## Need Help: Can You Model CO2 as a Greenhouse Gas (Or is This Just Wishful Thinking?)

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/teacher...02_03_nsn.html

3) SCIENCE EXPERIMENTS ON FILE™ Revised Edition (similar to the two above):
http://www.fofweb.com/Onfiles/SEOF/S...ments/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
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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.
 PhysOrg.com earth sciences news on PhysOrg.com >> NCAR joins massive field campaign to examine summertime air in Southeast>> Siberian caves warn of permafrost meltdown>> Ground monitoring equipment deployed on two Ethiopian volcanoes showing signs of unrest
 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.

## Need Help: Can You Model CO2 as a Greenhouse Gas (Or is This Just Wishful Thinking?)

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

 Quote by 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.
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
 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
 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.
 This looks like a pretty decent experiment to show the GHG effect: http://www.beloit.edu/sepm/Geology_a...h_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.

 Quote by natureteacher 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

Blog Entries: 9
Recognitions:
 Quote by Ray001 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
 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
 Blog Entries: 9 Recognitions: Science Advisor Good luck and keep us posted! -- sylas

 Quote by Skyhunter Here is the experiment I was thinking of.
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
 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.
 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.  Quote by cleanwater 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. Try this experiment 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 this paper from the Niels Bohr Institute.  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.
 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 GLIMS database of ~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.

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