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Global Temperature Anomalies. Photo: yeimayaDiscussion of climate change can seem so academic at times, and I wanted to make it a little more family friendly. Thus I was pleased when a commentator on this blog (Jason) wrote regarding global warming:

OK, this is the theory [referring to role of greenhouse gases in warming our climate, and the means by which they do this. Carbon dioxide included.] I thought you meant. I agree with the physics behind this theory, and consequently believe that it is true. (except for the part about positive feedbacks exceeding negative feedbacks, The models clearly assume substantial positive feedbacks, and I don’t think that the data supports this at all. But a model is just a model. Either it will prove right or it won’t. I can wait for experimental validation.)

But you said that this theory had been experimentally validated. I am not aware of any such validation and am fishing for a reference.

Swindled by Global Warming Sceptics

Jason claims he agrees with the physics, and yet he still wants to know about the experimental validation. I suppose this means that the theory is plausible to him, but he is not aware of experimental validation of the greenhouse effect (outside of the data from climatologists of course - but our warming our atmosphere is not a controlled experiment).

But rather than dredge up more scientific references, I thought we could add some fun to this question, and perform our own experiment. So here are instructions to build your own global warming experiment using CO2 and water vapour. Note that we could extend this to methane too, but the collection of household methane is usually a smelly process, best left to the more intrepid amateur scientist.

Equipment

• Two 2 litre plastic drink bottles
• Two thermometers (preferably digital ones)
• A drill bit to drill a hole large enough for the thermometer (if you have a large rectangular digital thermometer, you will need to improvise a bit!)
• Two clamp stands and clamps (or some ad hoc support!)
• Carbon Dioxide. (For me, the best way to get CO2 is from a Soda Stream, although there are other ways, using bicarbonate of soda for instance).
• Two desk lamps (don’t use energy saving bulbs - 60W or better incandescent bulbs are required)
• Plasticine (That staple of home physics experiments!)

Method

Remove the labels from the drinks bottles and drill holes in the tops large enough to allow the thermometers in. Set up the clamp stands close to the lamps. Make sure that the bottles will not be so close to the lamp that they will melt. Also be very careful about placement. The stands (and the bottles) must be placed identically for the two bottles - the same distance away, and keep the desk lamps at the same angle and the same height. Keep the lamps turned off for now.

Fill one of the bottles with carbon dioxide from your soda stream! screw the top on tight and plug any gaps with the plasticine. The other bottle should also be sealed with plasticine (but don’t fill it with anything. You just want the ordinary atmospheric air that is already in there).

Now check the temperature in the bottles. The carbon dioxide bottle may be cooler as it was filled from a canister of compressed gas. Wait until the temperatures equalise, and when they do so, switch on the lamps, note the temperature and time.

Over the next half hour, monitor temperature and time regularly (at least 5 minute intervals).

Expected Results

Over the course of the experiment, the temperature in the bottle filled with CO2 should rise higher than the bottle filled with just plain old air. For extra credit you could try altering the concentration of CO2 in the bottle to see how the concentration affects the results (rather hard to do scientifically with this equipment, but give it a go!)

Water Vapour

Water vapour is another greenhouse gas. You can repeat this experiment for water vapour. Instead of filling the bottle with CO2, fill it with water vapour. First make sure the other bottle is filled with air in a cool dry place. Next take the bottle to be filled with water vapour to the bathroom. Have a hot steamy bath. Take your bottle with you and during your bath, seal it as before.

Note that it is quicker to fill the bottle from a steaming kettle, but you will almost certainly scald your fingers, and much of the vapour will just condense in the bottle. Better off with the bath methodology.

Now repeat the experiment. If your atmosphere was quite humid when you performed this experiment you may not see much difference - try leaving the ordinary atmosphere bottle in the fridge for 10 minutes, then seal it quickly before removing it. Allow it to return to room temperature and repeat (this will reduce the water vapour in the bottle because cold air holds less water).

Most of all - have fun. This experiment is best performed with the help of young children. No animals were harmed in the making of this experiment.