This appendix includes excerpts from a research report originating from interviews completed during the 1992-93 academic year with middle school students who completed one of the six teacher-developed units of global warming that preceded this unit on global atmospheric change (please see the Introduction of this unit for background information). The paper was written by James A. Rye, Peter A. Rubba and Randall L. Wiesenmayer. A revised version of this report is in press for the International Journal of Science Education. The student alternative conceptions of global warming and ozone depletion revealed in the study, in fact, provided the initial impetus for expanding the focus of the unit beyond global warming to global atmospheric change. In the study, five alternative conceptions were found to be held by the students. These alternative conceptions all connected (stratospheric) ozone layer depletion and global warming (GW) in some way and were as follows: (a) ozone layer depletion is a major cause of GW; (b) aerosol sprays contain CFCs and destroy the ozone layer; © CFCs cause GW exclusively through their role in destroying the ozone layer; (d) carbon dioxide destroys the ozone layer; and (e) carbon dioxide causes GW exclusively by destroying the ozone layer. The findings suggest that middle school students may possess specific alternative conceptions that limit and confound their understanding of the nature, causation, and resolution of GW. Additionally, the findings have implications for instruction on GW and connection student make with ozone layer depletion, that is, initial exposure to GW may evoke thoughts in students about the ozone layer. Concepts such as ozone hole, ultraviolet rays, CFCs, and greenhouse effect may be "loose" in many students' knowledge and connected inappropriately to make sense of formal instruction on GW. Teachers need to be aware and attentive to these alternative conceptions.
This research was conducted as part of an NSF funded Teacher Enhancement Project in STS Education (TEP-9150232) sponsored by The Pennsylvania State University and West Virginia University. This four-year project, which is entitled: Teacher Development and Research in STS Education for Rural Middle School Science Teachers from Central Pennsylvania and Northern West Virginia, aims to develop a cadre of two dozen science teacher-leaders in STS education at the middle school level-teachers who have gained the capabilities to develop and deliver quality STS instruction and will engage in project dissemination activities that targets their peers.
GW was chosen as the STS theme of the project because it is a highly visible STS issue and lends itself to instruction on science concepts dealt with in life, earth, general and physical science courses taught at the middle school level. Project professional development activities for teachers commenced in 1992 with a three-week summer workshop comprised of (a) Sci-Tech Mini courses taught by university science faculty on various dimensions of GW (e.g. meteorology, carbon cycle, biodiversity, economics), (b) a review of research on effective STS instruction, © STS issue investigation and action unit development on GW for the middle school science courses, and (d) instruction on the use of e-mail (for project communications). Six STS issue investigation and action units on GW (henceforth referred to as STS-GW units) were developed, each by a five to six member team of teacher-participants. Examples of unit titles and the science courses for which they were developed include:
How Does Our Use of Landscape Impact Global Warming?
(6th grade science).
Global Warming: Are Rising Carbon Dioxide Levels Harmful or Beneficial to the Earth?
(7th and 8th grade science).
A Unit for Exploring the Impact of Our Lifestyles on Global Warming.
(7th and 8th grade earth science).
A project staff member oversaw the work of each team. Because each STS-GW unit followed the STS issue investigation and action model, they were organized around a four-phases common framework, including STS foundations, awareness, investigation, and action. As a result, the units included several similar activities and shared a core of content on the nature, cause, and resolution of GW. Figure 1 presents an "expert" concept map, which sets forth in a hierarchical conceptual network (Heinze-Fry & Novak, 1990; Jonassen, Beissner, and Yacci, 1993; Lomask, Baron & Grieg, 1993; Novak & Gowan, 1984) much of this core content shared by the four STS-GW units .
This expert map does not attempt to represent the total scope nor reflect the diversity of content inherent in each of the four STS-GW units studied by the subjects. It does, however, provide examples of the STS-GW unit-based scientific concepts and concept relationships (propositions) that explicate the nature, cause, and resolution of GW. The development of the expert map was informed by the work of Novak and Gowan (1984) and Heinze-Fry and Novak (1990). It was constructed by the first author after engaging in a thorough study of the objectives and content of each of the four STS-GW units. A core of concepts and propositions generally common to all four units were identified that pertained to the nature, causation, and resolution of GW. The identification of this common core and development of the expert map was informed by two other sources of data: (a) post-instructional concept maps prepared by the students'
teachers that illustrated the "desired" student understanding of GW as a result of instruction; and (b) post-instructional interview responses of the teachers to general questions about changes made in the STS-GW units during instruction and perceptions of what their students actually learned.
Each unit did have unique STS focus questions on GW and included content related to a targeted middle school science course and grade. Some of the units included content on ozone (as a greenhouse gas and component of "pollution") and/or ozone layer depletion. While the lesson plans in the units were detailed, the units served only as a guide; that is, the teacher-developers were free to mold the units to the needs of their students and their school situation during instruction.
The units were field-tested by each of the teachers on the respective teams during the 1992-93 academic year. As part of formative evaluation to inform the unit revision process, the project staff interviewed the teachers and a sample of their students approximately two-weeks following the end of the STS-GW unit. The purpose of the teacher interviews was to (a) gain their impressions of unit strengths and limitations as well as what the students had learned and (b) ascertain what changes they made while and recommend as a result of implementing the unit. The purpose of the student interviews was to (a) investigate their understandings relative to the STS-GW unit content, (b) ascertain what citizenship actions they had taken toward the resolution of GW, and © gain their perceptions of the importance as well as the strengths and limitations of the STS-GW unit. Findings from the teacher interviews are presented elsewhere (Rubba, Rye, and Wiesenmayer, 1994). This paper addresses the understandings of GW held by a sample of grade 6-8 students who had completed one of the STS-GW units, as ascertained through an analysis of interview transcripts.
Student understanding was examined in two ways: (a) an "expert" concept map was used to assess the degree to which students knew and understood scientifically appropriate concepts and concept relationships present in the STS-GW units; and (b) assertions were formulated and validated in regards to alternative conceptions students held about the nature, cause, and resolution of GW. The expert map based assessment of student understanding is presented elsewhere (Rye, Rubba, and Wiesenmayer, 1994). The specific focus of this paper is on students' alternative conceptions. Analysis of the data was guided by the following two questions: (a) What (post-instructional) alternative conceptions do students hold of the nature, cause, and resolution of GW? and (b) In what ways and to what extent do these alternative conceptions incorporate connections with ozone layer depletion?
The sample for this study was one of convenience, predominately white and drawn from students in four different grade 6-8 classrooms in rural schools from central Pennsylvania. Students had completed as part of their science course one of the four STS-GW issue investigation and action units, developed and taught by a teacher-participant of the project.
After the students completed the STS-GW unit, their teacher explained to them the purpose and nature of an opportunity to be interviewed by project staff member. Volunteers were obtained and informed consent and release from their parents was procured. From the pool of volunteers, each teacher selected a sample of 5 to 8 students to represent a cross-section of the class according to gender, culture, and (the teacher's perception of) overall academic ability. Informed consent and release also was procured from the students as the first step in the interview. Of the 26 student transcripts produced, two were omitted due to tape recording problems and incomplete interviews. Table 1 provides information on the distribution (percent) according to grade level, gender and teacher-perceived overall academic ability (high, medium, or low) on the remaining 24 students that comprised the sample. Males comprised a greater percent of the sample than did females. There were fewer students of low than medium and high overall academic ability. While a greater percentage of females than males were of high and low overall academic ability, there was little difference between gender on a group basis; that is, the average teacher rated "overall academic ability level" (3=high, 2=medium, and 1=low) was 2.2 for females and 2.07 for males.
% of students (n = 24)
Overall Academic Row
Ability Level/Gender Grade 6 Grade 7 Grade 8 Totals
High 25 4 8 38
Male 8 4 4 17
Female 17 0 4 21
Medium 25 8 4 38
Male 25 0 0 29
Female 0 8 4 8
Low 8 8 8 25
Male 4 4 4 13
Female 4 4 4 13
Total 58 21 21 100
Male 38 8 13 58
Female 21 13 8 42
A protocol for conducting standardized open-ended interviews (Patton, 1987) was developed by the authors, cleared by the respective university's institutional review board for the protection of human subjects involved in research, and field-tested on a sample of students who had completed the STS-GW unit. The design and sequence of the interview questions (some of which were follow-up probes) set forth in the protocol was informed by Osborne and Freyberg (1985) and shared many of the features cited as important by Novak and Gowin (1984). These questions focused on eliciting, sequentially, students' understandings and views in the following areas: (a) the nature and cause of GW, (b) what GW unit content was "important," © why GW is an STS issue, (d) possible citizenship actions to resolve GW, (e) actions actually taken to help resolve GW, (f) likes and dislikes about the GW unit, and (g) connections between GW and ozone.
Student responses to all questions were examined to validate researcher assertions about the presence of various alternative conceptions. However, 12 questions addressed more specifically the research focus of this paper and generally proved most effective in revealing student's alternative conceptions of GW. These questions are set forth in Table 2 (below), in the order in which they were posed.
Interview Questions on GW
The interview question sequence commenced with a broad query of minimal difficulty designed to help focus students' thinking and bring to the forefront knowledge held about GW. As such, this question and the related follow-up probe (Table 2, questions 1 and 2) might be thought of as a brief advance organizer (Germann, 1991; Jonassen et al., 1993) for facilitating eliciting as opposed to the enhancing knowledge and understanding. These questions generally were repeated before moving on to questions specifically targeting the nature and cause of GW (Table 2, questions 3-5), why GW is an STS issue (Table 2, question 6), and possible citizenship actions to resolve GW (Table 2, questions 7-8). As with the two advance organizer questions, these questions usually were repeated by the interviewers, along with some additional probing of student responses. The questions to elicit connections students perceived between GW and ozone (Table 2, questions 9-12) were placed at the end of the interview.
The researchers' recognize that asking questions about ozone in the context of an interview on GW may "lead" students. However, since the majority of the students interviewed had completed an STS-GW unit that did include content on ozone and the literature (Hocking et al., 1990; Koulaidis and Christidou, 1993) suggests students may confuse these two issues, such questions became important. The questions were positioned at the end of the interview so as not to influence students' thinking and subsequent responses to questions specifically targeting the nature, cause, and resolution of GW. Actually, the concern about the researchers "leading" students to connect GW with ozone layer depletion generally became a moot issue: the majority of students started talking about ozone in response to the two opening "advance organizer-type" questions on GW and 75% of students had broached the subject of ozone prior to the ozone-specific questions. These serendipitous findings provided considerable support for the inclusion of the ozone related questions at the end of the interview by serving as a means to confirm or reject assertions the researchers formulated, based on student responses to previous questions, about the presence of student held alternative conceptions that connected ozone and GW.
All interviews were held at the student's school in a private setting approximately two weeks following the end of the STS-GW unit. Each interview lasted approximately 20-30 minutes, was tape recorded and later transcribed. The researchers were not appraised of the student's overall academic ability level until after all interviews were completed at each school. The teachers of these students also were interviewed by either the first or second author of this paper on the same date about their implementation and post-instruction impressions of their STS-GW units. The procedures and findings associated with the teacher interviews are given elsewhere (Rubba, Rye & Wiesenmayer, 1994). However, this paper incorporates select findings from the teacher interviews, as they are relevant to various of the students' alternative conceptions, reported herein.
Pre-instruction interviews were not completed with the 26 students. Separate from this investigation, the first two authors conducted interviews with 22 middle school students who had not studied GW. These sixth and seventh grade students were from two different schools in one of the school districts from which sample members in this study were selected. The interview protocol included all of the questions shown in Table 2 except questions 6 through 8. Additionally, these students were asked about the source of their knowledge of GW.
In response to the first two interview questions (Table 2, questions 1 and 2), the vast majority (86%) of these 22 students provided answers indicating that they did not know or had not heard about GW:
Lois: The countries of the world and like on the globe and stuff . . . . Where I live . . . . Places that I would like to learn about.
Tom: Ah, I've never heard about it [global warming].
Vince: The sun heats the earth? But, I haven't really heard about it.
However, these two questions did evoke the thought "ozone layer" in eight (36%) of the students. All of these students who brought up "ozone layer" stated concerns about ozone layer depletion and one-half implicated carbon dioxide or sources thereof (e.g., smoke from cars and factories) as a cause of this depletion. The majority of these students also linked ozone layer depletion to the cause of GW as well as skin cancer or sunburn.
Three (14%) of the 22 students expressed thoughts or ideas about GW that approached scientific accuracy. However, two of these students were amongst those eight students who brought up "ozone layer" and, furthermore, indicated that ozone layer depletion was a cause of GW:
Interviewer: What causes global warming?
Melvin: Oh, I don't, well, back to the ozone layer. When there's a hole [it] lets in extra heat and then, see, the ozone layer will also, once it bounces off the surface of the earth, it will also like go out but if there is a depleted ozone layer it won't be able to escape the earth's atmosphere so it will gradually heat up.
The students who comprised this sample usually attributed any knowledge of GW and ozone to TV news and science documentary programs and related discussions with parents. Because the vast majority of middle school students in these separate interviews did not possess an understanding of GW, and those few that did describe GW tended to misconnect it with ozone layer depletion, pre-instruction interviews were not completed for the study reported on here: It was assumed that the middle school students in this sample possessed similarly limited conceptions of GW prior to studying the STS-GW units.
During the early phase of data collection, some of the students to be interviewed posed an unexpected question to the researchers. When told in the process of obtaining informed consent that the interview would be on GW, they appeared uncertain and asked: "Do you mean the greenhouse effect?" The researchers became concerned that elicitation of student understanding could be hampered severely without some prior qualification of terminology. Accordingly, we began asking students, prior to the interview questions, which of the two terms were they used to using or did their teacher use. The researchers followed up by stating that the student could think of the two terms as equivalent, but in this interview the researcher would use the term GW. The researchers believed this "scientifically compromised" qualification of terminology was critical for students to identify adequately with the central topic of the interview.
A content and frequency analysis of specific interview question (Table 2) responses of a subset of eight interviewees (representing equally males and females, students of high and low overall academic ability, and all four STS-GW units) was completed as a "first look" at the data, in an attempt to focus subsequent analysis. The finding of a high prevalence of alternative conceptions of connections between ozone layer depletion and the nature, cause, and resolution of GW led to an in-depth examination of each transcript for the presence of such conceptions. Specifically, researcher assertions of the presence of such conceptions, based on single or multiple instances in the transcript, were verified by studying the entire transcript for the presence of responses that would validate further or invalidate the assertions. A frequency analysis of certain responses to various questions (e.g., the mention of "ozone" prior to the introduction of this concept as a part of question 9 by the researcher) also was completed to be used in concert with the results and discussion of the prevalence of alternative conceptions. Fictitious names have been assigned in this paper to all students and teachers for whom transcript excerpts have been included.
Tammy: Yeah, I think it's basically, that everything works against the ozone and when the ozone breaks, that's when the global warming is going to come.
Candy: [We should] start buying things that like don't have those kind of gases in them. Like instead of buying hair spray with CFCs, you can buy some like in a pump or something.
Billy: . . . CFCs cause destruction of the ozone layer to let the sun, the ultraviolet rays, get in and heat up the Earth.
Evert: . . . And all those oil wells [on fire in the Middle East] gave off tons and tons of carbon dioxide. Which made the ozone layer just come apart and that's where the biggest hole came from.
Sally: It [carbon dioxide] comes out of the exhaust. And as it goes up to the ozone past the stratosphere. Then after it hits the ozone it like eats it up and then UV come and hit Earth.
The above are transcript excerpts taken from interviews with several students and speak to the principal findings of this study. They exemplify the five alternative conceptions found to be held by the students in this study. These alternative conceptions all connected (stratospheric) ozone layer depletion and GW in some way and were as follows: (a) ozone layer depletion is a major cause of GW (Tammy); (b) aerosol sprays contain CFCs and destroy the ozone layer (Candy); © CFCs cause GW exclusively through their role in destroying the ozone layer (Billy); (d) carbon dioxide destroys the ozone layer (Evert); and (e) carbon dioxide causes GW exclusively by destroying the ozone layer (Sally).
Table 3 (below) illustrates the prevalence of these alternative conceptions amongst all students interviewed and according to their overall academic ability level and gender. Although trends appear to be present in the degree to which students of different overall academic ability level and gender held these alternative conceptions, no statistically significant correlations (phi coefficients) were found. Additionally, significant correlations (point biserial)were not found between students' expert concept map scores and the prevalence of these alternative conceptions.
The prevalence in students of these alternative conceptions did not appear to differ appreciably across three of the four STS-GW units. Students who were the recipients of instruction from one of the units gave little evidence of believing that carbon dioxide destroyed the ozone and did not appear to believe that the exclusive role of CFCs in GW was via ozone layer destruction. However, this study was not designed to ferret out differences between students according to the unit of instruction completed. The number (5 to 7) of students interviewed (i.e., representing instruction) from each of the four units is too small to draw conclusions about any real differences that may have existed in the degree to which these alternative conceptions were held.
Below we examine in some detail our findings relative to each of the five alternative conceptions held by the students in this study. However, this separation is somewhat artificial. The transcripts of and excerpts cited herein from student interviews illustrate that these alternative conceptions are interwoven in students' cognitive structures and the idea that "ozone layer depletion is a major cause of GW" surfaces continuously.
Percent of Students Providing Evidence of Alternative Conceptions Related to the Nature, Causation, and Resolution of GW
Student overall academic ability level
Alternative Conceptions All
High Medium Low M F Students
N=9 N=9 N=6 N=14 N=10 N=24
Ozone depletion is major or
predominant cause of GW 33 77 50 64 40 54
Aerosol sprays contain CFCs 44 89 18 64 40 54
and/or destroy the ozone
layer
Carbon dioxidea destroys the 55 55 33 57 40 50
ozone layer
Exclusive role of carbon
dioxidea in GW is by 22 44 33 36 30 33
destroying the ozone layer
Exclusive role of CFCs in GW
is by destroying the ozone 22 33 18 29 20 25
layer
a In this instance, exhaust, smoke, and car pollution were also accepted as the equivalent.
Seventy-five percent of all students and the majority within each academic ability level believed that ozone layer depletion and/or increased ultraviolet (UV) radiation was involved in the causation of GW. This general idea is not necessarily an alternative conception: It does have a scientific basis. The scientific literature as well as papers targeting school teachers and their students have described various mechanisms by which ozone layer depletion may impact GW: Both positive and negative feedbacks have been postulated (Ashmore et al., 1991; Fishman, 1991; Lacis et al., 1990; Monastersky, 1992; Phillips, 1990; Smith, Prezelin, Baker, Bidigare, Boucher, Coley, Karentz, MacIntyre, Matlick, Menzies, Ondrusek, Wan, & Waters, 1992; Worrest & Grant, 1989). However, the majority (54%) of students in the study believed that ozone layer depletion (and/or consequent increases in UV or the sun's rays) is a major or predominant cause of GW. This idea does not have scientific support. Additionally, the underlying mechanisms described by students as to how ozone layer depletion/UV radiation may be involved in GW generally were not those set forth by the scientific community. More often, they were related to natural phenomena, e.g., the heat from the sun.
Almost 60% of the students began talking about ozone layer depletion and/or UV radiation in response to the "advance organizer" questions (Table 2, questions 1 and 2). Examples of transcript excerpts follow that illustrate how three students connected ozone and GW early in their interview. Julie suggests that ozone depletion allows sunlight to penetrate the atmosphere, warming the Earth.
Interviewer: Okay, is there anything else that comes to mind when you think about global warming?
Julie: Heat.
Interviewer: Heat. How does heat come to mind?
Julie: Umm, well, destroying the ozone layer and the sun making it warmer.
Jerome talks about pollution destroying the ozone, and infers the latter is the cause of GW.
Interviewer: You say, "When the sun comes in." Could you tell me a little bit more about that?
Jerome: Like the rays would come through the ozone and it won't go back out through sometimes because of pollution and stuff.
Interviewer: Okay. Umm. What pollution? What is it about pollution that. . . .
Jerome: Like it's, it's eating away the ozone and stuff.
Interviewer: . . . [W]hat are the various causes of GW?
Jerome: Umm. Just the ozone pretty much.
Interviewer: How is . . . the ozone a cause of GW?
Jerome: Like umm, it's like a screen. It will take the sun rays, the harm one, the harmful rays out and it will leave the ones that, like, the plants and we need to work.
Interviewer: Well, are there any other causes that come to mind at all for GW?
Jerome: Not much.
When Sally "thinks about GW," ozone deterioration due to CFCs comes to mind.
Interviewer: When you think about GW, what thoughts or ideas come to mind?
Sally: Ah, the ozone the and how it is being affected by CFCs, umm, carbon dioxide, and stuff that can cause the ozone to deteriorate. . . .
Interviewer: Okay, what makes you think about ozone?
Sally: Umm, mainly stuff that can harm the ozone layer. Like the CFCs and the air conditioners in cars and when the cars become old they leak. . . .
Interviewer: Okay, and how does it harm the ozone?
Sally: Well, there's like chloro-fluorocarbons that go up and eats the like ozone up. And causes the ozone hole to get bigger and bigger and then UV rays from the sun enter and hit Earth. . . .
Interviewer: Umm, and how is that, how is that related to GW though?
Sally: Well, the UV, umm, rays hit Earth and Earth will get warmer. And that's what causes GW.
The researcher queries Sally again about the ozone hole and GW later in the interview:
Interviewer: How is that [ozone] hole related to GW?
Sally: Well, what it does is, like I said, the sun UV rays come through the ozone. And then when it hits Earth, the Earth will warm. And that's how you basically get GW.
The study of Sally's entire transcript provides compelling evidence that she believes ozone layer depletion (and consequent increases in UV rays) is a major and, in her case, the predominant cause of GW. Such was also true for Julie and Jerome (transcript excerpts shown previously), as well as Barton:
Interviewer: Okay, . . . what is GW?
Barton: GW is when the ozone layer gets a hole in it. And the C or the CFCs burn a hole in the ozone layer and it allows more heat to come in through the ozone and it burns things on the surface.
The questions placed at the end of the interview (Table 2, questions 9-12) were for the purposes of further elucidating students' conceptions about connections between GW and ozone layer depletion. Most students who believed ozone layer depletion was a major cause of GW had already provided substantial evidence of this misconception by the time these questions were introduced. Still, student responses were useful in confirming this and other researcher-held assertions. The transcript excerpts shown below for Charles, Evert, Cecil, Zach, and Barton illustrate these student responses to the general query made by the interviewer, "When you think about ozone, do you also think about global warming?"
Charles: Well, a little bit because CFCs destroy the ozone. . . . UV rays are basically what global warming is when they come in, you know.
Interviewer: Okay.
Charles: And it worries me that they could come in faster and faster and then they could bounce off faster and get hotter and hotter and hotter. So, yes, whenever I think of the ozone, I think of the global warming too. . . . And whenever I think of global warming, I think of the ozone.
Evert: Well, yeah because the ozone is what, I think, is going to keep global warming out.
Cecil: Yeah. . . . Because the hole in the ozone is letting all the harmful, all the rays in, and that's what's heating up the Earth.
Interviewer: . . . [T]ell me a little bit more. I guess I am not understanding what you are talking about - how GW and ozone are connected.
Zach: Ah, well the ozone that's what really makes the GW cause if we didn't have the ozone to be heating GW, but since the ozone is having holes in it, and if it just eats all away, we will have a GW.
Interviewer: And why do you think about global warming when you think about ozone?
Barton: Because the global warming affects the ozone, it'll burn a hole in it.
As evidenced by the last transcript excerpt, Barton also believes that GW causes ozone depletion. Candy believes the greenhouse effect causes ozone depletion:
Candy: . . . [T]he greenhouse effect is when the gases and that are ruining, causing holes in the ozone which let off UV rays.
The idea that GW or the greenhouse effect causes ozone layer depletion may have been held by other students, given that many mentioned that (a) ozone layer depletion (and/or increased UV radiation) "comes to mind" when thinking about GW and (b) carbon dioxide destroys the ozone layer. This "construction" also could be the result of a surface understanding and inappropriate logic regarding the role of CFCs in both GW and ozone layer depletion, e.g., if CFCs cause GW and destroy the ozone layer, then GW destroys the ozone. Barton suggests that aerosol sprays containing CFCs play a central role in GW mediated destruction of the ozone layer.
Barton: Global warming, ah, it burns holes in the ozone layer and it can do that by using hair spray and stuff like that. Like aerosol sprays and stuff like that. . . . Hair spray has CFCs in it. And if you use enough of that it will burn a hole in the ozone layer. . . .
This idea surfaced many times in his interview. The alternative conception that aerosol sprays contain CFCs and destroy the ozone layer is explored more fully below.
The idea that aerosol sprays contain CFCs and/or destroy the ozone layer was an alternative conception found to be prevalent in over one-half (54%) of the students. On a global basis, aerosol sprays do account for about 15% of all CFC use (Kurtis Productions, 1993). However, the sale of aerosol cans containing CFCs has been banned in the United States (and Canada) since 1979 (University Corporation for Atmospheric Research, 1992). Hence, aerosol cans sold in the United States should not contain CFCs. Still, student references to aerosol sprays were not contextualized in any geographic locale. The researchers do not believe students were speaking in global terms when describing aerosol sprays, although this could be debated. (Evidence to support this contention is presented later, as we portray various suggestions students make to combat GW.) Nevertheless, the idea that, in the United States, aerosol cans or "hair spray" contain CFCs and, thereby, destroy the ozone layer is a prevalent and perhaps tenacious alternative conception (Kurtis Productions, 1993). A return to Barton's interview reveals the extent to which the researchers believe he holds this alternative conception:
Interviewer: Okay. . . what do you see as the causes of GW?
Barton: Hair sprays . . .
Interviewer: Can you explain to me please, how hair spray . . . causes GW?
Barton: Hair spray has CFCs in it. And if you use enough of that it will burn a hole in the ozone layer. . . .
Interviewer: . . . What is an important thing you learned from the unit on global warming?
Barton: The most important thing I learned is, how to prevent global warming from happening by, like using filters and stuff like that. And using hair spray that are like pump.
Interviewer: Okay. What can be done about global warming?
Barton: . . . You just have to kind of watch the products that you use.
Interviewer: And when you say, "Watch the products that you use," what are you suggesting in particular?
Barton: Hair spray.
Interviewer: Any other products?
Barton: Umm, I imagine some deodorants would have CFCs in them.
Of interest is that a greater percent of high (44%) and medium (89%) academic ability students provided evidence of holding this alternative conception than did those (18%) of low academic ability. Two high ability students put it this way:
Julie: Well, you're destroying the ozone layer with hair spray, any kind of aerosol that contains fluorocarbons. And it's destroying the ozone layer and the sun gets through quicker or absorbs faster down to the Earth.
Mason: Ah, well when you use hair spray. Anything that's in a canister like hair spray and cooking spray for your pans and stuff has CFCs so it, umm, will shoot out or compress air. And then it's CFC. And that stands for chlorofluorocarbons and they eat away at the ozone.
These data suggest that such alternative conceptions can result in misdirected citizenship actions towards issue resolution. In response to the interview questions about the resolution of GW, the majority of students holding this alternative conception stated actions targeted at decreasing the use of aerosols. Examples of such actions can be found in the transcript excerpt of the interview with Barton (presented above) and in excerpts of the interviews with Mason and Charles:
Interviewer: Do you have any specific suggestions [as to what can be done about global warming]?
Mason: Yeah, carpooling is, the driving the car is one of my main ones and trying to find hair sprays that they make in pump now that you can just spray the hair spray you go like this. Those would be two of my suggestions to use hair spray . . .
Interviewer: . . . [I]s there anything in particular that come to mind that you personally can do about global warming?
Charles: Well, like I said about the aerosol sprays. You, if you don't buy them, nobody will manufacture them and then they'll, like they won't be here anymore.
This alternative conception in students may have developed as a result of or been reinforced by GW-STS unit instruction. Some of the GW-STS units contained content stating that aerosol use has been a factor in ozone layer depletion. At the close of the Summer 1993 teacher workshop, one participant informed the researchers that she "stood corrected" and had been teaching students that aerosols sold at the present time contain CFCs.
In response to interview questions specifically targeting student understanding of the nature, cause, and resolution of GW (Table 2, questions 3-8), 50% of the students provided evidence of (the scientifically accurate) understanding that CFCs are a (potential) cause of GW. However, approximately one-half of these (and 25% of all) students ignored CFCs' central mechanism as a heat trap in GW (Mitchell, 1989) and, in fact, held the alternative conception that the exclusive role of CFCs in the causation of GW was through depleting the ozone layer. Several of the transcript excerpts presented previously suggest that certain students may hold this alternative conception of the singular role of CFCs in the causation of GW. Further questioning of Julie and Sally (transcript excerpts follow) on the role of CFCs in GW did not reveal an understanding of CFCs' "greenhouse gas" property, and provided further evidence that their conceptions of the mechanism of CFCs in the causation of GW is solely "ozone layer depletion."
Interviewer: Are they [CFCs] connected to global warming?
Julie: Yes, I think.
Interviewer: Okay. Can you tell me more about that?
Julie: Umm. Well, CFCs destroy the ozone layer and that , I think, that's what happened that there is a hole in it from the CFCs.
Interviewer: Okay. Is there another important thing you learned from the unit?
Julie: Umm, that CFCs are extremely harmful. Like before no one really worried about them and never thought about them. But now as soon as like you spray something it is in the air and.
Interviewer: Okay. And why is it important for you to know about the CFCs?
Julie: Well, like I said before, it eats the ozone layer and the sun gets much hotter and everyone will be so hot.
Interviewer: Okay. How do CFCs cause global warming?
Sally: Well, it [CFCs] like I said eats the ozone and UV rays hit Earth and causes people and plants to become ill and die.
Interviewer: When they get ill and die, what do they get ill and die from?
Sally: They die from the sun's radiation. It can cause skin cancer and cataracts. Which probably leads to death.
Interviewer: Anything else about it that makes them sick and die?
Sally: No, that's pretty much it.
Students who held the alternative conception that CFCs cause GW exclusively via ozone layer depletion also were likely to believe that carbon dioxide (or exhaust, smoke or car pollution) causes GW exclusively by destroying the ozone layer. A significant correlation (phi coefficient of r=.41, p < .05) was found between the holding of these two alternative conceptions. The idea that carbon dioxide causes GW exclusively through ozone layer depletion was a subset of the more widely held alternative conception that carbon dioxide destroys the ozone layer. Both are explored more fully below.
When asked specifically about the nature, cause, and resolution of GW (Table 2, questions 3-8), over 70% of the students provided evidence of understanding that carbon dioxide is a (potential) cause of GW. However, "ozone layer destruction" was sometimes cited as one possible or the mechanism for how carbon dioxide caused GW.
Interviewer: How are cars a cause of global warming?
Mason: When you use them a lot, the gas, I think it's carbon monoxide and dioxide from your exhaust form what's called a bad ozone and that's smog around the lower part of the Earth or make holes in the good ozone that surrounds the Earth.
The idea that carbon dioxide (or what they synonomously described as "exhaust", "smoke", or "car pollution") destroys the ozone layer was an alternative conception held by 50% percent of the students. Some of these students also provided a "scientifically acceptable" (or close to it) mechanism of action of carbon dioxide in GW; that is, they noted that carbon dioxide traps heat in the lower atmosphere (Mitchell, 1989). For example:
Interviewer: . . . Any other causes [of GW] come to mind?
Samuel: Umm. Methane, carbon dioxide are some of the gases that break down the ozone layer. And there's a bad ozone and, ah, nitrixoxide.
Interviewer: Okay, is there anything else about carbon dioxide and methane that make them a cause of GW?
Samuel: They keep the heat in.
One-third of all students (Table 3) gave evidence of believing that the exclusive role of carbon dioxide (or exhaust, smoke or car pollution) in the causation of GW was via destroying the ozone (layer). For example:
Interviewer: Okay, carbon dioxide. Whatever you see as being the causes [of GW], that's what I'd be interested in knowing about.
Andrew: That's like, when the carbon dioxide is let off and it breaks down the ozone layer, it lets more sunlight in and then that makes it get warmer. That's what I think is causing it.
The interviewer questions Andrew later about this:
Interviewer: Umm, is carbon dioxide related to GW?
Andrew: Yeah, I think because it breaks down some of the ozone layer.
Interviewer: Okay, it breaks down some of the ozone layer.
Andrew: Yeah.
Interviewer: Are there other ways that carbon dioxide would be related to GW?
Andrew: Umm. No, I don't think there is.
Another student who did not provide a mechanism for carbon dioxide in the causation of GW talked about the role of car pollution:
Interviewer: Hum hum, you seem pretty convinced that car pollution contributes to global warming.
Julie: Yeah, I think it does.
Interviewer: Okay, can you tell me any more about how it does? How you think it does?
Julie: Well, I'm not really sure, but I think it, I think that the gas like contains CFCs and things that help destroy the ozone layer. And that, then the sun.
Some of the students may have held this alternative conception that carbon dioxide (or exhaust, etc.) destroys the ozone layer because they perceived carbon dioxide as being similar to CFCs in several ways: (a) both CFCs and carbon dioxide contain the word carbon; (b) they are both greenhouse gases; and © they are both cited as components of "pollution." Amongst student responses to the interview questions, instances did exist of students lumping together various (greenhouse) gases as agents which deplete the ozone layer and of speaking collectively about carbons and pollution. Examples of this are provided below in the following transcript excerpts, some of which were embedded in excerpts shown previously:
Freddie: It's sort of like the gases that trap the sun rays also eat the ozone layer away.
Lanny: . . . And that a whole bunch of different gases are going up there and making it [the ozone] deplete.
Sally: . . . [T]he ozone and how it is being affected by CFCs, umm, carbon dioxide, and stuff . . .
Samuel: . . . Umm. Methane, carbon dioxide are some of the gases that break down the ozone layer.
Andrew: How to, ah, use things that don't have as much, ah, damaging things to ozone, like carbons and that.
Amanda: Umm, like cars and the pollution, like that they're sending out , you know, from umm, when they're being run. And factories and things like that. How they're, umm, deleting the ozone layer.
Most (75%) of the students who believed carbon dioxide destroys the ozone layer and all of the students who believed this was the exclusive role by which it caused GW, also held the alternative conception that ozone layer depletion is a major cause of GW. A significant correlation (phi coefficient of r=.65, p<.01 ) was found between students holding the latter two alternative conceptions.
Few students provided evidence of a scientifically complete (relative to the expert map presented in Figure 1) understanding of the radiative mechanism of greenhouse gases in the causation of GW. Students were more likely to state that various gases (or pollutants or car exhaust) trapped UV or the suns' rays, thereby causing GW, as opposed to trapping or absorbing infrared radiation given off by the Earth. The former is an alternative conception relative to the cause of GW and may reflect an unclear understanding of the role in GW of the different types of radiation. It also is apparently related to these students' conceptions of the connections between GW and ozone layer depletion. In our study, even the students who gave evidence of a relatively sound understanding of the radiative mechanisms underlying GW (greenhouse gases absorb infrared or long wave radiation emitted by Earth, that originated from shorter wavelength radiation from the sun, thereby trapping heat) were likely to see the consequences of both GW and ozone layer depletion as warming the Earth:
Interviewer: Okay, when you think about ozone do you think about global warming?
Mollie: Yeah. Because sometimes I do . . . And it [Earth] also gets like warmer because of there's a hole in the ozone. Then the rays are going to come in at like a hotter temperature.
Interviewer: Okay. What is it about ozone that makes you think about global warming?
Mollie: Like the, how the sun rays come in and make the Earth like warmer and like hotter. That like happens in both, so that what makes it, I think.
To facilitate the focus and clarity of instruction (Wise & Okey, 1983), teachers were advised to not include instruction on ozone in their GW-STS unit. However, an inspection of the GW-STS units suggested that three teachers did address ozone layer depletion during STS-GW instruction. This instruction may have played a role in the development of or in reinforcing the alternative conceptions (Table 3) that surfaced in this study. Post-instructional interviews with teachers did reveal that, (a) one dealt with ozone previous to and three dealt with ozone in their unit, and (b) they believed some degree of confusion (between GW and ozone layer) might exist amongst the students. The following are select responses from the four teachers to the related interview question, "Because we are going to ask your students, or we have asked your students, about ozone, we need to know how you dealt with ozone?"
Sue: Good or bad ozone? . . . We talked about both and that was a hard thing for them to understand. . . . I used the diagram, two different diagrams, that I had in the units to show them, ah, greenhouse effect, and what part the ozone played as well.
Mort: And I hope they know the fact is that it's [ozone depletion is] not related to GW. I don't know if all of them will know that.
Jack: As a separate problem that really had no connection with GW.
. . . There was one other problem I had. And it was separating in their minds, ah, the problem with ozone depletion and the problem with GW. . . . And then their were other articles [that the librarian put together] that actually drew a connection and it was the first time I had heard that the fact that the ozone is being depleted also is a negative feedback for GW. Is that right? . . . That . . . confused me.
Mary: . . . I don't feel we did a good job at that.
. . . [A]nd I could not avoid the ozone issue so I'm sure I don't know what your questions are for the students, but they might have some confusion. . . . [W]e just said try to keep them separate."
The interviews conducted separate from this study with a similar sample of students who had not completed instruction on GW suggest certain characterisitics about the pre-instructional understandings of the students in this study. Knowledge of GW likely was limited and embedded to some extent the in concept of the ozone layer and the two alternative conceptions that (a) ozone layer depletion is a major cause of GW and (b) carbon dioxide (or sources thereof) destroy the ozone layer. If held prior to instruction, these two alternative conceptions may be tenacious, given that they also were part of the post-instructional understandings of 50% or more of the students in this study.
Nonetheless, the findings reported above suggest that middle school students may possess specific alternative conceptions that limit and confound their understanding of the nature, causation, and resolution of GW. Additionally, these findings do not appear to be limited to our sample. The principal alternative conceptions (Table 3) discussed herein also surfaced in a recent study in Greece of primary students' understandings of ozone layer depletion and the greenhouse effect (Christakis, personal communication, April 22, 1994). In GW curricula targeting students of grades 7-10, Hocking et al. (1989) suggests "the hole in the ozone layer as a cause of the greenhouse effect" (p. 12) is a common "misconception," and so, teachers should explain to students that the additional UV light (consequent to ozone layer depletion) does not heat up the Earth very much.
As suggested in the transcript excerpts of the interviews with the teachers, it is difficult to follow a directive to not include content on ozone while teaching about GW. Initial exposure to the concept of GW may evoke thoughts in students about the ozone layer. The interviews we conducted with students who had not received instruction on GW revealed that "ozone layer" or came to mind in more than one-third of the students, as they "thought about GW." In retrospect, a directive to avoid the topic of ozone while teaching about GW is likely impractical and may not be conductive to helping students restructure related alternative conceptions. Several reasons follow to support these contentions.
Ozone is one of the greenhouse gases (Fishman, 1991) in our troposphere and is increasing, primarily due to photochemical reactions involving pollutants from the incomplete combustion of fossil fuels in motorized vehicles (National Research Council, 1991; Phillips & Pickering, 1991). Although the magnitude of its contribution to tropospheric warming generally is noted to be considerably less than that of carbon dioxide and cannot at present be quantified as well as some of the other greenhouse gases (IPCC, 1992), the greenhouse nature of this gas remains a scientific fact and one that may surface in literature to which students and their teachers are exposed. Moreover, unlike the other greenhouse gases, ozone in the troposphere has "serious direct impacts on plants [as a phytotoxin] and animals" (Ennis & Marcus, 1994, p. 19) and, related to global change, an issue likely to receive mounting future attention. Yet, given media coverage, students likely know "ozone" prior to GW instruction as a layer high in the sky that protects us from harmful (ultraviolet) rays. Thus, if content on ozone layer depletion is ignored, potential exists for students to confuse these two instances of ozone (tropospheric and stratospheric), their roles, as well as the types of radiation (infrared and ultraviolet) involved, as they pertain to the causation of GW.
Global warming and stratospheric ozone depletion both have significance at a global level, speak to atmospheric change, and are coupled through the involvement of CFCs in both problems. Thus, they may be addressed concurrently: Pomerance (1989) details some of the historical events behind and reasons for this. Furthermore, ozone layer depletion is considered a factor in global climate change, due to its potential to affect the radiative balance of our atmosphere (IPCC, 1992). As stated previously, papers targeting the scientific community, as well as school teachers and their students, connect these issues by describing various mechanisms by which ozone layer depletion may impact GW. Given the 1992 scientific assessment update of the Intergovernmental Panel on Climate Change (Houghton, Callendar, & Varney, 1992), the connection between these two issues may receive increased attention. This update reports that our understanding of ozone layer depletion relative to GW has advanced significantly: Ozone layer depletion over the past decade has contributed a negative feedback to GW, possibly offsetting the greenhouse effect contribution of CFCs over that same time period. Such evidence speaks to the importance of revealing and helping students to restructure the alternative conception frequently encountered in this study that ozone layer depletion causes GW.
By telling students that they could think of "the greenhouse effect" and GW equivalently, the researchers may have limited the findings of this study relative to disclosing students' mental constructs of the greenhouse effect and how it relates to GW. That is, student thinking may have been constrained and their use of the term "greenhouse effect" discouraged, in response to the subsequent interview questions. Indeed, only 38% of the students mentioned the "greenhouse effect" and generally had little to say about it. Alternatively, our relatively sparse findings may have been largely a function of the questions set forth in the interview protocol in that none of the planned questions in the protocol asked about "the greenhouse effect." We did not want to "provide" this concept and were interested in ascertaining if students would bring it up to explain the causation of GW (Figure 1). Actually, none of them specified that GW was caused by the greenhouse effect or any intensification thereof. However, some of these students did connect the greenhouse effect with changes in (atmospheric) ozone, as evidenced in the transcript excerpts of Candy, Tammy, and Barton:
Candy: . . . [T]he greenhouse effect is when the gases and that are ruining, causing holes in the ozone which let off UV rays.
Tammy: . . . [I]f the ozone wouldn't be there, the greenhouse effect like could happen already.
Barton: . . . [T]he greenhouse effect or the, ah, the other one. I can. . . . Global warming, ah, it burns holes in the ozone layer . . .
The "greenhouse effect" is part of the public vocabulary (Ennis & Marcus, 1994; Pomerance, 1989) and many students likely have heard the term prior to related formal instruction (Hocking et al., 1990). Understanding of the greenhouse effect may be limited to the idea that it is a problem and is synonymous with GW, "arriving" as a result of recent human influence (Shaw and Stroup, 1991; Pomerance, 1989). The idea that the greenhouse effect is "held off" by the ozone (layer) or that it is equivalent in meaning with GW are alternative conceptions. The greenhouse effect is a concept label for a natural phenomenon whereby specific (greenhouse) gases trap heat (as infrared radiation) in Earth's lower atmosphere. It is a necessity to sustain life as we know it on this planet (Graedel & Crutzen, 1989; Mitchell, 1989; University Corporation for Atmospheric Research, 1991). GW is a concept label that describes a global climate change and (potentially) is caused by the enhanced (or strengthened, etc.) greenhouse effect, or "greenhouse warming," which in turn is due to anthropogenically-induced increases in greenhouse gases (Graedel and Crutzen, 1989; Wigley & Barnett, 1990; Schneider, 1989). Some educators could argue that this is a scientific technicality or too sophisticated for middle school students who are developing an initial understanding of GW. Indeed, the expert concept map (Figure 1), which reflects content common to the STS-GW units and teacher constructed concept maps of the understandings they desired students (in this study) to develop, explicates the proposition "GW is caused by the greenhouse effect." Nonetheless, qualifying the greenhouse effect as being enhanced, intensified, or human induced as related to the causation of GW, would facilitate a more complete and scientifically accurate understanding amongst students of both concepts and their interrelationship.
We speculate that concepts such as ozone hole, ultraviolet rays, CFCs, and greenhouse effect may be "loose" in many students' knowledge and connected inappropriately to make sense of formal instruction on GW. Furthermore, there is real potential for student confusion and construction of alternative conceptions, when they are confronted with multiple phenomena that are explained through some of the same concepts. Three transcript excerpts from the interview with Candy are illustrative:
Interviewer: Okay. Let's say you were to explain global warming to someone else. What exactly is global warming? How would you explain it?
Candy: It's, well, I don't know. Let me think. . . Umm. It's when like CFCs and things. Or it's like greenhouse. Well, I kind of get , I kind of mix them together cause that's what you think about them. They're kind of , people like talk about them as the same thing. But they're not.
Interviewer: Sounds like you're unsure of something.
Candy: Yeah, I'm getting confused.
Interviewer: Tell me what you're unsure of.
Candy: I guess, it must be when I speak about global warming or greenhouse effect. You get the idea that they're exactly the same thing. But they're two different subjects and then I get confused . . . cause I know greenhouse effect is ozone depletion like.
Candy: You kind of get confused. Because both things [global warming and ozone] are like more heat or something getting into the Earth, which kind of confuses you sometimes when you try to think of which is which.
It follows that, in the design and delivery of GW instruction, concepts and propositions embedded in our findings of alternative conceptions need greater attention. Perhaps most important is an emphasis on clarifying the causes of and differences between ozone layer depletion and GW and that neither the ozone "hole" nor consequent increases in UV rays are established or principal causes of GW. Our findings suggest that such clarification should pay particular attention to the following: (a) the differences between incoming (solar) and outgoing (as emitted by Earth) radiation; (b) the absorption by greenhouse gases of the latter (but not the former) as the mechanism that underlies the greenhouse effect; © enhancement of the greenhouse effect due to atmospheric increases in greenhouse gases as the cause of GW; (d) that CFCs, but not carbon dioxide, have two undesirable effects on our atmosphere (i.e., action as a greenhouse gas and action in the destruction of stratospheric ozone), but that each of these effects cause a different environmental problem (enhanced greenhouse effect and ozone layer depletion, respectively); and (e) household aerosol "spray" cans in the United States do not contain CFCs. In addition, it is important to reiterate that the interrelationships between GW and ozone are complex and still unfolding. These previous points can be embellished with further details. As examples: the greenhouse gas methane also may play a role in ozone layer depletion (Thompson, Hogan, & Hoffman, 1992; Worrest, et al., 1989) and certain aerosol sprays used for medical purposes in the United States still contain CFCs (Kurtis Productions, 1993). While it is important for science teachers to keep current on GW and ozone layer depletion, and reflect major scientific thinking and consensus in related classroom instruction, we believe that efforts on the part of teachers to present "all the details" may be counterproductive in helping students initially to construct a clear understanding of GW.
Additionally, we recommend that classroom instruction on GW be preceded by efforts to disclose student understandings of the above and involve the use of conceptual change instructional strategies (Smith, Blakeslee, & Anderson, 1993; Wandersee, et al., 1994) to facilitate the restructuring of related alternative conceptions found to be prevalent among the students. Accordingly, aspects of the Generative Learning Model (Osborne & Freyberg, 1985) and concept mapping (Novak & Gowan, 1984) have considerable application in curriculum design and instruction on GW.
The findings of the alternative conceptions disclosed in the interviews reported on here proved useful in designing the second (Summer 1993) teacher workshop for participants, that was a part of the teacher enhancement project, during which they revised their field-tested STS-GW units. The Summer 1993 teacher workshop was devoted largely to the revision of the field-tested STS-GW units. Teachers were appraised (but not "blamed") of the researchers' tentative findings on the prevalence of the alternative conceptions reported above. In making curriculum revisions, teachers were encouraged to incorporate aspects of the Generative Learning Model and other conceptual change teaching techniques (e.g., students prepare preinstructional concept maps) in order to disclose and facilitate the restructuring of alternative conceptions. Teachers also received additional scientific content related to these alternative conceptions.
The teachers implemented these revised units during the 1993-94 school year and the researchers have continued to investigate, through structured interviews, the post-instructional understandings of students who have completed the units and the teachers perceptions of the effectiveness of the units. Results from these endeavors will be compared and used in concert with the findings of this study to produce a second revision of the STS-GW units.
The absence of actual pre-instructional interview data on the subjects of this study, as well as control groups, limits the findings reported herein. We cannot ascertain with great certainty the degree to which various alternative conceptions reported herein existed prior to or were formulated during instruction among the subjects who were interviewed. We cannot speak with high probability about the degree to which specific pre-existing alternative conceptions are resistant to various instructional interventions. We cannot detail a curriculum scope and sequence that would be focused and clear with respect to GW yet maximize the restructuring of pre-existing (and tenacious) alternative conceptions or reduce the degree to which the latter are formulated during instruction. Needed are studies that investigate student understandings both prior and subsequent to instruction on GW, as well as studies that compare specific instructional interventions that integrate as oppose to separate the issues of GW and ozone layer depletion.
The authors thank the students who participated in the interviews and their science teachers. Also, we thank Ms. Donna Dorough for the assistance she provided in completing this study.
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