Absorption of infrared radiation by carbon dioxide (CO2)

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In this video Pieter Tans, a scientist at the National Oceanic and Atmospheric Administration, sits in front of an infrared video camera, and the image captured by this IR video camera is shown as a visible-light image a computer screen. Carbon dioxide (CO2) is then placed between Pieter Tans’s face and the IR video camera by injecting CO2 into a tube. As the amount of CO2 between the scientist’s face and the IR camera increases, the image of Tans’s face fades in the infrared camera.
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1) Why does the scientist’s face disappear on the infrared camera when the tube fills up with CO2? Based on this demonstration, 2) how do you expect CO2 to interact with infrared radiation in the Earth’s atmosphere? More broadly, 3) what does this demonstration show us about the greenhouse effect in the Earth’s atmosphere? For this last question,4) it might help to think about where infrared radiation found in the Earth’s atmosphere and which direction it is, on average, propagating.