Guest Post by Willis Eschenbach
My thanks to Nick Stokes and Joel Shore. In the comments to my post on the effects of atmospheric black carbon, Extremely Black Carbon, they brought up and we discussed the results of Ramanathan et al. (PDF, hereinafter R2008). Black carbon, aka fine soot, is an atmospheric pollutant that has been implicated in warming when it lands on snow. However, despite many claims to the contrary, atmospheric black carbon cools the surface rather than warming it.
There is an important implication in Ramanathan’s work regarding the canonical claim of AGW supporters that changes in surface temperature slavishly follow changes in forcing. Their claim is that the change in surface air temperature ( ∆T ) in degrees Celsius is a constant “lambda” ( λ ) called the “climate sensitivity” times the change in forcing ( ∆F ) in watts per square metre (W/m2). Or as an equation, the claim is that ∆T = λ ∆F, where lambda( λ ) is the climate sensitivity.
In R2008 they discuss the effect of black carbon (BC) on the atmosphere. Here’s the figure from R2008 that I want to talk about.
Figure 1. Figure 2C from R2008 ORIGINAL CAPTION: BC [black carbon] forcing obtained by running the Chung et al. analysis with and without BC. The forcing values are valid for the 2001–2003 period and have an uncertainty of ±50%. [Presumably 1 sigma uncertainty]
This figure shows the changes in forcing that R2008 says are occurring from black carbon forcing. Here is R2008’s comment on Figure 1, emphasis mine:
Unlike the greenhouse effect of CO2, which leads to a positive radiative forcing of the atmosphere and at the surface with moderate latitudinal gradients, black carbon has opposing effects of adding energy to the atmosphere and reducing it at the surface.
R2008 also says about black carbon (BC) that:
… as shown in Fig. 2, for BC, the surface forcing is negative whereas the TOA forcing is positive (Fig. 2c).
What are the mechanisms that lead to that re-partitioning of energy between the atmosphere and the surface?
Before I get to the mechanisms, I want to note something in passing. R2008 says that the forcing values have an uncertainty of ± 50%. That means the “Atmosphere” forcing is actually 2.6 ± 1.3 W/m2, and the “Surface” forcing is -1.7 ± 0.85 W/m2. This means that there is about a 30% chance that their “TOA” forcing, which is atmosphere plus surface, is actually less than zero … just sayin’, because Ramanathan didn’t mention that part. But for now, let’s use their figures.
PART I – What’s going on in Figure 1?
According to R2008, atmospheric black carbon causes the surface to cool and the atmosphere to warm. The surface is cooled by atmospheric black carbon through a couple of mechanisms. First, some of the sunlight headed for the surface is absorbed by the black carbon, so it doesn’t directly warm the surface. Second, any sunlight intercepted in the atmosphere does not have a greenhouse multiplier effect. Together, they say these effects cool the surface by -1.7 W/m2.
The atmosphere is warmed directly because it is intercepting more sunlight, with a net change of + 2.6 W/m2.
R2008 then notes that the net of the two forcings, 0.9 W/m2, is the change in the top-of-atmosphere (TOA) forcing.
The authors go on to say that because black carbon (BC) has opposite effects on the surface and atmosphere, the normal rules are suspended:
Because BC forcing results in a vertical redistribution of the solar forcing, a simple scaling of the forcing with the CO2 doubling climate sensitivity parameter may not be appropriate.
In other words, normally they would multiply forcing times sensitivity to give temperature change. In this case that would be 0.9 W/m2 times a sensitivity of 0.8 °C per W/m2 to give us an expected temperature rise of three-quarters of a degree. But they say we can’t do that here.
This exposes an underlying issue I want to point out. The current paradigm of climate is that the surface temperature is ruled by the forcing, so when the forcing goes up the surface temperature must, has to, is required, to go up as well. And vice versa. There is claimed to be a linear relationship between forcing and temperature.
Yet in this case, the TOA forcing is going up, but the surface forcing is going down. Why is that?
To describe that, let me use something I call the “greenhouse gain”. It is one way to measure the efficiency of the poorly-named “greenhouse” effect. In an electronic amplifier, the equivalent would be the gain between the input and output. For the greenhouse, the gain can be measured as the global average surface upwelling radiation (W/m2) divided by the global input, the average TOA incoming solar radiation (W/m2) after albedo. For the earth this is ~ 390W/m2 upwelling surface radiation, divided by the input of ~ 235 W/m2 after albedo, or about 1.66. That’s one way to measure the gain the surface of the earth is getting from the greenhouse effect.
Note that the surface temperature is exquisitely sensitive to the surface gain of the greenhouse effect. The gain is a measure of the efficiency of the entire greenhouse system. If the greenhouse gain goes down from 1.66 to 1.64, the surface radiation changes by ~ 4 W/m2 … on the order of the size of a doubling of CO2. Note also that the greenhouse gain depends in part on the albedo, since the 235W/m2 in the denominator is after albedo reflections.
Here is the core issue. For the “greenhouse” system to have its full effect, the sunlight absolutely must be absorbed by the surface. Only then does it get the surface temperature gain from the greenhouse, because some of the surface radiated energy is being returned to the surface. But if the solar energy is absorbed in the atmosphere, it doesn’t get that greenhouse gain.
So that is what is happening in Figure 1. The black carbon short-circuits the greenhouse effect, reducing the greenhouse thermal gain, and as a result, the atmosphere warms and the surface cools.
PART II – Almost Black Carbon
R2008 discusses the question of the 0.9 W/m2 of TOA forcing that is the net of the atmosphere warming and surface cooling. What I want to point out is that the 0.9 W/m2 of TOA forcing is not fixed. It depends on the exact qualities of the aerosol involved. Reflective aerosols, for example, cool both the atmosphere and the surface, by reflecting solar radiation back to space. Black carbon, on the other hand warms the atmosphere and cools the surface.
Consider a thought experiment. Suppose that instead of black carbon (BC), the atmosphere contained almost-black carbon (ABC). Almost-black carbon (ABC) is a fanciful substance which is identical to black carbon in every way except ABC reflects a bit more visible light. Perhaps ABC is what is now called “brown carbon”, maybe it’s some other aerosol that is slightly more reflective than black carbon.
As you might imagine, because almost-black carbon reflects some of the light that is absorbed by BC, the atmosphere doesn’t warm as much. The surface cooling is identical, but the almost black carbon reflects some of the energy instead of absorbing it as black carbon would do. As a result, let us say that conditions are such that ABC warms the atmosphere by 1.7 W/m2 and cools the surface by -1.7 W/m2. There is no physical reason that this could not be the case, as aerosols have a wide range of reflectivity.
And of course, at that point we have no change in the TOA radiation, but despite that the surface is cooling.
Which brings me at last to the point of this post. To remind everyone, the canonical equation says that the change in surface air temperature ( ∆T ) in degrees Celsius is some constant “lambda” ( λ ) times the change in TOA forcing ( ∆F ) in watts per square metre (W/m2). Or as an equation, ∆T = λ ∆F, where lambda( λ) is the climate sensitivity.
But in fact, all that has to happen to make that equation fall apart is for something to interfere with the greenhouse gain. If the efficiency of the greenhouse system is reduced in any one of a number of ways, by black carbon in the atmosphere or increase in cloud albedo or any other mechanism, the surface temperature goes down … REGARDLESS OF WHAT HAPPENS WITH TOA FORCING.
This means that the surface temperature is not simply a function of the TOA forcing, and this clearly falsifies the canonical equation.
In fact, I can think of several ways that surface temperature can be decoupled from forcing, and I’m sure there are more.
The first one is what we’ve just been discussing. If anything changes the greenhouse thermal gain up or down, the TOA radiation can stay unchanged while the surface radiation (and thus surface temperature) goes either up or down.
The second is that clouds can decrease the amount of incoming energy. It only takes a trivial change in the clouds to completely counterbalance a doubling of CO2. This is a major function of the tropical clouds, which counteract increasing forcing by forming both earlier and thicker.
The third is that the system can change the partitioning between the throughput and the turbulence. The throughput is the amount of energy that is simply transported from the equator to the poles and rejected back to space. On the other hand, the turbulence is the energy that ultimately goes into heating the climate system. In accordance with the Constructal Law, the system is constantly evolving to maximize the total of these two.
Fourth, the El Nino/La Nina system regulates the amount of cool ocean water that is brought to the surface, as well as increasing the heat loss, to avoid overheating. (One curious consequence of this is that the surface temperature in the El Nino 3.4 area has not warmed over the entire period of record … but I digress).
Part III – CONCLUSIONS
The conclusion is that the simplistic paradigm of a linear relationship between temperature and forcing can’t survive the observations of Ramanathan regarding black carbon. For the surface temperature to vary without changes in the TOA forcing, all that needs to happen is for the greenhouse thermal gain to change.
w.
APPENDIX- How it works out
For the math involved, let me steal a diagram from my post, “The Steel Greenhouse”
Figure 2. Single-shell (“two-layer”) greenhouse system, including various losses. S is the sun, E is the Earth, and G is the atmospheric greenhouse shell around the Earth. The height of the shell is greatly exaggerated; in reality the shell is so close to the Earth that they have about the same area, and thus the small difference in area can be neglected. Fig. 2(a) shows a perfect greenhouse. W is the total watts/m2 available to the greenhouse system after albedo. Fig. 2(b) is the same as Fig. 2(a) plus radiation losses Lr which pass through the atmosphere, and albedo losses ( L_albedo ), shown as W0-W. Fig. 2(c) is the same as Fig. 2(b), plus the effect of absorption losses La. Fig. 2(d) is the same as Fig. 2(c), plus the effect of thermal losses Lt. These thermal losses can be further subdivided into sensible ( L_sensible ) and latent heat ( L_latent ) losses (not shown).
We are interested in panel (d) at the lower right of Figure 2. It shows the energy balances.
As defined above, the thermal gain ( G ) of a greenhouse is the surface temperature (expressed as the equivalent blackbody radiation) divided by the incoming solar radiation after albedo. In terms of the various losses shown in Figure 2, this means that the greenhouse thermal gain G is therefore:
where
The important thing to note here is that if any of these losses change, the greenhouse gain changes. In turn, the surface temperature changes … and the TOA balance doesn’t have to change for that to happen.
You wrote a better answer than my question deserved. I was thinking along the lines of “Absorption raises the electrons to higher energy states; emission occurs when they return to the lower state; if there is a collision then the high energy electrons are reduced to lower energy states without emission of photons .” I didn’t know if it was possible, and my ability to formulate a question totally vanished.
be commensurate with the energy differential of the levels involved to be probable. This is where classical assumptions break down. Or it requires the possibility of resonant transfer between commensurate levels in the colliding species.
for temperatures in this range to 
for frequencies in the IR band of CO_2. But I have class in a few minutes and don’t have time to do the lookups and multiplications. Probably somebody has done it for you (and better than I would on the back of an electronic envelope) if you google for it.
It can, as can its inverse, but it requires that
In a cold gas, collisions simply won’t either excite or de-excite most energy levels available to the molecules, I think. But they can bend them a bit, and if a recoiling molecule has enough translational energy compared to the energy levels involved it becomes more likely. Honestly, I have no idea what constitutes “cold” or “likely” for CO_2 in the temperature range of 170-300 K. I suppose I could figure it out — one needs to guestimate-compare
rgb
By the way, there is a model that can actually resolve some of this stuff. It’s the brainchild of one man, Mark Jacobson, as good things often are. It’s called GATOR-GCMOM, and it does the stuff the other models only pretend to do.
Yes, at the end of the day it’s still a model … but it’s a reasonable one.
Paper saved, thanks. If I ever do have time to mess with this, I’ll maybe start with this as a base on your recommendation. I’ve already got a few of the GCM sites/codes linked, but don’t think I’d found this one. I do so love large scale computation (and know a lot about simulations and so on) and would guess I can improve any model I look at, but starting with a decent one is a lot better than starting from one that is mostly crap.
And besides, “time” — who am I kidding? I’ll have time when I’m dead, most likely.
rgb
rgbatduke says:
March 30, 2012 at 9:03 am
That post and the one following constitute a major contribution to the debate, IMO. It is an important complement to the static model that is used in “Principles of Planetary Climate” by Raymond T. Pierrehumbert (a book I admire and respect.)
Thanks; gives some context to the cite by G&T of Schack:
RE
rgbatduke says:
@ur momisugly March 30, 2012 at 9:03 am
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Many thanks. Grateful for your time. I won’t pretend to properly understand all you have written but I was able to mostly follow your reasoning (when things get multi-deimensional, I get a bit lost) The whole subject of phase transition, stable states, critical points, complexity and emergent behaviours is really fascinating.
If you are able to link to your Physical Review paper (if publicly availably) I would really appreciate that…
I have this analogy in my mind that is probably not approapriate: petrol motors, even if not well-tuned can idle along well enough if the revs are sufficiently high. If the revs fall below some critical point, a motor begins to splutter and eventually stalls. If the evolution of our sun has been from dim to progressively brighter (increasing revs) might we reasonably expect that the boundary conditions where sputtering and stalling can occur (potential to flip to a cold stable state) will change/ evolve – such that crticial points (in a bistable system) are reached less frequently in the future? That is, entropy produciton motors attain some super-stable state? Or am I thinking complete nonsense?!
“Andrew says:
March 29, 2012 at 11:02 pm
the ice age phenomenon is addressed by the MEP principle in a paper?”
Andrew, a paper I have read is Entropy production and multiple equilibria: the case of the ice-albedo feedback, but a better one might be Orbital forcing and role of the latitudinal insolation/temperature gradient .
And yes, I agree with you on the Gaia hypothesis. I consider this little escapade in that paper as pointing at the fact that the mystified Gaia hypothesis may be explained as just a plain result of thermodynamics with the 2nd Law in particular.
Earth is just a big rock obstructing the solar flux. The radiation hitting earth gives opportunities for this energy to dissipate and increase in entropy. Photons hit the surface and 20 times as many leave as low quality IR photons. Others are converted into heat in the ocean and atmosphere, and this heat has to work its way out through maybe thousand of interlinked thermodynamical, mechanical, chemical and biological processes at various speeds. These are all one way or another following the 2nd Law / MEP and can result in self organisation.
So yes, lot’s of the processes are influenced by one or more other processes through the dynamical way all the different gradients in temperature, pressure and concentration evolve. These form a jungle of feedbacks working as described by Le Chatelier’s principle which is again the 2nd Law. And these feedbacks are negative so you get all these nice balances on earth.
rgb;
“These are all one way or another following the 2nd Law / MEP and can result in self organisation.”
With the interesting refinement of the interventions of biology; the atmosphere’s contents and composition are substantially, or even entirely, the result of life processes.
RE
Hans says:
@ur momisugly March 30, 2012 at 5:24 pm
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Many thanks Hans. These look great. Such an exciting area of science: starting to wish I had payed more attention to physics at school… Amazing isn’t it: the sophistication and power of emergent thought arising from the complex brain…
rgbatduke; Many physical laws look similar, but they work only when applied properly in proper situations.
According to the Kirchhoff’s law, an object that absorbs emits, and an object that emits absorbs. N2 and O2 do not emit because they do not absorb. In terms of math equation, ε σT^4 leads to 0 at whatever T if literally ε=0.
Now how to interpret the TOA IR spectra: for the CO2 absorption bands (e.g. 15 um one), the spectra detect the radiation by CO2 molecules within the layer from TOA down its absorption depth; therefore the radiation irradiance is determined by the “average” temperature of CO2 molecules within the layer. One can work out similarly what for the absorption bands for any other radiative gases. For the rest of bands, the spectra detect the radiation from the Earth ground surface.
Now a question arises: if the earth ground surface is filtered (or literally covered with a white cloth) so that there is no radiation for CO2 to absorb, will the TOA IR spectra show 0 over its absorption band 15 um? Of course not, CO2 emits only according to its temperature regardless whether gaining temperature by molecular collision or by absorption.
Kelvin Vaughan says:
March 28, 2012 at 1:57 am
Philip Bradley says:
Most studies show surface cooling and upper troposphere warming during the dry season.
Isn’t that due to less water vapour in the atmosphere?
I should have said,
Most studies show a surface cooling trend and an upper troposphere warming trend during the dry season.
rgb, thanks for a very interesting and informative series of posts.You highlight the role of albedo in moving between stable climate states. Early today in another thread I referenced a paper by Christy that showed a 3C increase in temperatures in California’s Central Valley over the 20th C due to irrigation and albedo changes from irrigation.
Humans have caused large scale albedo changes since hunter gathers 50K years ago started using fire to promote grasslands over forest. This continued with the spread of agriculture and albedo was further affected by large increases in irrigation over the last century. From memory 30% of all arable lands are irrigate today.
These anthropogenic albedo changes aren’t restricted to the land surface. As discussed above particulates are effectively changing the albedo of the troposphere.
Here in Western Australia we have an interesting natural experiment. There is a fence that runs for about a thousand kilometers with unirrigated wheat fields on one side and natural dryland forest on the other side. What is commonly observed in summer is that the forest side has substantial cloud cover, while the wheatfields side has no clouds. The boundary exactly follows the line of the fence.
This paper has a number satellite images showing the albedo and cloud cover differences on either side of the fence.
http://researchrepository.murdoch.edu.au/2090/1/Effects_of_land_use_in_Southwest_Australia.pdf
There is a case to be made that solar insolation and albedo changes are the anthropogenic effects that matter in climate change.
Philip Bradley says:
March 31, 2012 at 6:32 pm
“Humans have caused large scale albedo changes since hunter gathers 50K years ago started using fire to promote grasslands over forest. This continued with the spread of agriculture and albedo was further affected by large increases in irrigation over the last century. From memory 30% of all arable lands are irrigate today…”
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But what about all the wetlands that have been drained over the last 2 millenia to facilitate this agriculture (eg. throughout Europe and Asia); the desertification of vast areas (eg. in China, Africa); the disappearence of vast lakes and inland seas (in ex-Soviet Russia)… What effects do these man-made changes have your back-of-envelope albedo calclulations Philip?
To be fair, if you go back to rgb’s comments you will see that he made a big point that the paleoclimatic record shows no evidence of instability via run-away warming… he also emphasised how little we know about what has driven the Earth to flip between warm and cold stable states (assuming teh climate is in a bistable system) over geological time frames prior to humans, indeed, prior to the emergence of any life on this planet…
I think you’re anthropocentric (Gaia) world view overlooks the inconvient truth that the complex climate system moves to it’s own rhythm and we know very little about it.
Andrew says:
March 31, 2012 at 9:04 pm
My point was simply that we humans have made land use changes with local and regional effects on temperature substantially larger than the claimed GHG AGW effect. What the net effect of albedo changes on a global scale is, I have no idea. But they do seem large enough to have a significant effect on global averages.
As for disappeared lakes and inland seas, we have created many thousands of new lakes through dams.
I think this is the first time I have been called a Gaiaist.
FWIIW, I happen to think solar insolation changes due to aerosol, cloud seeding and possibly GCRs, have been at least as a significant effect on measured surface temperatures as GHGs over the last 50 years. What relationship measured surface and troposphere temperatures have to climate warming/cooling is a whole other discussion.
regards
rgbatduke says:
March 30, 2012 at 9:27 am
“A widely used and well accepted but misleading terminology is “reradiate” or “re-radiate.” Typical statement such as “carbon dioxide absorbs IR then reradiates the energy,” implies that carbon dioxide does not emit IR if it does not absorb first. Radiation physics, as indicated by the SB equation, says that CO2 emits 24/7 as long as its temperature is not 0 K, regardless whether it absorbs or not.”
Yeah, but quantum physics says otherwise. In this debate, quantum physics wins hands down.
Agreed
If kT is less than the excitation energy of an emitting level, BB radiation will be very small indeed. This guy named Planck, you might recall, worked on this. This is why radiation from O_2 and N_2 is not a major contributor to radiative cooling of the atmosphere in spite of the fact that they are in thermal equilibrium with the CO_2 — it isn’t that they don’t have levels that can radiate, it is that those levels don’t get excited by kT-level collisions. Neither, for the most part, do those of CO_2.
Absent a dipole N2 and O2 don’t radiate either. That’s why an electrically excited N2 molecule is able to collisionally excite a CO2 molecule in a CO2 laser and the CO2 emits not the N2.
If you doubt this, I refer you directly to TOA IR spectra that make the point conclusively. The CO_2 blocking of surface radiation in the IR bands, and its eventual reradiation at a much colder temperature in those bands is clearly a resonant absorption phenomenon, dominated by scattering and not simple radiative cooling. An atom has no “temperature”. A molecule has no “temperature”. It has some mix of translational and electronic energy.
Actually a mix of translational, rotational, vibrational, and electronic energy
Radiation comes from , rotational, vibrational, and electronic excitation energies, but most of its “thermal energy” is bound up in translation,
In the case of diatomics yes, but not polyatomics like CO2 and H2O where most of the energy is not in translation.
and it is the general case that when kT is too small to populate a quantum degree of freedom, those degrees of freedom are not in thermal equilibrium with T. Again, this is all laid out in kiddie physics books apparently better in chem. Books 😉, where it explains why monoatomic molecules have 3 degrees of freedom and diatomic molecules generally have 5, in spite of the fact that they should have 7 actually 6, it’s 3Nif one allows for axial rotations and vibrations. At most temperatures the axial rotation and vibratory quantum states are not excited.
At room temps the rotational are excited (and a small fraction have excited vibrations too), otherwise the specific heat of diatomics and poly atomics would be the same as monatomics.
The IR absorptions by the GHGs are in the vibrational and rotational levels, not electronic as mentioned in one of the other posts.
Tons of evidence (specific heats, etc).
Exactly.
Willis;
Philip’s ref., the SW Australia paper, suggests a fascinating extrapolation: ag land use causes a positive feedback moisture/temp cycle, while native vegetation operates as a negative feedback.
E.g., hotter in the middle of the summer on the ag land:
http://researchrepository.murdoch.edu.au/2090/1/Effects_of_land_use_in_Southwest_Australia.pdf
Now a question arises: if the earth ground surface is filtered (or literally covered with a white cloth) so that there is no radiation for CO2 to absorb, will the TOA IR spectra show 0 over its absorption band 15 um? Of course not, CO2 emits only according to its temperature regardless whether gaining temperature by molecular collision or by absorption.
I agree, within limits. Were we disagreeing about something like this? The point is that this is a self-consistent result, to the extent that the scattering is sufficiently multiple that the radiation remains at near-thermal equilibrium on the way up. If you truly cover the ground with a perfectly reflective cloth you will indeed change the temperature of TOA radiation, and not in a good way…;-)
To discuss the equilibrium of radiation plus atoms or molecules, however, is ultimately a problem in quantum stat mech, beginning with the assumption of thermal equilibrium. The point being that when certain rates are highly disparate in an open system, the system is in a state of broken ergodicity and hence is not in thermal equilibrium. These sorts of states happen all of the time — laser dynamics is predicated upon them — and are the reason that CO_2 does help radiate away energy but O_2 and N_2 and He all do not, given the outgoing radiation spectrum from the surface. At a different surface temperature, CO_2 might be a non-factor and O_2 and N_2 might be important (although probably not so much given their less complex spectra).
Again, all of this is perfectly visible in TOA spectra, which is why I think that we agree — if we agree that that spectra accurately reflects the underlying physics, how could we not but agree? Nor am I asserting that my multiple scattering model is a perfect one for upwelling/downwelling radiation — personally I intensely dislike that model from the beginning because it is an open invitation to abuse — but it does help one see how there is radiation redirected back to the surface of the Earth from the blanketing CO_2 fraction, as well as energy “trapped” in a retarded transit from the ground to where the atmosphere becomes optically transparent in the relevant bands. The radiation from those molecules is, as you note, still roughly thermalized with the base temperature of the molecules themselves at that point (from TOA IR spectra) which makes perfect sense.
rgb
To be fair, if you go back to rgb’s comments you will see that he made a big point that the paleoclimatic record shows no evidence of instability via run-away warming…
…from the Earth’s current warm phase state to a still warmer phase. Specifically, this figure:
http://en.wikipedia.org/wiki/File:Ice_Age_Temperature.png
shows antarctic ice core derived temperatures over the last 5 cycles — no third phase evident — and:
http://commons.wikimedia.org/wiki/File:Five_Myr_Climate_Change.png
shows temperature derived from deep sea sediment cores over the last 5 million years. This figure is positively fascinating, as it shows that the current interglacial temperatures are an excursion back to a warm phase that was stable up to 2.7 million years ago with no stable cold phase attractor. Since then the baseline mean temperature has dropped some 6 degrees Kelvin to ice age as the dominant stable state but with a puzzling return to a very chaotic warm phase (bistability) that has only appeared in the last million years, a bistability that appears to actually be stabilizing with more well defined cold and warm phase states but with very little time spent in warm phase. The interglacials are basically sharp spikes back to warm phase on the time scale of this figure.
There is no evidence whatsoever of a still-warmer phase that is feedback stable in this data. In particular, even when the warm phase was stable four million years ago, the global average temperature was a stable 1.5 K warmer than it is now, with remarkably little excursion or noise.
Personally, I think the best possible thing for the human race would be for the Earth to return to this stable warm phase “permanently”, no matter what the dislocations and cost. The catastrophic probability clearly evident in this figure is that on the scale of this figure, the entire Holocene is a spike away from global temperatures that truly are catastrophic; if I were told that this figure described the energy content of an absolutely arbitrary unknown open system I would immediately conclude that the lower energy state was the more probable, that the system is exhibiting bistability with hysteresis, and that the higher energy state is generically unstable with respect to the lower energy state nearly all of the time.
I’m in the process of writing a review-style article I hope to post to WUWT that will examine what I believe to be a serious risk factor — albedo modulation — that can trigger the transition. I’m busy and don’t know when I will finish, but I’ve already given the punch line for those that are familiar with the formula for a baseline greybody temperature — the 6% increase in albedo observed over the last 15 years corresponds to a drop in the baseline pre-GHE greybody temperature of the Earth of at least 2K. Depending on feedback, this might be further amplified or minimized. If the IPCC estimates of climate sensitivity are correct we can expect this temperature drop to be amplified by a factor of 2 to 5, more than enough to trigger a return to an ice age if the albedo remains so shifted for long enough (at least decades, possibly centuries).
This actually raises the disturbing possibility that ice ages are not due to Milankovitch cycles at all, that orbital resonances and so on are irrelevant to them. The emergence of the stable cold phase — actually, the gradual and systematic depression of the warm phase stable state to a colder stable phase but with increasing noise and recently emergent bistability — shows no sign whatsoever of orbital resonance periodicity until maybe the last million years, where it could well be a chaotic system with a bistable oscillation slaving to a weak non-causal perturbation that is otherwise irrelevant to the primary effect (the emergent nearly stable cold phase).
Could ice ages themselves be predominantly due to positive feedback albedo modulation due to very long timescale variability of the sun? They could. They could indeed. For example, as the sun bobs up and down across the galactic plane, it passes (one presumes) through zones where baseline particulate matter is more or less dense. While much of the small stuff is driven outward by photon pressure, all particles greater than a certain size have a tendency to infall (given the right initial conditions) and might well cause a gradual accretion of solar mass and consequent alteration of solar state. I’d be very interested in Lief’s opinion on this — could the Sun have very long term variability in its magnetic state (that is much more subtle than its surface brightness) that suffices to e.g. cause albedo modulation? Noting well that micrometeorite flux (also a cloud nucleation contributor) should independently increase during precisely the same periods, allowing for multiple channels for cloud albedo modulation to where it triggers positive feedback from glaciation…
rgb
Actually a mix of translational, rotational, vibrational, and electronic energy
Radiation comes from , rotational, vibrational, and electronic excitation energies, but most of its “thermal energy” is bound up in translation,
In the case of diatomics yes, but not polyatomics like CO2 and H2O where most of the energy is not in translation.
and it is the general case that when kT is too small to populate a quantum degree of freedom, those degrees of freedom are not in thermal equilibrium with T. Again, this is all laid out in kiddie physics books apparently better in chem. Books ;-), where it explains why monoatomic molecules have 3 degrees of freedom and diatomic molecules generally have 5, in spite of the fact that they should have 7 actually 6, it’s 3Nif one allows for axial rotations and vibrations. At most temperatures the axial rotation and vibratory quantum states are not excited.
Thanks for the correction — I don’t think as much about polyatomics (partly because they are so complicated:-). As for degrees of freedom, I was counting p_x, p_y, p_z, L_x, L_y, L_z, and k_z. If one visits here:
http://en.wikipedia.org/wiki/Degrees_of_freedom_%28physics_and_chemistry%29
(as I did to make sure that I’m not losing my mind:-) while you are correct that at room temperature one generally counts only three translation, two rotation, and one vibration, the reason is that it is very difficult to excite rotation around the (z) axis of symmetry so it is generally not counted. But this itself is a kT argument — it isn’t that the DoF isn’t there, it is that we can almost always neglect it (because its moment of inertia is so very small and because the molecule will probably come apart before we excite the mode thermally). I yes, I know, 3N is the standard textbook answer in the tables, but the actual explanation is that one neglects axial rotation which is there but irrelevant in exactly the same way other degrees of freedom can freeze out and become irrelevant if kT is too small.
But the point — as we seem to agree — is that one can’t pretend a problem in quantum statistical mechanics is a problem in classical statistical mechanics and get the right answer, as Planck demonstrated to usher in the quantum era in the first place. One can use semiclassical reasoning to a point, but that point stops short of saying that O_2 and N_2 will radiate just as much energy as CO_2 molecules that they are in thermal equilibrium with, a Commonly Made Mistake in thread comments on the blog (perhaps in addition to a list of FAQs we need a list of CMMs and their corrections whether or not anybody asks the “question” they should to avoid them:-).
rgb
rgbatduke says:
April 2, 2012 at 10:07 am
This figure is positively fascinating, as it shows that the current interglacial temperatures are an excursion back to a warm phase that was stable up to 2.7 million years ago with no stable cold phase attractor. Since then the baseline mean temperature has dropped some 6 degrees Kelvin to ice age as the dominant stable state but with a puzzling return to a very chaotic warm phase (bistability) that has only appeared in the last million years, a bistability that appears to actually be stabilizing with more well defined cold and warm phase states but with very little time spent in warm phase. The interglacials are basically sharp spikes back to warm phase on the time scale of this figure.
The formation of the Isthmus of Panama about 3 million years ago and the growth of the Himalayas may well have had something to do with that.
FWIIW, I happen to think solar insolation changes due to aerosol, cloud seeding and possibly GCRs, have been at least as a significant effect on measured surface temperatures as GHGs over the last 50 years. What relationship measured surface and troposphere temperatures have to climate warming/cooling is a whole other discussion.
Absolute agreement on my part, although I would be broader than just GCRs. We are just starting to appreciate how much “black junk” there is in the interstellar zones, not to mention the Oort cloud. The sun is also still very much a — ahem — “black” box as far as our ability to fully understand what is going on deep inside it is concerned, although as our ability to look at things like neutrinos improves and dynamo models start to work well enough to be long term predictive (if that ever occurs) and it may well have significant long term variability that feeds the process. But albedo is indeed an omitted variable in GCMs (at least as a variable) because if it weren’t, the GCMs would have been adjusted for the short term increase in albedo observed in the last fifteen years and their predictions would have moved rather radically cooler.
rgb
Jinan Cao says:
March 31, 2012 at 1:55 am
rgbatduke; Many physical laws look similar, but they work only when applied properly in proper situations.
According to the Kirchhoff’s law, an object that absorbs emits, and an object that emits absorbs. N2 and O2 do not emit because they do not absorb. In terms of math equation, ε σT^4 leads to 0 at whatever T if literally ε=0.
Now how to interpret the TOA IR spectra: for the CO2 absorption bands (e.g. 15 um one), the spectra detect the radiation by CO2 molecules within the layer from TOA down its absorption depth; therefore the radiation irradiance is determined by the “average” temperature of CO2 molecules within the layer.
Except that in the lower levels of the troposphere the CO2 band is optically thick so the observed emission is only from the thinner upper levels, so not the average T.
Phil. says:
April 2, 2012 at 10:38 am
Except that in the lower levels of the troposphere the CO2 band is optically thick so the observed emission is only from the thinner upper levels, so not the average T.
I said “the “average” temperature of CO2 molecules within the layer”, not the average temperature of the atmosphere.
rgbatduke says:
April 2, 2012 at 10:23 am
Thanks for the correction — I don’t think as much about polyatomics (partly because they are so complicated:-).
No problem, I generally didn’t work with monatomics because they are so simple. 😉
As for degrees of freedom, I was counting p_x, p_y, p_z, L_x, L_y, L_z, and k_z. If one visits here:
http://en.wikipedia.org/wiki/Degrees_of_freedom_%28physics_and_chemistry%29
(as I did to make sure that I’m not losing my mind:-) while you are correct that at room temperature one generally counts only three translation, two rotation, and one vibration, the reason is that it is very difficult to excite rotation around the (z) axis of symmetry so it is generally not counted. But this itself is a kT argument — it isn’t that the DoF isn’t there, it is that we can almost always neglect it (because its moment of inertia is so very small and because the molecule will probably come apart before we excite the mode thermally).
For sure since the moment of Inertia depends on the nuclear dimensions!
I yes, I know, 3N is the standard textbook answer in the tables, but the actual explanation is that one neglects axial rotation which is there but irrelevant in exactly the same way other degrees of freedom can freeze out and become irrelevant if kT is too small.
For nonlinear polyatomics all three rotations exist and you still get 3N. Of course no-one considers electronic dofs either.
But the point — as we seem to agree — is that one can’t pretend a problem in quantum statistical mechanics is a problem in classical statistical mechanics and get the right answer, as Planck demonstrated to usher in the quantum era in the first place. One can use semiclassical reasoning to a point, but that point stops short of saying that O_2 and N_2 will radiate just as much energy as CO_2 molecules that they are in thermal equilibrium with, a Commonly Made Mistake in thread comments on the blog (perhaps in addition to a list of FAQs we need a list of CMMs and their corrections whether or not anybody asks the “question” they should to avoid them:-).
I agree absolutely, I’ve lost count of the number of times I’ve been abused for making that point. Welcome to the club, I noticed you fighting the good fight on Tallbloke’s blog, I got banned for quoting N&Z, which contradicted him, so I didn’t go back to see how you made out.
Jinan Cao says:
April 3, 2012 at 3:22 am
Phil. says:
April 2, 2012 at 10:38 am
I said “the “average” temperature of CO2 molecules within the layer”, not the average temperature of the atmosphere.
But you defined the layer as:
“the spectra detect the radiation by CO2 molecules within the layer from TOA down its absorption depth”,
Where’s the bottom of the layer, all the way to the surface?
Phil. says:
April 4, 2012 at 4:40 pm
Jinan Cao says:
April 3, 2012 at 3:22 am
Phil. says:
April 2, 2012 at 10:38 am
I said “the “average” temperature of CO2 molecules within the layer”, not the average temperature of the atmosphere. But you defined the layer as: “the spectra detect the radiation by CO2 molecules within the layer from TOA down its absorption depth”,
Where’s the bottom of the layer, all the way to the surface?
The absorption depth is likely a figure of 1 km or 10 km. Actual value of the absorptin depth needs to be determined according to the Beer’s law, as well as the properties of CO2 such as concentration.
Welcome to the club, I noticed you fighting the good fight on Tallbloke’s blog, I got banned for quoting N&Z, which contradicted him, so I didn’t go back to see how you made out.
I didn’t wait to get banned, I just got tired of my posts being annotated or censored, and yeah, got a bit tired of trying to explain why a dimensionless functional form with totally nonphysical dimensioned quantities embedded was absurd. That and when I finally actually looked up the temperatures and pressures on the rest of Jupiter’s moons and plotted them, they didn’t fall anywhere near the supposed universal curve — including the result for Europa. In fact, it was pretty clear that the numbers were fit to the curve, not the curve to the numbers.
So I quit. N&Z is horse-hockey. So is Jelbring. The kind of thing that gives skeptics a bad name.
It’s a shame, actually. N&Z have one or two good ideas, and if they would stop with them instead of trying to assert a “miracle” curve that is neither a miracle nor a reasonable curve, it might actually contribute to the science instead of diverting a huge amount of energy on an obviously erroneous argument.
But that’s OT for this thread, I suppose. I am a card-carrying skeptic, highly dubious of CAGW, but I do, really, try to keep my skepticism based on sound physics and reasonable argument.
rgb
Robert – well said.
Tallbloke keeps digging his hole deeper and deeper over there. I now have a special category of link title for his “way out there” stuff.
Dragonslayers and the N&Z crowd just aren’t going to help climate skepticism in general, so they must be abandoned along the trail forward.