A light dawns
There are styles in science. Tamino, for example likes to look at statistical models. James Annan thinks about priors, Gavin Schmidt cranks up his GCM, Stoat goes rowing (we exaggerate for effect). Eli, OTOH, likes to think about and then do simple experiments or calculations (BOE aka Fermi problems: some interesting examples)
Recently, this blog, and others went to the mattresses about the idea that the greenhouse effect acts like a blanket. As you may recall Atmoz had previously used an actual blanket and concluded that blankets cut off convection and conduction, but don't have much effect on radiation. Eli pointed out that survival blankets do cut off radiation, but several people thought that they also cut off convection. For those of you who don't know, a survival blanket is a thin piece of plasticized metal foil that you wrap around yourself when the heat goes out on the space station, or your return capsule lands in Siberia. If you go to Eli's link you will see an example.
So Eli started thinking and came up with the following. Take a lightbulb and wrap it tightly with a thin layer of aluminum foil. This cuts off radiation from the light bulb (the lamp light is reflected from the shiny foil), but since the foil is a good heat conductor, conduction and convection from the surface of the foil should be pretty much unchanged with or without the foil.
This is an experiment that you should ONLY do if you have a clue about handling electical stuff. There IS a significant shock hazard if you let the foil touch the metal base of the lamp, but Eli IS an electric bunny, and stuffers are insulators, so he took a 75 W incandescent lamp and put it into a drop light (there is some danger of the lamp shattering if the temperature gets too high) and turned it on. Eli found that the top of the lamp was hottest, and he measured the temperature with a thermocouple (it's handy to have a lab): 160 +/- 5 C. Next he turned the lamp off, let it cool and wrapped it with a single layer of thin (cheap) aluminum foil and turned the lamp on again: 300 +/- 5 C.
Eli rests his case, besides which he just heard some guy on the Weather Channel talking about how clouds and water vapor act like thermal blankets when the sun goes down, and how it cools off a lot faster when the sky is clear and it is dry.
DO NOT DO THIS UNLESS "YOU" KNOW HOW TO WORK WITH LIVE ELECTRICAL EQUIPMENT. Eli Rabett, Rabett Labs and everyone else assumes no responsibility for anyone who tries to duplicate this. There is a significant chance you could be nominated for a Darwin Award if you are careless.
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47 comments:
"There is a significant chance you could be nominated for a Darwin Award if you are careless."
I'm feeling a little tipsy right now, so if you don't hear from me by tomorrow at least you'll know I died for a good cause. In such a case, please nominate me.
Oh. And I don't have a thermocouple handy. Will a banana do?
Experiments? Experiments are elitist. Good freedom-loving folks don't need experiments, all they need is Common Sense™.
OH YEAH! BUT THE PICTURE LOOKS FAKE!
:)
I tried to comment at Atmoz but it didn't work (the contact form neither as didn't commenting on a newer post NOR is there an email address). So I'll post here for Atmoz:
Your towel experiment was quite misleading.
If you look at Earth, the greenhouse gases affect energy transfer of the *warm earth* to the *cold space*. They don't affect visible light so it's the same as if the earth was heated by an electrical heater with the wire coming from outside. The source of Earth's initial energy inflow is out of the picture, it is just a given.
Hence if you want to simulate the greenhouse effect on Earth, you have to use an electrically heated object (warmer than the surrounding room, ie the earth is warmer than cosmic radiation) under a blanket vs one without the blanket. It doesn't matter in this case if the energy escapes or
returns by radiation, convection or conduction.
This is where the greenhouse effect IS like a blanket.
Now, with the ice cubes, even if you had a super greenhouse, with no light or other energy source the ice cubes would not melt at all. The experiment doesn't tell us anything about radiation vs convection or the greenhouse effect. The surrounding warmer environment heats the ice cubes and they melt. It's just a lot slower with the blanket in between.
I think your experiment is thus a red herring. It is not involved with either global warming or the greenhouse effect. Though it demonstrates the effect of insulation.
I enjoy your blog otherwise every now and then.
In a sense, you could demonstrate the greenhouse effect by putting a blanket covered water ice balloon in a big box of dry ice, then add an electrical heater there. There you could balance energy in- and outflow (heater power and blanket thickness) and could change the phase of the water accordingly (ice, water, steam).
This would demonstrate the difference between stock and flow.
After reading Dr Rabett's post I see that thought of pretty much the same thing!
OT: Looking for community response to Douglass, D.H., and J.R. Christy, 2008: Limits on CO2 Climate Forcing from Recent Temperature Data of Earth.
http://arxiv.org/ftp/arxiv/papers/0809/0809.0581.pdf
Walt Bennett:
Ask Douglass and Christy to submit their stuff to a real scientific journal. Let us know the reviewers' exact response.
That is all.
Magnus:
Also, the bunny is fat, just like Al Gore. Leni Riefenstahl would've been proud!
I am well aware where it was submitted. If it is so easy to bat down, please proceed.
Glad to hear that no hares were singed for that experiment, Eli.
There is a good reason why those thermoses we used to carry to school when I was a kid (to keep our hot chocolate warm) had a mirrored lining (which used to break on occasion)
Also, as I mentioned in the previous discussion (but way down in the comments), the only type of blanket (even of the ordinary type) that does not block radiative transfer of heat is a jet black one.
Count the number of black blankets on your bed (or in your house).
Eli - well done, even if this was obvious to most of us...
I'm wondering if part of the issue is simply confusion about thermal radiation and the implications of the numbers in, for example, the Kiehl-Trenberth diagram.
The existence of an infrared-absorbing atmosphere (GHG's, clouds, etc) implies both absorption and emission of thermal radiation - you can't have one without the other. By treating the absorbed (most of the upward radiation from the ground) and emitted (back-radiation) components as separate, Kiehl-Trenberth I believe confuses the physical picture. What you really have is not 390 W/m^2 coming from the ground and then 324 W/m^2 coming back, but a net 66 W/m^2 radiatively leaving the ground, split between 40 W/m^2 going straight into space, and 26 W/m^2 absorbed by the atmosphere.
In that way the "blanket" analogy should be clearer: an infrared-absorbing atmosphere reduces the net thermal energy flux from the ground via radiation from the 390 W/m^2 it would have if it all went straight into space, to a mere 66 W/m^2.
Nobody's claiming GHG's reduce conduction and convection - that's not the point of the analogy. GHG's are like a blanket (and like a greenhouse!) in that they significantly reduce a major component of net energy flow, leaving the ground warmer than it would otherwise be if the radiative energy were free to leave the planet.
Every analogy is a mapping in which some things match, and others do not. The point of the analogy is to draw lessons from the matching components; the non-matching ones are irrelevant to the analogy. If you had an exact match on all counts it wouldn't be an analogy! Duh...
"It is not involved with either global warming or the greenhouse effect. Though it demonstrates the effect of insulation."
That sounds familiar... almost like something I've written before. Like on the page Sr. Dr. Eli linked to that you supposedly read.
Oh, and the comments being turned off is intentional. The comment form not working is not... although it is a plus since the only mail I get is from people bitching. Thanks for providing me with the incentive to turn it off.
Adios.
So, Eli, let me see if I have this straight,
What you are saying is that I could conserve energy (cut my electric bill in half?) if I wrapped all my bulbs in tin foil?
This talking point (GHE violates thermodynamics) now has a place of honor in the crackpottery section of my "talk to a sceptic guide"
Even if you wrap the foil tightly, there is still the possibility (probability) that there will be some small air pockets trapped between the glass and the foil-- which will act to reduce conduction and convection.
I would gues the effect is probably small, but it could have some effect.
Perhaps it would be best to paint the bulb with shiny silver or gold paint? (and leave the room in case it catches fire)
just a thought.
Walt Bennett, folks have been batting down this stuff for years. There is no time for folks to bat it down, as the time spent batting this down was spent years ago. The scientific evidence is clear and time spent on this crap is wasting time better spent on other things.
Point being: if it was real, it would be in a real journal.
There is no debate except in the minds of the denialist fringe and in the PR firms' material.
Sorry to break it to you (although IME there is at least an equal chance you don't need to have this broken to you).
Best,
D
Dano,
I would just add that there are still people debating the validity/correctness of Einstein's Special relativity 100 years later.
The difference, of course, is that in this case, if we debate long enough, we won't have to worry about debating any more.
gravity loss: Atmoz was trying to look at heat flow, and it does not much matter which direction it goes. Eli's improvement, such as it was, was to limit one of the three ways in which heat can flow (radiation), while leaving the other two pretty much unchanged (convection and conduction).
In order to maintain energy balance the bulb had to heat up enough so that the IR emitted at the surface of the foil made up for the Visible/Near IR that was reflected back into the lamp by the foil.
Raffiniert ist der Herr Rabett, aber boshaft is er Nicht
I would just add that there are still people debating the validity/correctness of Einstein's Special relativity 100 years later.
the difference being the lensing data collected by satellite aren't being spun and handwaved as being directed by God or the cosmic muffin or some such. Maybe because corporations can't make money off of gravity lensing, or maybe credulous dupes aren't having their identity shown to be false because they haven't thought about their self-identification being tied to gravitational pulls.
Best,
D
Aber gefärlich is er doch!
WARNUNG (Will Robinson)!
Versuchen Sie nicht zu Hause!
I want to point out, as a side note, how stupid and even biologically ignorant the "Darwin Awards" are.
It has about the intelligence of the "Brights" movement.
jaeanon to Arthur:
Good clear post.
"Nobody's claiming GHG's reduce conduction and convection - that's not the point of the analogy. GHG's are like a blanket (and like a greenhouse!) in that they significantly reduce a major component of net energy flow, leaving the ground warmer than it would otherwise be if the radiative energy were free to leave the planet."
Yes. But are the convective losses being accounted for properly? If it were not for convection, the surface would be about twice as hot as it is in the daytime (i.e., we would have a de-facto greenhouse). So, convection is an extremely powerful heat transfer mechanism, no?
And I don't understand what Eli's experiment shows. It is all about REFLECTION of IR, not absorbtion/emission.
The reflected radiation is trapped in the lightbulb. The foil acts as a blanket which selectively cuts off the radiative loss leaving the convective and conductive losses constant.
As to the point about looking at net radiation, Eli has thought long (1.6 ns) and deep (it was a large, deep beer glass) about this and the answer is no, that is not a good way of thinking about things, because the re-radiation is from the sum of convective and radiative heating, not just from the radiative heating. If the re-radiation from the atmosphere were ONLY a result of radiative heating of the atmosphere that would make sense.
Dano:
"if it was real, it would be in a real journal."
You know what's the nicest thing? Apparently Douglass and Christy didn't even try to submit their latest pile to a journal and get some comments by that means.
I can hear it now: `I'm going to be suppressed! I'm going to be suppressed!'
I see that my response to club-member-in-good-standing bi was excised, no doubt via maximum judicious wisdom.
Nevermind! Somebody at RC (not Gavin, who is also too high and mighty to bother with laypeople) gave me some good info.
You boys go back to enjoying your club. Sorry to have intruded.
Bad me, I missed my response. It wasn't deleted!
Now you get free whacks at me.
's OK, I'm used to it.
But really, just now and then try to understand that somebody with a question may not be a troll.
Dano,
I wasn't sure if there was something new in the paper. I saw where it was published and I know their rep, but Christy was once taken seriously as a climate scientist and I just wasn't clear if this paper should be treated as reputable work or not.
I'm getting the idea that it's of the "or not" variety.
I did not immediately take this as a sort of Ball-like denial of theory, more like a "if the theory is true, why are we seeing these observations?", which may have valid explanations but which may not be clear to folks like me.
Thanks for taking the time to respond.
Atmoz, the point boils down to this sentence:
I don't quickly see how your test reveals anything about radiation vs conduction and convection?
This is not nitpicking or bitching. I'm trying to teach people something in occasional blog posts myself and I like feedback if people think I'm not making enough sense.
Of course, your subject matters raise the furor of a lot of idiots, so that probably heightens your threshold to accept or listen to criticisms or feedback. Fair enough. Just to say I'm on your side on this.
jae asks
But are the convective losses being accounted for properly?
If you actually look at that diagram that Arthur refers to (linked to on the other thread in response to your question about "cartoons"), you will see that convection is indeed being accounted for -- and it's effect is nowhere near the primary heat transfer mechanism (as you implied)
jae also says
I don't understand what Eli's experiment shows. It is all about REFLECTION of IR, not absorbtion/emission
From the standpoint of the net effect, there is no difference between "absorption/re-emission" and "reflection" -- especially for the case in which the absorption/re-emission happens at the same wavelength.
"Reflection" is actually what is termed a scattering process, which also involves an interaction of the photons with the electrons in the material that the photons impinge upon.
The difference between reflection and ordinary absorption/re-emission, is that in the case of "reflection" the photons do not correspond in energy to the difference between two energy levels in the atom or molecule.
Reflection is really a kind of absorption/re-emission involving "virtual" energy levels. But even in the case of reflection, the electrons do (momentarily) gain energy and then re-emit it.
The process of reflection is not really like most people envision it: tennis balls bouncing off a hard surface.
Feynman has a very clear exposition (perhaps the best I have ever read) of "reflection" in his little book "QED". He talks about it in the context of what most people normally refer to as interference between light "reflecting" from the front and back surface of a pane of glass. Feynman points out that in reality, what is really happening is that the light is interacting with the electrons in molecules in the glass all the way through and each scattering event makes a contribution to the net effect (which is obtained by just considering "reflection" from the top and bottom surfaces)
to anon from jaeanon:
"From the standpoint of the net effect, there is no difference between "absorption/re-emission" and "reflection" -- especially for the case in which the absorption/re-emission happens at the same wavelength."
Sounds right to me, but in Eli's experiment, most of the energy is directed inward. In a blackbody situation (or atmosphere), half the radiation goes "up" and half goes "down," right?
jae to anon:
"If you actually look at that diagram that Arthur refers to (linked to on the other thread in response to your question about "cartoons"), you will see that convection is indeed being accounted for -- and it's effect is nowhere near the primary heat transfer mechanism (as you implied)"
It is "accounted for," but I don't think correctly. And I think convection IS the primary transfer mechanism. That's why fans are normally used to dissipate heat, rather than simple irradiation.
jae to eli:
"As to the point about looking at net radiation, Eli has thought long (1.6 ns) and deep (it was a large, deep beer glass) about this and the answer is no, that is not a good way of thinking about things, because the re-radiation is from the sum of convective and radiative heating, not just from the radiative heating. If the re-radiation from the atmosphere were ONLY a result of radiative heating of the atmosphere that would make sense."
Well, you still have this problem: it is easy to show that the surface would essentially be a true greenhouse, were it not for convection; and temperatures would be about twice as high during the daytime.
jae says "I don't think correctly."
Can't disagree with that.
Sounds right to me, but in Eli's experiment, most of the energy is directed inward. In a blackbody situation (or atmosphere), half the radiation goes "up" and half goes "down," right?"
sure, but with regard to the process itself (interaction of electrons with e-m radiation) there is essentially no difference between reflection absorption/re-emission.
Even with the space blanket, not all the heat is being "reflected" backward (only about 80%)
I did not immediately take this as a sort of Ball-like denial of theory, more like a "if the theory is true, why are we seeing these observations?", which may have valid explanations but which may not be clear to folks like me.
Good thoughts.
The key is that this is still a human endeavor, and someone finding something interesting is motivated at numerous levels - ego, professional, gonads, Narcissism, yadayada - to share interesting findings with the world.
If you are at a level where you are doing stuff that adds to knowledge, you want to share it with as many practitioners as possible. We do that, today, in reputable journals.
Me, I'm an applied researcher. When I have an idea that translates down to practice for people on the ground, I go to places where they meet and give a Powerpoint and Q&A afterward (and pub that night), and, someday I'll get lucky and get accepted for publication. Or I write letters or e-mails directly to researchers or listservs. I don't write it in a blog (I use friends' blogs to work out ideas and issues, but not final stuff).
Point being: if someone has something to share, there are places to do it. E& E isn't it. Good for you to have alarm bells going off.
BTW - I've seen others ask similar questions to yours. It's a clue for some on this comment thread that something from a PR firm has been released. Just a thought.
Best,
D
"Point being: if someone has something to share, there are places to do it. E& E isn't it. Good for you to have alarm bells going off.
BTW - I've seen others ask similar questions to yours. It's a clue for some on this comment thread that something from a PR firm has been released. Just a thought."
Yeah, and as usual, a useless thought. A published article in EE is far more worthwhile than your innane, inconsequential, non-substantive posts. LOL.
Oh, the (Socratic) Irony...
Professor Rabett, you could do the test again with a black covering too.
anon 7:23 said A published article in EE is far more worthwhile than your innane, inconsequential, non-substantive posts. LOL.
"innane" as opposed to inane?
According to the Urban dictionary,
"nane" is the shortened version of punane. Also known as vagina.
So innane means "in vagina"? ( sex??)
I don't recall Dano ever mentioning anything about sex or even vaginas.
maybe I missed that one (damn)
I tend to not equate the va-jay-jay with lack of manhood or lack of intelligence.
And the folks that are unable to publish anywhere and thus rely on E&E aren't the va-jay-jay or punane either, so the comparison wouldn't arise.
Best,
D
Anonymous 9:08am: Must be all the talk about "survival blankets" and stuff. And regarding that... (NSFW)
You can pretty much predict who's been excited enough to comment on this one
http://www.google.com/search?q=Douglass%2C+D.H.%2C+and+J.R.+Christy%2C+2008%3A+Limits+on+CO2+Climate+Forcing+from+Recent+Temperature+Data+of+Earth
It I fold the tin foil into a hat, and wear it on my head, will it keep me warm?
If you did it in a vaccuum the foil wrapped bulb would have to glow i the visible?
Don F
subtract a c...add an n.
If you know the wattage can you calc the temp?
Don
Convection and conduction around the foil-bulb are not kept the same; the foil gets hotter than the glass was, so its transfer of thermal energy can go up by whatever % it takes to dump the 5% or so of the filament's emissions that would normally go out as visible EM plus as direct IR EM from the filament. Since one channel of heat dissipation has been blocked, the others carry the load. For thermal dissipation to occur faster, the surface must get hotter.
Foil is infinitely opaque. Is the optical depth of the atmosphere at CO2 frequencies infinite? Miskolczi says not, though that presumption is built-in to the basic formulae--suitable for stellar analysis, but mis-applied to the much "smaller" planetary environment. Various (nearly) instantaneous feedbacks kick in to maintain the optical depth of the atmosphere at 1.87, whether CO2 is at 200 ppm or 2,000.
This is not easily modeled or analogized with lightbulbs, blankets, and foil, I'm afraid.
You can paint the thing black, put a partial coat on, pull the current down so only IR is emitted, or whatever you want. Go do the experiment. It works the same way.
Or you can do what is done with some commercial quartz halogen lamps which is to coat the glass with a dichroic coating which reflects IR and transmits visible (aka 'hot' mirror). This causes the lamp to run hotter and increases the output (as I recall a 37W lamp has the same output as a 50W conventional lamp).
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