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Re: [Phys-l] lab suggestion for teaching about the greenhouse effect?



On 02/11/2011 02:59 PM, Fowler, Rebecca SHS Staff wrote:
Use two separate 2 L bottles. In one, place some carbonated cola poured
from a freshly opened bottle. In the second, place an identical volume
of cola that has gone nearly completely flat.

There are eleventeen things that can complicate this experiment.

In some scientific sense, it's a great experiment, because it tells
you that CO2 is not the whole story when it comes to the so-called
greenhouse effect. In fact there is a lot of other stuff going on
... which is quite important.

In pedagogical terms (as opposed to real-world scientific terms)
this complexity may or may not be what you want.

In particular, it turns out that in some sense, the most important
greenhouse gas is _water vapor_.
http://irina.eas.gatech.edu/irina/EAS8803_Fall2009/Lec6.pdf

This does not mean we should stop worrying about CO2; in fact it
means we should worry all the more, because the water vapor can cause
positive feedback leading to instability, and that means small inputs
can have very large consequences. There can also be surprising
consequences, such as cooling in some places even as there is warming
overall.

In the case of your experiment, to get consistent results you will
need to control for water vapor, and super-especially to control for
stray bits of liquid water.