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Pitfalls of Metaphors: Does Warm Air Hold More Water?

Preface

The following is a guest post by Glenn Dolphin (aka "Flipper"), of the University of Calgary Department of Geosciences.

This discussion first appeared in the ESPRIT list server, a lively forum for discussion of earth science teaching, mostly at the secondary school level. When Flipper's ideas below came forth, there had been an extensive multi-person, multi-day discussion of whether it was useful or misleading to tell students, during their study of weather and climate, that "warm air holds more water vapor than cold air." Although this and synonymous statements are common in popular science treatments (for example, here), this form of explanation has been roundly criticized in other expositions for the public (for example, here and here).

A point of view held by several teachers could be summarized by one who wrote: "As I see it, declaring that air 'holds' water isn't nearly as awful as it's made out to be." I was reminded of my blog post and followup comments about Telling Lies to Children, asking where is the borderline between a pedagogically valuable simplification and a lie. Air "holding" water is not literally true; it is a metaphor in which air is compared to a container with a limited holding capacity. Metaphors can be valuable tools for helping the human mind come to grips with (another metaphor) an unfamiliar concept. But they also have pitfalls, as explored in the guest post below.

-----Kim Kastens--Earth & Mind co-editor

Guest blog post

In my research, I am looking at the metaphors we (experts, for the most part) use in science and their effect on how students (novices) understand them. We use many metaphors (selfish gene, black hole, big bang, electron cloud, tectonic plate). As experts, we may very well be able to use "hold" if we have a good physical understanding for the air/water system. However, people who don't, like our novice students, will generate meaning based on their own physical experiences of containers that hold things. This could then lead to difficulties in understanding, most likely because they will always start from this point, and not give other meanings a chance. More

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