Do you know of a simple tabletop experiment demonstrating the GHG effect of CO2 ?

My issue with experiments like this is that what you are mostly measuring is the interactions (and heat transfer) of the gas with the sides of the container.

Trevor,

A few questions.

1.) Your graph has the CO2 and Methane together.

2.) It looks like your methods may tend to add more H2O into the CO2 bottle. How did you account for this difference.

3.) It looks like your methods would tend to make the Methane and CO2 bottle pressurized, or at least more pressurized than your normal bottle. Since it is known that denser air tends to hold more heat, did you do anything to account for this.

Trevor, The temps would have to be the same prior to placing the cap on to ensure the same overall pressure. Clearly if one is colder, it will have a higher pressure than the others after the temps are equal. Your processes would likely change the temps. The indigestion tablets in water would most likely change the H2O content.

Trevor, Clearly not, and I am not suggesting that your experiment is bad for a lab top. I would simply change how I did it slightly. I would keep the set-up the same, but place a small chunk of dry ice in one. Place the cap on so that it is closed, but not tight enough that no air escapes. Then, when the temps meet, I would tighten the caps. Same temp, same pressure, more CO2 in one. Otherwise I would keep the experiment the same.

Trevor gives a good simple experiment for the kitchen table. The object is to demonstrate the effect rather than to mimic the atmosphere. I answered the same question previously with an alternate experiment (all my answers are public). You asked for pablum, you got YA pablum. Now graduate to solid food. Get a tunable pulsed laser, a cryostat with an internal gas cell with KBr optic flats and a step-scan FTIR spectrometer with a 1 m OPD and an MCT detector. Put a 1 ns pulse through the gas cell and measure the radiation at 175 degrees (or as close as you can put the MCT to 180 degrees) as a function of time. Tune the laser through a CO2 absorption line. Measure the emission spectra of both CO2 and Ar at pressures that approximate different levels of the atmosphere with the FTIR spectrometer. Subtract the Ar signal from the CO2 signal. Calibrate the signal with a NIST standard. I would be willing to do this experiment for Exxon. I think that ONE hour of Exxon's global revenue would be a very small price to pay for Exxon to get a definitive result and fair compensation for me.

Yes, just use your tabletop infrared spectraphotometer to measure the infrared absorptance of CO2. If you don't like that you could use line-by-line integration to calculate it, using your desktop computer.

Or you could just trust that it could be done in a well-equipped lab.

EDIT: The reason I suggested doing things this way is because it's too easy to make a small experiment which purports to show something, but actually operates in other ways--it's also too easy to bring up objections which may or may not be valid and criticize others' experiments, which is what I think your point is in asking the question. The greenhouse effect is real, there is no doubt about that, once you see that IR absorption band then you know that CO2 is a greenhouse gas. Most of science can't be shown with tabletop experiments, but it doesn't make it any less real.

Cool quesiton and good comments all.

I would also place a dessicant in all three bottles. Havign a dry gas in all three helps to verify you compare apples to apples.

If you have a pressure gauge, push enough air into the control bottole to match the presusre you get in the CO2 and Methane bottles. This should account for most of the differences you would get for differing pressures. However "desk top" is not controlled enough to get scientific results.

I'm concerned that Trevor is mentioning methane (flammable) and a heat source. I'd skip that part.

The comment about the water vapor concentration seems valid to me as well.

Edit: Now that I think more about this, a more proper experiment would compare regular atmospheric composition with the same composition but all CO2 removed (or with the CO2 level doubled). I'm not sure that can be done at home.

A great way to demonstrate the effect of CO2 in the atmosphere is this.

Fill two identical crystal clear containers with 1 gallon of crystal clear water.

Add one drop of lemon juice to one container & two drops to the other.

The resulting difference in water clarity is the effect of man made CO2 on Global temperatures.

See the problem you face is that Global Warming is a hoax, so there is no demo that doesn't commit to the hoax,

AGW theory IS a YouTube type hocus-pocus.

Now Trevor isn't lying

CO2 is ABSOLUTLY a greenhouse gas.....

If our atmosphere was 97% CO2 and 96 times thicker (like Venus) the greenhouse effect would be HUGE.

But in Earth's comparativly thin atmosphere at concentrations of 0.2 to 0.4 parts per thousand.... well your demo themometer would need to be accurate in the hundredth of the degree range to show any difference.

It's a cool experiment sure, but when you try to transfer your new found "knowledge" to the climate, you will almost certainly be wrong.

It's like learning about the bernoulli effect, and then thinking you understand aerodynamics. The only difference being that if you know the bernoulli effect, you know a great deal more about aerodynamics than this experiment can teach you about climate.

In terms of a simple tabletop experiment, a fairly crude one you can do at home is as set out below. I've written the instructions so as to compare air, methane and carbon dioxide but you could of course just compare air and CO2. In a laboratory environment the experiment can be extended and when you get down to the atomic level the causes and effects can be observed.

OBJECTIVE

To compare the thermal properties of carbon dioxide, methane and air.

EQUIPMENT

• 3 identical plastic bottles

• 3 temperature probes

• 3 pre-drilled bungs (optional, helpful)

• Stopwatch

• Carbon dioxide

• Methane

• 3 Clamp stands if you have access to them (not essential)

• Lamp (or other heat source)

METHOD

• Clean and dry the bottles (they should be dry inside as well)

• Remove any labels

• Insert temp probes through the bungs. If you haven’t got bungs then drill holes in the bottle caps and insert the temp probes through the hole, seal the edges of the hole with plastecine or similar.

• Fill one bottle with carbon dioxide. If you’ve got a soda stream use that, if not put some indigestion tablets into a balloon containing some water, hold the neck of the balloon closed and wait for it to fill with carbon dioxide given off by the tablets. Fill the bottle with the carbon dioxide from the balloon.

• Fill one bottle with methane – from the normal domestic gas supply.

• Seal all three bottles with the bung or the cap

• Secure a bottle in each of the clamp stands

• Place all three bottles equidistant from an indirect heat source such as a lamp (don’t switch the lamp on yet)

• Wait until the temp in all three bottles is identical

• Switch on the lamp

• Take temperature readings from all three bottles for the next 30 minutes at one minute intervals

• Plot the results on a graph

RESULTS

This graph shows the results of an experiment we did a few years ago using just carbon dioxide and air, you should be able to achieve similar results in your experiment

http://www.flickr.com/photos/trevorandclaire/45588...

CONCLUSION

The experiment should demonstrate that carbon dioxide and methane will retain more heat than air.

LIMITATIONS

The experiment does not explain why the greenhouse gases retain more heat than air, this is explained at the quantum physics level and isn’t something that can be done at home. Here’s an answer I provided a while back which explains the physics http://answers.yahoo.com/question/index;_ylt=AnmTu...

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RE: YOUR ADDED COMMENTS

You mentioned that the experiment demonstrates that the CO2 bottle warms quicker than the bottle with air in. But how can that be? If the bottles are receiving the same amount of heat then they warm at the same rate, the increase in temperature can only be caused by greater heat retention.

The experiment I described is a simple one. You would need to run the same experiment several times to eliminate any noise and to verify that all factors were constant apart from the variable under test. For comparison purposes it would be necessary to use different concentrations of the gases and to use greater or lesser amounts of heating.

As you know, in science you can’t perform a single experiment like this and draw conclusions from it. It must be performed many times with each variable being isolated and put to test.

Spectroscopy isn’t an area I’ve ever needed to know much about, the last time I studied it was in uni 26 years ago. Hopefully d/dx will answer your question as spectroscopy is one of his areas of expertise.

Here’s a good site for explaining the role of CO2 as a greenhouse gas http://brneurosci.org/co2.html. As I mentioned originally, you need to delve into QM for cause and effect, any table top experiment can only ever demonstrate effect.

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EDIT 1: TO I EXPEL

1) Methane isn’t plotted on the graph

2) On the occasions we’ve done this experiment it’s been done in lab conditions so the contents of each bottle can be precisely controlled. In a home environment there are bound to be inconsistencies which is why the experiment should be run multiple times, in such conditions it isn’t possible to draw precise conclusions. It’s like mixing hot water with cold water, you can prove that by pouring hot water into a half filled bucket of cold water the temp will increase, but unless you know the precise starting volumes and temps you can’t say exactly how much the temp will increase per unit of hot water added – you can get close but not precise.

3) The pressures would be the same in each bottle as the gas isn’t being forced under pressure into a sealed container.

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EDIT 2: TO I EXPEL

The question asks for a “simple tabletop experiment” which is what I described – something using very basic items that can be found in most homes or sourced at minimal cost. It was designed specifically so that anyone could see the heat retaining ability of the greenhouse gases for themselves. I hope it's obvious that this isn’t the kind of work that goes on in science labs and that the results aren’t going to be precise. Why should they be? The premise is to demonstrate a concept at "simple tabletop" level not mathematically and scientifically quantify it.