As predicted in 1967 by Manabe and Wetherald, the stratosphere has been cooling.
A new paper by Ben Santer and colleagues has appeared in PNAS where they extend their previous work on the detection and attribution of anthropogenic climate change to include the upper stratosphere, using observations from the Stratospheric Sounding Units (SSUs) (and their successors, the AMSU instruments) that have flown since 1979.
So SSU me
Like MSU trends, these records reflected a weighted average of atmospheric temperatures, and the three SSU channels progressively weight higher levels in the stratosphere, roughly centered on 30km, 40km and 45km above the surface but with quite a bit of overlap. Until relatively recently, there were some discrepancies in what the climate trends were from these instruments because of the usual issues with remote sensing – instrument trends, orbital shifts, inter-satellite calibration etc. Thompson et al. (2012) described the issues as ‘mysterious’, but efforts to better correct the record for non-climatic effects soon bore fruit, and the ‘mystery’ became history (Maycock et al., 2018). We are using the NOAA-STAR version 3.0 of these products (Zou et al., 2014).
Since then, these records have been used to assess the solar contributions to stratospheric temperatures and as a standard part of the GISS Model evaluation (most recently in Casas et al., 2023) and also in the “Climate Drivers” animation. The Santer et al contribution is the first time I’ve seen these diagnostics calculated for the CMIP6 models (or at least a subset of them), and so this is a great opportunity to add the SSU trends to our catalogue of model-observation comparisons that can be maintained going forward.
A couple of things to note before we get to that analysis though. First, the internal variability of the global mean values of these records is much smaller than for the tropospheric MSU trends, and that means that the (forced) signal to noise is much higher. The dominant factors are changes in CO2 (a cooling), ozone depletion (a cooling), warming from big volcanoes, and oscillations related to the solar cycle.
But why is the stratosphere increasingly chill?
For some reason, this has been poorly communicated among otherwise knowledgeable folk, and our early efforts to explain this were not very good (this featured in the only RealClimate post we ever basically retracted – though you can find it if you care to look!). Part of the confusion related to the role of the ozone layer in the lower stratosphere, but it turns out that is just a distraction, since the cooling due to increasing CO2 is seen everywhere above the tropopause – not just in regions with lots of ozone.
The basic concept is easy to grasp though. Concentrations of CO2 are increasing throughout the atmosphere and while we might think of greenhouse gases as absorbers of infra-red radiation from the surface, they are also emitters of IR radiation, so whether they warm or cool a region of the atmosphere is due to whether the net change (increased absorption vs increased emission) is positive or negative. The upper atmosphere is different from the troposphere in that pressure is much less, and it’s very dry. That means the greenhouse substances are basically just CO2 and ozone, and they absorb in quite different parts of the spectrum. In the band of radiation where CO2 absorbs a lot (~15 $\mu$m), increasing CO2 levels in the troposphere make it ever harder for those photons to get to the stratosphere or above. The upward IR comes increasingly from the water vapour or cloud bands, which because the upper atmosphere is so dry, does not get absorbed significantly on it’s way out.
Looking down from above, our extra stratospheric CO2 molecules then see less radiation to absorb coming up, but they are totally happy emitting more – half of which goes up into space. So the net effect is less absorption and more emittence, and thus they give a cooling. The effect is larger the further up you go.
How well do the models do?
As in previous comparisons, I’ll plot the envelope of the CMIP6 ensemble, in this case there are 32 individual runs from 9 distinct models. Unlike in the MSU or SST comparisons, there is no significant variation in the trends as a function of climate sensitivity, and so there is no need to plot the screened models separately. [This might be surprising, but remember that the variation in climate sensitivity is dominated by cloud feedbacks which are not very important in the stratosphere].
The two big warming events in the earlier part of the record are the impacts of the El Chichon and Mt Pinatubo eruptions (and you’ll note quite a wide spread in magnitude of the latter event) and if you squint, you can see the solar cycle (maxima around 1981, 1991, 2002, 2014). The trends are dominated by the CO2 changes (more so as you move higher), but there is also a component from ozone depletion. As mentioned above, the internal variability and structural uncertainty in the model ensemble is smaller than in the troposphere, and so mismatches between the models and the observations are likely due to small issues in the forcings (particularly ozone, but perhaps also small volcanoes). It’s possible that the quality of the stratospheric circulation and it’s sensitivity to warming may be important. However, the discrepancies in the trends are small.
- B.D. Santer, S. Po-Chedley, L. Zhao, C. Zou, Q. Fu, S. Solomon, D.W.J. Thompson, C. Mears, and K.E. Taylor, "Exceptional stratospheric contribution to human fingerprints on atmospheric temperature", Proceedings of the National Academy of Sciences, vol. 120, 2023. http://dx.doi.org/10.1073/pnas.2300758120
- D.W.J. Thompson, D.J. Seidel, W.J. Randel, C. Zou, A.H. Butler, C. Mears, A. Osso, C. Long, and R. Lin, "The mystery of recent stratospheric temperature trends", Nature, vol. 491, pp. 692-697, 2012. http://dx.doi.org/10.1038/nature11579
- A.C. Maycock, W.J. Randel, A.K. Steiner, A.Y. Karpechko, J. Christy, R. Saunders, D.W.J. Thompson, C. Zou, A. Chrysanthou, N. Luke Abraham, H. Akiyoshi, A.T. Archibald, N. Butchart, M. Chipperfield, M. Dameris, M. Deushi, S. Dhomse, G. Di Genova, P. Jöckel, D.E. Kinnison, O. Kirner, F. Ladstädter, M. Michou, O. Morgenstern, F. O'Connor, L. Oman, G. Pitari, D.A. Plummer, L.E. Revell, E. Rozanov, A. Stenke, D. Visioni, Y. Yamashita, and G. Zeng, "Revisiting the Mystery of Recent Stratospheric Temperature Trends", Geophysical Research Letters, vol. 45, pp. 9919-9933, 2018. http://dx.doi.org/10.1029/2018gl078035
- C. Zou, H. Qian, W. Wang, L. Wang, and C. Long, "Recalibration and merging of SSU observations for stratospheric temperature trend studies", Journal of Geophysical Research: Atmospheres, vol. 119, pp. 13,180-13,205, 2014. http://dx.doi.org/10.1002/2014JD021603
- M.C. Casas, G.A. Schmidt, R.L. Miller, C. Orbe, K. Tsigaridis, L.S. Nazarenko, S.E. Bauer, and D.T. Shindell, "Understanding Model‐Observation Discrepancies in Satellite Retrievals of Atmospheric Temperature Using GISS ModelE", Journal of Geophysical Research: Atmospheres, vol. 128, 2022. http://dx.doi.org/10.1029/2022JD037523
42 Responses to "CMIP6: Not-so-sudden stratospheric cooling"
My phones google account notified me of this a couple of days ago: “The Upper Atmosphere Is Cooling, Prompting New Climate Concerns. A new study reaffirming that global climate change is human-made also found the upper atmosphere is cooling dramatically because of rising CO2 levels. Scientists are worried about the effect this cooling could have on orbiting satellites, the ozone layer, and Earth’s weather.” (Yale climate connections)
[Response: I don’t know why this would prompt new climate concerns? As I said this was predicted more than 50 years ago, and has been validated many times before now. The impact on low earth orbit spacecraft is that density is decreasing and so there is less friction and so satellites would be expected to last longer on orbit. – gavin]
Nick Palmer says
Fred Pearce’s article uses an old rhetorical trick by saying things like ‘scientists are worried…’ which many might think implies that ALL scientists are worried. Ben Santer himself is quoted as being ”worried’ by his results but the implication in zhe article is that Santer has new worries from these trsults that he didn’t have before. As Gavin says, these stratospheric effects have been predicted to occur for 50 years
I think the tone of Pearce’s article is at least misleading, verging on alarmist – or at least that is how it will be represented by the denialist faction but, on the other hand, it will be eagerly promulgated by alarmist activists
Nick Palmer says
Sorry about the two typos – fat fingers on a mobile strike again…
I believe we have a serious climate change problem, but I’m not some sort of alarmist activist out on the extreme fringes of the global warming issue.
I posted the article only because it seemed relevant, arrived on my phone just recently, and it raised some issues not mentioned in the article. I’m struggling to see what’s wrong with that.
The article said “Scientists are worried about the effect this cooling could have on orbiting satellites, the ozone layer, and Earth’s weather. and went into some detail on these things” I was hoping for some feedback on whether the three claims were valid.
Karsten V. Johansen says
Should the effects regarding the thinning of the ozone layer in the northernmost parts of the northern hemisphere really be of no concern? Maybe not to people living in the USA, and then it is of course without any relevance here on realclimate… ;-)
Is realclimate silently becoming a site for the people Michael Mann rightly calls *the lukewarmers*, and/or *are we here looking at some kind of strategic planning for survival under the rule of Musk/DeSantis/Putin/Xi&Co. and even more augmented liberalist-totalitarian ignorance and mediocrazy?* Cfr. this https://www.nature.com/articles/s41467-021-24089-6 .
More generally most people also here seems to be rather completely ignoring the main problem with economic growth, discussed here: https://m.youtube.com/watch?v=sI1C9DyIi_8&pp=ygURYWxiZXJ0IGEgYmFydGxldHQ%3D and the problems with what often rather misleadingly is called “our society”, discussed by writers George Orwell, Joseph Conrad (ex. the novel “Typhoon”…), Karel Capek, Victor Serge, August Strindberg and Aldous Huxley, among others.
After all the instigator of the reformed trumpist/fascist coup attempt of january sixth 2021 was never arrested and put before a jury, as he surely and immidiatly would have been in a democratic system. But not so in an oli-/oiligarchy for sure. More fumbling and pre-senile joking-mumuring by mr. Biden and his rich buddies surely won’t make up for that grave historical mistake, and I’m not sure the ukrainians are strong enough to rescue what little is left of democracy by now, even if they are really doing all they can.
Even geophysical science does not exist in a bubble, even if you often get that impression here. This many came to realize during the last big downturn in capitalism ca. 1914-1945. Now the frontal collision between growth and the ecological niche of mankind is at least an order of magnitude greater than it was then. Economic healing by a third global war is not an option now, if you wondered.
Ray Ladbury says
I would note that the most significant piece of climate legislation yet to signed into law bears Joe Biden’s signature. Is it enough? Most certainly not. But half the country right now is batshit crazy
Don’t worry, the ensuing global recession that occurs when the US defaults on its debt ought to shave a couple points of of GDP for a few years.
The basic problem remains: Humans are stupid. The good news is that there is a remedy called the scientific method. The bad news? Most people are too stupid to realize they are stupid and so in need of a remedy.
Nick Palmer says
I think the problem is the rhetorically misleading use of ‘scientists’ rather than the more accurate ‘some scientists’. Furthermore, that the article implicitly insinuates that these are new worries, and not 50 year old well known worries, should make people wary of this source
Nick Palmer, I agree the framing of the issue as ‘scientists’ say xyz lacks accuracy. Its a common media trick I find annoying.
However for me the content of the article was quite good, and that is the main point. I haven’t heard anyone say they were wrong. And it was explained in easy to understand language…
John N-G says
The Yale article notes that, while satellites stay up longer, so does space junk, increasing the chances of a collision.
This is in keeping with the journalistic principle that every silver lining has a cloud. Cue The Onion: “Philanthropist gives $100 bill to every man, woman, and child on Earth; scientists worry about deforestation”
Kevin McKinney says
Thanks for the update on this. As you say, Gavin, a lot of folks aren’t aware of this effect, and it’s a lovely ‘fingerprint’ (especially with reference to the “sun did it” folks).
Paul Pukite (@whut) says
Plenty of fingerprints in the stratosphere but IMO not enough detective sleuthing going on. In the upper stratosphere, the equatorial winds do a complete east-west to west-east and back reversal exactly twice a year. If the sun isn’t responsible for this, not sure what is, since the sun crosses the equatorial ecliptic plane twice a year. That one is obvious to amateur sleuths. Directly below this in the stratosphere is an equatorial layer that does a round-trip reversal every 28 months, what’s called the QBO. It so happens that the moon AND sun cross the Earth’s ecliptic plane near simultaneously twice every 28 months. That is what’s called matching a unique fingerprint — the pattern is there, the supporting evidence exists, and an inference with strong statistical significance provides a working model that can be verified in the future.
In contrast, the stratospheric cooling is a single degree-of-freedom model — heads or tails, it will either cool or heat. Not a lot to go on as far as a unique fingerprint is concerned.
patrick O'twentyseven says
The physics of the QBO is quite interesting. The part I have memorized: upward propagating (group velocity*) fluid mechanical waves, carrying eastward and westward momentum, emanating from the troposphere, are absorbed in the stratosphere (and mesosphere). The absorbtion depends on the type of wave and, among other things, the vertical wind profile. The eastward and westard momentum of the different waves are preferrentially deposited at different heights, changing the wind profile, thus changing where the momentum is absorbed, and so on. If I remember correctly, this produces anomalies that shift downward over time, eastward, then westward, etc. The frequency of the QBO is not driven by an external cycle of like frequency of any sort.
(Similar wave-mean interaction is important in other parts of atmospheric circulation – ??eg., the eddy-driven jet of the midlatitude storm-tracks (correct??). The Brewer Dobson circ. is driven by quasi-stationary vorticity waves coming up from below, if I recall correctly.)
Paul Pukite (@whut) says
Reminder that for QBO, there’s no lab experiment that features gravity, a rotating sphere, and Coriolis, so every model including the current consensus model is just as much conjecture.
You may not have read what I wrote in the previous comment. The less dense layer above the QBO is driven by an cycle of exactly half a year. That’s an external forcing, with 100% certainty. The denser QBO layer is driven by this cycle amplified by the analogous lunar nodal cycle, with just as much certainty based on the predicted value of the period. The way science works is that you have to debunk this model, based on a perfectly valid fingerprint.
Consider an analogy: old man Moon is a suspected murderer since his fingerprints are all over a crime scene, according to forensics (me). You can say that I made a mistake, and if you double-checked and found out the match was off, the moon can go scot-free and my assertion is debunked. I have no problem with that, but given the evidence of a unique fingerprint you have to assume the Moon is guilty.
This is such a strange scientific discipline — qualitative reasoning doesn’t cut it in any other scientific field.
MA Rodger says
Of course, Old Man Moon could have been innocent with his fingerprints having been transferred “all over the crime scene” by somebody carefully putting them there. So they were Old Man Moon’s fingerprints but there is an intermediate process which nobody assessing his guilt has yet picked up on.
And then there is the delightful form of argumentation that denialists so often present.
How can it be Old Man Moon wot dun it as he has an alibi. The Cat and the Fiddle saw him the other side of town with the Cow. And if you are concerned that this a situation requires that the whole science of dactyloscopy used to uniquely identify people to be wrong, do remember this science uses the still not proven concept that “no two people have identical prints”. So it is not a problem asserting that such use of science is entirely wrong and quite useless, this despite the worldwide evidence of more than a century demonstrating otherwise. I mean, who are you going to believe? A couple of lovable fictional characters or some mad scientist?
Paul Pukite (@whut) says
I don’t care if you argue with my analogy, that’s just rhetorical posturing. What you need to debunk is my peer-reviewed published model of QBO :
The originator of early QBO models, Richard Lindzen, tried to find a connection between QBO and lunisolar atmospheric tides. A couple of citations clarify his thoughts:
“For oscillations of tidal periods the nature of the forcing is clear.”
“Planetary waves on beta-planes”, R Lindzen, Monthly Weather Review, 1967
“One rationale for studying tides is that they are motion systems for which we know the periods perfectly, and the forcing almost as well (this is certainly the case for gravitational tides). Thus, it is relatively easy to isolate tidal phenomena in the data, to calculate tidal responses in the atmosphere, and to compare the two. Briefly, conditions for comparing theory and observation are relatively ideal. Moreover, if theory is incapable of explaining observations for such a simple system, we may plausibly be concerned with our ability to explain more complicated systems.
Lunar tides are especially well suited to such studies since it is unlikely that lunar periods could be produced by anything other than the lunar tidal potential.”
Lindzen, Richard S., and Siu-shung Hong. “Effects of mean winds and horizontal temperature gradients on solar and lunar semidiurnal tides in the atmosphere.” Journal of the atmospheric sciences 31.5 (1974): 1421-1446.
Alas, Lindzen could not find the fingerprint of tides in any of the wind data, and perhaps that dissuaded anyone else from looking the past 50 years. Yet there are other ways of discovering these fingerprints, foremost by looking at aliasing of signals with other signals. An aliasing analysis is essentially what I did to discover the pattern. It’s not that hard, Recently I helped a researcher walk through the analysis here:
Recommend reading through this because it provides a good example of how one goes about cross-checking a model.
Barton Paul Levenson says
If you could write up your findings about celestial influences on ENSO (if I have that right) and send it to a journal, you could either make a real contribution to the science, or at least, if it’s rejected, find out where you went wrong.
Paul Pukite (@whut) says
The ENSO model was already published long form in late 2018, and presented short form at a couple of AGU conferences prior to that.
BTW, I wouldn’t personally refer to it as a “celestial” influence as it downplays the massive gravitational forcing of a direct tidal influence.
patrick O'twentyseven says
Holton, James R. “An Introduction to Dynamic Meteorology” 3rd ed. 1992, Academic Press, New York – see section 12.6 – describes QBO caused by 2 types of vertically propagating equatorial waves: Kelvin and Rossby-gravity. It’s possible the basic understanding has been refined and revised since then (?other waves?), but it doesn’t seem to have been overturned:
I may have confused matters a bit by mentioning the mesosphere; the specifics of what I described was for the QBO, but there are waves (I don’t know the latitudinal distribution) that get up there and cause stuff (a pole-to-pole overturning which refrigerates the summer polar mesopause, if I recall correctly).
Meanwhile you haven’t offered any causal mechanism (unless you’re implying the seasonality of solar heating, which for the twice-yearly cycle higher up might be right???). And is the correlation holding up?
patrick O'twentyseven says
“In contrast, the stratospheric cooling is a single degree-of-freedom model — heads or tails, it will either cool or heat. Not a lot to go on as far as a unique fingerprint is concerned.”
That seems to treat the stratosphere as if it were a single height at a single latitude at a single longitude (in case that matters?) at a single time of day at a single time of year (at just one phase of ENSO (in case that matters?)… )
(The climate system is 4+ dimensional)
This is also interesting.
Early in the climate dispute, I had to take to what I knew and have learnt and saw that it is mostly physical geography, meteorology and physical chemistery that has to go together. Who fights that, regardless of argument, is having it wrong.
Then CO2, what can it be?
I knew the eqviparitation law. and the thermal modes of natural gases. And that of absoption and emission of electromagnetic wave radiation. Air is relatively transparent because it has no absorption- emission bands in visible light but fameous lack of transparency in UV and infrared. That is known from astronomy.
And then the Planc curve of black body thermal emission.
Then, if CO2 has got a strong absorption band that relates to thermo- molecular vibration, that vibration will also collide with oxygen and nitrogen that has only translation and rotation thermal modes. It will thus heat up the further air by collision. But that reaction is reversible, can go both ways and hot air will collide and thus cause CO2 to vibrate and emit electromagnetic IR to empty space on that absorption band.
This alltogether makes the lapse- tate with its distinct knick in the tropopause and the unbelieveable but real temperatures there, plausible and explainable.
This was a first criterium for me. The tropopause isoterm layer knick of lapsrate the cool side of the globe to be explained first, else you are not qualified for climate dispute!.
This is the compact theory that I was able to design without believing in or having to ask websites and experts, But rather judge expertise that ignores it or denies or fight this directly or indirectly.
That chill of the tropopause and the slightly rising temperatures from there and upwards, was discovered by 2 or 3 men in a balloon in 1905, with barometer thermometer and oxygen masks, and is found ever since by the worlds fleet of weather balloons.
Those men fainted slighty above the tropopause and woke up again alive as the balloon had begun to settle to higher air pressures again.
Higher ballooning and aeronautics, Picard & al had to use pressure suits and chambers with pure oxygen.
Later, further chilling of the lower stratosphere is said to be a “fingerprint” of the CO2 AGW- effect.
Which seems also plausible then.
As for CO2 in the climate and its importance at very low concentrations, I recommend to discuss it as a catalysator in the process. Then we can show to many other similar processes.
The remaining water from hydroxyl radical (OH) reacting with CH4 in the lower stratosphere, how does that fit into the new conclusions?
The thought, with increased CH4, OH reactions and the subsequent water vapor -H2O can radiate more heat – but cooler in the upper layers of the atmosphere.
Perhaps this acts like a natural cooling mechanism?
I have checkede up.
The OH-. radical is but a very short- lived intermediate stage in the UV- irradiated atmospheric chemistery system.
As I can see, it is prouced and follows the fameous UV – production of ozone from Molecdular bi- atomic O2- Oxygen,, by first splitting it into O. + O. 0ne of which re- combines with O2. to give O3
Ozone is a further extreemly potent and corrosive molecular substance.
NO and NO2 discussed as “NOx” is another fameous very reactive-corrosive free- radical system that fameously transforms or catalyzes burnt sulphur SO2 into SO3 that gives H2SO4 sulphuric acide together with oxygen and water vapour and gives acid rain. That reaction is known from the fameous lead- chamber method of sulphuric acid production where nitrous gases serve as a catalyst. As H2O2 also oxidizes SO2 to SO3, I guess that burning of sulphur in air will eat ozone.
Then you have the reactions with turpenes, that are fresh healthy smells of nordic taiga and high mountain spuce forests under especially blus sky ove white snow smelling ozone….,….. and further diesel and coalsmoke. unsarurated carbon bonds react with ozone giving ozonides, that are ugly smelling oils that detonate when touched.
Only traces of nitrous gases on the glasswares in the lab will eat all your ozone , and ozone furter eats laboratory rubber and cork, latex condoms and paints, and car tyres..
So the glasswares must be thorroughly rinsed and mounted only with clean white paraffin wax = pure alifatic hydrocarbons. Methane, an aliphatic hydrocarbon, will remain quite resistant to those agressive gases then.
But methane is also corroded high up there in the stratosphere giving what remains of traces of water, sulphuric and nitric acid, that is found up there, , and I think that rather takes especially sharp and especially much and especially shortwaved UV. And that the special molecule underway, the OH free radicfal, however popular, is not the good way to present, to understand, and to discuss it.
There is one more way that you should be aware of.
The occurance of http://www.polar/stratospheric/clouds
“pearl mother clours are stratospheric clouds from 15 to 25 km high and are shown to conscist of H2O . H2SO4 . HNO3 solid state cristals at very low temperatures. We are to explain how water, sulphuric acid and nitric acid can get up there and dense enough to cristallize out of empty and extreemly thin air.
For noctilucent clouds we must explain the same up at 60 to 90 Km high in the mesosphere.
Water that manages to get through the chill of the tro0popause will have condensed and fallen out at that heighth and be way to diluted to condense further up. But Methane and SO2 and NH3 do not condense and can pass the tropopause and get higher up. Until there is UV and ozone enough to transform it into extreemly hygroscopic strong sulphuric acid and smoking nitric acid.
with freezing point rather up at + 10 celsius.
With cristal zizes in the plain magnitude of wavelength of light. Giving beautifully opaque pearl mother shine.
Noctilucent clouds have much smaller partices than that, in the magnitude of nanoparticles. But it is diffuse reflection of rather shortwave blue direct and visible sunlight.
I was told that noctilucent clouds are not UV or X- ray fluorescens, that it may look like. I tried for myself, it is not polarized light either. ,
It is direct diffuse reflection real clouds in direct sunshine. And showing Fraunhofer lines that you can also see in common white clouds.
It is known that the Space shuttle and the Falcon x have contributed quite a lot to high mesosphaeric clouds
Hardly the volcano water, but rather the sulphur is what can get above the troposphere and give lasting stratospheric clouds.
Just came across this, cooling of the stratosphere was pretty much mainstream, even Exxon used it (see graphic in the video description, or around the 4 minutes mark of the video) https://earthclimate.tv/video/what-exxon-knew/
There is one aspect that is n0t quite clear to me, and that is WHY the lower stratosphere cools down when the mol- proportion of CO2 to air increases.
Benestad has stated that the isoterm-layer, the tropopause, gets hitgher and the troposphere thicker, That can be understood from when the partial CO2 pressure gets low enough so that CO2 IR radiation does not hit any further CO2 molecules but goes right to space.
But, why that should make a lower air temperature in the stratosphere when the isoterm layer comes higher up to a lower air pressure, I cannot quite understand. But it seems to have been elementary to the pioneers who predicted it as you say, thus it must have an elementary explaination also.
A suggestion from my side is that when molar CO2 / air increases, there is more CO2/ air that can conduct and radiate given air heat over to empty space.
Thain is , More traces of CO2 in that thin air, that can cool it further down.
Is that true?
Tomáš Kalisz says
thank you very much for this interesting point, to that I have an additional question:
Are there data showing that molar ratio of CO2 to N2 and O2 increases with altitude?
If so, what is actually a reason therefor? Is it the methane oxidation, irrespective whether through hydroxyl radicals you mentioned above, or through any other mechanism?
That can be answered, but I have no recent data.
My best teachbook of classical chemistery Ernst H Riesenfeld states that the mixture of gases in the atmosphere is practically constant up to 23 Km. That is as high as they could get with weather balloon, and tells that the atmospheric gases mix well and soon regarloess of molar weight.
Recent data of CO2 shows that it takes a year or two before it mixes fully from Mahuna Loa to Antarktis.
Still further data by satelite shows that it begins to separate up in the thermosphere due to the eqviparitation principle , all gas molecules will adapt to the same chinetic energy so that lighter molecules will moove faster, and at the top of the atmosphere the lightest Hydrogen and helium enters satelite speed in the given gravitational field and temperature so that some hydrogen split from water by sharp sunshine will “evaporate” from earth all the time. And the heaviest, Krypton and Xenon will remain and “settle” rather low.
But no practical separation of that kind in the gravitational field up to what is measured by weather balloons. Whereas heavier particles, dust rain and snow fall down., not kept mooving and afloat by thermomolecular moovement.
A surrealist suggested that CO2 is a heavier molecule that will fall and settle down to earth among the lighter atmosphere gases.
But, that is as ignorant as thinking that the very heavy Particle system of Caesium iodide or lead iodide will fall down and settle on the bottom when dissolved in water. But osmotic pressure is very much higher than gravitational force and follows Boyles law of gas behaviour, PV=nRT.
As the partial pressure of CO2 has gone from 3 to 4, we can guarantee by Riesenfeld from 1946 that it rules as high as the weather balloons.
The molar ratio of CO2 to O2 ans N2 does not increase by altitude but it increases steadily over the years in all the atmosphere by human burning of fossile fuels.
Barton Paul Levenson says
I don’t think CO2 incidence increases with altitude. It is “well mixed” within the troposphere and stratosphere, which between them account for about 99% of the mass of the atmosphere.
Helge Goessling says
Thanks for this nice article, Gavin!
As for the explanation why/how CO2 cools the stratosphere and mesosphere, Sebastian Bathiany and I made an attempt at disentangling the two basic mechanisms contributing to the cooling, and their varying contributions at different heights. We used a complex model (AGCM) as well as a simple model (1D grey-atmosphere) to get that straight.
We also provided an analogy for one of the mechanisms, the “blocking effect”, describing how the skin temperature of a house with windows changes when insulation is added to the walls (keeping the inner heating rate and windows unchanged); spoiler, and not surprisingly, the equilibrium skin temperature of the walls goes down. The analogy takes the phenomenon from spectral to geometric space, but I still consider it a useful analogy.
The other mechanism, the “indirect solar effect”, is active where in particular ozone absorbs solar radiation and increases the equilibrium temperature beyond what would otherwise be the longwave(CO2)-only equilibrium. This latter mechanism is the one which is more often mentioned in explanations of stratospheric cooling (such as in David Neelin’s book “Climate Change and Climate Modeling”). However, both effects are comparably strong, and it depends on height which of them dominates.
If someone’s interested, here’s the paper: https://doi.org/10.5194/esd-7-697-2016 . It’s also cited in the Santer et al. paper discussed here. Any feedback is very welcome.
Need to read your paper. But I’m having trouble with the analog. As the interior temperature rises, the skin temperature ultimately also increases. I don’t think the stratosphere warming is a feature of the current imbalance? I have to admit I always had trouble with the various explanations. Gavin’s explanation above implies that in the stratosphere there is no local thermodynamic equilibrium. I guess that works. I always figured that vertical temperature gradients had something to do with also….
patrick O'twentyseven says
No, LTE still holds. The greenhouse gas molecules effectively glow according to their temperature and absorb, both according to their spectrally-varying absorption cross sections. Adding CO2 produces an instantaneous radiative forcing that increases goin down from TOA until it peaks at some level and then declines towards the surface (then sharply to 0 going into the surface). This variation produces (at least instantaneously) cooling and warming at different heights…
(One thing I think might confuse people is that the net flux can be toward higher temperature locally, because if a layer is optically thin, much of what you can see is eg. the cold black of space through the ‘gaps’ between the upper stratospheric cross sections.)
Helge Goessling says
Hi Axel, the overall (TOA) imbalance indeed has only a small role to play (called the “transient component of the blocking effect” in our paper). When you say “As the interior temperature rises, the skin temperature ultimately also increases”, this is indeed true, BUT: in the new equilibrium, it will still be cooler than before you add the insulation. This is because there will be a warmer skin temperature over the windows, and thus a larger fraction of the heat lost through the windows. Recall that the windows are unchanged and there the increased interior temperature must lead to an increased outer skin temperature and heat loss. This is similar in the atmosphere after adding CO2: At the TOA, in the new equilibrium, you will see lower long-wave-emissions in the CO2 bands, which is compensated by higher long-wave-emissions in other bands (assuming the net-TOA-short-wave to be unchanged).
I think you make it too complicated.
Radio waves and IR through a gas mixture of N2,O2, and Argon hardly interferes with that gas at all. It cannot heat it up. Neither can visible light.
H2O condenses and freezes out before it enters the stratosphere.
What can only heat up the gas in that stratosphere is gas- molecular collision between exited CO2 CH4 N2O NH3 SO2…. oligo atomic gases with IR absorption bands, but they will absorb less of the whole radiated IR on those narrow bands.
(Ozon is an exeption, heated by solar UV)
But the bulk atmosphere will moove random and collide and heat up those fameous oligo atomic climate gases, so they are the the HEAT RADIATORS of the lower stratosphere.
And when it gets more of them compared to the bi and mono- atomic gases, they will drain more heat from the common air that gets less and less also upwards, and radiate out more.
Thus cool down the lower stratosphere if it becomes more of it in the air..
Try rather and discuss a radiator that receives heat by molecular collision and conduction, and is able to radiate it out to empty space as electromagnetic waves.
It is also how they cool satelites that are beeing overheated in empty space, they use intelligent radiators on it and enough of them.
patrick O'twentyseven says
… of course where there is sufficient opaqueness (strongest parts of CO2 band), parts of the stratosphere can have a net downward radiant flux.
removed from TOA, When the central part of the band is saturated, there is 0 net flux, and doubling tends to effectively widen CO2’s effect over the spectrum, closing the spectral windows to either side, and the forcing is approx. the net flux absent CO2 in those parts of the spectrum, times band widenning. That net flux which is being cut is mainly among the surface, H2O vapor, clouds, and space, with cooling and sometimes warming (base of cloud layer) of those things; and so CO2 reduces that. This is approximate – log(CO2 absorption cross section) is not a perfect triangle centered at 667 cm-1, the Planck function’s temperature sensitivity and H2O optical thicknesses vary over the spectrum, and the CO2 absorption spectrum’s shape depends on T and p (line strength redistribution and line broadenning) so eg. I’m guessing there is less widenning in the lower stratosphere vs. lower troposphere, typically.
At TOA, the net radiant flux won’t go to 0 at saturation (if it could be called that) so long as the air is warmer than the Cosmic Microwave Background, which is actually ~2-3 K but we can just say approx. 0K. So the forcing is less; ?less still when the temperature increases toward TOA? (unless this is compared to just a very warm isothermal layer at TOA?)
patrick O'twentyseven says
Clarification: When the central portion of the CO2 667 cm-1 (~15 microns) band is saturated (generally meaning zero net spectral flux), consider where the effective margins (where the CO2 goes from nearly transparent to ‘pea-soup’) and their spectral locations in the shift between initial and final CO2 amounts. Remove all CO2 holding everything else fixed; the net spectral flux at those band-margin locations can be multiplied by the margin-shifts to approx. get the forcing.
(spectral x = x per unit of spectrum; spectral x * bandwidth = an amount of x)
where there is a temperature discontinuity (as is generally the case at TOA), the saturated net spectral flux is not 0, and the forcing… (if saturation is attained – which is not the case on Earth because the temperature continues to go up and down and up again (almost fractal-like relative to mass path) … is then the difference between the no-CO2 and saturated net spectral fluxes * band margin shifts.
when there is an inversion involved, true saturation is the final approach to the final net spectral radiance; the net spectral flux can go past zero and flip direction before coming back for it’s final approach
CO2 is generally saturated in the central part of the band up to at least the tropopause, at least approximately. But other things being =, It takes more CO2 to reach saturation when the temperature changes faster over distance. In particular, if line-broadenning and line strength were constant with height, it takes more CO2 (molar ppm ie. ppmv) to approach saturation when the temperature, in terms of the Planck function, changes more per unit mass path.
patrick O'twentyseven says
“CO2 is generally saturated in the central part of the band up to at least the tropopause, at least approximately. ”
based on the graphs from Modtran; I’ve looked at clear sky values
“Adding CO2 produces an instantaneous radiative forcing that increases goin down from TOA until it peaks at some level and then declines towards the surface (then sharply to 0 going into the surface). ” – no clouds case; clouds will introduce jumps
patrick O'twentyseven says
… and theres a little overlap between CO2 and a weak O3 band and N2O (also a weak CO2 pair of bands overlaps the main O3 band…)
PS equilibrium temperature response won’t generally match instantaneous forcing exactly (even without H2O, cloud, snow ice, etc. feedbacks) – of course convective fluxes can respond (eg. convective adjustment in troposphere in a 1-D model, hence tendency for surface and troposphere to warm up together, aside from lapse rate feedback’s effect), but also because when a layer warms, it’s abs. cross sections brighten, which will have a warming effect on any layer which would absorb some of that radiance; likewise a cooling layer can have a cooling effect on other layers.
A really strong example: imagine if cloud layers were forcings, and we just insert another cloud layer between two overcast layers. There is no immediate TOA or surface forcing, but if this is above the troposphere (obviously this is hypothetical), the equilibrium effect would be warming below the new cloud layer. There would initially be cooling of the upper cloud layer, which would create a TOA imbalance, which would allow a net accumulation of heat into the total column; that upper cooling would dissappear at equilibrium, unless there’s something going on I haven’t mentioned…right?
Okay. I’m going to look at that paper now, too (I would say more but I figure they’ve probably already said it.)
patrick O'twentyseven says
… hypothetical clouds in this scenario are transparent to solar radiation
(PS for complete accuracy, many (all?) greenhouse gases also absorb some solar radiation. (famously O3, but esp. H2O; CO2 and CH4 do as well; clouds both scatter and absorb solar rad. and absorb and emit LW rad.). And the surface is not a perfect blackbody, of course).
and assuming any solar heating below the lower cloud, the preexisting equilibrium temperature profile is cooling with height from the lower to higher cloud layer (because it’s a greybody case); the new middle cloud layer is assumed to initially have an intermediate temperature.
Well, that seems plausible, thank you. thicker isolation and the same heating inside gives lower temperatures outside and hotter inside.
Sabine Hossenfelder’s take on how the Greenhouse effect actually works also explains stratospheric cooling pretty well: https://www.youtube.com/watch?v=oqu5DjzOBF8