Model CO2 as Greenhouse Gas: Tips & Results

[Ray001]

I recently came across several apparently reputable sources (e.g., NASA, PBS) that describe a simple, elegant experiment intended to demonstrate carbon dioxide's role as a greenhouse gas. Each of them involves two sealed containers with thermometers - one containing air, the other containing high levels of CO2, both exposed to sources of light.

The problem I'm having is that I haven't been able to obtain the anticipated results in any reliable way. In fact, I'm seeing no consistent variation in the temperatures of the two containers, and I'm starting to wonder if this experiment is based on wishful thinking rather than on hard science.

My question is: Is anyone aware of any reliable, published experimental data demonstrating that CO2 in a sealed container will heat up more quickly and reach steady state at a higher temperature than a container filled with air?

Here is my short list of sources:

1) NASA (I've copied the text of NASA's experimental procedure below. Note that this site claims "Some people measure a difference of five degrees Celsius or more". I'm not getting anywhere near that kind of temperature difference.)
http://glory.gsfc.nasa.gov/globalwarmingexperiment.html"

2) PBS/NOVA (This one comes complete with an interesting disclaimer: "NOTE: As with any demonstration, the results should, but do not necessarily, match those expected. If the temperatures in the bags do not support the role of greenhouse gases in heat capture, discuss the nature of scientific experimentation, including the importance of multiple trials, control of conditions, and measurement challenges." I also think the baggie concept is very flawed - I used a rigid plastic container.):
http://www.pbs.org/wgbh/nova/teachers/viewing/0302_03_nsn.html"

3) SCIENCE EXPERIMENTS ON FILE™ Revised Edition (similar to the two above):
http://www.fofweb.com/Onfiles/SEOF/Science_Experiments/1-15.pdf"

I'm a chemical engineer by training and I think that my lab technique is still good enough to eliminate most sources that could bias the results of this experiment. I'm getting inconclusive results despite using a variety of light sources (sunlight, incandescent bulb, heat lamp) at a range of distances from the containers and a large number of runs.

I am pretty apolitical on this topic ... my sole interest in this matter is to advise my son about his science project, which he's put a lot of effort into.

Thank you for any advice on reliable sources of information regarding results of similar experiments.

Ray
= = = = = = = = = = = =

Here's the experimental procedure presented on the NASA (GLORY satellite mission) webpage:

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In this activity, you will measure the effect of excess carbon dioxide on the temperature of gas inside of soda bottles and see what the effects of aerosols are on the heating of the gas.

Materials:
Two or more 2-liter clear soda bottles with the label removed.
Identical thermometers for each soda bottle
Opaque tape
Source of carbon dioxide (CO2)
Spray paint or spray glitter
Modeling clay
For your source of carbon dioxide, you may use one of the following methods:

Dry CO2 source - Seltzer bottle charges - fill a dry seltzer bottle with one charge of carbon dioxide. You will use the carbon dioxide in the seltzer bottle to fill one of the bottles with carbon dioxide. For this method, both bottles can be left dry.
Wet CO2 source - Alka-seltzer - you will put a cup of water into both bottles, then put a couple of alka-seltzers into the water in one of the bottles. A tablespoon of baking powder can be substituted for the Alka-seltzer.
Wet CO2 source - Put a cup of club soda or seltzer water in one of the bottles and a cup of tap water into the other bottle

Method:

Drill the caps of the bottles to the same diameter as your thermometer. Place the thermometers through the holes in the caps several inches. Use the modeling clay to hold the thermometers in place and seal the hole.

Use the seltzer bottle to fill one of the bottles with CO2, or, for the wet CO2 source, (method 2) fill the bottles with identical quantities of water and place the Alka-seltzer into one of the bottles, or (method 3) place identical quantities of seltzer/club soda into one of the bottles and plain tap water into the other. Make sure the liquids are at the same temperature when starting the experiment.

Place the caps with thermometers onto the tops of the bottles.

Put the bottles into sunshine. Make sure they receive the same amount of sun. NOTE: a heat lamp may be substituted for the sun, but you must be very careful to place the bottles exactly the same distance from the lamp.

Shade the thermometers by putting a strip of opaque tape on the outside of the bottles. The tape must be the same length on both bottles.

Measure the temperature of the bottles over time. Record the temperature of each bottle every five minutes for a half hour.

The effects of carbon dioxide on the temperature

The bottle with carbon dioxide in it will heat up faster and will stabilize at a higher temperature than the bottle with air. Some people measure a difference of five degrees Celsius or more, or the difference between a warm spring day and a hot summer day.

What you will learn

The Earth's temperature would be much colder without the CO2 in our atmosphere we have naturally. When we add more, the Earth warms up.

The effects of atmospheric CO2 and aerosols on our planet's temperature are measurable with simple tools anyone can use. The effects are as real as touching the hoods of black and white cars that have been standing in the sun.

 

[sylas]

Sounds like a fun experiment. I can't help you much, but here's another description of this sort of experiment, at picotech.com.

It may help to keep in mind the underlying physics you're trying to uncover. None of these are credible as simulations of a climate... they are all just a way of showing the CO2 interacts more strongly with infrared radiation than ordinary air.

This means I am a bit puzzled by some of the experiments described. For example, the NASA experiment advises placing a bottle in the sun, or under a heat lamp. That bothers me a bit.

Part of the reason for a greenhouse effect is that CO2 does NOT interact all that strongly with sunlight! The greenhouse effect works because of absorption of infrared radiation from the ground. What exactly is happening with bottles placed out in the Sun I am not sure! Maybe it is picking up background infrared.

Ironically, carbon dioxide can have a cooling effect in some circumstances! For instance, if there isn't a lot of infrared around, and the bottle itself is getting warmed from the sun, then the CO2 can be heated by conduction from the bottle itself, and then act as a more efficient radiator for shedding the absorbed heat. This might be an effect -- maybe -- if a bottle is placed to get much better sunlight than the general background environment, with a lot of trees or shade. The bottle can end up warmer than the surroundings, and then the CO2 helps keep it cooler by radiating into those surroundings.

The heat lamp would would better -- I think -- because it has a larger amount of infrared in the spectrum. In this case, you can be pretty sure that the impact from absorbtion is stronger than the impact of emission. Alternatively, you can try and make sure there's plenty of background infrared involved.

Here's a thought, just off the top of my head. Place the bottles outside, but suspended with string above a dark surface. You minimize conduction by having them suspended, and you increase the infrared background with the dark surface. Maybe. It would be interesting to try out a few variations and see what the difference is.

I'd would have liked to see a more detailed physical account of what's going on with these kinds of kitchen table top experiments, rather than just a somewhat spurious comparison with what happens for an entire planet.

On the other hand -- I love home experiments like this. Good luck with it!

Cheers -- sylas

PS. It also occurs to me that the material of the bottle might make a big difference. If you use glass, that is opaque to infrared, there may not be much difference at all with CO2, since the radiation that makes the most difference never gets into the bottle. Again, I'm not sure...

 

[natureteacher]

I've gotten it to work. I had to make sure that the bottles were completely sealed (the modeling clay works), and I used a heat lamp and baking soda and vinegar as my CO2 source. I've gotten differences of as much as 10 degrees between the bottle with high CO2 and normal CO2. However, I don't know of any published data that duplicates the effects.

Sylas, thanks for the ideas! I'll have to try them out.

 

[Ray001]

Sylas, thank you very much for your analysis - you point out some of the problems with these experiments that bother me a lot and that I've tried to address. These conceptual flaws seem so great to me that I wonder how anyone can achieve the expected results consistently using the procedures described in the experiments. You identified two of the major problems:

1) With sunlight as the light source, very little infrared radiation reaches the CO2 inside the bottle in the NASA experiment. I agree with you - if you place a clear plastic bottle filled with nothing but carbon dioxide (and a thermometer) in the sunlight, what is the source of IR that supposedly interacts with the CO2? I've tried to address this problem by placing a sheet of black paper inside the container so that it lines half of the interior surface - some of the sunlight shining on the paper should be radiated as IR. Still no luck - my results are pretty random.

2) Heating of the surface of the container may overwhelm all other factors causing temperature rise inside the containers. The surface that faces the source of light becomes noticeably warm to the touch (particularly when using a heat lamp) - much warmer than the side that faces away from the light. Some of the light shining on the container passes through the plastic, but it's obvious that some of it is absorbed in the plastic. If the gas inside the container is heated by conduction through the container wall, then that's not the effect that I'm trying to measure. I've tried to address this by moving the source of light (e.g., heat lamp) further away from the container to minimize surface heating, but without noticeable success. I suppose I could try to find a material that's transparent to IR, but I doubt I'm going to find a 1.5 gallon container made of pure polished salt anytime soon.

I'm also bothered by the experiments that suggest using two separate lamps as sources of light - it seems to me that the distance and angle of the incident light is critical, not to mention variations in light output of the two bulbs. I'm using a single light source and trying to aim it as precisely as I can on both containers.

Water vapor content may also be an issue, but since I'm using a wet source for CO2 (vinegar/baking soda), I'm guessing that the moisture content in both containers is pretty similar. I suppose I could try using a dessicant in both containers, but this may be grasping at straws.

I would think that since the CO2 content of the containers differs by a couple orders of magnitude (< 1% CO2 in room air versus an estimated 70% - 90% in the CO2 container), I should be able to measure some consistent differences in temperature rise, if the experiments that I cited are correct. I'm starting to wonder if these experiments fall into the category of "urban legend" ... a "good idea" passed from one source to another without a lot of verification. Considering how much attention the topic of greenhouse gases has received, surely there must be some empirical lab data that measures the absorption and radiation of IR by carbon dioxide.

Thanks again,
Ray

 

[Ray001]

I've gotten it to work. I had to make sure that the bottles were completely sealed (the modeling clay works), and I used a heat lamp and baking soda and vinegar as my CO2 source. I've gotten differences of as much as 10 degrees between the bottle with high CO2 and normal CO2.

Ten degrees ! That is a huge difference (I'm assuming it's degrees Fahrenheit). It seems like we have a pretty similar setup - I'm using 1.5 gallon plastic containers (the plastic is the same thickness as the plastic of a soda bottle) with a six inch diameter, screw-on, air-tight lid - so gas leakage is not a problem. We're both using the same source of CO2 (I test the CO2 level using an open flame before I start a run). I'm using a 150W heat lamp.

I have no idea how long ago you did this experiment or if you remember the details, but if you have the answers to any of these questions, I'd be grateful for any responses:

1) Did you get this result consistently?
2) Did you see a large temperature spike at the start of your run, or did the temperature difference increase gradually?
3) Did you see any difference in the cooling rates?
4) Did you eventually reach a steady state, with temperatures in both containers levelling off (if so, what were the temperatures)?
5) What type of heat lamp did you use (i.e., how many watts) and about how far away from the containers did you position the lamp?

Thanks,
Ray

 

[natureteacher]

Ray,

I haven't tried this experiment in sunlight, but I have done it with a heat lamp with a bulb of 200 w. I use one heat lamp, and I place both bottles at the same distance from it; everything is the same except one bottle has baking soda in it (I place the same amount of vinegar in both bottles). I still get differences of at least 10 degrees between both bottles. Perhaps some of of the heat is absorbed by the plastic, but with all else being equal, could we attribute the difference to the presence of CO2? I get consistent results every time.

I think that inherently, we will get a "greenhouse effect" in the way greenhouses are heated; the glass of a greenhouse traps energy, and the plastic of the soda bottles also trap energy (I've seen but not tried demos that have students taking the temperature of sealed soda bottles and soda bottles with vents cut out--the temperature rises faster in the sealed soda bottles). But I do get differences in temperature with higher CO2; so even though some of the higher temperature comes from this being a greenhouse, it can't be the entire reason why there is a difference.

Here's what I'm confused about: isn't the energy from the heat lamp IR in addition to visible light energy? Are you saying that all of the IR energy is absorbed by the plastic and is then conducted to the air?

I'm going to try a hair dryer next!

Susan

 

[Skyhunter]

I saw a similar classroom experiment online. Except I seem to remember two sealed chambers that had water in them as well, and were each heated with an ordinary light bulb.

 

[HeadOutOfSand]

This looks like a pretty decent experiment to show the GHG effect:

http://www.beloit.edu/sepm/Geology_and_the_enviro/Earth_warming.html

It involves simulating day and night with a control jar under a sunlamp, and measuring the results every 15 min. Then putting some alka seltzer to simulate the desired amount of CO2, all other variables remaining the same, and measuring the results.

 

[Ray001]

Here's what I'm confused about: isn't the energy from the heat lamp IR in addition to visible light energy? Are you saying that all of the IR energy is absorbed by the plastic and is then conducted to the air?

Hi Susan,

I agree with you that a heat lamp emits IR in addition to visible light - obviously, the IR emitted from a heat lamp is much higher proportionally in comparison to a normal incandescent bulb or sunlight.

I'm not saying that all of the IR energy is absorbed by the plastic and then conducted to the air, but when I ran my experiment, I noticed that the side of the container facing the lamp was very hot to the touch, while the side facing away from the lamp was roughly room temperature. My concern is that the surface heating effect was so great in magnitude that it may have overwhelmed any smaller differences in the temperature of the two gases. I saw a similar temperature rise in both containers. I tried to reduce the surface heating effect somewhat by moving the heat lamp further away from the containers, but the results were still pretty random.

One thing that I did notice is that the positioning of the lamp is very critical. If you aim the lamp just slightly more towards one container than the other, you will get a very noticeable difference in temperature rise between the two containers. That's why I was wondering if you did many runs of the experiment and the results were consistent, or if it was just a single run. I'm interested to read that you obtained consistent results, but also exasperated that I haven't!

It also struck me that I've been to many science museums across the US and many of them had displays about greenhouse gases, but not a single one of them had this very simple, elegant (and inexpensive) experiment that would beautifully display the temperature rise caused by absorption of IR by carbon dioxide. Also, the experiments that I cited seem to have logic gaps (see above regarding the NASA experiment in sunlight) and not much in the way of data (The experiment cited by Sylas did have a graph, apparently from a single run, but I really question the different positioning of the two lamps in the photo, a big potential source of error).

Thanks also for the post about the beloit.edu experiment, but I'm also very skeptical about that one - their method involves weighing out a miniscule amount (0.0083 grams) of an Alka Seltzer tablet to produce a CO2 concentration of only 700 ppm CO2 ! I would love to see the data for this one - I can't get results with concentrations of 70 - 90 PER CENT CO2 !

Ray

 

[sylas]

Considering how much attention the topic of greenhouse gases has received, surely there must be some empirical lab data that measures the absorption and radiation of IR by carbon dioxide.

I suspect professional experimental work is at a whole different level, looking for things like absorption spectrum and so on. The underlying effect of extra absorption has been known for well over a century; so I think for actual professional experimental confirmation of the kind of effect we are looking at here, it will be best to look for experiments made back in the nineteenth century.

Following this lead, I've found the work of John Tyndall, around the 1850s. This link is to wikipedia, and the article has lots of details, and links to public domain copies of Tyndall's own writings. Tyndal was a prominent physicist of the time, and particularly outstanding for his experimental work, on a range of subjects.

It was already known at this time that the Earth's atmosphere was trapping heat and giving a warmer surface temperature than would otherwise be the case, but the relevance of different gases was not understood. Tyndall was trying to measure the absorption characteristics of gases, and had failed to find any significant effect with the major atmospheric gases (Oxygen, and Nitrogen).

Reading his own account of these experiments is well worthwhile! A DjVu reader will be required, and with this you can read Contributions to Molecular Physics in the Domain of Radiant Heat (Tyndall, 1872) [17 Mbyte djvu file, 446 pages]. Chapter 1 is the relevant chapter for gases, and very interesting for an account of his experimental difficulties and for the amazement on first seeing just how opaque "carbonic acid" (CO2) was to thermal radiation. There is also an eloquent little public lecture reproduced therein, on what we now call the greenhouse effect, on pages 421-424. Those Victorian scientists could write well! The major focus of that lecture is water vapour.

Here is a picture of Tyndall's apparatus:

It would be interesting to try these home experiments as well using very dry air. If whatever process you use to get CO2 into a bottle also means a reduction in the water vapour, you might get less absorption as a result -- though at your concentrations the extra CO2 should more than compensate. It's worth remembering that the Earth's greenhouse effect arises from a vertical column of atmosphere many kilometers high, having about 10 tonnes of gas per square meter. You are trying to see the effect in a bottle; and that is why higher concentrations are needed.

Cheers -- sylas

 

[Ray001]

Sylas -

The report on Tyndall's work is fascinating - it illustrates that regardless of the level of technology utilized, good experimental design is the key to getting meaningful results. I particularly like the salt plugs and cold water jacket concepts, which address sources of error identified for the CO2 experiment under discussion.

I'm still working on tweaks for the experiment, but the results I'm getting still show the temperature profiles for the CO2 and air containers moving pretty much in lockstep, with only minor (1 or 2 deg. F) differences in readings between the two. I have no doubt that with proper controls, higher temperatures for CO2 should be detectable, but the setup I'm using may just be too crude for that.

On the bright side, I've looked at the data I've collected and I think I've just discovered cold fusion. Thought you'd like to be the first to know.

Thanks,

Ray

 

[sylas]

Good luck and keep us posted! -- sylas

 

[Skyhunter]

http://www.espere.de/Unitedkingdom/water/uk_watexpgreenhouse.htm"

 

[Ray001]

http://www.espere.de/Unitedkingdom/water/uk_watexpgreenhouse.htm"

Thank you for the link ... I was especially interested in the water screen method that the experimenters used to prevent surface heating of the gas containers. I might be able to set up something similar to that. If a large glass pan of water is too impractical, a pane of insulating glass might accomplish the same thing (i.e., filtering out most of the IR, keeping the surfaces of the gas containers at room temperature). I was curious about why they would put their black cardboard underneath the containers as opposed to inside them - perhaps it's a translation error. The data are interesting - I'd be happy to achieve even half of the results that they got!

Ray

 

[Mk]

Hey Ray, I'll copy you one. You've got me interested, I'll follow this thread and try to do the experiment this week.

 

[cleanwater]

These experiments are worthless - the minute you introduce water into the container you are not measuring the effect of CO2 . Water and water vapor absorb far more IR than even 100% CO2. CO2 absorbs IR at only 2 wavelengths-app. 400 nm and 900 nm which represents a very small portion of the total light spectrum. Water and water vapor absorb both visible ,UV and IR radiation. Now a very important known fact- The work of Niels Bohr Nobel prize winner in 1922- proved that when a gas absorbs electromagnetic radiation it does not heat the gas- it causes the electrons in the molecule to gain energy and move to a higher electron shell. Gasses heat by conduction or convection- which result in the molecule moving at higher velocity that is the heat we can measure with a thermometer.
One or two of the commenters above have correctly noted that when they measured the temperature of the container it was getting noticeable hotter on the side nearest the light source- this is what causes the gas inside the container to heat up. Also as was noted in the description of the experiment-it is necessary to shield the thermometer from the light source or you are measuring the IR absorbed by material of the thermometer,not the actual gas temperature. Why not use IR thermometers- they are readily available today for under $60. and you do not have any issues of heating of the measuring devise itself.
It has been mentioned above that the use of glass containers can be a problem as glass is know to absorb IR. The wavelengths that are absorbed are dependent on the composition of the glass. The plastic containers absorb some heat therefore it will be necessary to measure the heating effect of the light on an air only sealed container.
After all these experiments it will be found that CO2 does not cause global warming,It was proved in 1909 by R.W. Wood that the ghg effect does not exist and the concept Violates the Second Law of thermodynamics. .
Mother nature is doing a better job of proving that the ghg effect and man-made global warming is a political hoax. Things like the glaciers in all of the northern hemisphere are growing, more ice in the north and south poles, first significant snow in Argentina in 89 year, average temperature as measured by NASA has not increased in fact has been decreasing since 1998 in spite of more and more CO2. .
I will be adding an experiment description in the next day or two that shows that the ghg effect is a fair-tale. The experiment uses 100 % CO2, natural gas(CH4 and CO2) , butane, and air with water vapor ,air without water vapor.

 

[Skyhunter]

These experiments are worthless - the minute you introduce water into the container you are not measuring the effect of CO2 .

Since all things are equal in the chambers, except for CO₂, then it follows that the difference in temperature from one container and the other is attributable to variance in CO₂.

Water and water vapor absorb far more IR than even 100% CO2.

The atmosphere on Venus is 97% CO₂, 2.5% nitrogen, and 0.5% other gases. The surface temperature on Venus is 737K. The blackbody temperature on Venus is 232K. (737-232=505) In other words the greenhouse effect from carbon dioxide is warming the surface of Venus by over 500 degrees celsius.
http://www.espere.de/Unitedkingdom/water/uk_watexpgreenhouse.htm using 100% CO₂. 100% CO₂ absorbs more IR than air with some water vapor. Since there were no steps taken to remove the water vapor from the normal air it is safe to assume that there is water vapor in the second container.

CO2 absorbs IR at only 2 wavelengths-app. 400 nm and 900 nm which represents a very small portion of the total light spectrum. Water and water vapor absorb both visible ,UV and IR radiation.

The following chart clearly shows that CO₂ absorbs in ten bands not two, in three of those bands the absorption is 100%.

Now a very important known fact- The work of Niels Bohr Nobel prize winner in 1922- proved that when a gas absorbs electromagnetic radiation it does not heat the gas- it causes the electrons in the molecule to gain energy and move to a higher electron shell.

You are misunderstanding the relevance of this discovery. Higher energy is higher energy, IE higher heat. The mechanism in which a molecule absorbs photons does not change the fact that once the energy is absorbed the molecule is excited and in a higher energy state.
Here is an article covering http://www.climate.unibe.ch/~stocker/papers/jouzel07sci.pdf .

Gasses heat by conduction or convection- which result in the molecule moving at higher velocity that is the heat we can measure with a thermometer.

Gases do not heat by convection. Convection is the movement of gases not the transfer of heat from one gas to another, that occurs by conduction, friction, the result of collisions between molecules. When a molecule is more excited the probability that it will collide with another molecule is increased. Absorption of energy whether through collision with another molecule or absorption of electromagnetic energy results in more motion which equals more heat.

One or two of the commenters above have correctly noted that when they measured the temperature of the container it was getting noticeable hotter on the side nearest the light source- this is what causes the gas inside the container to heat up. Also as was noted in the description of the experiment-it is necessary to shield the thermometer from the light source or you are measuring the IR absorbed by material of the thermometer,not the actual gas temperature. Why not use IR thermometers- they are readily available today for under $60. and you do not have any issues of heating of the measuring devise itself.
It has been mentioned above that the use of glass containers can be a problem as glass is know to absorb IR. The wavelengths that are absorbed are dependent on the composition of the glass. The plastic containers absorb some heat therefore it will be necessary to measure the heating effect of the light on an air only sealed container.

Again I suggest you check out the experiment I linked since it addresses all your criticisms.

After all these experiments it will be found that CO2 does not cause global warming,It was proved in 1909 by R.W. Wood that the ghg effect does not exist and the concept Violates the Second Law of thermodynamics. .

This statement is preposterous. If there were no GE the Earth would be an iceball.

Mother nature is doing a better job of proving that the ghg effect and man-made global warming is a political hoax.

The SSTs in June 2009 were the warmest ever recorded. June 2009 was the second warmest June in the instrumental record. All this while the Sun is at the lowest level of activity since we began measuring solar activity in 1979.

Things like the glaciers in all of the northern hemisphere are growing,

? Where?
Can you support that statement with a citation?
Here is http://nsidc.org/glims/glaciermelt/index.htmlof ~1600 glaciers worldwide. Clearly the melting trend is pronounced and obvious.

more ice in the north and south poles,

Again you have your facts reversed.
Arctic sea ice.

While average Antarctic sea ice has increased slightly, this is a function of ozone depletion and it's effect on circulation patterns in the Antarectic, not some alleged global cooling. other areas of the Antarctic, especially the western peninsula, are experiencing a sharp decline in average sea ice extent.
Antarctic total ice mass is decreasing to the tune of about 84 gigatons of ice per year.

first significant snow in Argentina in 89 year,

This is a weather event, not a climate event. The reasons why it snowed once in 90 years could as easily be attributed to weather patterns, IE precipitation in SH winter, as to temperature.

average temperature as measured by NASA has not increased in fact has been decreasing since 1998 in spite of more and more CO2. .

Wrong again. The last decade was the warmest decade of the instrumental record, IE the warmest decade since 1880.

I will be adding an experiment description in the next day or two that shows that the ghg effect is a fair-tale. The experiment uses 100 % CO2, natural gas(CH4 and CO2) , butane, and air with water vapor ,air without water vapor.

I am looking forward to seeing it.

 

[BrianG]

I find these experiments very intriguing. I'm curious; there have been thousands of atmospheric tests on manmade aerosols and climate cooling. Aerosol debris has been generated by atmospheric and ground nuclear bursts and controlled forest fires. My question is, why have there been no atmospheric tests on manmade GHGs and warming? I'd bet it’s because the effect is insignificant.

If you take the results from these experiments:


http://www.picotech.com/experiments/global/globalwarming.html


http://www.espere.net/Unitedkingdom/water/uk_watexpgreenhouse.htm

You find a very small warming, four to six degrees between the two sample atmospheres. One sample is pure CO2 (1,000,000ppm) and the other is air (approximately 380ppm CO2). If the concentration of CO2 in the air sample was doubled a little over 12 times, it would be equal to the pure CO2 sample atmosphere. Using the greenhouse effect theory, we can divide the six degree temperature difference by 12, to find the approximate temperature increase caused by doubling CO2 in the air, that's a little less than 0.5 degrees. That's significantly less than the IPCC's climate value for doubling CO2.

I'd like to encourage you all to keep up this line of research, and I will follow this thread very carefully. Thank you all for your good work!

 

[cleanwater]

Hello Skyhunter: let's start with the experiment at the University of Bremen-It does not prove what it claims. It is so full of errors that a high school student could do better. Below are my comments when I was linked to it by Colby:
1. Are the two containers the same size, shape and type of glass? Different types of glass absorb different wave lengths of IR and heat up differently.
2. Where are the thermometers located relative to the light? Are they in the light path were they would absorb some of the IR thus skewing the data.
3. If the greenhouse gas effect exists there should be a different temperature of the black cardboard in the CO2 container. The temperature was not measured therefore this experiment only illustrates that the CO2 heats up. Does it heat from absorption or from conduction of different heating of the container?
4. Was the experiment done with other “greenhouse gases?” as CH4 butane, natural cooking gas, Nitrogen trifluoride ?
5. Did the experimenters reverse the gases to the other container to evaluate differences in the set-up.?
6. Was more than one set of test done? Is there more data to evaluate?
7. Did you monitor the temperature of the water in the trays? If the trays are in contact with the gases there is conduction of heat from the bottom of the glass trays to the gases.
8. I can not be sure from the photos but it appears that the top of C1 container is closed ,if this is true then you have created a confined space heating container (greenhouse effect). It has been proved by R.W. Wood and others that the heating in a greenhouse is caused by the restriction of heat convection and not back radiation of IR. The top of C2 appears open thus keeping the temperature lower by convection. Good job of cheating..
9. What you have shown is what has been known from IR spectroscopes that different gases absorb different wave lengths of IR.
10. I have done a similar experiment except I used clear Mylar balloons (very little or no absorption of IR as opposed to glass) Based on IR thermometer reading and available data on IR absorption by glass much of the heating in the experiment was from the glass. This was not measured in the experiment. By using Mylar balloons in bright sunlight there was no heating of the gases inside 4 balloons above ambient temperature (measured with an IR thermometer reading to O.1 degrees F. The contents were 100% CO2, 100% butane, natural gas (CH4 and CO2) and air. The black cardboard I used did not show any differential heating between areas in the “shadow” of the balloons compared to “unshadowed” areas –no back radiation from the “greenhouse gas effect” The black cardboard did increase in temperature from ambient of 95 degree F to 175 degree F. uniformly across the surface.
11. If the greenhouse gas effect exist why hasn’t it been applied to something useful like thermopane window filled with a “greenhouse gas” that would back radiate IR into the house and create insulated windows with R=30 values.
You ask the question “Why can it be warmer at night than during the day? Any elementary school students that can read a weather report know that daily temperature are effected by hot or cold air masses moving across the area. It is also obvious that
on a clear night the temperature will cool down much faster that on a cloudy night. Water is not a greenhouse gas in spite of what many people say- it has known properties that explain temperature differences 24/7/365. There is no back radiation –there is reflection of light or blockage of light(clouds) energy release as lightning and other thermal effects that are within the Laws of physics and thermodynamic.
When you find reliable experimental data that proves that the “greenhouse gas effect exists please share it with the world.
In the mean time read “Falsification of the Atmospheric CO2 greenhouse effects within the frame of Physics” by Gerhard Gerlich and Ralf D. Tscheuschner and when you understand it in five or ten years( a PhD level –way above your level of intelligence) and the global temperature has dropped by the 0.6 degrees that it has gone up over the passed 120year you will realize that man-made global warming is a hoax.
Posted by: cleanwater | May 14, 2009 3:09 PM
The graph you included to illustrate the absorption is mathematical junk. The horizontal axis of the incoming radiation has been manipulated as there has to be an overlap into the IR long wave IR. There is no way that 320 ppm of CO2 will absorb enough IR to prevent significant IR from hitting the Earth. The CO2 graph has been cut at the top to give the impression that it is totally absorbed. If this actually happened IR spectromophy would only work if the tested gases was less than the 320 ppm CO2-anyone that has worked with IR spectromophy knows this is not the case.

another point was that I said that gasses are heated by convection and conduction: You then went on to describe both fenomenon. You contradicted yourself.

You went onto talk about Venus-you stated that its black body temperature should be 232 c- that's only a few degrees higher than Earth BBt-considering that Venus is much closer to the Sun this does not make sense. You have ignored the fact that there is a cloud layer of sulfuric acid above the 97% CO2. This cloud layer is what causes the surface temperatures to be warmer than BBT.

You talk about Earth temperatures being the second warmest July,seeing we're not thou July where did you get your data.
To find out about glaciers in the US look up the web-site of Robert Felix. Your own graph shows that the ice in the North polar region is greater than in 2007. The last time I looked at this same graph the lower line was labeled as being for 2004.

 

[cleanwater]

Hello Brian G: your comments about the effect of particulates in the atmosphere is far more important than the effect of CO2. The ghg effect is a proven fairy-tale. The ghg effect was disproved in 1909. I have been trying to show the many ghg gang that it does not happen.
If we talk about particles in the atmosphere it has been demonstrated by volcanoes and other sources that it causes cooling. The Mt.Saint Helena irruption caused measurable decreases in the Northern hemisphere for about a year or more .

 

[Skyhunter]

I find these experiments very intriguing. I'm curious; there have been thousands of atmospheric tests on manmade aerosols and climate cooling. Aerosol debris has been generated by atmospheric and ground nuclear bursts and controlled forest fires. My question is, why have there been no atmospheric tests on manmade GHGs and warming? I'd bet it’s because the effect is insignificant.

If you take the results from these experiments:


http://www.picotech.com/experiments/global/globalwarming.html


http://www.espere.net/Unitedkingdom/water/uk_watexpgreenhouse.htm

You find a very small warming, four to six degrees between the two sample atmospheres. One sample is pure CO2 (1,000,000ppm) and the other is air (approximately 380ppm CO2). If the concentration of CO2 in the air sample was doubled a little over 12 times, it would be equal to the pure CO2 sample atmosphere. Using the greenhouse effect theory, we can divide the six degree temperature difference by 12, to find the approximate temperature increase caused by doubling CO2 in the air, that's a little less than 0.5 degrees. That's significantly less than the IPCC's climate value for doubling CO2.

I'd like to encourage you all to keep up this line of research, and I will follow this thread very carefully. Thank you all for your good work!

Your simple calclation 12/6 is no more accurate than dividing the 500 degree increase on Venus by 12; 500/12=42. (approximately) Also note that the water vapor feedback on Venus is nonexistent.
Straight contribution from CO₂ per doubling would be ~1.2C, add the other climate feedbacks and you get 2.0C to 4.5C per doubling.

 

[sylas]

Hello Brian G: your comments about the effect of particulates in the atmosphere is far more important than the effect of CO2. The ghg effect is a proven fairy-tale. The ghg effect was disproved in 1909. I have been trying to show the many ghg gang that it does not happen.

You are mixing up two things. 1909 was an experiment on glass greenhouses; not greenhouse gases. It confirms that a glass greenhouse works mainly by restricting convection. It does not even attempt to deal with the atmospheric greenhouse effect. It is a useful demonstration that the atmospheric greenhouse effect is something of a misnomer... and that's all.

If we talk about particles in the atmosphere it has been demonstrated by volcanoes and other sources that it causes cooling. The Mt.Saint Helena irruption caused measurable decreases in the Northern hemisphere for about a year or more .

Yes, it does. The effect of particles on light is quite different from the effect of a gas on light. Is this news??

Cheers -- sylas

 

[BrianG]

Hello cleanwater, Skyhunter and Sylas. Thanks for your replies, you’ve given me something to think about. I’m not a scientist but I am very interested in the issue of climate mitigation.

I’m using the formula from Arrhenius:

“if the quantity of carbonic acid increases in geometric progression, the augmentation of the temperature will increase nearly in arithmetic progression.
This simplified expression is still used today:

ΔF = α ln(C/C02)”

I found it here: http://en.wikipedia.org/wiki/Svante_Arrhenius

Skyhunter, how did you derive your CO2 sensitivity results? Is it from the IPCC? Too bad, these experiments only test air and pure CO2, other concentrations of CO2 would be very helpful.

Please continue your work on experimental verification of the Greenhouse theory and I’ll try to keep up.

 

[Skyhunter]

Cleanwater,
That is not a refutation, it is a list of denials.
A list of unfounded suspicions as to why the experiment must, in your mind be flawed. Then you claim to have conducted your own experiment with mylar balloons and short-wave electromagnetic radiation instead of infrared. You failed to fully describe your experiment, but just the fact that you are using high energy radiation instead of infrared exposes your own ignorance of the phenomenon you are trying to disprove.
What your response demonstrates is that you believe you are right, therefore any evidence to the contrary must be wrong.
Open your mind a little, the scientific method is surest way to overcome a confirmation bias.

 

[Skyhunter]

The graph you included to illustrate the absorption is mathematical junk. The horizontal axis of the incoming radiation has been manipulated as there has to be an overlap into the IR long wave IR. There is no way that 320 ppm of CO2 will absorb enough IR to prevent significant IR from hitting the Earth. The CO2 graph has been cut at the top to give the impression that it is totally absorbed. If this actually happened IR spectromophy would only work if the tested gases was less than the 320 ppm CO2-anyone that has worked with IR spectromophy knows this is not the case.

This is nonsense, There is so little incoming IR that measuring how much is "coming in" would be quite difficult. The graphic has not been manipulated, it is in agreement with textbook spectroscopy.

another point was that I said that gasses are heated by convection and conduction: You then went on to describe both fenomenon. You contradicted yourself.

Instead of using your perception to attack me personally, please point out the contradiction and offer an explanation as to why it is contraictory.

Also, are you admitting that convection dos not heat gases?

You went onto talk about Venus-you stated that its black body temperature should be 232 c- that's only a few degrees higher than Earth BBt-considering that Venus is much closer to the Sun this does not make sense. You have ignored the fact that there is a cloud layer of sulfuric acid above the 97% CO2. This cloud layer is what causes the surface temperatures to be warmer than BBT.

Where is your citation to support this assertion?

You talk about Earth temperatures being the second warmest July,seeing we're not thou July where did you get your data.

http://www.ncdc.noaa.gov/oa/climate/research/2009/jun/global.html#temp" July was a typo and should have read June. I will correct it.

To find out about glaciers in the US look up the web-site of Robert Felix. Your own graph shows that the ice in the North polar region is greater than in 2007. The last time I looked at this same graph the lower line was labeled as being for 2004.

The onus is on the poster to provide citations to support their assertions.

2007 was an anomalous year and only pertinent when setting new records. The significant point is that the cryosphere worldwide is in decline. This was to me the most compelling evidence for global warming. The ice is melting.

 

[BrianG]

Your simple calclation 12/6 is no more accurate than dividing the 500 degree increase on Venus by 12; 500/12=42. (approximately) Also note that the water vapor feedback on Venus is nonexistent.
Straight contribution from CO₂ per doubling would be ~1.2C, add the other climate feedbacks and you get 2.0C to 4.5C per doubling.

Isn't Venus closer to the sun? How did you get your figure of 1.2C?

 

[sylas]

Isn't Venus closer to the sun? How did you get your figure of 1.2C?

The effect of doubling CO2 is for conditions on Earth, where CO2 is a small part of the atmosphere. It's a fairly well constrained result that doubling CO2 in Earth's atmosphere, and holding everything else fixed, will give an additional 3.7 W/m² of forcing.

You can get approximately the right result here by using a crude estimate of

$$Q = \epsilon \sigma T^4$$​

Q here is the energy out the top of the atmosphere, T is the absolute temperature at the surface, σ is the Stefan-Boltzmann constant, and ε is a constant, written here a bit like emissivity, although it is is not actually an emissivity term.

T at Earth's surface is about 298, and Q is about 239 W/m².

Differentiating, we have

$$\frac{dQ}{dT} = \epsilon \sigma 4 T^3 = \frac{4Q}{T} = 3.2$$​

With dQ at as about 3.7, the value dT to restore energy balance is about 3.7/3.2 = 1.16. In practice, this calculation is done over the whole surface of the Earth, and is a bit more complex, but this approximation here gives a good ballpark for "non-feedback" response.

That is, raising the surface temperature by about 1.1 to 1.2 degrees is enough to restore Earth's energy balance in response to the forcing from a doubling of CO₂, as long as nothing else changes.

However, other things do change. Ice melts. Vegetation cover varies. Weather patterns and cloud cover alters. The lapse rate shifts in response to a different specific humidity. And so on. All these things in turn have a further effect on temperatures, and the net effect is a positive feedback. But it is not well known precisely what gain is given by this feedback. There have been a range of methods applied to try and constrain it, but so far the best we can say is that it will actually take something from 2 to 4.5 degrees temperature rise to restore the energy balance in practice.

Cheers -- sylas

 

[Skyhunter]

Isn't Venus closer to the sun?

Yes it is, however it has a higher albedo, and therefore absorbs less energy.

 

[Andre]

That is, raising the surface temperature by about 1.1 to 1.2 degrees is enough to restore Earth's energy balance in response to the forcing from a doubling of CO₂, as long as nothing else changes.

In MODTRAN it's hard to get values above 0.9 degrees, to get 1.2 degrees one has to keep relative humidity constant, which is already a positive feedback.

All these things in turn have a further effect on temperatures, and the net effect is a positive feedback. But it is not well known precisely what gain is given by this feedback. There have been a range of methods applied to try and constrain it, but so far the best we can say is that it will actually take something from 2 to 4.5 degrees temperature rise to restore the energy balance in practice.

(emphasiz mine)

Typical response characterical differences between positive and negative feedback can be discerned. Positive feedback has a 'persistant' character, pushing an output value like temperature for instance into the direction of the disturbance, while negative feedback does the opposite.

Guess how long we know already that we cannot discern positive feedback behavior in the temperature series?:

http://www.aai.ee/~olavi/2001JD002024u.pdf

...Estimating long-range dependence between the increments reveals a remarkable difference between the two temperature series. Global average tropospheric temperature anomaly behaves similarly to the solar irradiance anomaly. Their daily increments show antipersistency for scales longer than 2 months. The property points at a cumulative negative feedback in the Earth climate system governing the tropospheric variability during the last 22 years...

Of course persistence (positive feedback) or anti-persistence (negative feedback) can be checked on any climate data series, anytime. So I wonder if studies exist, which demonstrate this persistence in any data series.

 

[sylas]

In MODTRAN it's hard to get values above 0.9 degrees, to get 1.2 degrees one has to keep relative humidity constant, which is already a positive feedback.

I don't know what you are doing there. I get completely the opposite. Holding relative humidity fixed gives you much greater values than 1.2, as I would expect from the positive feedback of an additional greenhouse effect from the increased specific humidity.

MODTRAN is really geared towards looking at a specific column of atmosphere under a certain profile; to get from that to a value for the whole planet would be a lot of work... and closer to what is really done in practice rather than the simple approximation I presented.

See http://geosci.uchicago.edu/~archer/cgimodels/radiation.html at the Uni of Chicago, courtesy of David Archer. The values we are giving here are basically 3.7 / (dQ/dT). You can read off an estimate for dQ/dT from MODTRAN by boosting surface temperature by 1 degree and seeing how much the output radiation changes.

Strictly speaking it is probably best to look down from an altitude of 18 km or so, near the tropopause; but you'll get roughly comparable results with the default 70km, so that doesn't matter much. I'll use the default 70km here, and you can check that 18km would also show the same ball park. You can pick various atmospheres, and hold pressure (specific humidity) or relative humidity fixed. Here are results I obtained with the calculator:

$$\begin{array}{cccccc} \text{atmosphere} & \text{base Iout} & \text{+1C, fix spec h} & \text{Plank Response} & \text{+1C, fix rel h} & \text{Plank Response} \\ \text{Tropical} & 287.844 & +3.674 & 1.01 & +2.198 & 1.68 \\ \text{Std 1976} & 258.862 & +3.297 & 1.12 & +2.229 & 1.66 \end{array}$$​

In other words, using MODTRAN and holding the water vapour pressure fixed gives something close to what I estimated previously with my approximation of a T⁴ power relation. Holding relative humidity fixed... which corresponds to an increase in specific humidity and a smallish positive feedback... gives you a greater value of about 1.7 or so.

How did you get 0.9?

Typical response characterical differences between positive and negative feedback can be discerned. Positive feedback has a 'persistant' character, pushing an output value like temperature for instance into the direction of the disturbance, while negative feedback does the opposite.

Guess how long we know already that we cannot discern positive feedback behavior in the temperature series?:

http://www.aai.ee/~olavi/2001JD002024u.pdf

Thanks... I've never seen that paper before.

I don't really follow what he is doing there; I've had a quick look but I need to read it more carefully. This result runs counter to all the research, both theoretical and empirical, that I have seen on the matter.

There have been several threads where the literature on constraining feedback has been discussed. We've already shown just above that water vapour should give a positive feedback. There are multiple empirical studies confirming this as a significant effect, as we should expect from basic physics given that water is such a strong greenhouse gas. A recent thread on cloud studies also suggests another strong positive feedback ([thread=327161]Clouds and Global Warming[/thread]). We've discussed the paper by Schwartz, which originally proposed an anomalously small positive feedback, but in response to some criticisms of his method he acknowledged the problems and revised it upwards to be rather stronger. See especially [post=2195419]msg #47[/post] of thread "Estimating the impact of CO2 on global mean temperature". In the [post=2162699]OP of that thread[/post], I describe empirical studies of the response to volcanic eruptions which appears to use a method somewhat similar to your reference; they find that the response to an eruption has a long tail (persistence) indicative of a substantial positive feedback. That post also cites Annan and Hargreaves (2006) showing a range of empirical studies which imply positive feedback. In particular, a negative feedback on climate would make the large temperature swings of the ice ages pretty much inexplicable. The forcing required would be enormous.

However, I grant that it is rather unsatisfactory to merely cite all the evidence (and there's a lot of it!) for positive feedback. If Karner is incorrect, then there's a problem that should be able to be identified in his methods or data; and if that is not known, then we have a legitimate mystery.

I must admit my own bias up front. I am pretty sure Karner can't possibly have a credible case; the case for a positive feedback both empirically and theoretically is very strong and backed up with many different studies. But I admit my bias with a view to recognizing it, so that I can avoid merely prejudging and giving a fair reading as best I can. If you can explain the method in your own words, that may help and I'll be grateful. But I will look at it in any case.

Of course persistence (positive feedback) or anti-persistence (negative feedback) can be checked on any climate data series, anytime. So I wonder if studies exist, which demonstrate this persistence in any data series.

There's the volcano data I mentioned, which shows a strong persistence effect. The reference is Wigley, T. M. L., C. M. Ammann, B. D. Santer, and S. C. B. Raper (2005), Effect of climate sensitivity on the response to volcanic forcing, in J. Geophys. Res., Vol 110, D09107, doi:10.1029/2004JD005557.

You have to compare the temperature time series with the forcing, or you can't even get started. Karner appears to use the solar forcing from the sunspot cycle. It may be instructive to compare with Schwartz' work, mentioned above. But as I say, I'll have to look at it more carefully.

No matter what I think of the matter... thanks for the reference!

Cheers -- sylas

 

[Andre]

... gives you a greater value of about 1.7 or so.

How did you get 0.9?

From the default http://geosci.uchicago.edu/~archer/cgimodels/radiation.html settings ...

(CO2 (ppm> 375
CH4 (ppm) 1.7
Trop. Ozone (ppb) 28
Strat. Ozone scale 1

Ground T offset, C 0
hold water vapor pressure
Water Vapor Scale 1

Locality Tropical Atmosphere
No Clouds or Rain

Sensor Altitude km 70
Looking down

...We get an output of:

Iout, W / m2 = 287.844
Ground T, K = 299.70

Now we change only:

(CO2 (ppm> 750

and the output changes to

Iout, W / m2 = 284.672
Ground T, K = 299.70

So obviously less IR energy reaches the sensor and we have to increase the temperature to get the original / apparently equilibrium I-out back (287.844 w/m2)

So we put in Ground T offset, C the value +0.89 to see an output of

Iout, W / m2 = 287.844
Ground T, K = 300.59

hence we have to increase the surface temp with 0.89 degrees according to MODTRAN to regain radiation equilibrium.

Now we go back to the defaults and change hold water vapor Rel. Hum. which does not change the output from the basis, however if we double CO2 now, the output is

Iout, W / m2 = 284.672
Ground T, K = 299.70

And now we have to enter 1.48 degrees in ' Ground T offset, C' to regain the equilibrium value again.

For the 1976 standard atmosphere these values are 0.88 and 1.30 degrees respectively

Perhaps it's better to give Karner a dedicated thread as we explore the characteristix of feedback in general.

 

[chriscolose]

sylas, Michael Tobis had this to say a while back in a RC comment (to Andre actually) on Karner.

33.Re #3, specifically to the references to work by the Estonian statistician, O. Karner.

Karner has been taking single time series of diurnal temperature differences and showing that they act as if they are constrained to return to a fixed value. The statistical properties of this time series are “antipersistent” and may be associated with a feedback in a simple lumped parameter model. This is a purely statistical rather than physical model, and it shows there is a homeostatic process, with a number that can be considered “the feedback”.

Unfortunately, it appears to me that Karner confuses this mathematical property with the H2O amplification of radiative forcing, a physical quantity with which Karner’s feedback constant has only a distant relationship.

Indeed, there is an antipersistence in temperature anomalies on Earth, and the mechanism is well-known: radiative equilibration. In this phenomenon, water vapor plays an important role but it isn;t a soliloquy. Thus, when Karner says things like (see http://www.aai.ee/~olavi/2001JD002024u.pdf )

The revealed antipersistence in the lower tropospheric temperature increments does not support the science of global warming developed by IPCC [1996]. Negative long-range correlation of the increments during last 22 years means that negative feedback has been dominating in the Earth climate system during that period. The result is opposite to suggestion of Mitchell [1989] about domination of a positive cumulative feedback after a forced temperature change

to my reading he is confused. (I am surprised this text passed review at JGR-A.)

His subsequent paper ( http://www.aai.ee/~olavi/cejpokfin.pdf ) seems to show increased awareness on the matter:

Using the H estimates to ascertain the cumulative feedback sign dominating in the Earth climate system for the particular variable. In the present study the term feed-back is used in the sense of total reaction of the variable to customary forcing in the Earth climate system. Such an understanding is unavoidable in statistical analysis of meteorological time series because, as a rule, they are affected by many forcing types including the seasonal and daily cycles in solar radiation. In climatology the term feedback is usually connected to the corresponding feedback loop, e.g ice-albedo feedback [13]. For the whole climate system this means that one has to consider many feedbacks at the same time.

Karner’s methodology does not separate out specific physical mechanisms but is simply a way of characterizing a time series. It in some sense includes but (as I understand it) in no sense measures the impact of water vapor feedback on radiative equilibrium.

My own reading of the Karner paper is that it has little at all to do with attribution or long-term climate feedback, and thus claims as in the abstract are unsupportable. I don't quite understand the statistical end of things in the way Tobis does, but the relation to long term climate feedback is kind of evident.

 

[Andre]

Chris, the articles of Olavi Karner are peer reviewed and the physics of feedbacks are clear albeit complex.

How about some remark of somebody, challenging that? Is this also peer reviewed? If there is a discussion about this in a formal scientifically recognized magazine then it would be nice to quote that, however there is a strong viewpoint here about the autority of blog discussions.

There are more papers by the way, for instance:

http://www.aai.ee/~olavi/E-Ac-Sci-07.pdf

..The analysis of the OLR time series indicates that a negative feedback should dominate in the Earth climate system...

 

[chriscolose]

One way to think about the no-feedback case is to assume that the emission temperature and surface temperature are linearly related, and so it follows that


$$\lambda$$ (planck feedback only) =$$\left(\frac{\partial ( \sigma T^{4}_{eff})}{\partial T_{s}}\right) ^{-1}$$

Please note that the resultant $$(4 \sigma T^{3}_{eff})^{-1}$$ requires the emission temperature (i.e., 255 K) as an input, not the surface temperature. This evaluates to roughly 0.27 $$K (W m^{-2})^{-1}$$

which says that you get about a quarter degree change in temperature for each Watt per square meter forcing. The forcing for a doubling of CO2 is nearly 4 watts per square meter. This would imply a very stable climate since it would take a 23 W/m2 change in solar constant just to produce a 1 C change in global temperature, about the same as a doubling of CO2. Thus you'd need the equivalent of several doublings of CO2 and/or unreasonable changes in solar irradiance to be consistent with the magnitude of deep-time paleo changes.

Those arguing for net neutral, and especially negative feedbacks are simply not correct.

 

[sylas]

OK... thanks. I now see what you are doing with MODTRAN. You are actually calculating something rather different to the Planck response; although the reason for this gets a bit subtle.

The forcing for a doubling of CO₂ is known to be 3.7 W/m². This number is well constrained; with about 10% accuracy or so. The major reference for this value is Myhre et al., (1998) http://www.agu.org/pubs/crossref/1998/98GL01908.shtml, Geophysical Research Letters, Vol 25, No. 14, pp 2715-2718; and similar values are obtained in other work as well. It is not something that should be in serious dispute.

Unfortunately, you can't read this off MODTRAN very well. There are two reasons for this. One is that it depends on the latitude. The second is that it depends on the altitude of the sensor.

Part of the problem is the appropriate definition of a forcing. I describe it, with references, in [post=2162699]msg #1[/post] of "Estimating the impact of CO2 on global mean temperature". It corresponds to a change in energy balance at the top of the tropopause. There's a reason for measuring there rather than at 70km; and it is because of the rapid response of the stratosphere to a forcing... a response that this MODTRAN calculator omits. In [post=2165483]msg #3[/post] of that thread I repeat pretty much the calculation you have given here, but with a detector at 20km. Here is a tabulation of some results:

$$\begin{array}{cc|cccc} \text{Atmosphere} & \text{Altitude, km} & 375 \text{ppm} & 750 \text{ppm} & \text{difference} & \text{extra T reqd} \\ \hline \text{Tropical} & 20 & 288.378 & 283.856 & 4.522 & 1.385 \\ \text{Tropical} & 70 & 287.844 & 284.672 & 3.172 & 0.89 \\ \text{Std 1976} & 20 & 258.893 & 255.47 & 3.423 & 1.03 \\ \text{Std 1976} & 70 & 258.862 & 256.004 & 2.858 & 0.88 \end{array}$$​

The reason you get a difference at higher altitude is that the atmospheric temperature profile in this calculator is held fixed, and so the calculator actually has stratospheric warming as a response to an increase temperature offset. What happens in reality is that the stratosphere cools; mainly because of the increased emissivity of carbon dioxide which makes it shed heat more rapidly. Furthermore, this cooling response is very rapid, since it is a purely radiative effect. That is why the formal definition of forcing includes settling of the stratosphere, but not of the troposphere. Informally, you can say that the stratosphere response (which has little impact back to ground level) is considered so fast that it is part of the forcing, and not a separate feedback process.

The upshot is that to get a sensible value for the forcing response to doubled CO2, you should really take the lower altitude sensor. Also, you can't have a tropical atmosphere over the whole planet. The value you get will be somewhere between the tropical atmosphere and the standard 1976 atmosphere; and you also need to consider clear sky and cloud as well.

All told, the MODTRAN calculator will get you into the right ball park; but it can't serve as a refutation of the forcing for doubled CO2, which is about 3.7 W/m² to 10% accuracy or better.

Perhaps it's better to give Karner a dedicated thread as we explore the characteristix of feedback in general.

That's a good idea. I'll let you start it. Furthermore, if I don't join in right away it will be because I am reading, rather than trying to jump in before I understand it more.

Cheers -- sylas

PS. Added in edit. I see I've missed Chris' input since writing this.