started hammering on "convection goes both ways" with you in late December of last year. Go down that road far enough, and you get a perpetual heat engine of the worst kind. I bunged it up a bit myself in the Venus Part 2 article when I forgot that Joules can be expressed as kg m2 s-2. Since F = ma, we can express the effect of gravity in Newtons as F = kg m s-2. So yes, gravity supplies a compressive force on the atmosphere, but unless gravity is causing a continuous pressure increase, no net work is being done to it, and thus there is no gain in energy.

      Remember, treated as a whole, the atmosphere is isochoric -- net convection can be thought of a constant volume process. You taught me the term for it. For every air parcel being compressed by gravity-induced force from the mass of atmosphere above as it moves ground-ward is another air parcel rising away from the surface against the gravity well, expanding as it goes. Net work done is eggzactly zero, otherwise known as female goose zygotes. IOW, nada. You speak often of cancelling out ... this is as clear a case of it as I can think of.

      Think about what happens to a ball thrown vertically in a vacuum, and coming to rest again in the exact place it started. Gravity does no net work in that scenario. The ball comes back to the launch point at the exact same velocity as it left it, only the sign of the vector has flipped. At the top of the trajectory where velocity was zero for less than an instant, potential energy against the gravity well exactly equals the kinetic energy the ball gained during the launch. Stopping it at the bottom requires the same exact amount of energy as the launch.

      You can safely bet the ball will be slightly warmer at the end; however, that heat came NOT from gravity, but the acceleration of launch and deceleration of landing.

      Staying with the adiabatic paradigm here, only temperature changes. Gravity isn't the energy source, the Sun is -- analogous to the gas burner in your excellent hot air balloon example.

      Convection only tweaks it a bit on Venus, but a lot on Earth.

      There you're somewhat at odds with your Nikolov and Zeller citation from above, specifically:

      Our analysis of interplanetary data in Table 1 found no meaningful relationships between ATE (NTE) and variables such as total absorbed solar radiation by planets or the amount of greenhouse gases in their atmospheres. However, we discovered that NTE was strongly related to total surface pressure through a nearly perfect regression fit via the following nonlinear function ...

      And rightfully so, I think, because if convection is relatively minimal, rising/descending air parcels have more time to exchange energy radiatively and sensibly with surroundings, thus the process becomes "less" adiabatic, and therefore deviates from a -g/Cp prediction.

      They do a good job predicting lapse rate. That's about as much good as I can say about that particular article.

      This might be difficult, but very worthwhile IMO.

      Indeed ... it's already been both.

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    9. I think I'm answering unlabeled part 1 just up.

      1) The real lapse rate differs from the dry adiabat, implying that a rising (or falling) air parcel is either exchanging energy with its surroundings and/or gaining/losing heat due to phase changes of water.

      Sure, considering the whole system is the atmosphere, these internal energy changes don't count. Ie, they balance out.

      2) A rising/falling air parcel is gaining/losing potential energy wrt the gravity well.

      Same thing. There is no net change potential or kinetic energy as long as the energy leaving the surface equals that lost to space. Of course this never happens, but I'm analyzing a theoretical case.

      3) Both convection and advection imply a change in kinetic energy due to acceleration.

      Same answer.

      "I think I understand completely where you're going with the hot-air balloon example."

      No, I didn't intend for the balloon to enter into it at all. I just wanted you to consider the atmosphere at rest. Look instead at a P vs. V diagram for ONE mole of a gas at some altitude in the lower troposphere. Plot an adiabatic curve for a pocket of air rising. The pressure goes down while the volume goes up. Make sure to go real slow so that no net heat goes in or out. The change wrt altitude happens exponentially for pressure and volume, but the temperature drops linearly.

      "Another way of putting it is that LW flux in the troposphere makes the actual lapse closer to the dry adiabatic lapse rate than it would otherwise be due to the effects of latent heat exchanges driven by the moist adiabatic lapse rate."

      Let me try to parse both statements. Dr. Spencer says

      "The net effect of greenhouse gases is to warm the lowest layers, and to cool the upper layers."

      By this he means while the atmosphere is cooled at altitude, the sun's energy is warming the air near the surface. The net effect is a temperature profile steeper than the existing lapse rate at the moment. It doesn't matter whether the air is relatively dry or moist. The theoretical dry lapse rate is about as steep as you can get. So in that respect the first half of your statement is correct:

      "...LW flux in the troposphere makes the actual lapse closer to the dry adiabatic lapse rate..."

      The second half of your statement has me struggling. Closer than it would otherwise be due to something. You call that something "the effects of latent heat exchanges driven by the moist adiabatic lapse rate."

      I don't consider the moist adiabatic lapse rate the driver. If anything I would say today's latent heat exchanges drive or define what today's lapse rate is. In any case, the latent heat exchanges warm the upper tropopause and cool the surface. The more exchanges, the less steep (more gradual) is the moist adiabatic lapse rate. You seem to be saying the LW flux would be less steep, but for the moist adiabatic lapse rate. I say the opposite: The more latent heat exchanges hense more gradual the moist adiabatic lapse rate, the farther the actual lapse rate will be from the dry adiabatic lapse rate.

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    10. This goes with part 2:

      I want to make a distinction between my "its gravity, not LW flux" position from anyone out who is saying you can predict an absolute temperature from a lapse rate without knowing other crucial variables. All I'm saying is the LW flux does not produce or define a LINEAR lapse rate. A linear lapse rate only occurs where the atmosphere has sufficient IR-active gas concentration to raise the Teff above the surface. In a sense I'm trying to bridge the divide between folks who think it's all gravity or all LW flux. The density of the IR-active gases determines the locus of the AEE. Solar flux determines the Teff. Height above the surface will determine the surface temperature.

      "There you're somewhat at odds with your Nikolov and Zeller citation from above...."

      I have to take another look and see where they go wrong. :-)

      Delete
    11. Chic,

      There is no net change potential or kinetic energy as long as the energy leaving the surface equals that lost to space. Of course this never happens, but I'm analyzing a theoretical case.

      That's the steady state equilibrium condition. To me it means, in theory, that the net of all fluxes everywhere is zero (on balance).

      I just wanted you to consider the atmosphere at rest.

      That's easy. With no energy inputs, the atmosphere at rest will tend to become isothermal.

      Look instead at a P vs. V diagram for ONE mole of a gas at some altitude in the lower troposphere. Plot an adiabatic curve for a pocket of air rising. The pressure goes down while the volume goes up.

      As soon as you start moving air parcels around, the atmosphere is no longer at rest.

      Make sure to go real slow so that no net heat goes in or out.

      To ensure an adiabatic process, you want to move relatively quickly so that other energy exchanges DON'T have a chance to affect the results.

      The change wrt altitude happens exponentially for pressure and volume, but the temperature drops linearly.

      Yes, I agree. The plots I made already demonstrate that linearity that when I leave Cp constant instead of varying it by temperature and pressure. Other than some quibbles about what the value of Cp should be, his part of it is not in dispute between us.

      By this he means while the atmosphere is cooled at altitude, the sun's energy is warming the air near the surface.

      He means MORE than just that and he spells it out quite explicitly at the end of the post. But yes, that's one thing he's saying.

      The net effect is a temperature profile steeper than the existing lapse rate at the moment. It doesn't matter whether the air is relatively dry or moist.

      The way I think about it is this: the LW flux gradient makes the lapse rate steeper than it would be than the combination of the dry and moist adiabatic rates.

      The theoretical dry lapse rate is about as steep as you can get.

      That checks out when I use -9.8 K/km as the dry adiabat.

      So in that respect the first half of your statement is correct:

      "...LW flux in the troposphere makes the actual lapse closer to the dry adiabatic lapse rate..."


      Ok good ... so noted.

      The second half of your statement has me struggling. Closer than it would otherwise be due to something. You call that something "the effects of latent heat exchanges driven by the moist adiabatic lapse rate."

      Moist adiabatic lapse rate is listed as -6.4 K/km on average, compared to -9.8 K/km for the dry lapse rate, yes?

      As moist air rises and begins to saturate, latent heat is released as water condensates out. That release of energy heats the air parcel, driving further convection, and effectively lowering the lapse rate from what it would be in a completely dry atmosphere.

      I don't consider the moist adiabatic lapse rate the driver.

      I'm not sure I understand what that means ... it also seems to contradict:

      If anything I would say today's latent heat exchanges drive or define what today's lapse rate is.

      Sure, environmental lapse rate is a function of the dry and moist adiabatic lapse rates as well as sensible and radiative heat exchanges.

      In any case, the latent heat exchanges warm the upper tropopause and cool the surface.

      Agreed.

      You seem to be saying the LW flux would be less steep, but for the moist adiabatic lapse rate.

      I was saying that the LW flux gradient means that environmental lapse rate is steeper than it would be if temperature profile were determined by the dry and moist adiabats alone.

      I say the opposite: The more latent heat exchanges hence more gradual the moist adiabatic lapse rate, the farther the actual lapse rate will be from the dry adiabatic lapse rate.

      I agree with that. It need not be one or the other.

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    12. Chic,

      All I'm saying is the LW flux does not produce or define a LINEAR lapse rate.

      Two weeks ago I would have had a big problem with that. It's taken some reading and modelling on my part, and as a result I agree with you.

      A linear lapse rate only occurs where the atmosphere has sufficient IR-active gas concentration to raise the Teff above the surface.

      Not exactly how I'd put it because I think convection would still happen with minimal or no LW-active gasses and sufficient local heating. But yes, the implication is that in such a scenario, Zeff would be essentially at the surface, and thus Tsurf = Teff more or less ... i.e., cooler all else being equal.

      In a sense I'm trying to bridge the divide between folks who think it's all gravity or all LW flux.

      I think that's what Benestad (2016) was also trying to do as well. Between the two of you, it's beginning to work.

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    13. CB

      Perhaps:

      The density of the IR-active gases determines the locus of the AEE. Solar flux determines the Teff [at equilibrium]. [Change in] Height [of AEE] above the surface will determine the [change in] surface temperature.

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    14. Brandon,

      "That's easy. With no energy inputs, the atmosphere at rest will tend to become isothermal."

      After reading the gravito-thermal papers and having all this tire and balloon discussion, you still think that? Try to explain what would happen if you filled a well-insulated 10 km long column of air lying horizontally 3 km up and then flipped it vertical? Do you still think the temperature gradient would remain iso-thermal? What would prevent the gravitational force redistributing the molecules to match the atmosphere?

      "To ensure an adiabatic process, you want to move relatively quickly so that other energy exchanges DON'T have a chance to affect the results."

      Actually moving quickly only makes the process irreversible. I should be able to explain why that doesn't matter. The main thing is that any heat exchanges will be compensated for by stipulating that no net heat leaves the system. IOW, all the heat lost to the rising parcel is compensated by the heat gained by the descending parcel.

      "The way I think about it is this: the LW flux gradient makes the lapse rate steeper than it would be than the combination of the dry and moist adiabatic rates."

      OK, but I don't understand why you would want to complicate matters that way. Any possible lapse rate will be some combination of the extremes.

      "I was saying that the LW flux gradient means that environmental lapse rate is steeper than it would be if temperature profile were determined by the dry and moist adiabats alone."

      This is another convoluted way of putting it. Why don't you do a separate post on this? Unfortunately, I can't do it now myself. Maybe later.

      Delete
    15. Brandon,

      "I think that's what Benestad (2016) was also trying to do as well."

      This is a good place for me to opt out for awhile. I have some much neglected other issues to take care of. Then I have to read this paper and some others that we've been discussing. And then there's the modelling. So much to do, so little time.

      bbd,

      "The density of the IR-active gases determines the locus of the AEE. Solar flux determines the Teff [at equilibrium]. [Change in] Height [of AEE] above the surface will determine the [change in] surface temperature."

      Yes. To a first approximation, this should be acceptable to most reasonably educated climate aficionados.

      The task ahead is to determine how much of a change in the height affects the change in surface temperature. At the AEE, the linear lapse rate no longer applies. So it is not acceptable to limit predictions to algebraic equations. Also models have to properly handle the contribution of convection.

      Delete
    16. -1 K in 425 ky

      -5 K in 35 My

      http://www.columbia.edu/~jeh1/2008/TargetCO2_20080407.pdf

      Delete
    17. Fail to see your point or how it relates to what Hansen actually says.

      Delete
    18. The Scottish Sceptic has a post apropos to our discussion of competing mechanisms and interglacial temperature change.

      http://scottishsceptic.co.uk/2016/03/09/can-variations-in-lapse-rate-cloud-cover-explain-ice-age-temperature-changes-and-the-inter-glacial-hard-stop/

      Delete
    19. That man is a lunatic. I am actually shocked that you read his stuff. I do not.

      * * *

      What Hansen is saying is that you are wrong to claim that the increase in CO2 will have little warming effect because there is good evidence from palaeodata to the contrary. In fact there is *nothing* in Hansen08 that lends support to your position and much that militates against it. For example Hansen et al. (2008) (p. 6):

      The large (~14°C) Cenozoic temperature change between 50 My and the ice age at 20 ky must have been forced by changes of atmospheric composition. Alternative drives could come from outside (solar irradiance) or the Earth’s surface (continental locations). But solar brightness increased ~0.4% in the Cenozoic (41), a linear forcing change of only +1 W/m2 and of the wrong sign to contribute to the cooling trend. Climate forcing due to continental locations was < 1 W/m2, because continents 65 My ago were already close to present latitudes (Fig. S9). Opening
      or closing of oceanic gateways might affect the timing of glaciation, but it would not provide the climate forcing needed for global cooling.

      CO2 concentration, in contrast, varied from ~180 ppm in glacial times to 1500 ± 500 ppm in the early Cenozoic (42). This change is a forcing of more than 10 W/m2 (Table 1 in 15), an order of magnitude larger than other known forcings. CH4 and N2O, positively correlated with CO2 and global temperature in the period with accurate data (ice cores), likely increase the total GHG forcing, but their forcings are much smaller than that of CO2 (43, 44).


      Now that really couldn't be plainer, could it?

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    20. Yeah, it's plain as mud. 14 K change from 50 My BP to now and 5 K from glacial to now both amount to a sensitivity greater than 4 K/doubling of CO2. From the last 150 years it's been less than 2 k/doubling CO2. In either case, those are only correlations and speculations. No one has verified a model or a formula that predicts what temperature should be as a function of [CO2]. More importantly, no one has data that shows what temperature increase will result from an incremental increase in CO2.

      Delete
    21. In which CB confuses ECS with ESS...

      And indulges in a spot of denial.

      Delete
    22. BBD,

      ESS? I'm sure I could look it up, but I'm lazy at the moment ...

      Delete
    23. ESS = Earth System Sensitivity including slow feedbacks. See for example the first sentence of the abstract of Hansen08, which CB referenced but either has not read or has not understood:

      Paleoclimate data show that climate sensitivity is ~3°C for doubled CO2, including only fast feedback processes. Equilibrium sensitivity, in
      cluding slower surface albedo feedbacks, is ~6°C for doubled CO2 for the range of climate states between glacial conditions and ice-free Antarctica.


      More discussion under the heading 'Slow Feedbacks' on p. 4. The concepts of ECS and ESS are more fully developed in later papers (eg. Hansen & Sato 2012; Hansen et al. 2013). I notice that CB is alarmingly shaky once he gets off his tropospheric hobby horse. This is a key problem with his discourse: it is excessively limited in focus. Climate behaviour viewed in the context of palaeoclimate is strongly indicative that CO2 is an efficacious forcing on all timescales Ma to centennial. This would be obvious to him if he were to emerge from the tropospheric rabbit hole.

      Delete
    24. From the last 150 years it's been less than 2 k/doubling CO2

      And to top it off, he's confused the transient response with ECS, treating observed warming as if were the equilibriated rather than the transient response. An old Lindzen trick. Either that, or he doesn't understand why Nic Lewis' stuff is wrong.

      Delete
  15. Chic,

    Responding to this part of your comment in this thread because it seemed more relevant here.

    "In the atmosphere, IR light can be absorbed and re-emitted multiple times before its energy reaches the emission level where it is free to escape to space (Pierrehumbert 2011)."

    I don't know why you think you have to repeat this to me.


    Because I'm not convinced we actually agree on it.

    What I have to keep repeating to you is the emission level part.

    I don't understand why you think you need to keep repeating THAT! :)

    Let me be abundantly clear about this -- I do believe that there is a mean altitude at which upwelling LW becomes more likely than not to escape into space. The wrinkle is that it's wavelength-dependent. IOW, each frequency has its own AEE if you will. MODTRAN is an excellent tool for demonstrating this. Whenever I get back to writing that series, remind me to take that up if I don't remember to address it.

    Near the surface these absorptions and emissions cancel out. Only when the density of the atmosphere thins, does the net LW radiation go to space. There should be no disagreement on that or you are disagreeing with Peirrehumbert himself.

    It's the "emissions cancel out" language I'm tripping over. If Peirrehumbert says that, I'm not aware of where. What "emissions cancel out" means to me is that they have a negligible effect.

    Benestad's "emission temperature of 254K at around 6.5 km above the ground" translates to 5.2 K/km lapse rate. But he doesn't call it that. Instead it is a "radiative heating profile" due to convective adjustment. The standard atmosphere vertical temperature profile is 6.5 K/km not 5.2 K/km.

    I'm no longer using a standard atmosphere to evaluate this on Earth, I've gone to gridded reanalysis data by pressure level. It's as close to observational data as I can get at the spatial resolution I want. My numbers thus far don't match Benestad's exactly but they're close. Globally, I get -5.86 K/km for observed lapse rate, Zeff of 6.32 km when I set Teff to be 254 K. Teff being the free parameter used to calculate Zeff obviously wants justification and scrutiny, which I have not yet done. But the lapse rate is what it is in the 30-year observational means (1981-2010) I'm using.

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    Replies
    1. "It's the "emissions cancel out" language I'm tripping over. If Peirrehumbert says that, I'm not aware of where. What "emissions cancel out" means to me is that they have a negligible effect."

      I shouldn't assume Prof. Pierrehumbert said that. Somewhere I posted an explanation by Ed Caryl. I'll look for another source.

      By emissions cancelling, I mean the upward LW = downward LW, but this only applies when considering the wavelengths outside the window. IOW, H2O and CO2 molecules are absorbing and emitting at similar rates once up to an elevation sufficient to have absorbed all LW from surface.

      "I'm no longer using a standard atmosphere to evaluate this on Earth...."

      Are saying the standard atmosphere is wrong or out-of-date? I'm not disagreeing, just wondering why so many use the std numbers if there is a more accurate database.

      Delete
    2. Chic,

      By emissions cancelling, I mean the upward LW = downward LW, but this only applies when considering the wavelengths outside the window.

      Ok, I think you may have defined that earlier and I missed it. That's a somewhat tricky calculation to come by, but may be essential. At the surface, it's not true going by the energy budgets. By K&T, it would be 356 up, 333 down, -26 W/m^2 net. Barring inversions, on balance I'm going to say that it only gets more negative with altitude until about 12 km (above AEE), and then stays roughly the same all the way to TOA and out.

      We might safely assume the window is -40 W/m^2 all the way up and out as drawn in the cartoon, but I don't think that's strictly true, and is something I've been wanting to test in MODTRAN.

      IOW, H2O and CO2 molecules are absorbing and emitting at similar rates once up to an elevation sufficient to have absorbed all LW from surface.

      Isn't this the saturation argument again? Look at the energy budget, for every 1 W/m^2 emitted by the surface, it gets 0.84 W/m^2 back. That agrees with my MODTRAN plot above, where the ratio is 0.83. It gets rapidly smaller with altitude according to MODTRAN ... well, here:

      Alt Ratio
      0 0.83
      1 0.73
      2 0.65
      3 0.57
      4 0.50
      5 0.43
      6 0.37
      7 0.31
      8 0.25
      9 0.19
      10 0.14
      11 0.10
      12 0.07
      13 0.05
      14 0.04
      25 0.02
      30 0.02

      A big part of that falloff is due to water vapour decreasing rapidly with altitude. I can, and will, run the same MODTRAN experiments up to 30 km with wv only and CO2 only to show how they compare. The data and plot are contained in this Gnumeric spreadsheet if you'd like to play with it yourself. If your spreadsheet program won't convert the file, let me know and I can save it off into pretty much any format of your choice.

      Are saying the standard atmosphere is wrong or out-of-date? I'm not disagreeing, just wondering why so many use the std numbers if there is a more accurate database.

      The standard atmospheres aren't typically globally representative. The other fluxes vary a great deal by altitude and latitude, also seasonally. I'm starting with annual by zonal means at all provided pressure levels, but I'll eventually want to test monthly/seasonal differences as well. Since I'm already getting those fluxes from NCEP/NCAR reanalysis products as gridded monthly means over the 1981-2010 between 10 and 1000 mb, it made sense to start with temperature data by pressure level and month over the same interval, from the same provider. Hence, I've rolled my own "standard" atmosphere.

      How I'm going to work MODTRAN into that scheme, I've not yet figured out. Probably some curve-fitting and interpolation, unfortunately. Short story long, I'm actually building a 2D model, not 1D.

      Delete
    3. "That's a somewhat tricky calculation to come by, but may be essential."

      That's what I'm working on, but I'm stuck and have other things to get done before I can return to it. Maybe you'll have it figured out by then.

      "At the surface, it's not true going by the energy budgets."

      You won't be surprised to hear that I don't swear by energy budget estimates.

      "Isn't this the saturation argument again? Look at the energy budget, for every 1 W/m^2 emitted by the surface, it gets 0.84 W/m^2 back."

      The MODTRAN results give me greater pause. But remember I discount the window because that amount of W/m2 is not being absorbed at the surface. So the fraction "back" is 333/356 = 0.94 . Still that's less than I would expect especially at the surface. I'm also surprised at how quickly the fraction drops. I'll see what your spreadsheet can do.

      2D model? Impressive.

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    4. 2D model sort of. It's really a 1D model that I can look at in terms of zonal means. And it's seriously not working at the moment, I'm quite stumped on how to compute moist lapse rate.

      So the fraction "back" is 333/356 = 0.94

      Yes, right ... 6%. I think I like it better allowing for the window, thus 84%. But 94% makes MY case stronger .... :)

      That little spreadsheet doesn't do much, was only intended to create the plot. I have a more developed version for parsing the MODTRAN output, I'll try to clean one up and publish it for you to play with.

      Delete
  16. Chic,

    Posted out of sequence for scroll:

    After reading the gravito-thermal papers and having all this tire and balloon discussion, you still think that?

    Yesssss .....

    Try to explain what would happen if you filled a well-insulated 10 km long column of air lying horizontally 3 km up and then flipped it vertical? Do you still think the temperature gradient would remain iso-thermal? What would prevent the gravitational force redistributing the molecules to match the atmosphere?

    No, a temperature gradient forms, with the lowest levels heating due to compression, upper layers cool due to expansion. If our hypothetical column were a perfectly insulated (closed) system, after the initial perturbation, the pressure gradient would remain but the temperature gradient would gradually go away.

    Actually moving quickly only makes the process irreversible.

    https://en.wikipedia.org/wiki/Reversible_process_%28thermodynamics%29

    Note the image.

    The main thing is that any heat exchanges will be compensated for by stipulating that no net heat leaves the system.

    No heat exchanges with surroundings is THE defining characteristic of a "perfectly" adiabatic process.

    IOW, all the heat lost to the rising parcel is compensated by the heat gained by the descending parcel.

    This is a critical disagreement between us. My understanding is that a parcel undergoing adiabatic expansion OR compression does not gain or lose heat it only changes temperature. Change in entropy is zero, change in enthalpy equals the amount of work done to surroundings (in the case of expansion) or work done to it (in the case of compression).

    See: https://en.wikipedia.org/wiki/Isentropic_process

    "The way I think about it is this: the LW flux gradient makes the lapse rate steeper than it would be than the combination of the dry and moist adiabatic rates."

    OK, but I don't understand why you would want to complicate matters that way.


    It's my understanding of how the real system works. I keep bringing up the Carnot cycle for a reason because that's how I think of the atmosphere, a great big heat engine with the hot reservoir at the surface where most of the solar SW is absorbed and the cold reservoir as deep space. The only way for the system to "communicate" with the cold reservoir (and not lose mass) is radiatively. For conceptual convenience, assume that Zeff is the only place that can happen. If we raise Zeff to a higher altitude, it implies that the hot reservoir must get warmer for convection to lift air parcels from the surface to the point that radiative loss can occur.

    It follows that the hot reservoir temperature in a dry atmosphere in either case will warm thus: dZeff * g/Cp.

    If we can agree on that much -- and I think we actually do -- then we might be able to set this other stuff aside for now and progress toward dealing with the implications of a moist atmosphere.

    Any possible lapse rate will be some combination of the extremes.

    I agree, and believe I have already said so.

    "I was saying that the LW flux gradient means that environmental lapse rate is steeper than it would be if temperature profile were determined by the dry and moist adiabats alone."

    This is another convoluted way of putting it. Why don't you do a separate post on this?

    I had been planning on it when I finished my quasi 2D radiative convective model becase the visual might make the above description seem less convoluted.

    Unfortunately, I can't do it now myself.

    Not for the first time, I get the feeling you have your own blog?

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    Replies
    1. PS:

      This is a good place for me to opt out for awhile.

      Understood. Fare thee well, your participation and contributions have been most welcome and helpful. Please don't be a total stranger.

      Best regards.

      Delete