Benchtop Global-Warming Demonstrations Do Not Exemplify the Atmospheric Greenhouse Effect, but Alternatives Are Available

Abstract

The atmospheric greenhouse effect is a topic in many science courses. A number of lecture demonstrations with carbon dioxide purport to show how infrared-absorbing atmospheric gases “trap” energy. The demonstration described here shows that the temperature change observed in these demonstrations is a consequence of the density of carbon dioxide relative to air, not its infrared-absorbing property. Since the pedagogical value instructors report for the usual demonstration is based on an incorrect interpretation of the temperature change and can lead to a misconception about global warming, suggestions are made for possible replacement demonstrations.

Correction to “Exploring the Phases of Carbon Dioxide and the Greenhouse Effect in an Introductory Chemistry Laboratory”

“…A paper published by Jerry A. Bell alerted us to the works of Wagoner et al and Berto et al, which were published in the physics literature and demonstrate a flaw in the greenhouse effect activity used in previously published work − as well as in our paper . The version in our paper uses the setup shown in Figure where an incandescent lightbulb is used to warm gases within a beaker, and then increased warming is observed when the beaker is enriched with carbon dioxide as compared to air-only.…”

Reply to “Benchtop Global Warming Demonstrations Do Not Exemplify the Atmospheric Greenhouse Effect, but Alternatives Are Available”

“…A paper by Jerry A. Bell brought the works of Wagoner et al and Berto et al to our attention. These papers, published in the physics literature, demonstrate a fundamental flaw in the classic greenhouse gas demonstration that was published previously − and was included in our recent paper .…”

“…In addition to detailing the physics of the flawed demonstration, the paper by Bell also offers different ways of scaffolding the topic of the atmospheric greenhouse effect to nonexperts, such as those in an introductory university chemistry class. Bell prefers to focus the learners’ perspective on a macroscopic view of the atmosphere, looking at energy flows into and out of the Earth system.…”

“…In addition to detailing the physics of the flawed demonstration, the paper by Bell also offers different ways of scaffolding the topic of the atmospheric greenhouse effect to nonexperts, such as those in an introductory university chemistry class. Bell prefers to focus the learners’ perspective on a macroscopic view of the atmosphere, looking at energy flows into and out of the Earth system. A useful tool for this purpose is the one-layer atmosphere model, which describes photon absorption and re-emission within the Earth system using energy flows in W m –2 . , Another perspective is to provide students with a microscopic view of the atmosphere focusing on the molecules present and how they interact with the photons flowing through the system .…”

“…The paper by Bell specifically references this learning objective and comments that it provides learners with an incomplete understanding of the atmospheric greenhouse effect. While it is true that this mental model is not complete, most mental models presented to introductory learners are not complete, including the macroscopic view of the atmosphere described by Bell …”