Simple Demonstration of The Warming Effect of Carbon Dioxide

With Earth Day approaching, you might want to try out the experiment published in the Journal of Chemical Education.¹ It outlines a fantastic way to demonstrate the warming influence that atmospheric CO₂ has on our planet. I followed the procedure and offer a video of the results.²

Notice how this experiment connects to a description of the greenhouse effect: Visible light from the sun (modeled by the lamp) easily penetrates the atmosphere (modeled by the air in the cup) and warms the earth (modeled by the black rocks in the cup). The earth, like any warm body, emits infrared (IR) light. Greenhouse gases in the atmosphere (such as H₂O, CO₂, and methane) absorb this emitted IR light, slowing its escape from the planet. This has a warming effect. If earth had no greenhouse gases in its atmosphere, the IR light would escape more quickly, allowing for a cooler planet. Increasing the concentration of greenhouse gases in the atmosphere from fossil fuels use (modeled by the input of CO₂ through the tube from dry ice) therefore warms the atmosphere.

It is of note that this experiment features the measurement of temperature in a system that is open to the atmosphere. This allows for a direct demonstration of the warming of our atmosphere due to the addition of CO₂ alone. Conducting the experiment in a system open to the atmosphere eliminates the interference from additional warming that occurs in sealed systems due to trapped air being conductively warmed.

If desired, this set up allows students to try out inquiry-based explorations. For example, what happens if different gases are sent into the system? I would be interested to see if exhaled breath causes warming in this system (exhaled breath contains roughly 4-6% H₂O and 4% CO₂, both of which are greenhouse gases). If trying this experiment, students would have to be sure to cool the exhaled breath (which is presumably at 37^oC) to room temperature prior to sending it into the air in the cup. To do so, students could immerse a coiled tube into a large bath of water at room temperature. Students could then exhale into one end of the tube, which would send the exhaled breath into the coil where it would be cooled to room temperature. The other end of the tube would of course be positioned to transfer the cooled exhaled breath into the cup.

You can learn more about this experiment in the February 2019 issue of the Journal of Chemical Education.

Reference

1. D’eon, Faust, Browning, and Quinlan. Exploring the Phases of Carbon Dioxide and the Greenhouse Effect in an Introductory Chemistry Laboratory, J. Chem. Educ., 201996 (2), 329-334.

2. Tom Kuntzleman, Does increased carbon dioxide in the atmosphere cause warming? Tommy Technetium YouTube Channel (accessed 3/27/19).