Discussion > Greenhouse Effect
Has it been shown experimentally that reflecting 100% of emitted ir back to a heated radiator plate [eg by a mirror] will cause an increase in temperature in the plate?
In the real world, where convective cooling of the surface is dominant, any increase in surface temperature is usually accompanied by increased convection currents [thermals] thus swamping any minor heating supposedly due to 'back radiation'.
The oceans, due to the properties of water, are opaque to infra red 'back radiation' and block ir penetration further than the top few microns of the surface, any heat generated being instantly removed by convection currents and air movements in general, thus adding to atmospheric temperature. There is no process for ir 'back radiation' to heat the ocean depths. There has been no increase in atmospheric temperature for around 17 years, whilst CO2 levels have continued to increase, which indicates that the sensitivity of the atmosphere to CO2 has been wildly exaggerated.
RKS
That fact that CO2 concentration has gone up in the last 15 years and temperatures have not only proves that the relationship between them is non-linear, or not tightly autoregressive. It's too short a term to disprove a linkage between them. Climatic changes take many years.
There is a reasonable chance that both can be correct - that CO2 concentration does have a temperature effect - up to a point - a point we have perhaps passed or are getting close to - then the effect is diminished, due to other interfering effects.
Until the science understands the (possible) linkage between CO2 concentration and temps (which it does not) - it's up for debate.
TheBigYinJames
Jan 8, 2014 at 1:24 PM | Unregistered CommenterTheBigYinJames>>>>
Agreed!
It would be nice to see experimental confirmation that so called 'back radiation' leads to a quantified increase in surface temperature.
On the length of time it takes for the atmosphere to respond to a change in it's composition, one should note that, depending on which set of statistics are used, global surface temperatures rose during a MAXIMUM of just 22 years out of the past 72 years, and in fact cooled for the period up to 1975.
After just 10 years of this warming trend, which is looking increasingly like normal natural variation, the 'climate scientists' advocating AGW pointed to this short period of warming as proof of man made global warming, with the Aero Engineer turned 'climate scientist' Hansen even warning in 1988 of tipping points [unprecedented in the history of the world] and New York being under one foot of sea water by the year 2000.
Paleantological evidence has been shown to indicate that past increases in atmospheric CO2 have always followed increases in global temperature by up to 800 years, indicated oceanic out gassing due to rising temperatures rather than increased temperature being due to CO2 levels.
We see many differing opinions of climate sensitivity to CO2 [ 1, 2 or even 4C for a doubling of CO2] with little empirically derived evidence for these personal preferences.
RKS
A great deal of confusion is caused in this debate by the fact that there are two distinct explanations for the greenhouse effect: one based on that developed by Fourier, Tyndall, etc. which works for purely radiative atmospheres (i.e. no convection), and the radiative-convective explanation developed by Manabe and Wetherald around the 1970s, I think. (It may be earlier, but I don’t know of any other references.)
That was Nullius in Verba on Climate Etc. in November 2010. He goes on to give a good summary of the radiative-convective view and why people so often remain confused.
Richard Drake
The lack of a simple experiment to prove the IR effect is something we've lamented in various threads here. Part of the problem is that IR is not very easy to work with in small scales.
Saying that, I still think it's an experiment that could be done. The reason it's not is because for science, it falls under the category of "proving the obvious", and there's no money or appetite for that, especially if it's just to satisfy a "bunch of deniers" who would simply ignore it anyway. They have a point.
In its absence, you can measure it in the real world by measuring LW outside at night. You can buy inexpensive pyrometers (less than £20) that will measure the 'temperature' of the sky at night. Dr Roy Spencer did it already and took photographs to prove it.
http://www.drroyspencer.com/2010/08/help-back-radiation-has-invaded-my-backyard/
TheBigYinJames
munroad
If you are skeptical and open minded this Paper by Joe Postma is worth considering
http://www.principia-scientific.org/publications/Absence_Measureable_Greenhouse_Effect.pdf
Ross Lea
Also please read its refutations.
TheBigYinJames
Has it been shown experimentally that reflecting 100% of emitted ir back to a heated radiator plate [eg by a mirror] will cause an increase in temperature in the plate?
In the real world, where convective cooling of the surface is dominant, any increase in surface temperature is usually accompanied by increased convection currents [thermals] thus swamping any minor heating supposedly due to 'back radiation'. (...)
Jan 8, 2014 at 1:21 PM RKS
A school science teacher told me as a kid that convective cooling completely dominates radiative cooling in the case of objects that are only moderately hot and I assumed he was correct, in view of the 4th power law.
But when I had the job of specifying heat sinks for power transistors, I was a bit surprised to find that radiative cooling is a good proportion of the heat loss.
Transistor heat sinks are invariably black (well almost invariably - I have a Quad 303 amplifier in front of me with a non-black heat sink). The fact that a matt black heat sink runs cooler than a polished aluminium one surely answers your question in the affirmative? (ie that even if somewhat less than 100% of radiation is suppressed, a radiator plate heated at constant power will be significantly hotter.)
Martin A
Thanks for your replies.
I am a frequent and long serving visitor to this site and if there was an air of naivety in my original posting it was intended. My approach can be likened to the philosophy of the chinese warrior Sun Tzu.....I felt the need to know my enemies (and myself!).
My own field of interest has been respiratory medicine and I was lacking in the basic science put forward by the capnophobes. In particular I knew nothing about the vibrational spectra of infra red absorption by different gases.
I now have plenty of bed time reading. I hope the discussion continues to stimulate interest.
munroad
"thus swamping any minor heating supposedly due to 'back radiation'. (...)"
I am one of those who think that "heating via 'back radiation' " is nonsense. It's a red-herring that misleads lots of people.
An object, heated by some source of heat, that receives a proportion of its radiation reflected back will be hotter than one that can radiate without obstruction.
But it is the heat source that does the heating, not the 'back radiation'.
Martin A
For me real life is a million miles from Al Gore and his graph "see how temperature follows CO2"
..And the fact that no establishment scientist was able to stand up on the western media and say "say hey, that's misleading" shows to me that the modern era climate debate is dirty politics rather than proper science & logic.
.. trust in VALIDATED science : Yep
.. trust in The Establishment, media & scientists : Nope
(then reconfirmed by hockey stick graph, climategate, & every overhyped green/alarmist story which turns out to be hollow)
stewgreen
stew, the danger is reading any sort of conspiracy into this. This whole phenomenon has been a meme pushed by a few, picked up by the stupid, jumped on by the corrupt, and now continued by the out-of-touch.
TheBigYinJames
This whole phenomenon has been a meme pushed by a few, picked up by the stupid, jumped on by the corrupt, and now continued by the out-of-touch.
Jan 8, 2014 at 4:25 PM TheBigYinJames
How true.
From Crop Circle Was a Publicity Stunt: Why 'Experts' Were Fooled:
Why do people fall for such obvious hoaxes? Part of the answer is that the human brain is hardwired to seek meaning, even when there is no meaning to be found. In psychology, the tendency for the mind to find coincidences, patterns and connections in random data is called apophenia. In statistics, there is even a name for this type of fallacy: a Type I error. A common example of a Type I error is a false positive result on a medical test.Carl Sagan, in his book "The Demon-Haunted World: Science as a Candle in the Dark," discussed the psychology of this phenomenon. "The pattern-recognition machinery in our brains is so efficient in extracting a face from a clutter of other detail that we sometimes see faces where there are none," he wrote. "We assemble disconnected patches of light and dark, and unconsciously try to see a face. The Man in the Moon is one result."
Martin A
Another pair of new words for the vocabulary.
Capnophiles are microorganisms which thrive in the presence of high concentrations of carbon dioxide.
splitpin
munroad TheBigYinJames
Rather than look at Skeptical Science attempts at a debunk of Joe Postma's article (can you point to a better attempt by someone with credibility I am open minded and would like to read any available ?) I suggest you see Joe's answers to his critics at the well respected site of Judith Curry. There are over 1000 comments so it generated a lively debate Joe's Comments are mostly near the top.
http://judithcurry.com/2011/08/16/postma-on-the-greenhouse-effect/
Ross Lea
I did skim the JCurry thread at the time, and although he defended himself rigorously, I felt by the end it was generally felt that the points he made that could be agreed on were smallish and not very revolutionary. I didn't think he came off particularly well.
But each to their own. I wouldn't tell anyone not to read Postma, but as with any new theorem, you learn more about it by seeing the attempts at rebuttal than the article itself.
TheBigYinJames
BigYin I am CERTAINLY not calling conspiracy., you can't do that without strong evidence.
But there is what I call a cultural accidental conspiracy effect,
that produces the same outcome as a conspiracy
eg. Where a dogma is accepted whilst other ideas are refused to be considered.
stewgreen
Jan 8, 2014 at 3:42 PM | Martin A
Martin, why would a black heatsink be cooler? A quick read seems to imply anodizing may have an effect. I can't quite see how somethings colour in the visible spectrum would effect its emission spectra in the IR.
Rob Burton
Martin, why would a black heatsink be cooler?
Rob - it's because black pigments are normally black at IR wavelengths as well as visible wavelengths*. Note that 'black' = 'low reflectivity at all relevant wavelengths'. Obviously, all radiation from a transistor heatsink is at IR wavelengths.
Low reflectivity = high emissivity. (Because, for an opaque surface, reflectivity + emissivity = 1)
If the emissivity of the surface of a heatsink is high, then to radiate a given power its temperature will be lower than an otherwise similar heatsink with low emissivity.
Does that adequately answer the question?
* I believe there are some visually 'black' pigments, based on dyes, which are transparent to IR. Obviously, they would be unsuitable for heatsink applications. Carbon black does not suffer from this disadvantage.
Martin A
Does that adequately answer the question?
Yep, totally Martin. I didn't know visible and IR characteristics carried over so readily. It's hard to find definitive experiments or equivalent on the Internet demonstrating this. (Or perhaps I just wasn't very good at looking.)
Rob Burton
see The facebook group No Greenhouse Effect
And the top pinned post : Derek_Five_fatal_flaws_of_GHE _theory_Xmas_2012 _pdf.pdf
stewgreen
munroad
Radiative heat transfer happens at the speed of light. In order for an additional component in a system otherwise in equilibrium to cause a temperature increase there has to be a capacitance effect. Minute increases in CO2 cannot produce a capacitance effect great enough for the temperature increase attributed to it and hence the concept of back radiation took hold. The number placed on that is currently 333 Watts/m^2. This quantity endlessly circulates from surface to atmosphere and back to surface. It is perpetual motion. The proof of that is by simple inspection of any of the 'energy budget' diagrams that incorporate it. Remove the 333 going in both directions and the diagram of outgoing and incoming doesn't change.
However, energy that is able to do work flows in one direction only and is known as the flux. The flux from surface to space is partly intercepted by the atmosphere where some energy is transferred to the non-radiative gases by conduction. There is the capacitance. The atmosphere is warmer because of it. The temperature difference between the two increases causing the surface to warm to maintain the flux. The flux must be maintained as the source (sun) and sink (space) temperatures remain unchanged. From this, you could conclude that the non-radiative gasses are the greenhouse gasses and CO2 is merely a working fluid. But if you did then it would not be possible to show as large effect as CO2 alarm requires.
Basically, if you don't confuse potential energy (f x temperature) with kinetic energy (f x temperature difference), wood emerges from the trees.
ssat
ssat said:
Radiative heat transfer happens at the speed of light. In order for an additional component in a system otherwise in equilibrium to cause a temperature increase there has to be a capacitance effect. Minute increases in CO2 cannot produce a capacitance effect great enough for the temperature increase attributed to it and hence the concept of back radiation took hold.
Radiative heat transfer does NOT happen at the speed of light.
This is for two reasons:
1. The speed of light you refer to is the speed of light in a vacuum, not in a mixture of gases. The speed of light in the atmosphere is slower than the speed of light in a vacuum because of quantum mechanical effects.
2. Whilst photon transfer happens at the speed of light (or close to) the absorption, vibrational model, and reemission of the photons by the gas does not. A greenhouse gas molecule which absorbs a photon can hang into it for a long time (comparatively). It can also transfer the energy of the photon to other molecules (by collision) - if this other molecule is N2 or O2, those atoms cannot emit the energy again and can ONLY lose it by collision - this introduces a time delay - thermal delay - or the 'capacitance' that you refer to above.
3. Since greenhouse theory contains a thermal delay (capacitance) then the rest of your post is rendered meaningless - it's not 'perpetual motion' or impossible.
TheBigYinJames
TBYJ
1. The speed of light is not the speed of light but in fact the speed of light. Huh?
2. For the system in equilibrium, incoming and outgoing are in balance and both fluxes are travelling at the speed of light. The system itself has a thermal capacitance which reduces the difference between temperature max and min during diurnal and annual cycles (lunar max - min difference for an example of lower thermal capacitance). It is the slower speed of energy flows within the mass of the system that dictate thermal capacitance, conduction, convection etc being examples. This 'steady state' has been arrived at over a long period of time. Now add a small quantity of CO2 to the atmosphere (ignore the heat in the gas from combustion, assume it to be neutral) and wait for a new steady state to occur. Now measure temperatures and find that both the surface temperature and the atmospheric temperatures have increased. We know that the additional CO2 will have absorbed some surface emitted infra-red and some of that energy will have been passed by conduction into the atmosphere as a whole thereby raising its temperature but what of the increase in temperature at the surface? Is it from 'back radiation' from the CO2? No because that would be against the flux and we know that the flux is always from higher to lower temperature (Martin A, Jan 8, 2014 at 4:00 above sums that up well). It is only the net flux that can do work as it is only that that has kinetic energy. So let's stay with flux, specifically surface > atmosphere > space. As we are in steady state, outgoing is the same as before and equals the unchanged incoming. Flux is a function of area x temperature difference, atmospheric temperature has increased and so its radiating area has increased to compensate and therefore maintaining atmosphere > space flux. The surface sees a higher atmospheric temperature and warms to maintain surface > atmosphere flux (maintain temperature difference). Additional atmospheric CO2 has warmed the surface-atmosphere system. There is no reason to invoke 'back radiation'.
3. Popular greenhouse theory relies on 'back radiation'. But as explained, by its very nature it is against the net flux and is not kinetic energy – it does no work. Look at a global energy flow diagram, here is one chosen at random, remove the 333W back radiation and the same quantity from the surface radiation (the perpetual motion) and the diagram still works.
ssat
I posted in 'Unthreaded' a request for pointers to enlightenment about the theory of CO2 acting as a 'greenhouse gas".
HaroldW TBYJ and stewgreen have kindly replied.
Our host has very reasonably requested that we take this to 'Discussion' so I have Cut & Pasted the discussion so far.
@Munroad I'll bite..
There is the laboratory world and there is the real world, and often they can be very different.
In the recent era real world
- the temperature is what it is
- the CO2 level is what it is
Whilst CO2 levels have gone up massively (about 310 to 400ppm since 1950) temperatures do not seem to have gone up inline.
So any relationship between CO2 and temperature has NOT been VALIDATED. (rather there is DIVERGEANCE)
.. So it looks as if in the recent era other factors are largely responsible for driving variations in temperature.
Jan 8, 2014 at 12:32 PM | stewgreen
munroad,
There are many sources for this explanation, there are even some on this site, but here's a potted explanation of the standard position on greenhouse theory:
1. Forget the term 'greenhouse' - it's a bad name, the effect is radiative, not convective.
2. Sunlight (at wavelengths shorter than 5µm, because the sun is hot) travel through space and hit the top of the atmosphere.
3. The atmosphere, being mostly O2 and N2, cannot absorb (much of) this high energy radiation, so it mostly gets to the ground unhindered. A notable exception is when it hits a cloud, which is white, thus has a high albedo it gets reflected back out into space. About 30% of the sun's energy bounces straight back out into space unhindered from snow, clouds, desert and other high albedo surfaces. This energy takes no part in warming the earth.
4. The ground, being composed of many different elements, CAN absorb the remaining 70%, and warms up. Note that via convection (i.e. kinetic heat transfer) the ground is then able to heat the atmosphere near the surface. So N2 and O2 molecules get heated up by collision.
5. The ground (and lower atmosphere) emit photons of a longer wavelength (5-20µm) because of their temperature (Stefan-Boltzmann law) - unfortunately, the atmosphere is no longer transparent to them in the way the original high-energy solar photons were - various gases in the atmosphere can absorb them in known quantities - mostly H2O, CO2 and CH4 (methane).
6. A percentage of the upward moving long wavelength photons are absorbed by these 'greenhouse' gasses.
7. Some of the energy gained by these gases is passed onto O2 and N2 molecules by collision, and they heat up.
8. Some of the energy gained by these gases is re-emitted in all directions.
9. A percentage (about half) of the photons ends up hitting the ground again, heating it further. A percentage escapes into space at the top of the atmosphere.
10. The result is that the ground (and lower atmosphere) is warmer than it would be without the presence of 'greenhouse' gasses.
Hope this explains the standard position, you may want to start a Discussion thread if you want to talk more about it. Please note that Greenhouse Theory (or the Greenhouse Effect) does not automatically mean that changing the amount of greenhouse gas automatically changes the temperature in a proportionate way. It's perfectly acceptable for a sceptic to believe in the GHE but not in AGW (despite what others may say!)
Jan 8, 2014 at 12:22 PM | TheBigYinJames
munroad: "Please can anyone point me to a sensible account of how CO2 acts as a greenhouse gas?"
Although I haven't visited in a couple of years, the website Science of Doom was helpful to me.
Start here.
Jan 8, 2014 at 12:19 PM | HaroldW
Please can anyone point me to a sensible account of how CO2 acts as a greenhouse gas? A quick search through the web reveals sites that are rather emotive and doom laden.
I have some knowledge of science with a good grade in A level physics in 1969 (!).
Many thanks,
Jan 8, 2014 at 11:01 AM | munroad