Guest Post by Willis Eschenbach
There’s a recent paper paywalled here, called Arctic winter warming amplified by the thermal inversion and consequent low infrared cooling to space. Fortunately, the Supplementary Online Information is available here, and it contains much valuable information. The paper claims that during the arctic winter, the atmospheric radiation doesn’t go out to space … instead it is directed downwards, increasing the surface warming.
Now I haven’t figured out yet how that works, radiation being “directed downwards”. But that’s what they say. From their Abstract:
We find that the surface inversion in fact intensifies Arctic amplification, because the ability of the Arctic wintertime clear-sky atmosphere to cool to space decreases with inversion strength. Specifically, we find that the cold layers close to the surface in Arctic winter, where most of the warming takes place, hardly contribute to the infrared radiation that goes out to space. Instead, the additional radiation that is generated by the warming of these layers is directed downwards, and thus amplifies the warming. We conclude that the predominant Arctic wintertime temperature inversion damps infrared cooling of the system, and thus constitutes a positive warming feedback.
Hmmm … so their basic claim is that the (poorly named) “greenhouse effect” is strengthened by the temperature inversion in the winter, that this slows the surface cooling, and that as a result the surface ends up warmer than it would otherwise be. A second claim is that the cause of additional Arctic winter downwelling radiation at the surface is a temperature inversion. The third claim is that this Arctic inversion is not unusual, but that there is a “predominate” winter temperature inversion in the Arctic.
Now, all of these claims can be investigated using the CERES satellite radiation dataset. To look at their first claim, I thought I’d follow the lead of the estimable Ramanathan and consider how much of the upwelling radiation from the surface is absorbed during the Arctic summer versus the Arctic winter. Ramanathan proposed the use of this atmospheric absorption of surface radiation as a measure of the strength of the greenhouse effect. Obviously, the more upwelling longwave that is absorbed by the atmosphere, the warmer the surface ends up. Figure 1 shows the strength of the greenhouse effect using Ramanathan’s measurement (absorbed radiation as a percentage of surface radiation) in June and in December.
Figure 1. Strength of the poorly-named “greenhouse effect”, as measured by the percentage of the surface upwelling longwave radiation (thermal infrared radiation) that is absorbed by the atmosphere. The situation is shown for the month of June (upper panel) and December (lower panel). Following Ramanathan, the absorbed radiation is calculated as the upwelling surface radiation minus the upwelling TOA radiation.
As you might imagine, and can see in Figure 1, the greenhouse effect is strongest where there is water. As a result, the effect is strongest in the tropics, and is stronger over the ocean than over the land. For the same reason, the greenhouse effect is weaker over the deserts and at the poles.
Now, their claim is that there is additional greenhouse warming in the Arctic in the wintertime compared to the summertime, slowing the radiative cooling of the surface. However, the CERES data disagrees, and indeed it shows the opposite. The CERES data says that at both poles, the greenhouse effect is stronger in the summertime, not weaker. This makes sense, because there is more water vapor in the air in the summer.
Note also that while there are areas of temperature inversions (shown in blue), and they do occur in a few areas in the Arctic winter(lower panel), they are not a general feature of the Arctic. On the other hand, large areas of the Antarctic do have a temperature inversion in winter (upper panel, blue).
So the CERES data doesn’t agree with the study regarding the slowed cooling in winter. The CERES data says the opposite, that cooling is easier in winter because less upwelling surface longwave is absorbed by the atmosphere. Nor does the Arctic temperature inversion seem to be as widespread or pervasive as the authors state.
Next, they claim increased downwelling longwave at the surface in the Arctic winter. To investigate this claim, Figure 2 shows the June and December downwelling longwave surface radiation, once again as a percentage of the upwelling longwave surface radiation.
Figure 2. Downwelling surface longwave radiation as a percentage of the upwelling longwave surface radiation, June (upper panel) and December (lower panel).
The main oddity in Figure 2 is that most places, most of the time, the downwelling radiation is about 86-88%, with not much difference summer to winter or place to place, particularly in the ocean. I wouldn’t have guessed that. Note that Figure 2 also reveals the widespread winter temperature inversion in the Antarctic winter (upper panel, red) indicated by downwelling longwave radiation exceeding upwelling surface radiation, and the lack of such a widespread inversion in the Arctic winter (lower panel, red).
More to the current point, we have a curiosity related to the authors’ claims about the Arctic. Note that in Antarctica in the wintertime (upper panel) there is a marked increase in the downwelling radiation as a percentage of the surface radiation compared to their summer (lower panel). The difference is large, 98% versus 64%. Presumably, this is the increased downwelling that they describe in their paper (although as expected the upwelling also increases).
But in the Arctic, where the paper claims this phenomenon of increased downwelling radiation is occurring, there is no difference between the downwelling surface longwave in the summer and the winter (88% in both cases).
So we do in fact find the phenomenon they point to of increasing downwelling radiation … but we don’t find it in the Arctic as they claim, we find it at the opposite pole.
Summary
1. Their claim, that there is “reduced cooling” in the arctic in wintertime that affects the surface temperature, is not supported by the CERES data. To the contrary, the CERES data shows the Arctic radiative cooling is much more rapid in the winter than the summer, because the atmosphere is absorbing much less radiation. Note that this is what we’d expect, due to the reduced amount of water vapor in winter.
2. Their claim, that the Arctic temperature inversion is widespread, is not supported by the CERES data. It shows general wintertime temperature inversion in the Antarctic, but not in the Arctic.
3. Their claim, that the Arctic downwelling longwave radiation increases in the winter, is not supported by the CERES data. Curiously, it is true in the Antarctic. In the Arctic, however, there is almost no difference between summer and winter.
Now, how did they get this so wrong? From their methods section (emphasis mine):
An often used method to increase the signal-to-noise (i.e. climate change- to-variability) ratio is to study multi-model output, such as those obtained in the CMIP3 initiative for ‘realistic’ forcing scenarios. The general idea then is to apply statistics on the multitude of independent members (individual models) to reduce the noise, and also to use intermodel differences to relate climate processes to feedbacks2.
Another method, the one employed here, is to use one climate model and apply a sufficiently large forcing (e.g. 2xCO2) to obtain a climate change signal that is much larger than the noise. The advantage of this approach is that dedicated experiments can be carried out, including changing certain model processes in order to link these to feedbacks (as is done in this study).
So … as usual, rather than mess with ugly observational data, it’s models all the way down. Actually it’s worse, it’s the output of one single solitary model all the way down. Or as a typical adulatory media report of the story says:
Pithan and co-author Thorsten Mauritsen tested air layering and many other Arctic climate feedback effects using sophisticated climate computer models.
Hey, as long they used a sophisticated climate model, and it is reportedly “based on true physics” in the best Hollywood tradition, what’s not to like?
Best to everyone,
w.
The Usual Request: If you disagree with something I say, please quote my exact words so we know what you are referring to. I can defend my own words. I cannot defend some vague claim like “Willis, your logic is wrong”. It may well be … but we’ll never find out unless you quote exactly the logical claims I made that you don’t like.
Data and Code: CERES calculated surface data (in R “save()” format) is here, 110Mbytes. and the CERES measured TOA data is here, 230 Mbytes. CERES Setup.R and CERES Functions.R are needed for the analysis. Finally, the code for this post is Arctic Amplification.R
Also, it’s worth noting that while the CERES top-of-atmosphere data is from measurements, the surface data is calculated from the TOA data using energy balance considerations. Obviously, a global set of observational surface radiation data would be wonderful … but since we haven’t got that, the CERES data is the best we have.
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@Willis Eschenbach-I’ve noticed, with some consternation, that Mosher has taken to a “hit and run” approach when commenting at WUWT. Sad, really.
At any rate, though, it seems that we have an interesting situation. I’ve examined some reanalysis data, which seems to indicate that a widespread winter time inversion is thought to occur in the Arctic atmosphere, especially in winter-weather models have this feature, when you input into them various sources of weather data.
However, you point out that the radiation data show an absence of an effect that would be expected if such an inversion where really widespread throughout the Arctic. This raises several questions:
Is the expected effect a correct prediction that *must* arise if an inversion is present?
If so, why do current weather models have such a feature that is not apparent in reality?
If not, why not?
I for one would appreciate if Mosher could answer such questions, rather than showing up, firing off a snippy comment, then disappearing to do who knows what.
MaxLD says:
February 4, 2014 at 1:34 pm
Question all you want. I’m just reporting what the CERES data says, which is that the inversion exists at both poles, but it is much more widespread and much stronger in the Antarctic.
The real question is not whether “dealing with dramatic and persistent low level winter temperature inversions is a part of the forecasting situation” for the Canadian Arctic. The question is, how widespread and how persistent and how dramatic are the inversions?
To answer that, look at the bottom panel in Figure 2. You are 100% correct. There are indeed areas of persistent, fairly widespread inversions OVER THE CANADIAN ARCTIC, the exact region you have been forecasting for … but despite what Canadians might believe, that’s only a small fraction of the Arctic, and the CERES data says that the inversions do NOT appear in a widespread fashion over the entire Arctic.
w.
Robert Clemenzi says:
February 4, 2014 at 1:48 pm
Sorry for the lack of clarity, Robert. I say that the greenhouse effect is not that strong in Antarctica because (using the measure of Ramanathan) the CERES data shows clearly that it is not that strong … that’s what Figure 1 shows.
My explanation is that the weak greenhouse effect is a result of the lack of water vapor in the polar atmosphere.
Finally, the poles both get huge infusions of warm air and water from the tropics. It is that imported heat which keeps them from freezing, not the greenhouse effect.
w.
MaxLD says:
February 4, 2014 at 9:33 pm
Thanks for that, Max. I just took a quick look at that data. What I see is that the structure of the atmosphere is quite different over the sea ice and over the land. Under the ice is flowing water, which is obviously above freezing. As a result, the surface temperature over the ice doesn’t typically go that low, while the land surface is under no such constraints. It’s why the Antarctic gets much, much colder than the Arctic.
The fact that the ice is warmer than the land, of course, means that inversions will be less common over the ice … but most of the measurements (except those from satellites) are made over the land, as are most of the forecasts.
Regards,
w.
Willis:
George E. Smith is quite correct about the historical derivation of the S-B radiation law for black bodies in equilibrium. It is only then that the temperature can be accurately determined from the incident power flux. Geiger, on the other hand is also correct, in that the emitted radiation of various grey bodies can be quite accurately determined via S-B–provided that their temperature IS KNOWN. The geophysical problem, however, lies in the fact that the atmosphere is NOT a grey body (see http://speclab.cr.usgs.gov/PAPERS.refl-mrs/giff/300dpi/fig3b3.gif)! That’s been suspected theoretically in bona fide meteorology since the early 20th century. This constitutes a huge fly in the ointment of simplistic radiative algebras that still pervade “climate science.”
Willis, I am certainly willing to concede that the Arctic inversion is not nearly as strong and widespread over the sea ice for the reasons you mentioned. I think that I am so used to forecasting for the land areas, where the inversion is very strong and persistent, that in my haste I sometimes forget about the sea ice areas. I thank you for pointing that out. Maybe the authors made the same assumption, that the land temperature profile in the low levels was the same as over the ice.
I am not a CERES expert by any means, but in the Figure 1 could it not be that the low level inversion in the Arctic over land does not show up because you are only using the surface and TOA LW radiation, which does not give information about the low level inversions. Most often the TOA temperature is still colder than the surface, even when there is a strong low level inversion.
1sky1 says:
February 5, 2014 at 2:15 pm
1sky1, let me start by saying that when we are talking about the energy flows around the climate system, the emissivity is immaterial. Makes no difference in the slightest. It is only when we wish to convert between radiation and temperature that we encounter difficulties. Please note that in my analysis above, I’m discussing radiation, except for the question of the “temperature inversion”.
Next, you say that the atmosphere is NOT a gray body … it’s not clear what you mean by this, and I fear that the graph didn’t help. Considered across the thermal infrared spectrum, the atmosphere acts very much like a gray-body with an emissivity of around 0.8 or so. However, this is an average, and it is temperature dependent. However, this is made more complex by clouds, which essentially are black-bodies for thermal IR.
There’s more info here.
w.
MaxLD says:
February 5, 2014 at 3:08 pm (Edit)
Thanks, Max. I haven’t used TOA temperature. The first figure shows atmospheric absorption vs surface radiation. The second figure shows downwelling surface longwave vs surface radiation. However, they give very similar results regarding the strength and location of the inversions.
All the best,
w.
Willis:
You say: “let me start by saying that when we are talking about the energy flows around the climate system, the emissivity is immaterial. Makes no difference in the slightest. It is only when we wish to convert between radiation and temperature that we encounter difficulties.” Inasmuch as any quantitative determination of thermal energy flows within the system has to take into account the net radiative (as well as convective and conductive) transfer, the emissivity of bodies cannot be blithely ignored. While many natural materials have epsilon close to 1, others (as well as polished metals and many man-made materials) are much less emissive.
Quoting you further: “you say that the atmosphere is NOT a gray body … it’s not clear what you mean by this, and I fear that the graph didn’t help. Considered across the thermal infrared spectrum, the atmosphere acts very much like a gray-body with an emissivity of around 0.8 or so.”
A gray body, by definition, is one that radiates a spectrum proportional to the Planck function. Despite what may be taught in soft science courses nowadays, TOA emission spectra clearly show that the atmosphere has no such simple proportionality!
I may have time tomorrow to elaborate, if need be.
1sky1 says:
February 5, 2014 at 5:48 pm
I fear that all you’ve done is restate your claim, that we have to take emissivity into account. You have not said why.
Here’s an example of why your claim is incorrect. Suppose we have an object. It has incoming radiation at say 340 W/m2 at the surface. Here’s the question
What will be the amount of outgoing radiation when the object is at thermal equilibrium?
Well, obviously, it will warm until it is radiating what it is absorbing, that is to say 340W/m2 … and that doesn’t depend in the slightest on the emissivity of the object in question.
There is an example of making a “quantitative determination of thermal energy flows within the system” which, contrary to your claim, does NOT have to take into account the emissivity.
Q.E.D.
Mmm … you are right, but I’m not sure what difference it would make to my analysis above. It’s true that the emissivity of gases is frequency dependent. So you’re right, they’re not truly “gray bodies”.
However, in general we’re not talking about surface radiation of a single frequency. Solid bodies emit thermal IR over a host of frequencies. As a result, we can approximate the absorption over a wide range of frequencies by means of what is called the “gray body assumption”, discussed here which is the assumption that the emissivity is NOT frequency dependent. And for most climate analyses, this assumption is close enough.
And when it’s not, well, then scientists hitch up their sleeves and do the line-by-line or other analysis necessary to deal with that.
Finally, with the atmosphere we end up with an “effective emissivity”, which is compounded of all of the gases and all of the frequencies. It measures, in the real world, how much of the radiation is absorbed by the atmosphere. The effective emissivity is shown in Figure 1. Note that it is different in different areas of the planet, as you’d expect. Globally, an average of about 40% of the total upwelling energy is absorbed by the atmosphere … so by Kirchoff’s law, the average atmospheric emissivity would be the same, 0.40.
However, none of that matters to what I’ve done in the head post, because I’m dealing with flows of energy, not with temperatures. As a result, I fail to see what your objection, while technically true, would change about my analysis above.
w.
Willis Eschenbach says:
February 5, 2014 at 6:18 pm
Willis Eschenbach says:
February 5, 2014 at 4:29 pm
Am I missing something?
Willis:
It’s easy to arrive at Q.E.D. –when you assume that which needs to be proved! Your example ASSUMES that the “body” subjected to a uniform irradiance will HAVE to emit at the SAME intensity to come thermal equilibrium, i.e., a black body. But if that body is a sea, whose energy transfer to the atmosphere is predominantly through evaporation, or a forest, where solar power is consumed by plant growth, that equality naturally breaks down. It is only in space that radiative intensity can be equated to energy flux. When radiation interacts with matter, it’s a whole different ballgame physically. Unlike energy, radiation is not a CONSERVED metric in the real world and there is no simple algebra to account for energy fluxes based upon BB estimates of radiation alone.
This makes a considerable difference vis a vis your present interpretation of CERES data regarding their relationship to near-surface temperatures. There simply is no physical basis to expect any close relationship. In fact, according to La Bourget’s Law, there is every reason to expect that—aside from certain narrow spectral windows—TOA emissions come from various atmospheric layers rather than the surface. Even stratospheric temperature variations are poorly coherent with those recorded much nearer the surface. While there’s much to criticize in the conclusions drawn by the authors, your ostensible disproof of their contentions regarding winter-time near-surface inversions and their effect upon land surface temperatures is likewise on shaky ground.
1sky1, please provide a link to La Bourget’s Law – Google was not helpful.
1sky1 says:
February 6, 2014 at 5:22 pm
You claimed that we HAD to take emissivity int\o account. I gave an example where we didn’t HAVE to take emissivity into account …
Now, you want to talk about another situation, where there is convective and evaporative parasitic loss. Heck, I can do that too … but my Q.E.D. still stands, and your claim that we HAVE to take emissivity into account is still falsified.
In any case, what is typically done is to express the flows of energy in the form of sensible heat and evapotranspiration in the same units, which are W/m2. This allows them all to be compared, as in this diagram of the major energy flows in the climate system:
Note that there is no need to include any emissivity anywhere in that look at the global energy budget, despite the fact that it includes evaporation.
Not true in the slightest. Radiative intensity means the amount of energy flux, what do you think it means? It means the strength of the radiation, the amount of energy flowing, whether in space or at the surface. That’s how night vision goggles work, for goodness sake. They show you the energy flux, the radiative intensity, of the infrared radiation (energy flux) from warm things like say the human body.
Again, not true at all. Radiation in W/m2 is a measure of energy. You are claiming that energy is not conserved …
In addition, you keep harping on black bodies … but there is no mention of black bodies in any of this.
1sky1, please, I beg of you. Get a good textbook on thermodynamics that covers the physics and math of radiation. Truly, you are putting forward nonsense, and obviously you believe it but … it ain’t so, and you’re not doing yourself any favors with your claims.
w.
Robert Clemenzi says:
February 5, 2014 at 8:41 pm
Yeah, that wasn’t very clear. One includes the parasitic losses (70 W/m2 atmospheric absorption of incoming solar, 100 W/m2 of sensible and latent heat loss surface to atmosphere), one doesn’t.
w.
Willis:
From the beginning, my comments have been directed at the issue, raised here
by George E. Smith, of how realistic is the tacit BB/GB assumption involved
in the uncritical use of the S-B relationship in “climate science.” My
argumentation has been couched always in the context of empirically
validated physics and how it conflicts with academic idealizations. Your
counter-example patently involves circular reasoning, while indefensibly
ignoring that real-world context.
It’s even more dismaying that you should now present a modification of
Trenberth’s cartoon, based upon unvalidated GCM simulations, ostensibly
disproving my contentions. But even there, simple arithmetic shows that if
the surface receives only 169W/m^2 solar power density on average, it can
only output the same in steady-state conditions. That balance in energy
flux is achieved not by the intensity of upward surface radiation, but by the NET result of radiative exchange between surface and atmosphere, whose oppositely directed components are much greater. I hope this brings home the physical distinction between conservative energy flux (an extensive metric)and nonconservative radiation (a local intensive metric).
With so much effort required to explain basic physical distinctions, your
plea that I should improve my training in physics is ironically amusing, at
best. If I have time tomorrow, I’ll address the stark difference between
phenomenology and real-world physics in your presentation.
Robert Clemenzi:
Try Bouguer’s Law.
Robert Clemenzi:
Just an quick addendum to my ultra-brief reply yesterday, as I was rushing to a meeting:
R. H. Stewart’s “Methods of Satellite Oceanography” (whence came the apparently abberant name of the law governing the decay of radiative intensity in an absorptive medium, a.k.a. Lambert’s Law) provides a nice explanation of what can be sensed at TOA and how. The basic reason we have reliable SST satelite data is the UNIFORMITY of GB emmissivity from the ocean surface. Taylor & Francis (http://www.tandfonline.com/doi/abs/10.1080/01431168708954793)
however, point out that land surfaces display no such uniformity, thereby frustrating analagous satellite sensing of LST That’s why CERES provides only CALCULATED pseudo-data for the surface.
1sky1 says:
February 7, 2014 at 4:27 pm
Thanks.
While the logarithmic law is valid for a single frequency at constant temperature and pressure, it needs to be integrated over those 3 variables to determine what the atmosphere does.
***
Also, I disagree with your reasoning with respect to sea surface temperature. The reason SST can be determined by satellite is because there is a well defined relationship between the actual temperature and the temperature at about 4 feet – the height that “surface air temperatures” are measured. Over land, the actual surface temperature (the value seen by a satellite) is typically plus or minus 20C, and frequently more more, with respect to the reported (measured) air temperature and there is no way to determine one from the other.
Yes, I read the abstract you referenced – its basic assumptions are simply wrong. While it is correct that the surface emissivity causes a problem, it ignores the fact that the surface temperature is almost never equal to the temperature measured in a Stevenson screen.