2012-01-13 23:54:29Greenhouse Effect Basics: Warm Earth, Cold Atmosphere
Tom Curtis

t.r.curtis@gmail...
112.213.158.82

The 0th draft version of this blog is now complete.

I am not happy with the wording of the conclusion as it stands, but am too tired to revise it coherently at the moment.  However, the blog is complete enough that comments can reasonably be made, so I thought I'ld post now rather than waiting the day or to for draft 1.

2012-01-15 00:36:43
Rob Painting
Rob
paintingskeri@vodafone.co...
203.96.201.28

It may languish feeling unloved, but this is a great idea Tom. I know Glenn has talked about covering the basics before but no one has ever got around to it. I've quickly read through it - it's good, but I think you need a few sentences or a paragraph about what wavelengths are, early in the "heat flow to space' segment. Also, the piece about revving the car engine is not very clear. And there's a few typos "supose","brocken" 

The basics should also become a feature unto themselves, rather than being buried among thousands of posts. Assuming we get enough of them. I'm working on one myself - about silicate & carbonate weathering, but it's very slow going because I'm having to finally bite the bullet and teach myself how to create illustrations and graphics. It's doing my head in, but there's no way around it, there simply isn't anything suitable that I can find on the internet.   

2012-01-15 01:28:16Place on the Homepage?
BaerbelW

baerbel-for-350@email...
93.231.165.19

If more basic information is made available, the series may be suitable for a third button like "Newcomers Start here" and "The Big Picture" at the top of the homepage.

2012-01-15 03:28:51
Ari Jokimäki

arijmaki@yahoo...
91.154.97.114

Link or reference to Conrath et al. would be nice.

2012-01-15 07:46:12
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.104.224

BaerbelW - that's what I was getting at. I know some contributors suggest that we shouldn't try to be the be-all-and-end-all of climate science communication, but by covering the basics readers can see how all those studies we write about fit into a coherent scientific framework. Whereas the skeptic assertions don't.

Also, is beats the pants off trying to explain things to some noob, or troll posing as a noob, in the comments threads.

2012-01-15 14:40:28
Tom Curtis

t.r.curtis@gmail...
112.213.158.82

First revision completed.  I reworded both paragraphs discussing engines in the first section, hopefully making them clearer in the process.  I have corrected the identified spelling errors, and inluded a link to Conrath et al 1970 (the experiment was in 1969).  I have also reworded the penultimate paragraph for clarity as well.

Except for potentially spelling or grammatical errors I have not identified, I am happy with the article in its current form.  However, Rob raises an interesting point about wavelength.  Rather than including a discussion of wavelength in this post, however, I would rather do a preliminary post discussing radiation.  I believe that including it in this post would break the logical coherence and be trying to teach too many facts at once.  If that is thought to be a good idea, I would rather that that blog be posted before this one.

2012-01-15 15:24:45
Glenn Tamblyn

glenn@thefoodgallery.com...
121.213.210.107

Tom

I have been snowed under with work lately hence only a few coments on the forum. But I am looking at an animated GIF of the curves from ModTran progressively adding GH Gases to an otherwise GH Gas Free atmosphere. Also adjusting the Iout value so that it is roughly the same for each permutation. Also possibly then including future CO2 scenarios.

If you can wait a few days I can complete the GIF and you can have a look.

This was to be the second stage of an article with the animated Planck curve tool that jg is looking at being the first teaching tool for the truely scientificaly illiterate. ModTran results are fantastic for a more literate audience. But too much for the less literate. The preliminary article would use some basic notes on ER radiation, what is it made of, what does it mean to call something 'radiation' , a term that bothers many people and why IR, Visible, X-Rays, Microwaves etc are all actually the same 'stuff'. Most people don't getr that. Then lead into the Planck curve with analogies like pokers in a fire and the idea of spectrum's like in a rainbow. Then the concept of the 'colours' in the IR. This then gives a metaphor for GH Gases absorbing things. They absorb different IR 'colours'.

Possible 3rd article would then go from the ModTran results to what happens in the atmosphere in more detail - Absorption by molecules, why GH gases all have 3 or more atoms while the non-GH ones tend to be mono or bi-atomic. Then how collisions completely dominate energy transfer once the initial absorption has occurred. I even have a metaphor for this - a cloud. When you drop out the bottom of the cloud you can see the ground, out of the top you can see the sky. Inside all you can see is cloud. Then go through the temperature with altitude in more detail, H2O dropping off in concentration with altitude and how this appears on the spectrum. Then the fact that the shape of the CO2 notch, including the central peak, directly corresponds to the temperature profile of the atmosphere - cooler, then stable then warmer again with altitude.

That ModTran graph is an absolute killer tool for explaining AGW - IF you can get what it means into peoples heads!

2012-01-15 16:37:58
Rob Painting
Rob
paintingskeri@vodafone.co...
118.92.45.100

"That ModTran graph is an absolute killer tool for explaining AGW - IF you can get what it means into peoples heads!"

Glenn - Umm...that's where your ability to communicate these scientific concepts will come under intense scrutiny - it's a stumbling block for many a scientist.

Tom - Agreed about trying to cram too much into one post. A prior blog post about electromagnetic radiation and wavelengths would indeed be very handy.

We expect many readers, whom we want to reach, know this stuff, but they probably don't. I know not everyone will want to read the basics, but it will come in very handy. It'll also elevate us as a go-to-site for climate science communication.

As for the post:

Typo - (under heat flow to space) complicate = complicated

In that section, you mention infra red without explaining what that is first. Same with photons. You probably need to hyper-link to the ER & wavelength post here. Also maybe need to hyper-link to a graphic displaying what the troposphere and stratosphere are.

Point 4 under No More Armwaving" - "molecules in the atmosphere radiate less energy to space than the absorb from the surface" = than they absorb from the surface.

I like it.

2012-01-15 17:01:33
Tom Curtis

t.r.curtis@gmail...
112.213.158.82

Glenn, I love the idea of a modtran giff, but think it would be too complicated for this blog.  I would rather keep things simpler in this post using my graph, and then use the giff in a follow on blog about the enhanced greenhouse effect, if that is OK with you.

 

Rob, typos fixed.  Will now start work on a preliminary blog on radiation before trying to fix links on this one.

2012-01-15 19:01:05
Glenn Tamblyn

glenn@thefoodgallery.com...
121.219.103.221

Tom, Rob

 

This is what I have so far as a simple crude animated GIFF:

2012-01-15 22:40:22
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.30.86

Glenn, I can see that that is going to be very, very cool. Here's a suggested outline for your post:

 

Basically this is an identity parade like The Usual Suspects. One of those 'perps' is your bad guy. Tell the story like a Police investigation and it might be more likely to stick in the readers head.

Building on that, I was thinking it might be told like one of those Hollywood movies where some computer program is running, trying to match a suspect photo with felons in a Police database. You have the gif animation with the known/observed outgoing radiation (your perp/suspect), and below that you have the gif animation running through possible matches. When you get the match with CO2, the words "match" in ginormous red letters flash across the screen. Dramatic Hollywood-style music to accompany it would be even better, but I digress.

Anyways, tacky maybe, but one suggestion that might get a better response then the standard nerdy way of approaching this. 

 

2012-01-15 23:10:07
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.30.86

A great image would be a cartoon modeled on The Usual Suspects poster above. CO2, CH4 etc standing in a line-up with their shadows being cast onto the wall. Yeah, I know I'm getting carried away, but I'd like for us to be able to do stuff like that. 

2012-01-16 12:36:36
Glenn Tamblyn

glenn@thefoodgallery.com...
124.179.99.38

Rob. I Like it. It was gong to be called 'A Picture is worth 1000 Words' but this line is better. Maybe a Kojak type theme?

2012-01-16 12:41:26
Glenn Tamblyn

glenn@thefoodgallery.com...
124.179.99.38

Tom

One observation. The SB Eqn and this description "J-star equals epsilon sigma T to the fourth power". What level of audience are you targetting? This is slightly upper end language even though the concept is valid. Perhaps simplify the way you are using the equation. Perhaps E for energy rather than J*. Not quite the formal usage but more comprehensible to a lay audience. And if you are introducing sigma & epsilon, they need to be explained - most people don't even know the Greek alphabet.

Perhaps also with your conclusion some comment that the observations from 1969 have been multiply replicated by multiple satellites and high altitude aircraft since then so you are not just relying on what might seem like an old reference.

2012-01-16 13:45:24
Tom Curtis

t.r.curtis@gmail...
112.213.158.82

Glenn, I understand the concerns about the Stefan-Boltzmann law.  However, using S-B is already a simplification from the even more fundamental Plancks Law:

I did not use Planck's law because I do not think somebody who has learnt linear algebra (9th year of schooling standard) would recognize the temperature dependence of I(nu,T), to put it mildly.  On the other hand, I do not want readers rellying on my say so for the temperature dependance of radiation, which is the central point of the post.  I certainly intend to come back to emissivity and the Stefan-Boltzmann constant, but thought for simplicity, just the form of the equation is the thing.

I think the verbal description of the equation is important because, from my own experience if you do not know the name of a symbol it comes out as a blank in your thoughts.

So, IMO, the equation needs to be there, but I have added the minimum of complexity in my discussion of it.  However, if you would like to suggest alternative text, I'll certainly consider it.

 

Your suggestion about referencing more recent observations is a good one.   Do you think I should include an additional graphic to establish that point.  There are two good ones available.  The first is from Dessler 2008, and the second from Pierre-Humbert 2011:

 

 

The disadvantage of including any new graphic is that (I think) it will unbalance the blog visually.   If we include the Dessler graphic, it is more impressive to those who know how to read it, but may require more explanation than does the Pierre-Humbert graphic (which is of the same sort as two already introduced).  Further, the Pierre Humbert graphic would be linked to an introductory article.  Either of the two graphics that we do not include, I think I will add into the notes, regardless.

My fealling at present would be to simply add text saying, that "Conrath's comparison between the predicted radiation of energy upward to space, and that actually observed has since been confirmed by hundreds of thousands of observations", with a link to the Dessler graphic.  However, I am interested in your suggestions.

 

2012-01-16 13:46:56
Tom Curtis

t.r.curtis@gmail...
112.213.158.82

I should add, both graphics, if not used in the article will probably pop up very quickly in comments if I have anything to do with it.

2012-01-16 16:45:55
Glenn Tamblyn

glenn@thefoodgallery.com...
121.213.163.196

Tom

 

I would consider replacing your para after the SB eqn with this - you will need to add links. And you can use the WSYIWIG editor to superscript characters.

'where:
J* (use the superscript button on the editor) is the rate energy is radiated from a single square meter in Watts/M^2
e is the emissivity of the surface (* add wiki link*)
a is the Stefan-Boltzmann constant (* add wiki link*)
T is the surface Temperature in Kelvin (* add wiki link*).
What we need to notice is that J* is proportional to the fourth power of T, ie, temperature.  If the temperature doubles, the energy radiated increases sixteen-times.  If it triples, it increases eighty-one- times.  A red-Hot poker just glows red; but at the temperature of the surface of the Sun, it is so bright that even from 150 million kilometers away it is literally blinding, such is the power of that T4 term. So, if the temperature of the atmosphere is different from that of the surface, the absorption, redistribution and re-emission of IR radiation by molecules in the atmosphere will certainly change the rate at which heat escapes to space.'

With other references, link to R P-H. That graph from Dessler isn't explanatory enough. And R P-H's article is a great reference.

2012-01-16 16:51:54
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.146.212

Uh-oh, sounding less and less like a basics introduction.

2012-01-25 07:30:35
Kevin C

cowtan@ysbl.york.ac...
94.8.233.102

I think the article is excellent in it's current form.

(I wonder if there is scope for an article on what MODTRAN does? SoD did a series on roughly this I think, but a condensed non-technical version would be interesting)

2012-02-22 18:33:56
Kevin C

cowtan@ysbl.york.ac...
94.9.118.143

I think this post deserves a bump. And here it is.

2012-02-22 18:52:31
Glenn Tamblyn

glenn@thefoodgallery.com...
138.217.87.89

Generally I think this is good to go Tom. As others may have observed, I am not the ideal person to spot every spelling and grammar error but I think this is good.

Hopefully I can put up a follow-on post within a week - animated GIF from Modtran of different gas combinations then disect the OLR diagram to do a teaching moment on GH gases, vertical temperature profiles and such.

I think this is a useful approach we can take. Rob P and I ended up doing the same thing serendipitously on OHC. Several posts on a single technical subject at differing levels of complexity staggered several days apart. Like a 1-2 (-3-4-5) punch.

2012-02-22 20:35:15
Tom Curtis

t.r.curtis@gmail...
112.213.180.137

The sticking point on this post is the suggestion that it needs an explanation of wavelenght/frequency of light.  I bumped around a few approaches to that in my head, and was never happy with any of them.  Currently my feeling is that I'ld rather just go with this post as is.  If everybody is happy with that, Dana can queue it and I'll start working on the next in sequence I have in mind.

 

Glenn, I like the idea of a post on Modtran.  My idea was to follow this up with a post on lapse rates and the greenhouse effect to explain the simplest climate model that is a reasonably accurate predictor of what is going on.  The third post was to then introduce the grey slab model and build it up to to include partial absorption in layers, and energy transfer by convection and latent heat.  The idea is first that readers will have a basic idea of how models work, and second that they will be able to recognize how distorted are the models used in all the argumetns that the greenhouse effect defies the laws of physics.  All of this kept on the same basic level of this post.  Logically, your post on modtran would fit very neatly after the third in my series, but that is not necessarilly reason to delay it.  Certainly I will be taking advantage of your efforts by linking across if you go ahead.

 

Kevin, thanks for the bump.

2012-02-23 02:41:10
MarkR
Mark Richardson
m.t.richardson2@gmail...
192.171.166.133

Tom, I think the first graph you posted there would be good enough for a single post.

It's a 'teachable moment' about how theories are tested.

2012-02-23 03:04:51
dana1981
Dana Nuccitelli
dana1981@yahoo...
64.129.227.4

Let's plan on posting this next week.

2012-02-23 08:42:37

76.17.37.231

A couple more typos:

1)  "But in eighty percent of the Earth's atmosphere is in the troposphere. . ."  (Just under "higher is Colder".)  Delete first "in."

2)  "The reason is that sometimes odd effects occure that render verbal reasoning mute."  (Under "No more arm waving.")

a)  Correct to "occur."

b)  "Moot" for "mute," maybe?  If verbal reasoning is 'mute', we have rather a syntactic tangle here!  I may be over-interpreting the meaning, but how about ". . . is that purely verbal logic doesn't allow us to evaluate the comparative strength of competing effects?"

3)  ". . . theories whos only support. . ."  Correct to "whose."

 

A little more substantively, as a reader, I'd understand better what the Modtran runs do if the initial run conditions were not left to a note.  Something like:  ". . . I graphed the energy radiating upward as it is 'seen' at 70 kilometers above the surface."  Giving the specific altitude helps me connect with the 0 km in the succeeding sentence.

I like this post a lot!

2012-02-23 13:33:55
Tom Curtis

t.r.curtis@gmail...
112.213.180.137

To the mystery commentor,

Thanks for the comments.  I have corrected the typos and mispellings as suggested.  I have also extensively rewritten the section on modtran to try and make it clearer and more accurate what I have done.

 

On reflection, Glenn's Modtran's post is probably best done following this post.  If somebody could also do a post explaining how to use modtran in detail so that people will start playing with it themselves, that would make a usefull third blog in the sequence.  I think actually playing with the model will clear up a lot of the low level confusions of some deniers, although possibly not for those deniers who are very tenacious in error.

2012-02-28 10:18:23ready?
dana1981
Dana Nuccitelli
dana1981@yahoo...
64.129.227.4

I've got this on the schedule tomorrow Tom.  Is it ready?

2012-02-28 10:37:20
Tom Curtis

t.r.curtis@gmail...
112.213.200.254

Dana, it is ready IMO. 

2012-02-29 01:47:30
Sphaerica

Bob@Lacatena...
72.74.77.39

This is not true:

That the atmosphere gets cooler as you get higher, so that the Infra-Red absorbing molecules in the atmosphere radiate less energy to space than they absorb from the surface.

At equilibrium they must emit as much as they absorb (or the layer would warm), and temperature does not affect this balance.  They are colder because they absorb less (because the air is more rarefied), and they emit less because they absorb less.

If you increase the amount of GHGs, until the system reaches equilibrium at a new, higher temperature, then more IR will be absorbed than is emitted.  But once equilibrium is achieved the balance is restored, and emission = absorption.

All layers of the atmosphere emit less to space than they absorb because they absorb the full amount from beneath, but emit in all directions so not all emissions have a chance to "escape into space".

What does happen with an increase in GHGs is that the altitude at which effective emission takes place increases.

I'm not sure which of these points you are trying to make... but deniers will be all over the statement as it is phrased.

2012-02-29 02:21:54
Tom Curtis

t.r.curtis@gmail...
112.213.200.254

Sphaerica:

 

 

Emissions absorbed by the atmosphere from the surface: 356 W/m^2

Emissions from the atmosphere to space: 199 W/m^2

199 < 356

 

If you increase the GHG concentration, the result is primarilly that the effective altitude of radiation to space rises.  Because it rises, it comes from a cooler gas, which radiates less upward, thereby reducing the OLR.  This results in a surface warming which then heats the gas column above the surface until equilibrium is reached.  It is essential to this process that raising the effective altitude of radiation to space results in less IR radiation to space, ie, that the gas higher up is cooler.

At equilbrium the gas must emit as much energy as it recieves, either from adjacent layers by radiation, or by convection and latent heat transfer.  Without the later the lapse rate would be much greater than it is, so that convection and latent heat transfer in fact cool the planet.   However, even ignoring those, radiative transfer imposes a thermal structure such that the higher you go in the atmosphere the cooler it gets, and emission is a function of temperature.   

2012-02-29 05:04:12
Sphaerica

Bob@Lacatena...
72.74.77.39

Tom,

Yes.  Everything you said is correct, but your IF A THEN B do not go together.  The fact that the upper atmosphere is colder is not the reason that more energy there is absorbed than emitted into space.  The actual reason is the same as holds for any layer of the atmosphere, which is that the energy is emitted back down as well as up, so only a fraction (roughly half) of what comes from below heads into space.

The mutliple slab atmosphere model gets more complicated than that, obviously, when you consider incoming radiation for every layer above and below, but now its getting too complicated for a simple explanation.  But either way, relative temperature has nothing to do with the imbalance.  At equilibrium a layer must emit as much as it receives, and it emits less into space because it is emitting in two directions but absorbing primarily from below.

You are going to get hammered for that one sentence (which appears twice), especially by the likes of RW1 and his sort.

2012-02-29 06:21:15
Tom Curtis

t.r.curtis@gmail...
112.213.200.254

Sphaerica, I disagree.  We only need to know that the atmosphere gets colder as it gets higher, and that colder bodies radiate less to infer the greenhouse effect.  What you are explaining is why the atmosphere gets colder as it gets higher, which is necessary for a complete explanation.  The think about basics, however, is that you cannot explain everything at once.  Therefore I'm happy sticking with the fact that the atmosphere gets colder as you get higher.  If any denier wants to dispute that, they're quite welcome to trash their credibility by doing so.

2012-02-29 06:44:45
Sphaerica

Bob@Lacatena...
72.74.77.39

I agree with everything you are saying.  I'm only pointing out that you explicitly tied two things together that do not in any way tie.  So far no one is pointing it out, so maybe it will get by, but I'm still not sure what it is that you want to say with those statements.

Is your point simply that because the temperature drops with altitude, emission also drops with altitude (regardless of absorption)?

2012-02-29 06:51:40
nealjking

nealjking@gmail...
84.151.45.245

Tom,

I don't think there is a disagreement about the basic argument. What S. is objecting to is the sentence:

That the atmosphere gets cooler as you get higher, so that the Infra-Red absorbing molecules in the atmosphere radiate less energy to space than they absorb from the surface.

 

 

 

2012-02-29 11:22:25
Tom Curtis

t.r.curtis@gmail...
112.213.200.254

Sphaerica, neal, the sentence in question asserts a causal relationship.  As such, it is correct.  The cooler temperatures do not cause the IR absorbing molecules to absorb less.  (Actually, they do a little, because of pressure broadening, but that's an unnecessary complication.)  But they do cause them to emit less energy to space than they absorb. 

If you consider a given layer of atmosphere.  For that layer absorptivity = emissivity.  It follows that for that layer its upwards emission is less than its absorption from lower layers for any given wavelength  if and only if its temperature is less than the brightness temperature of the absorbed radiation from below for that wavelength.  Ergo, it follows that provided the radiation from below is thermal radiation from a source with an emissivity equal to or greater than the layer of atmosphere at any given wavelength, if that layer is cooler than the emitting layers beneath it, its upward radiation will be less than that absorbed from the lower layers.  As the emissivity of the surface approximates to 1, that condition is automatically satisfied, and hence can be left out in what is intended to be a grade 10 level explanation.