Like many scientific concepts, climate change and the carbon cycle are both processes that humans can't sense directly—they are too large, too gradual, or simply invisible. In order to understand them, it is necessary and natural for humans to use metaphors to relate these concepts to our sensed experience of the world. For example, a common metaphor in climate change science is that of the greenhouse effect, where people imagine an easily visualized physical object (the greenhouse) and their physical experience of being inside of it (warm); then they are asked to apply this metaphorical imagining to the entire atmosphere. However, taking this metaphor a step further, while climate scientists and a common person might both be using the same metaphor of the greenhouse, the common person may not have the correct understanding of the mechanism that is causing global warming. The authors address this and several other issues in this article.
The main goal of this research was to develop effective strategies for teaching about the greenhouse effect and the carbon cycle. To develop these strategies, the authors first investigated the metaphors that climate scientists and high school students use to understand these concepts. Better understanding the existing metaphors enabled the researchers to develop hands-on teaching strategies that allowed the students to discover the problems with their incorrect concepts and also to discover the correct conceptual model, based on the climate scientists' understanding.
To understand the scientists' understanding of these concepts, the authors examined scientific textbooks and the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC 2007). To gather data about commonly held beliefs and understandings of the causes and processes of climate change, the authors reanalyzed 24 empirical studies on everyday concepts of global warming. The authors also conducted a study with 35 18-year-old students in German schools (16 female, 19 male). None of the students had any prior climate change instruction. Before the teaching intervention, the authors interviewed the students about their concepts of greenhouse gases or the role of atmospheric CO2 in the carbon cycle. These interviews were transcribed and, along with all the other data, were examined to identify the most common metaphors used by both scientists and nonscientists to explain the greenhouse effect and the carbon cycle.
Based on the results of this first phase of the study, the authors set up and evaluated 10 different teaching experiments with the same high school students. Each experiment lasted approximately 65–90 minutes and was conducted with small groups of two or three students. Students reflected on the experiential learning and their new or changed conception of the greenhouse effect or the carbon cycle (depending on the teaching experiment in which they were involved). Researchers recorded all interviews and videotaped all teaching experiments.
With regard to the greenhouse effect, the researchers were surprised to find scientists and nonscientists/students used the same basic metaphor to conceptualize the process—a container with a balance of stuff coming in (light from the sun) and stuff going out (light or heat). The researchers call this the “container-flow model.” The earth forms the bottom of this container, and the atmosphere is the content; light or heat is the “flow” that needs to be balanced. However, the specifics about the top boundary of the container and the processes happening within it were different. Specifically, the authors identified two everyday misconceptions about the greenhouse effect: (1) it is caused by a hole in the ozone layer, and the hole is created by CO2; and (2) it is caused by a layer of greenhouse gases at the top of the atmosphere, which lets light in but does not let light out. By contrast, the scientists view CO2 as part of the content of the container or atmosphere (not an ozone-destroying compound, or only the top layer of the atmosphere). Secondly, the scientists understand that CO2 is permeable to light rays, but impermeable to heat rays, which is why it shifts the “radiative equilibrium,” or warms the earth.
To “restructure the container” to match the scientific understanding, the researchers identified two questions for students: (1) Consider the top border of the container: is it an ozone layer, a CO2 layer, or just assumed? and (2) Consider the role of CO2: does it form the top border of the container or is it the content? Does it destroy the border or trap heat?
Using these questions as a guide, the researchers designed different hands-on teaching exercises. One of the exercises used a strong light bulb to heat two glass containers with open tops and black bottoms. One container was filled with air and the other with CO2. The students measured the temperature inside both containers, which was hotter in the container with CO2. In interpreting the phenomenon, the students were able to correct misperceptions about the role of the ozone layer and also start to understand the heat-trapping properties of CO2.
A second exercise used a light bulb shining through one plastic bag filled with air and one filled with CO2, measuring the brightness and temperature behind each. The brightness behind both bags was the same, but the temperature behind the bag with CO2 was lower. This allowed students to correctly deduce that CO2 is permeable to light rays but not heat rays. The authors found that the combination of these two teaching methods allowed the students to correct their misconceptions of the greenhouse effect and discover the correct concept.
The researchers repeated these processes with the concept of the global carbon cycle. In this case, the authors found scientists use the metaphor of a balance or scale, where carbon going into the atmosphere is balanced (or imbalanced) relative to carbon being sequestered back into the earth or oceans. The students did not use this metaphor, and held one of two primary misconceptions: (1) that there is a difference between natural and manmade CO2; or (2) that all CO2 is created by humans (that is, a “normal” atmosphere doesn't contain CO2). In addition to correcting these misconceptions, the authors wanted to explain climate change based on the idea of imbalanced carbon flows (more carbon being released than sequestered). One of the methods the authors used to accomplish this involved creating a model of the carbon cycle that used plastic containers to represent different carbon stores (for example, fossil carbon, atmosphere, ocean, or vegetation) and plastic balls to represent carbon (a container-flow model). The students were given a story that involved carbon cycling and asked to model the movement of carbon in the story using the containers and balls. Other activities helped them understand that manmade and natural CO2 are the same and that CO2 is a natural component of the atmosphere.
The Bottom Line
Using metaphors—such as containers or balance scales—is essential for understanding scientific concepts such as the greenhouse effect or the carbon cycle. Students' conceptions are often incongruous with scientific conceptions, but they rely on similar metaphors. Establishing a teaching environment where students present their misconceptions, experience a concrete manifestation of the correct metaphor, and then reflect on this experience allows students to develop a more scientifically correct understanding of climate change.