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:

https://pielkeclimatesci.wordpress.com/2011/07/08/new-paper-illustrates-another-failure-of-the-ipcc-mullti-decadal-global-model-predictions-on-the-warming-in-the-tropical-upper-troposphere-models-versus-observations-by-fu-et-al-2011/

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.