Given the severity of the climate change problem, and the resources now being devoted to educating students about it, the authors set out to understand how students think about the greenhouse effect. Previous studies, most of which have been conducted outside the United States, suggest that students lack a clear understanding of how the greenhouse effect works. This study focused on 225 seventh-grade students in three small, rural communities in the U.S. Midwest. The students varied in their academic ability, were primarily Caucasian, and were roughly evenly divided between males and females. About 30% were eligible for free or reduced lunch programs.
The students participated in an instructional development project coordinated by the authors. The authors asked students to complete an activity in which they would draw the greenhouse effect and then explain their drawing. The researchers analyzed the student responses and grouped the responses into the following five categories representing the students' mental models of the greenhouse effect:
Model 1: “Greenhouse” for growing plants (29%)
Model 2: Greenhouse gases cause ozone depletion or formation, which either allows more of the sun's rays to reach the Earth or causes the sun's rays to be “trapped” or ”bounced” back toward Earth (6%)
Model 3: Greenhouse gases, but no heating mechanism; simply gases in the atmosphere (17%)
Model 4: Greenhouse gases “trap” the sun's rays, heating the Earth (may or may not identify specific greenhouse gases) (35%)
Model 5: Sun's rays are “bounced” or reflected back and forth between the Earth's surface and greenhouse gases, heating the Earth (may or may not identify specific greenhouse gases) (13%)
Based on their analysis, the authors conclude that most of the students “lacked a clear understanding of the greenhouse effect.” Nearly a third of the students described the greenhouse effect in terms of Model 1 (greenhouse for growing plants), which the authors believe indicates that the students did not understand the greenhouse effect.
But all is not lost. The authors also note that “on the bright side, students who hold Mental Models 3, 4, and 5 and probably students who hold Mental Model 2 have fairly well developed mental models that are likely to be easily modified with the appropriate curriculum and instructional experiences.”
The authors suggest that, in teaching students about the greenhouse effect, instructors and curriculum developers should work to dispel the misunderstandings that the greenhouse effect “traps” all of the sun's energy, that carbon dioxide is the only greenhouse gas, and that all air pollution contributes to the greenhouse effect. In particular, the authors suggest that the following concepts should be addressed in educational materials dealing with the greenhouse effect:
• Carbon cycle, fossil fuels (energy), and greenhouse gases
• Other human and natural sources of greenhouse gases (e.g., forest fires, animal waste, landfills, land use)
• Greenhouse gases (e.g., water vapor, carbon dioxide,methane, nitrous oxide)
• Uniform distribution of greenhouse and atmospheric gases
• Absorption and radiation of energy—energy transfer
• Greenhouse effect, radiative forcing (infrared radiation), and the Earth's energy balance
• Distinction between types of solar radiation, and solar and terrestrial radiation
• Greenhouse gases and ozone depletion
• The greenhouse effect and global warming
• Natural versus human sources of greenhouse gases and personal solutions and actions
Finally, the authors urge educators to remind students that any model or demonstration of the greenhouse effect they might use in a classroom activity is not complete. Educators should stress the limits of these models and demonstrations and point out the ways in which they differ from reality.
The Bottom Line
<p>Although many students may have a broadly accurate mental model of climate change, most students' understanding of how the greenhouse effect works is not complete, and some lack any meaningful understanding. Moving students toward accurate mental models will require instruction that more fully explains solar energy and the Earth's energy balance, all the greenhouse gases (not only carbon dioxide and those from human sources), distinctions between greenhouse gases and ozone depletion, and distinctions between greenhouse gases and other forms of air pollution.</p>
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