Models of students’ thinking concerning the greenhouse effect and teaching implications Vasilis Koulaidis and Vasilia Christidou, University of Patras
During the last fifteen years research in science education has studied children’s ideas about a wide variety of concepts and phenomena. The researchers in this field have recognized that the students’ conceptual framework is distinct from the school science’s framework and at the same time that teachers’ awareness concerning this distinction is necessary for any effective teaching so as to promote understanding of science (e.g. Driver, 1985; Osborne & Fryberg, 1985; Matthews, 1994).
This paper presents results of the most salient and important students’ models concerning the greenhouse effect and certain teaching implications that these results bring out. Students’ conceptions of important environmental issues, such as the ozone depletion, or global warming due to the enhanced greenhouse effect can be used in order to design and evaluate teaching material for different educational contexts (e.g. environmental education projects, science lessons, or Science Technology and Society courses). The results of the project referring to the ozone layer, its depletion and the consequences of this depletion have already been presented (Christidou, 1997; Christidou & Koulaidis, 1996).
Environmental issues such as the greenhouse effect have been introduced in the science curricula in many countries since the rapid development of science and technology emphasize the need for scientifically and environmentally literate citizens. The social character of such phenomena links them to the everyday habits of individuals, as well as to the future of our planet (Fleming, 1988; Lucas, 1988; Solomon, 1988). Moreover, the greenhouse effect is a scientific phenomenon that involves complex processes, which call for an interdisciplinary approach in order to be explained and understood. Therefore, developing an adequate understanding of the greenhouse effect concerns every student and teaching this issue could aim at (Brody, 1991; Zoller & Weis, 1983; Ross, 1991; Bybee, 1993):
i) providing students with the appropriate problem solving and decision making skills;
ii) inducing positive environmental attitudes to the public;
iii) making science lessons more popular and topical by connecting them to real and important situations;
iv) helping students to appreciate the complex interdependence of different environmental factors;
v) illustrating that science and technology -apart from strictly structured information and knowledge- also involve values and ethics.
However, addressing these educational aims presupposes the organization of curricula founded on research data (Osborne & Freyberg, 1985; Solomon, 1993; Brody, 1994). In other words we could first determine the students’ alternative conceptions concerning the greenhouse effect if we are to i) design effective teaching material; ii) determine the appropriate concepts and learning experiences that will challenge the students’ conceptions; iii) modify teachers’ pre-service and in-service training in order to meet these requirements; and iv) be able to evaluate the whole attempt.
Previous research has revealed students’ as well as teachers’ and student teachers’ views of the greenhouse effect. The results reflect the existence of some common elements in children’s and adults’ thinking (Hann, Brosnan & Ogborn, 1992; Koulaidis & Christidou, 1993; Boyes & Stanisstreet, 1993; Francis, Boyes, Qualter & Stanisstreet, 1993; Rye, Rubba & Wiesenmayer, 1994; Dove, 1996). These common elements include: a) the tendency to confuse the greenhouse effect with the ozone depletion, or to causally attribute the former to the latter, b) the tendency to understand and interpret the greenhouse effect exclusively as an environmental problem, ignoring the fact that it is the result of a natural mechanism, c) the tendency to attribute the greenhouse effect to specific gases over others, or d) the reference to specific expected consequences of the manmade greenhouse effect, such as an increase in the planet’s mean temperature and sea level.
The rest of the paper is organized in the following sections:
the method which is adopted for the collection and analysis of the data;
the results of the data analysis and their interpretation i.e. children’s views which are incorporated in wider constructs referred to as models;
the teaching implications emerging from the discussion of children’s models.
Forty primary school students from 3 state urban schools in the area of Thessaloniki form the sample in this research. The schools were chosen so as to assure that children with different socio-economic backgrounds would be included in the sample. The sample consisted of 22 boys and 18 girls, while 13 of the students were in the Fifth Grade (approximately 11 years old) and 27 were in the Sixth Grade (approximately 12 years old). The distribution of the students forming our sample is illustrated in Table 1.
No particular criterion was used for the selection of the students in terms of their performance. The students had received no prior teaching concerning specifically the greenhouse effect. The Greek National Curriculum for Primary Science (which is compulsory for all schools in the country) does not include specific chapters concerning the greenhouse effect. However, concepts and ideas that are central to this phenomenon are infused in the official school textbooks (the use of which is compulsory for all schools) in several cases and in different contexts. Specifically,
in the Fifth Grade’s science textbook (Daskalakis et al., 1990) there is a chapter about light. The sun is discussed as a source of light and heat, which makes life on earth possible. Light and the formation of shadows is introduced, as well as the speed of light. In the same chapter white light is described as an entity, composed of different, simple colors. Simple colors are defined as radiation of different, specific wavelengths. In order to explain why objects have different colors, the concepts of refleciton and absorption of light is introduced, illustrated with various examples (one of which refers to the absorption of light by the atmosphere and clouds). Finally, the uses of solar energy, in which the function of greenhouses is explained on the basis of the atmospheric clouds, which “trap terrestrial thermal radiation [...] making the temperature near the ground higher than it would be with a clear, cloudless sky” (ibid., p.18).
in the Fifth Grade’s science textbook (Daskalakis et al., 1990), there is a chapter about the air, where the concept of air is presented from different aspects: the air as matter / a material body, the atmosphere and its parts (troposphere, stratosphere, mesosphere, ionosphere, exosphere), air as a mixture of different gases. At the end of the chapter the concept of atmospheric pollution is introduced, defined as an alteration of the atmospheric composition due to human activities.
in the Sixth Grade’s science textbook (Alexopoulos et al., 1991), there is a chapter about the sulphur compounds, in which thermal pollution is mentioned, a term corresponding to the enhanced greenhouse effect -although this connection is not made explicit. The phenomenon is not presented extensively, nor explained by any text. There is a picture, however, which attributes thermal pollution to “layers of carbon dioxide”, released in the atmosphere by combustion.
For the selection of the data the method of individual, semi-structured interviews was used. Interviews are flexible means for providing direct access to the students’ cognitive structures, making the recording of their knowledge easier and more reliable and precise (Solomon, 1992; Cohen & Manion, 1989).
Each student participated in two interviews. The first interview served as an introduction to the discussion and aimed at setting the context. Children were presented with popularized, mass media type information about the greenhouse effect, as well as photos illustrating some major causes of global warming and were asked to state what they thought were the main messages or points of the material.
The second interview was designed so as to (a) encourage students to focus the discussion on specific scientific aspects of the greenhouse effect, by relating different concepts and explaining a variety of processes that they considered to be relevant to this phenomenon and (b) give access to students’ views by setting the conditions of a natural discussion (West & Pines, 1985). Thus, each student was presented with 19 cards labeled with the main terms relative to the greenhouse effect. These cards were used in three distinct activities of gradually increasing complexity.
The questions posed to the students were designed in such a way as to focus the discussions on the mechanisms, processes and interactions involved in the greenhouse effect.
During the first activity of the second interview children were asked to group the cards, in order to get familiarized with the main terms on the cards. This process also helped students to form the first associations between the main concepts involved in the greenhouse effect. The second activity attempted to study the causal relations between different terms. For this purpose they were asked to work with two cards each time, following the general scheme ‘A changes B’. During this part of the discussion children had to specify what kind of change the concept marked on card A caused to the concept marked on card B and in what way this change was caused. Finally, during the third activity of the second interview students were asked to answer a structured set of questions. While answering each question they had to put the relevant cards on a piece of cardboard and to state what were the relations between the cards, in order to construct a complex concept map. This map corresponded to the reconstruction of the ‘general picture’ of the greenhouse effect, that is to a synthesis that incorporated the previously explained processes and relationships to an integrated conceptualization of the phenomenon.
The interviews lasted approximately 60-70 minutes. They were tape-recorded and subsequently transcribed. The first step of the data analysis involved the production of a ‘condensed’ version of each discussion. For this purpose the students’ original statements were isolated and grouped in terms of thematic coherence. In this way, each interview transcript provided a ‘story’ concerning the greenhouse effect, that is a condensed collection of original statements reflecting students’ views of the greenhouse effect’s causes, the processes and the mechanisms involved in it, as well as its consequences.
Based on children’s ‘stories’ we inferred a number of models of their thinking for the greenhouse effect. (Each model is accompanied by a diagram representing graphically its main elements). For the development of these models children’s views were categorized on the basis of a set of explicit, predefined criteria. Below we present these criteria as well as the process of their application.
The position and distribution of the greenhouse gases: children’s views were categhorized regarding the position and distribution of the greenhouse gases, either
ii) as forming a relatively thin layer found at a high altitude above the ground.
The existence of connections between the greenhouse effect and the ozone layer, or the ozone layer depletion. In respect to this criterion three alternative categories were used for the classification of the data:
i) there was no connection of the greenhouse effect and the ozone depletion,
ii) the two issues were seen as two distinct but causally related phenomena, or
iii) the two issues were confused and conceptualized as one phenomenon.
The kinds of radiation related to the greenhouse effect: Here students’ views regarding the nature of radiation were categorized as follows:
i) to thermal rays, or heat coming from the sun, or
ii) to solar rays in general, or
iii) to ultraviolet rays entering the atmosphere from the ozone hole(s) that are generally considered to be ‘strong’, hence extremely hot.
These types of solar radiation are distinctively represented in the model diagrams following the notation illustrated in Figure 1.
ultraviolet rays (UV)
thermal rays, or heat (IR)
Figure 1. The notation used to represent different kinds of solar radiation in children’s models
The analysis of data based on the above criteria (which led to the inference of models of students’ thinking) involved two researchers who worked independently. One of these researchers was engaged in the collection of the data while the other was not. They found differences in modelling children’s thinking respecting the above mentioned criteria in only two cases. These differences were further discussed with the students’ teachers who were asked to read and further explain how they understood the original statements made by the students that were ambiguous. Ambiguities were also discussed with a third researcher in order to clarify how the two students viewed certain entities and processes, and were finally resolved (Finch, 1986; Cohen & Manion, 1989).
The children’s models allow the identification of a variety of teaching implications, that is elements in the children’s conceptualization of the greenhouse effect that lead them to adopt a model radically different from the scientific or any appropriate simplified version of it. The selection of a limited number of important teaching implications and their transformation into achievable educational targets is considered to be a functional analytical tool for the researcher (Verin & Basan, 1992).