Concepções Alternativas Sobre o Efeito Estufa Por Estudantes

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An investigation of middle schoolstudents alternative conceptionsof global warmingJames A. Rye a , Peter A. Rubba b & Randall L.Wiesenmayer ca Department of Curriculum & Instruction, West VirginiaUniversityb Science Education, Penn State Universityc Department of Curriculum & Instruction, West VirginiaUniversityPublished online: 24 Feb 2007.

To cite this article: James A. Rye , Peter A. Rubba & Randall L. Wiesenmayer (1997):An investigation of middle school students alternative conceptions of global warming,International Journal of Science Education, 19:5, 527-551

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INT. J. sci. EDUC., 1997, VOL. 19, NO. 5, 527-551

An investigation of middle school students'alternative conceptions of global warming

James A. Rye, Department of Curriculum & Instruction, West VirginiaUniversity, Peter A. Rubba, Science Education, Penn State University andRandall L. Wiesenmayer, Department of Curriculum & Instruction, WestVirginia University

Because global warming presents a serious potential threat to our biosphere, it is receiving considerableattention by scientists, policy makers, and educators. This article presents alternative conceptions aboutglobal warming held by a sample of 24 grade 6 to 8 students. Students completed interviews on global'warming approximately two weeks after instruction from a Science-Technology-Society (STS) globalwarming unit. The majority of students introduced 'ozone layer' or 'ultraviolet radiation' in response tothe question, 'When you think about global warming, what comes to mind?' Approximately one-half ofthe students held the alternative conceptions that ozone layer depletion is a major cause of globalwarming and that carbon dioxide destroys the ozone layer. These and other alternative conceptionsevidenced by the students suggest that global warming instruction should help students clarify thatozone layer depletion and global warming are different environmental problems and that the ozone'hole' does not enhance the greenhouse effect.

Introduction

Global or 'greenhouse' warming presents a serious potential threat to our bio-sphere, with posssible economic and climatic consequences that range from aloss in biodiversity to the flooding of coastal areas to regional changes in soilmoisture and food production (Ennis and Marcus 1994, Mackenzie andMackenzie 1995; Schneider 1989). The Intergovernmental Panel on ClimateChange (Houghton et al. 1992) has made clear that key uncertainties affect ourprediction of global warming, but conclude that human activity is increasing con-siderably the concentration of greenhouse gases in our atmosphere, and the globalmean surface air temperature of earth has increased from 0-3 to 0-6 degrees cen-trigrade over the past 100 years. Whereas the latter amount of warming is 'of thesame magnitude as natural climate variability' (Houghton et al.: 19), there is theopposing consideration that 'this variability and other factors would have offset astill larger human-induced greenhouse warming'.

Accordingly, global warming is receiving considerable attention by scientistsand policy makers worldwide (Houghton et al. 1992, National Academy of sciences1992, United Nations Conference on Environment and Development 1992) andthere is much interest in educating both school pupils and college students aboutproblems connected to global atmospheric change (Activities for the ChangingEarth System 1993, Adler 1992, Globe Program 1995, Mayer and Armstrong

0950-0693/97 $12-00 1997 Taylor & Francis Ltd

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528 J. A. RYET^L.

1990, Poore 1993, Rutherford 1989, Rye et al. 1995, Sherman 1992, Subcommitteeon Global Change Research 1993, Trenberth et al. in press, UniversityCorporation for Atmospheric Research 1991, 1992). Several studies (Boyes andStanisstreet 1993, Christidou 1994, Dorough et al. 1995, Francis et al. 1993,Koulaidis and Christidou 1993, Plunkett and Skamp 1994), which are summarizedbelow, have investigated upper elementary and secondary school students' under-standings of concepts related to global atmospheric change, such as the greenhouseeffect, global warming, and (stratospheric) ozone layer depletion. These studieseither state explicitly that they are pre-instructional in nature or appear not tofollow any specific global atmospheric change instruction. The findings of thesestudies indicate that students hold, to an appreciable degree, conceptions aboutglobal atmospheric change that differdo not appear to 'fit'expert scientificknowledge (Abimbola 1988). In this article, we consistently employ the term'alternative conception' to label such student conceptions, as opposed to termsthat have a negative connotation (e.g. 'erroneous idea' and 'misconception') andmay be condescending towards learners (Abimbola 1988). The use of the termalternative conception implies a 'conceptual change view of student science knowl-edge' (Abimbola 1988: 178) and attributes considerable value to 'experience-basedexplanations constructed by the learner to make a range of natural phenomena andobjects [more] intelligible' (Wandersee et al. 1994: 179). The arguments and phi-losophical underpinnings of the use of this term, and the need to employ a singleterm to label such conceptions throughout a single research report, are describedin detail by both Abimbola and Wandersee et al.

Christidou (1994) conducted a series of three interviews with 41 grade 5 and 6students to investigate how they processed information about ozone layer deple-tion and the greenhouse effect. Approximately 26 (63%) of the students believedthat increased ultraviolet (uv) radiation consequent to ozone layer depletion wouldwarm up the earth and/or melt polar ice caps. Some students mentioned that thelatter was the primary cause of the greenhouse effect. Overall, the findings sug-gested that students had greater familiarity with ozone layer depletion than thegreenhouse effect, and that students often conceptualized these two phenomena asone.

Francis et al. (1993) administered a questionnaire about the greenhouse effectto 565 children aged 8 to 11, and interviewed a small subset (15) of these indivi-duals. In these interviews, many students introduced the phenomenon of ozonelayer depletion. Various students' responses suggested that they fused, and as suchconfused, the ideas of global warming and ozone layer depletion. The authorsconclude that such may be 'embedded in an apparently logical conceptual frame-work: the idea that damage to the ozone layer allows the "sunshine" to penetrateand so warm the earth' (390).

Boyes and Stannisstreet (1993) reached conclusions similar to those of Franciset al. (1993) from their study that investigated understandings about the green-house effect in 861 students ranging in age from 11 to 16. Their study consisted ofa questionnaire administered to all students, along with follow-up interviews of 60students. The results of the questionnaires revealed that the majority of the stu-dents believed that chlorofluorocarbons (CFCS) from spray cans accelerate thegreenhouse effect and that the latter is made worse by the ozone layer hole; andthat the greenhouse effect is accelerated because of an excess of the sun's raysreaching earth. The findings from the interviews supported the results of the

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GLOBAL WARMING: ALTERNATIVE CONCEPTIONS 529

questionnaires in regards to the holding of the alternative conception that ozonelayer depletion causes global warming. The authors conclude that students linkCFCS primarily to ozone layer depletion and that they blend the ideas of globalwarming and ozone layer depletion: 'There is a likelihood of pupils reaching thecorrect conclusion via an erroneous pathway, in that an affirmation that CFCS affectglobal warming may arise from a knowledge of the CFCozone connection and aconfusion between the two global environmental effects' (550).

Plunkett and Skamp (1994) interviewed 45 students, from grades 4 through 8,about the ozone layer and ozone hole. They found that about 20% of studentsbelieved that aerosol sprays destroyed the ozone layer and over 25% believedthat the ozone layer hole would lead to climatic changes that included the meltingof polar ice caps. These authors state as the main conclusion of their study thatstudents have a conceptual framework that confuses ozone layer depletion and thegreenhouse effect.

Dorough et al. (1995) investigated the pre-instructional understandings aboutglobal warming and ozone of 22 grade 5 and 6 students. About 40% of the studentsintroduced the concept of ozone or ozone layer, in response to the query, 'Whenyou think about global warming, what thoughts come to mind?' Several of thesestudents gave evidence of believing that ozone layer depletion is a major cause ofglobal warming. Few students gave evidence of knowing about CFCS or the green-house effect.

A finding common to each of the above studies is the holding by students ofthe alternative conception that ozone layer depletion causes global warming.Interestingly, this alternative conception is in direct conflict with current scientifictheory (Houghton et al. 1992): 'Ozone [layer] depletion leads to a cooling effectthat offsets half to all of the potential greenhouse warming due to the accumulationof CFCS in the atmosphere' (Mackenzie and Mackenzie 1995: 324-25). This scien-tific theory is based on radiative balance calculations and accounts for the fact that'Ozone is an effective greenhouse gas both in the troposphere and the stratosphere'(Houghton et al. 1992: 8). Accordingly, a decrease in the amount of ozone meansthat less (as opposed to more) infrared radiation will be radiated back towardsearth.

The study reported herein examined middle grade level students' post-instruc-tional understandings of global warming. The degree to which learners are able toconstruct scientific understandings about global warming during instruction maybe influenced by, amongst other things, the tenacity of alternative conceptions heldprior to formal instruction about global warming, the instructional modelemployed by the teacher, alternative conceptions they develop during classroominstruction to help instruction 'make sense', and their level of cognitive develop-ment relative to the capacity for formal or abstract thinking (Benson et al. 1993,Driver et al. 1985, Eylon and Linn 1988, Osborne and Freyberg 1985, Wanderseeet al. 1994). According to Piagetian theory of cognitive development, middle levelstudents (ages 12 to 14) are making the transition from concrete to formal levelthinking (Eylon and Linn 1988, Hassard 1992). Global warming is a complexphenomenon: an accurate understanding of the causation of global warminginvolves abstract concepts about the electromagnetic spectrum, such as the absorp-tion and re-emission of electromagnetic energy of different wavelengths, theinverse proportionality that underlies electromagnetic wavelength and energy

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530 J. A. RYE ETAL.

level, and the relationship of 'long-wave' infrared energy to heat and the green-house effect.

While the mechanisms and feedback loops that underlie global warming aremultiple, interrelated, and sophisticated (IPCC Working Group I 1992, Mackenzieand Mackenzie 1995, National Academy of Sciences 1992), global warming ulti-mately is related to the natural phenomenon of sunlight, or more precisely, thesolar radiation incident upon the earth. Learners will bring to global warminginstruction the intuitive knowledge (West and Pines 1985) that the sun feelswarm and that a sunburn makes us hot. Such intuitive knowledge can interactwith new information to yield unintended learning outcomes, e.g. the alternativeconception that the extra sunlight or ultraviolet radiation, coming through the'hole' in the ozone layer, heats up the planet.

Other potential influences on the construction by learners of alternative con-ceptions surrounding global warming are the coverage given to the ozone layer'hole' by the media (Hanif 1995) and classroom instruction that attempts to pre-sent both global warming and ozone layer depletion within the same instructionalunit (Koulaidis and Christidou 1993). Learners may formulate the erroneous ideathat ozone layer depletion is the principal cause of global warming due to theinvolvement of incoming solar radiation and CFC greenhouse gases in both envir-onmental problems (Hocking et al. 1990, Monastersky 1992, Pomerance 1989).Worrest et al. (1989) do recommend addressing ozone layer depletion and globalclimate change as parts of a whole. However, the interrelationships betweenchanges in atmospheric ozone and global warming are complex. (Ashmore andBell 1991, Fishman 1991, IPCC Working Group I 1992, Lacis et al. 1990), andaccordingly, the development of scientifically appropriate conceptions of globalwarming may be confounded by integrating the study of both topics. On the otherhand, because CFC-induced ozone layer destruction (and consequent increases inultraviolet radiation) have received considerable attention in the popular media(Hanif 1995, Pomerance 1989), providing surface or no coverage of ozone mayresult in the development of alternative conceptions about the cause of globalwarming. Consider the following excerpt from 'Can capitalism save the ozone'from the New York Times (Nasar 1992):

But it [eliminating energy subsidies] would also cut emissions of carbon, the sub-stance whose buildup, scientists fear, could eventually destroy the ozone layer, result-ing in higher average temperature and harmful climate changes around the world.(D2)

This excerpt is perhaps an extreme example of the media's potential to facilitateinappropriate understandings about scientific phenomena and was 'corrected' inthe next day's edition of the newspaper ('Corrections', 8 February 1992).However, it speaks directly to the principal alternative conceptions found to beprevalent amongst students in this studythat carbon dioxide or exhaust causesozone layer destruction and that ozone layer depletion is a major cause of globalwarming.

Background and purpose

The research reported on here examined learners' understanding of global warm-ing from the perspective of 'focus on concept learning' (Eylon and Linn 1988) and

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strove to make a meaningful contribution to the research base on alternative con-ceptions in science education (Wandersee et al. 1994). This research was con-ducted as part of a National Science Foundation (NSF) funded TeacherEnhancement Project in STS Education (TEP-91 50232)Teacher Developmentand Research in STS Education for Rural Middle School Science Teachers fromCentral Pennsylvania and Northern West Virginiasponsored by PennsylvaniaState University and West Virginia University. Global warming was chosen as theSTS theme of the project because it is a highly visible STS issue and lends itself toinstruction in the science concepts dealt with in life, earth, general, and physicalscience courses taught at the middle school level. The purpose, activities, andoutcomes of this four-year project, which included the publication of an STS'issue investigation and action' curriculum (Rubba and Wiesenmayer 1985,1993) on global atmospheric change (Rubba et al. 1995), are described in detailelsewhere (Rubba et al. 1996).

During the first year of the project, six STS issue investigation and action unitson global warming were developed, each by a five or six member team of teacher-participants. The units included several similar activities and shared a core contenton the nature, cause and resolution of global warming. Figure 1 presents an'expert' concept map, which sets forth in a hierarchical conceptual network(Heinze-Fry and Novak 1990, Jonassen et al. 1993, Lomask et al. 1993, Novakand Gowin 1984) core content on the nature, causation and resolution of globalwarming that was shared by these units.

This expert map does not attempt to represent the total scope nor reflect thediversity of content inherent in each of the STS global warming units. For example,some of the units included content on ozone layer depletion and/or on ozone as agreenhouse gas and component of 'pollution'. The development of the expert mapwas informed by the work of Novak and Gowin (1984) and Heinze-Fry and Novak(1990) and is described elsewhere (Rye et al. 1994).

These STS global warming units were field-tested by each of the teachers onthe respective teams during the 1992-93 academic year. To inform the unit revi-sion process that was to occur during the summer of 1993, the project staff inter-viewed the teachers and a sample of their students approximately two weeksfollowing the end of the unit. The purpose, procedures and findings associatedwith the teacher interviews are given elsewhere (Rubba et al. 1994). However, thisarticle does incorporate select findings from the teacher interviews as they arerelevant to students' various alternative conceptions. The purpose of the studentinterviews was to investigate their understandings relative to the STS global warm-ing unit content, to ascertain what citizenship actions they had taken towards theresolution of global warming, and to learn about their perceptions of the impor-tance as well as the strengths and limitations of the STS global warming unit. Thispaper reports only on the understandings of global warming held by a sample ofgrade 6-8 students who had completed one of the STS global warming units, asascertained through an analysis of interview transcripts.

Students' understandings were examined in two ways: an 'expert' concept mapwas used as a template to assess the degree to which students gave evidence ofholding scientifically appropriate concepts and concept relationships present in theSTS global warming units; and assertions were formulated and validated in regardsto alternative conceptions students held about the nature, cause and resolution ofglobal warming. The expert map based assessment of student understanding is

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STS Issue

becauseis to

because

Problem

th

OpposingVUwpnlnt.

Science Technology Society

. -

Global Wanning

Earth'sTemperature

GreenhouseF.fTprt

due to

CFCs

PoliticalAction

(example:plant trees)

(example:encourageparents tocarpool)

(example:purchaseproducts inrecyclable orreturnablecontainers)

(example:writelegislator)

ipping

Figure 1. Expert concept map of global warming.

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presented elsewhere (Rye et al. 1994). The specific focus of this paper is on stu-dents' alternative conceptions. Analysis of the data was guided by two questions:What post-instructional alternative conceptions do students hold of the nature,cause and resolution of global warming? In what ways and to what extent do thesealternative conceptions incorporate connections with ozone layer depletion?

Design and procedures

Sample and pre-interview instruction

The sample for this study was one of convenience. It was predominately white anddrawn from students in four middle level classrooms (two grade 6 and one each ofgrades 7 and 8) in rural schools in central Pennsylvania. The students in each ofthese classrooms had completed (as part of their science course) a different one ofthe six STS global warming 'issue investigation and action' units, developed andtaught by a teacher-participant of the project. Therefore, the students in thisstudy, collectively, represented instruction in four of the six STS global warmingunits that had been developed by the teacher-participants in the STS Institute.Students representing instruction from the other two units were not included inthis study due to the high school level focus of one unit and teacherparticipantattrition associated with the other.

After the students completed the STS global warming unit, their teacherexplained to them the purpose and nature of an opportunity to be interviewedby project staff. The parents of students who volunteered for the study receivedletters from the investigators that described the study, stated that their child hadvolunteered for the study, and requested informed consent and release for the childto participate. From the pool of volunteers whose parents had provided consent,each teacher selected a sample of five to eight students to represent a cross-sectionof the class according to gender, culture and (the teacher's perception of) overallacademic ability. Of the 26 student transcripts produced, two were omitted due totape recording problems and incomplete interviews. Table 1 provides informationon the distribution (per cent) according to grade level, gender and teacher-per-

Table 1. Grade, gender, and overall academic ability level of subjects

Overall Academic AbilityLevel/Gender

HighMaleFemale

MediumMaleFemale

LowMaleFemale

TotalMaleFemale

Grade 6

258

172525

0844

583821

% of students

Grade 7

440808844

218

13

(n=24)

Grade 8

844404844

2113

8

RowTotals

3817213829

8251313

1005842

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534 J. A. RYE ET Ah.

ceived overall academic ability (high, medium or low) for the remaining 24 stu-dents that comprised the sample. There were more males than females. There werefewer students of low than medium and high overall academic ability. While agreater percentage of females than males were of high and low overall academicability, there was little difference between gender on a group basis; that is, theaverage teacher-rated overall academic ability level (3=high, 2=medium, l=low)was 2-2 for females and 2-07 for males.

Interviews

A protocol for conducting standardized open-ended interviews (Patton 1987) wasdeveloped by the authors and field-tested on a sample of students who had com-pleted an STS global warming unit. The design and sequence of the interviewquestions (some of which were follow-up probes) set forth in the protocol wasinformed by Osborne and Freyberg (1985) and shared many of the features cited asimportant by Novak and Gowin (1984). These questions focused on eliciting,sequentially, students' understandings and views in the following areas:

the nature and cause of global warming what global warming unit content was 'important' why global warming is an STS issue possible citizenship actions to resolve global warming actions actually taken to help resolve global warming likes and dislikes about the global warming unit connections between global warming and ozone.

Student responses to all questions were examined to validate researcher asser-tions about the presence of various alternative conceptions. However, 12 questionsaddressed more specifically the research focus of this paper and generally provedmost effective in revealing students' alternative conceptions about global warming.These questions are set forth in table 2, in the order in which they were posed.

The interview question sequence commenced with a broad query (table 2,question 1) of minimal difficulty designed to help focus students' thinking andbring to the forefront knowledge held about global warming. As such, this ques-tion and the related follow-up probe (question 2) might be thought of as anadvance organizer (Germann 1991, Jonassen et al. 1993) for facilitating the elicita-tion of understanding. These questions generally were repeated before moving onto questions specifically targeting the nature and cause of global warming(questions 3 to 5), why global warming is an STS issue (question 6), and possiblecitizenship actions to resolve global warming (questions 7 to 8). As with the twoadvance organizer questions, these questions usually were repeated by the inter-viewers, along with some additional probing of student responses. The questionsto elicit connections students perceived between global warming and ozone(questions 9 to 12) were placed at the end of the interview.

The researchers recognize that asking questions about ozone in the context ofan interview on global warming may 'lead' students. However, since the majorityof the students interviewed had completed an STS global warming unit that didinclude content on ozone, and the literature (Francis et al. 1993, Hocking et al.1990, Koulaidis and Christidou 1993) suggests students may confuse these twoissues, such questions became important. The questions were positioned at the end

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Table 2. Interview questions on GW.

Advance organizers for GW:1) When you think about GW, what thoughts or ideas come to mind?2) What is it about GW that makes you think this?Nature and cause of GW:3) What is GW?4) What causes GW?5) How is this a cause?Why GW is an STS issue:6) What is it about GW that makes it an STS issue?Citizenship actions to resolve GW:7) What can be done about GW?8) What can you do about GW?Connections between GW and ozone:9) When you think about ozone, what thoughts and ideas comes to mind?10) When you think about ozone, do you also think about GW?11) What is it about ozone that makes you think about GW?12) Is there anything else you would like to tell me about ozone?

of the interview so as not to influence students' thinking and subsequent responsesto questions specifically targeting the nature, cause and resolution of global warm-ing. Actually, the concern about the researchers leading students to connect globalwarming with ozone layer depletion generally became a moot issue: the majority ofstudents began talking about ozone in response to the two opening advance orga-nizer questions on global warming and 75% of students had broached the subject ofozone prior to the ozone-specific questions. These serendipitous findings providedconsiderable support for the inclusion of the ozone related questions at the end ofthe interview by serving as a means to confirm or reject the assertions the research-ers formulated, based on student responses to questions posed earlier, about thepresence of student held alternative conceptions that connected ozone and globalwarming.

All interviews were held at the student's school in a private setting approxi-mately two weeks following the end of the STS global warming unit. Each interviewlasted about 20 to 30 minutes, was tape recorded and later transcribed. Theresearchers were not appraised of the student's overall academic ability leveluntil after all interviews were completed at each school.

During the early phase of data collection, some of the students to be inter-viewed posed an unexpected question to the researchers. When told (in the processof obtaining informed consent) that the interview would be on global warming,they appeared uncertain and asked 'Do you mean the greenhouse effect?' Theresearchers became concerned that elicitation of student understanding could behampered severely without some prior qualification of terminology. Accordingly,we began asking students, prior to the interview questions, which of the two termswere they accustomed to using or did their teacher use. The researchers followedup by stating that the student could think of the two terms as equivalent, but inthis interview the researcher would use the term global warming. The researchersbelieved this 'scientifically comprised' (global warming is not the same as thegreenhouse effect) qualification of terminology was critical for students to identifyadequately with the central topic of the interview.

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536 J. A. RYE ET AL.

Analysis of the dataA content and frequency analysis of specific interview question (table 2) responsesof a subset of eight interviewees was completed as a first look at the data, in anattempt to focus subsequent analysis. These interviewees represented equallymales and females, students of high and low overall academic ability, and instruc-tion from the four STS global warming units. The finding of a high prevalence ofalternative conceptions about connections between ozone layer depletion and thenature, cause, and resolution of global warming led to an in-depth examination ofall transcripts for the presence of such conceptions. Specifically, researcher asser-tions of the presence of such conceptions, based on single or multiple instances inthe transcript, were verified by studying the entire transcript for the presence ofresponses that would further validate or invalidate the assertions. Principles ofinductive and logical analyses (Patton 1990) were employed to a limited extentin order to label and combine into broader categories the emergent alternativeconceptions. A frequency analysis of certain responses to specific questions (e.g.the mention of 'ozone' prior to the introduction of this concept as part of question9 by the researcher) also was completed to be used in concert with the findings anddiscussion of the prevalence of alternative conceptions. (Fictitious names havebeen assigned in this paper to all students and teachers.)

Findings and discussion

Tammy: Yeah, I think it's basically, that everything works against the ozone andwhen 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 inthem. Like instead of buying hair spray with CFCS, you can buy some like ina pump or something.

Billy: CFCs cause destruction of the ozone layer to let the sun, the ultraviolet rays, getin and heat up the earth.

Evert: And all those oil wells [on fire in the Middle East] gave off tons and tons ofcarbon dioxide. Which made the ozone layer just come apart and that's wherethe biggest hole came from.

Sally: If [carbon dioxide] comes out of the exhaust. And as it goes up to the ozonepast the stratosphere. Then after it hits the ozone it like eats it up and then uvcome and hit earth.

These transcript excerpts are taken from interviews with several students andspeak to the principal findings of this study. They exemplify the five alternativeconceptions found to be held by the students in this study. These alternativeconceptions all connected ozone layer depletion and global warming in someway and were as follows:

ozone layer deletion is a major cause of global warming (Tammy) aerosol sprays contain CFCS and destroy the ozone layer (Candy) CFCS cause global warming exclusively through their role in destroying the

ozone layer (Billy) carbon dioxide destroys the ozone layer (Evert) carbon dioxide causes global warming exclusively by destroying the ozone

layer (Sally).

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Table 3 illustrates the prevalence of these alternative conceptions amongst all24 students interviewed and according to students' overall academic ability leveland gender. No statistically significant correlations (phi coefficients) were foundbetween overall academic ability level or gender and the degree to which any ofthese alternative conceptions were held. Additionally, Rye et al. (1994) did not findsignificant correlations (point biserial) between the degree to which students held aspecific scientific understanding about global warmingthe score derived byassessing their interview transcript against the expert concept map (figure 1)and the prevalence of these alternative conceptions. The authors readily acknowl-edge that these statistical findings as well as other correlations reported subse-quently are limited in that they are derived from a small volunteer sample(Roberts 1992).

The prevalence of these alternative conceptions did not appear to differ appre-ciably across three of the four STS global warming units. Students who were therecipients of instruction from one of the units gave little evidence of believing thatcarbon dioxide destroyed the ozone and did not appear to believe that the exclusiverole of CFCs in global warming was via ozone layer destruction. However, thisstudy was not designed to ferret out differences between students according tothe unit of instruction completed. The number (five to seven) of students inter-viewed (i.e. representing instruction) from each of the four units was too small todraw conclusions about any real differences that may have existed in the degree towhich these alternative conceptions were held.

Below we examine in some detail our findings relative to each of the fivealternative conceptions held by the students in this study. However, this separa-tion is somewhat artificial. The transcripts and cited excerpts illustrate that thesealternative conceptions are interwoven in students' cognitive structures and theidea that 'ozone layer depletion is a major cause of global warming' surfaces con-tinuously.

Table 3. Percentage of students providing evidence of alternative con-ceptions related to the nature, causation and resolution of GW.

Alternative Conceptions

Ozone depletion is major orpredominant cause of GWAerosol sprays contain CFCsand/or destroy the ozone layerCarbon dioxidea destroys theozone layerExclusive role of carbondioxidea in GW is bydestroying the ozone layerExclusive role of CFCs in GWis by destroying the ozonelayer

HighN=9

33

44

55

22

22

Student

MediumN=9

77

89

55

44

33

overall

LowN=6

50

18

33

33

18

academic ability level

MaleN=14

64

64

57

36

29

FemaleN=10

40

40

40

30

20

AllStudentsN=24

54

54

50

33

25aIn this instance, exhaust, smoke, and car pollution were also accepted as the equivalent.

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538 J. A. RYE ETAL.

Ozone layer depletion as major cause of global warmingSeventy-five per cent (n=18) of all students and the majority within each academicability level believed that ozone depletion and/or increased uv radiation wasinvolved in the causation of global warming. More importantly, 54% (n=13) ofall students gave evidence of believing that ozone layer depletion, and/or conse-quent increases in UV or the sun's rays, was a major or predominant cause of globalwarming. Often, students' supporting reasons were related to natural phenomena,e.g. the heat from the increased sunlight heats up the planet.

More than half the students began talking about ozone layer depletion and/oruv radiation in response to the advance organizer questions (table 2, questions 1and 2). The following transcript excerpts illustrate how three studentsJulie,Jerome and Sallyconnected ozone and global warming early in their interview.

Julie suggests that ozone depletion allows sunlight to penetrate the atmo-sphere, warming the earth.

Interviewer. Okay, is there anything else that comes to mind when you think aboutglobal 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 thecause of global warming

Interviewer: You say, 'When the sun comes in'. Could you tell me a little bit moreabout that?

Jerome: Like the rays would come through the ozone and it won't go back outthrough sometimes because of pollution and stuff... Like its [pollution]eating away the ozone and stuff.

Interviewer: What are the various causes of global warming?Jerome: Umm. Just the ozone pretty much.Interviewer: How is . . . the ozone a cause of global warming?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 weneed to work.

Interviewer: Well, are there any other causes that come to mind at all for globalwarming?

Jerome: Not much.

Sally had this to say, when asked about what ideas came to mind when she'thought about global warming':

Sally: Ah, the ozone 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 raysfrom the sun enter and hit earth

Interviewer: Umm, and how is that, how is that related to global warming through?Sally: Well, the uv, umm, rays hit earth and earth will get warmer. And that's

what causes global warming.

The researcher queries Sally again about the ozone hole and global warminglater in the interview:

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Interviewer: How is that [ozone] hole related to global warming?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 youbasically get global warming.

The study of Sally's entire transcript provides compelling evidence that shebelieves ozone layer depletion (and consequent increases in uv rays) is a major and,in her case, the predominant cause of global warming. This was also true for Julieand Jerome.

The questions placed at the end of the interview (table 2, questions 9 to 12)were for the purposes of further elucidating students' conceptions about connec-tions between global warming and ozone layer depletion. Most students whobelieved ozone layer depletion was a major cause of global warming had alreadyprovided substantial evidence of this alternative conception by the time thesequestions were introduced. Still, student responses were useful in confirmingthis and other researcher-held assertions. The transcript excerpts shown belowfor Charles, Evert and Barton illustrate these student responses to the generalquery made by the interviewer, 'When you think about ozone, do you also thinkabout global warming?'

Charles: Well, a little bit because CFCS destroy the ozone . . . UV rays are basicallywhat global warming is when they come in, you know... And it worriesme that they could come in faster and faster and then they could bounceoff faster and get hotter and hotter and hotter.

Evert: Well, yeah because the ozone is what, I think, is going to keep globalwarming out.

Interviewer: And why do you think about global warming when you think aboutozone?

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 global warm-ing causes ozone depletion. Candy believes the greenhouse effect causes ozonedepletion:

Candy: The greenhouse effect is when the gases and that are ruining, causingholes in the ozone which let off UV rays.

The idea that global warming or the greenhouse effect causes ozone layerdepletion may have been held by other students. Many of these students men-tioned that ozone layer depletion (and/or increased uv radiation) comes to mindwhen thinking about global warming, and carbon dioxide destroys the ozone layer.This construction also could be the result of a surface undertanding and inap-propriate logic regarding the role of CFCs in both global warming and ozone layerdepletion, e.g. if CFCs cause global warming and destroy the ozone layer, thenglobal warming destroys the ozone. Barton suggests that aerosol sprays containingCFCS play a central role in global warming mediated destruction of the ozone layer.

Barton: Global warming, ah, it burns holes in the ozone layer and it can do that byusing hair spray and stuff like that. Like aerosol sprays and stuff likethat.. . Hair spray has CFCS in it. And if you use enough of that it willburn a hole in the ozone layer.

This idea surfaced many times in his interview. The alternative conception thataerosol sprays contain CFCS and destroy the ozone layer is explored more fullybelow.

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Aerosol sprays contain CFCs

The idea that aerosol sprays contain CFCs and/or destroy the ozone layer was analternative conception found to be prevalent in 54% (n=13) of the students. On aglobal basis, aerosol sprays do account for about 15% of all CFC use (KurtisProductions 1993). However, the sale of aerosol cans containing CFCs has beenbanned in the United States (and Canada) since 1979 (University Corporationfor Atmospheric Research 1992). Hence, aerosol cans sold in the United Statesshould not contain CFCS. Still, student references to aerosol sprays were not con-textualized in any specific geographic locale:

Mason: Ah, well when you use hair spray. Anything that's in a canister like hairspray and cooking spray for your pans and stuff has CFCS so it, umm, willshoot out or compress air. And then it's CFC. And that stands for chloro-fluorocarbons and they eat away at the ozone.

The researchers do not believe students were speaking in global terms whendescribing aerosol sprays, although this could be debated. (Evidence to supportthis contention is presented later, as we refer to suggestions students make tocombat global warming.)

The idea that, in the United States, aerosol cans or hair spray contain CFCS andthereby destroy the ozone layer is a prevalent and perhaps tenacious alternativeconception (Kurtis Productions 1993). A return to Barton's interview reveals thegreat extent to which the researchers believe he holds this alternative conception:

Interviewer: What is an important thing you learned from the unit on global warm-ing?

Barton: The most important thing I learned is, how to prevent global warmingfrom happening by, like using filters and stuff like that. And using hairspray 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... Hair

spray... Urn, I imagine some deodorants would have CFCS in them.

The excerpts from the interview with Barton suggest that alternative concep-tions can result in misdirected citizenship actions towards issue resolution. Inresponse to the interview questions about the resolution of global warming, themajority of students who held the alternative conception that aerosols contain CFCsand destroy the ozone stated actions targeted at decreasing the use of aerosols.Examples of such actions can be found in the interview excerpts with Candy andBarton.

Some of the STS global warming units stated that aerosol use has been a factorin ozone layer depletion. Therefore, this alternative conception in some studentsmay have developed as a result of, or been reinforced by, instruction from theunits. This contention was supported by a comment made by one of the STSInstitute teacher-participants during a workshop that followed this study. Theteacher informed the researchers that she 'stood corrected' and had been teachingstudents that aerosols sold in the United States at the present time contained CFCS.However, this teacher was not one of the instructors of the students who partici-pated in this study.

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Singular role of CFCS in global warmingIn response to interview questions specifically targeting student understanding ofthe nature, cause and resolution of global warming (table 2, questions 3 to 8), 50%(n=12) of the students provided evidence of the scientifically accurate understand-ing that CFCs are a (potential) cause of global warming. However, approximatelyhalf of these students (n=6, 25% of all students) ignored CFCs' central mechanismas a heat trap in global warming (Mitchell 1989) and, in fact, held the alternativeconception that the exclusive role of CFCs in the causation of global warming wasthrough depleting the ozone layer. Several of the transcript excerpts presentedpreviously suggested that certain students may hold this alternative conceptionof the singular role of CFCS in the causation of global warming. As an example,further questioning of Julie on the role of CFCS in global warming did not reveal anunderstanding of CFCs' 'greenhouse gas' property, and provided further evidencethat her misconceptions of the mechanisms of CFCs in the causation of globalwarming was solely 'ozone layer depletion'.

Interviewer: Are they [CFCS] connected to global warming?Julie: Yes, I think. . . 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 wor-

ried about them and never thought about them. But now as soon as likeyou spray something it is in the air.

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.Students who held the alternative concepton that CFCS cause global warming

exclusively via ozone layer depletion also were likely to believe that carbon dioxide(or exhaust, smoke, or car pollution) causes global warming exclusively by destroy-ing the ozone layer. A significant correlation (phi coefficient of r =-41, p

542 J. A. RYE ETAL.

are common sources of carbon dioxide. When such instances were collapsed withexplicit references to carbon dioxide as a destroyer of ozone, collectively 50%(n=12) of the students were found to hold the alternative conception that carbondioxide (or exhaust, etc.) destroys the ozone layer. The authors do acknowledgethat some of the students who spoke of exhaust (etc.) as a destroyer of ozone mayhave been thinking about an ingredient in exhaust (etc.) other than or in additionto carbon dioxide. For example, one student stated that she thought car pollution'contains CFCS and things that help destroy the ozone layer'.

Some of the students holding the alternative conception that carbon dioxide(or exhaust, etc.) destroyed the ozone layer also provided a 'scientifically accep-table' (or close to it) mechanism of action of carbon dioxide in global warming.They noted that carbon dioxide traps heat in the lower atmosphere (Mitchell1989). Excerpts from the interview with Samuel serve to illustrate such students'thinking:

Interviewer: Any other causes [of global warming] 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 global warming?Samuel: They keep the heat in.

One-third of all students (table 3) gave evidence of believing that the exclusiverole of carbon dioxide (or exhaust, etc.) in the causation of global warming was viadestroying the ozone layer. Excerpts from the interview with Andrew provide anexample of this alternative conception:

Interviewer: Okay, carbon dioxide. Whatever you see as being the cause [of globalwarming], 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 theozone layer, it lets more sunlight in and then that makes it get warmer.That's what I think is causing it.

Interviewer: Are there other ways that carbon dioxide would be related to globalwarming?

Andrew: Umm. No, I don't think there is.

Some of the students may have held the alternative conception that carbondioxide (or exhaust, etc.) destroys the ozone layer because they perceived carbondioxide as being similar to CFCS in several ways: both CFCS and carbon dioxidecontain the word carbon; they are both greenhouse gases; and they are both cited ascomponents of pollution. In responding to the interview questions, several stu-dents lumped together various greenhouse gases as agents that deplete the ozonelayer and spoke collectively about carbons and pollution. One student put it thisway: 'It's sort of like the gases that trap the sun rays also eat the ozone layer away'.Other examples of this thinking can be found in excerpts shown previously fromthe interviews with Sally and Samuel, and in those that follow from the interviewswith Andrew and Amanda:

Andrew. How to, ah, use things that don't have as much, ah, damaging things toozone, like carbons and that.

Amanda: Umm, like cars and the pollution, like that they're sending out, youknow, from umm, when they're being run. And factories and thingslike that. How they're umm, deleting the ozone layer.

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Most (75%) of the students who believed carbon dioxide (or exhaust, etc.)destroys the ozone layer, and all of the students who believed this was the exclusiverole by which it caused global warming, also held the alternative conception thatozone layer depletion is a major cause of global warming. A significant correlation(phi coefficient of r = 0-65, p < 0-01) was found between students holding thelatter two alternative conceptions. These findings warrant further investigation.The STS global warming units emphasized that carbon dioxide could be a majorcause of global warming. Therefore, perhaps these students' logic was that, sincecarbon dioxide destroys the ozone layer, it follows that ozone layer depletion mustbe a major cause of global warming.

Few students provided evidence of a scientifically complete (relative to theexpert concept map presented in figure 1) understanding of the radiative mechan-ism of greenhouse gases in the causation of global warming. Students were morelikely to state that various gases (or pollutants or car exhaust) trapped uv or thesuns' rays, thereby causing global warming, as opposed to trapping or absorbinginfrared radiation given off by the earth. The former is an alternative conceptionrelative to the cause of global warming and may reflect an unclear understanding ofthe role of the different types of radiation. It also is apparently related to thesestudents' conceptions of the connections between global warming and ozone layerdepletion. In our study, even the students who gave evidence of a relatively soundunderstanding of the radiative mechanisms underlying global warming(greenhouse gases absorb infrared or long-wave radiation emitted by earth, thatoriginated from shorter wavelength radiation from the sun, thereby trapping heat)were likely to see the consequences of both global warming and ozone layer deple-tion as warming the earth. Mollie's thoughts, as verbalized in the interview, pro-vide an example of this conception:

Interviewer: Okay, when you think about ozone do you think about global warming?Mollie: Yeah. Because sometimes I d o . . . And it [earth] also gets like warmer

because of there's a hole in the ozone. Then the rays are going to come inat like a hotter temperature.

Interviewer: Okay. What is it about ozone that makes you think about global warm-ing?

Mollie: Like the, how the sun rays comes in and make the earth like warmer andlike hotter. That like happens in both, so that what makes it, I think.

To facilitate the focus and clarity of instruction (Wise and Okey 1983), tea-chers were advised to not include instruction on ozone in the STS global warmingunit. However, an inspection of these units suggested that three of the four tea-chers (of students who participated in this study) did address ozone layer depletionduring STS global warming instruction. This instruction may have played a role inthe development of or reinforcing the alternative conceptions (table 3) that sur-faced in this study. Post-instructional interviews with these four teachers didreveal that one teacher dealt with ozone previous to, and three dealt with ozonein their unit; and they believed some degree of confusion between global warmingand ozone layer might exist amongst students. The following are select responsesfrom the four teachers to the related interview question, 'Because we are going toask your students, or we have asked your students, about ozone, we need to knowhow you dealt with ozone'.

Sue: Good or bad ozone?... We talked about both and that was a hard thing forthem to understand.. . I used the diagram, two different diagrams, that I

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544 J. A. RYE ETAL.

had in the units to show them, ah, greenhouse effect, and what part theozone played as well.

Mort: And I hope they know the fact is that it's [ozone depletion is] not related toglobal warming. I don't know if all of them will know that.

Jack: As a separate problem that really had no connection with global warming.... There was one other problem I had. And it was separating in theirminds, ah, the problem with ozone depletion and the problem with globalwarming... And then there were other articles [that the librarian puttogether] that actually drew a connection and it was the first time I hadheard that the fact that the ozone is being depleted also is a negative feed-back for global warming. Is that right? . .. That.. . confused me.

Mary: I don't feel we did a good job at that.. . and I could not avoid the ozoneissue so I'm sure, I don't know what your questions are for the students, butthey might have some confusion... we just said try to keep them separate.

Implications and recommendations

The findings reported above suggest that middle school students may hold specificalternative conceptions that limit and confound their understanding of the nature,causation and resolution of global warming. The principal alternative conceptions(table 3) discussed also surfaced in a recent study in Greece of primary students'understandings of ozone layer depletion and the greenhouse effect (Christidou,personal communication, 22 April 1994). One limitation of the study reported herewas that pre-instructional interviews on global warming were not conducted withthe students. Such data would have proven useful in determining alternative con-ceptions that appear to develop in students as a result of formal instruction, andwhat pre-instructional understandings appear to interact with formal instructionto yield those unintended learning outcomes (Wandersee et al. 1994). There is aneed for studies that investigate in what ways students' understandings aboutglobal warming change as a result of formal instruction.

The studies (Boyes and Stanisstreet 1993, Christidou 1994, Dorough et al.1995, Francis et al. 1993, Plunkett and Skamp 1994) reviewed earlier on students'understandings related to global atmospheric change do suggest characteristicsabout the pre-instructional understandings of the students in this study. Mostimportant is the idea that students likely entered instruction with a greater aware-ness of the ozone layer than of global warming, and that some students may havebegun instruction with the alternative conception that the 'hole' in the ozone layercauses global warming. If held prior to instruction, this alternative conception maybe tenacious, given that over half the students in this (post-instructional) studybelieved that ozone layer depletion was a major cause of global warming. In globalwarming curricula targeting students of grades 7 to 10, Hocking et al. (1990: 12)suggests 'the hole in the ozone layer as a cause of the greenhouse effect' is acommon 'misconception', and so, teachers should explain to students that theadditional uv light (consequent to ozone depletion) does not 'heat up' the earth.

As suggested by the transcript excerpts from interviews with the teachers ofthe students in this study, it appears difficult to follow a directive to not includecontent on ozone while teaching about global warming. Initial exposure to theconcept of global warming may evoke thoughts in students about the ozonelayer. The pre-instructional interviews on global warming conducted byDorough et al. (1995) revealed that 'ozone layer' came to mind in more than

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one-third of the students, as they 'thought about global warming'. Francis et al.(1993) also reported that students often introduced, during interviews about thegreenhouse effect, the concept of the ozone layer. There is a need for studies thatcompare students' conceptions surrounding instructional units that integrate orseparate the issues of global warming and ozone layer depletion. Given that, to ourknowledge, such studies have not been reported, our current position is that adirective to avoid the topic of ozone while teaching about global warming isimpractical and may not be conducive to helping students restructure relatedalternative conceptions. Several reasons follow to support these contentions.

Ozone is one of the greenhouse gases and is increasing in our troposphere(Fishman 1991), primarily due to photochemical reactions involving pollutantsfrom the incomplete combustion of fossil fuels in motorized vehicles (NationalResearch Council 1991, Phillips and Pickering 1991). Although the magnitudeof its contribution to tropospheric warming generally is noted to be considerablyless than that of carbon dioxide and cannot at present be quantified as well as someof the other greenhouse gases (IPCC 1992), the greenhouse nature of this gasremains a scientific fact and one that may surface in literature to which studentsand 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 and Marcus 1994: 19) and, related to global change, an issuelikely to receive increasing future attention. Yet, given media coverage, studentslikely know 'ozone' prior to global warming instruction as a layer high in the skythat protects us from harmful (uv) rays (Hanif 1995). Thus, if content on ozonelayer depletion is ignored, the potential exists for students to confuse these twoinstances of ozone (tropospheric and stratospheric), their roles, as well as the typesof radiation (infrared and ultraviolet) involved, as they pertain to the causation ofglobal warming.

Global warming and stratospheric ozone depletion both have significance at aglobal level, speak to atmospheric change, and are coupled through the involve-ment of CFCs in both problems. Thus, they may be addressed concurrently:Pomerance (1989) details some of the historical events behind and the reasonsfor this. Furthermore, ozone layer depletion is considered an important factor inglobal climate change, due to its potential to affect the radiative balance of ouratmosphere (IPCC 1992). Papers targeting the scientific community (Ashmore et al.1991, Fishman 1991, Lacis et al. 1990, Smith et al. 1992, Worrest and Grant1989), as well as school teachers and their students (Monastersky 1992, Phillips1990), have connected these issues by describing various mechanisms throughwhich ozone layer depletion may impact global warming. It is important to notethat some of these papers have postulated that ozone layer depletion may contri-bute a positive feedback to global warming. However, in our study, the underlyingmechanisms described by students as to how ozone layer depletion/increased uvradiation may contribute a positive feedback to (i.e. cause) global warminggenerally were not those set forth by the scientific community. Often, students'supporting reasons were related to natural phenomena, e.g. the heat from theincreased sunlight warms up the planet.

Given the 1992 scientific assessment update of the Intergovernmental Panelon Climate Change (Houghton et al. 1992), the connection between ozone layerdepletion and global warming may receive increased attention. This update reportsthat our understanding of ozone layer depletion relative to global warming has

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advanced significantly: ozone layer depletion over the past decade has contributeda negative feedback to global warming, possibly offsetting the greenhouse effectcontribution of CFCS over that same time period. Such evidence speaks to theimportance of revealing and helping students to restructure the alternative con-ception frequently encountered in this study that ozone layer depletion causesglobal warming.

By telling students that they could think of the greenhouse effect and globalwarming equivalently, the researchers may have limited the findings of this studyrelative to disclosing students' mental constructs of the greenhouse effect and howit relates to global warming. That is, student thinking may have been constrainedand their use of the term 'greenhouse effect' discouraged, in response to the sub-sequent interview questions. Indeed, only 38% of the students mentioned thegreenhouse effect and generally had little to say about it. Alternatively, our rela-tively sparse findings may have been largely a function of the questions set forth inthe interview protocol in that none of the planned questions in the protocol askedabout the greenhouse effect. We did not want to 'provide' this concept and wereinterested in ascertaining if students would bring it up to explain the causation ofglobal warming (figure 1). Actually, none of them specified that global warmingwas caused by the greenhouse effect or any intensification thereof. However, someof these students did connect the greenhouse effect with changes in (atmospheric)ozone, as evidenced in the transcript excerpts of Candy and Tammy:

Candy: The greenhouse effect is when the gases and that are ruining, causing holesin the ozone which let off uv rays.

Tammy: If the ozone wouldn't be there, the greenhouse effect like could happenalready.

The 'greenhouse effect' is part of the public vocabulary (Ennis and Marcus1994, Pomerance 1989) and many students likely have heard the term prior torelated formal instruction (Hocking et al. 1990). Understanding of the greenhouseeffect may be limited to the idea that it is a problem, and is synonymous withglobal warming, 'arriving' as a result of recent human influence (Shaw and Stroup1991, Pomerance 1989, Schwartz et al. 1994). The idea that the greenhouse effectis 'held off by the ozone (layer) or that it is equivalent in meaning with globalwarming are alternative conceptions. The greenhouse effect is a concept label for anatural phenomenon whereby specific (greenhouse) gases trap heat (as infraredradiation) in earth's lower atmosphere. It is a necessity to sustain life (Graedeland Crutzen 1989, Mitchell 1989, University Corporation for AtmosphericResearch 1991). Global warming is a concept label that describes a global climatechange and (potentially) is caused by the enhanced (or strengthened) greenhouseeffect or greenhouse warming, which in turn is due to anthropogenically-inducedincreases in greenhouse gases (Graedel and Crutzen 1989, Wigley and Barnett1990, Schneider 1989). According to Schwartz et al. (1994: 81), the question asgenerally posed, about whether or not the greenhouse effect has begun 'impliesalterations in climate that are a consequence of human activity'. Some educatorscould argue that making the distinction between the greenhouse effect and globalwarming is a scientific technicality and is too sophisticated for middle schoolstudents who are developing an initial understanding of global warming. Indeed,the expert concept map (figure 1), which reflects content common to the STS globalwarming units, explicates the proposition 'global warming is caused by the green-

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house effect'. Nonetheless, qualifying the greenhouse effect as being enhanced,intensified, or humanly induced, as related to the causation of global warming,would facilitate a more complete and scientifically accurate understanding amongststudents of both concepts and their interrelationship.

We speculate that concepts such as ozone hole, uv rays, CFCs, and greenhouseeffect may be 'loose' in many students' cognitive structures and connected inap-propriately to make sense of formal instruction on global warming. Furthermore,there is real potential for student confusion and construction of alternative con-ceptions when they are confronted with multiple phenomena that are explainedthrough some of the same concepts. Transcript excerpts from the interview withCandy 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 andthings. Or it's like greenhouse. Well, I kind of get, I kind of mix themtogether cause that's what you think about them. They're kind of, peoplelike 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'retwo different subjects and then I get confused. . . cause I know green-house effect is ozone depletion like . . . Because both things [global warm-ing 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 iswhich.

It follows that, in the design and delivery of global warming instruction, con-cepts and propositions embedded in our findings of alternative conceptions needgreater attention. Perhaps most important is an emphasis on clarifying the causesof and differences between ozone layer depletion and global warming and thatneither the ozone 'hole' nor consequent increases in uv rays are established orprincipal causes of global warming. Indeed, as reported earlier, current scientificthinking is that ozone layer depletion provides a negative feedback to global warm-ing (Houghton et al. 1992, Mackenzie and Mackenzie 1995). Posed early ininstruction, the idea that the 'hole' in the ozone layer leads to cooling as opposedto warming can present a real discrepancy for many students, effecting in them astate of cognitive disequilibrium (Driver et al. 1985), and thereby piquing theirinterest for subsequent study. In addition, our findings suggest that such clarifica-tion should pay particular attention to the following:

the differences between incoming (solar) and outgoing (as emitted by earth)radiation;

the absorption by greenhouse gases of the latter (but not the former) as themechanism that underlies the greenhouse effect;

enhancement of the greenhouse effect due to atmospheric increases in green-house gases as the cause of global warming;

that CFCS, but not carbon dioxide, have two undesirable effects on our atmo-sphere (i.e., action as a greenhouse gas and action in the destruction of strato-spheric ozone), but that each of these effects cause a different environmental

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problem (enhanced greenhouse effect and ozone layer depletion, respec-tively);

household aerosol spray cans in the United States do not contain CFCS

The authors are aware that the above points can be embellished with manydetails, and that the science that underlies global warming and ozone layer deple-tion is complex and still unfolding (Houghton et al. 1992, Mackenzie andMackenzie 1995, Thiemens et al. 1995). As examples: the greenhouse gas methanealso may play a role in ozone layer depletion (Thompson et al. 1992, Worrest et al.1989) and certain aerosol sprays used for medical purposes in the United Statesstill contain CFCS (Kurtis Productions 1993). While it is important for scienceteachers to keep current on global warming and ozone layer depletion, and reflectmajor scientific thinking and consensus in related classroom instruction, webelieve that efforts on the part of teachers to present 'all the details' may becounterproductive in helping students to initially construct a clear understandingof global warming. More important is for teachers to help students realize that ourunderstandings about such complex phenomena as global warming, includinginterrelationships with ozone layer depletion, are somewhat tenuous and maychange as scientific studies reveal new data.

Additionally, we recommend that classroom instruction on global warming bepreceded by efforts to disclose student understandings and the use of conceptualchange instructional strategies (Smith et al. 1993, Wandersee et al. 1994) to facil-itate the restructuring of alternative conceptions. Accordingly, aspects of theGenerative Learning Model (Osborne and Freyberg 1985) and concept mapping(Novak and Gowin 1984) have considerable application in curriculum design andinstruction on global warming.

Note

The STS curriculum on global atmospheric change that emanated from the NSFfunded Teacher Enhancement Project in STS Education is available at the follow-ing World Wide Web site: .

Acknowledgements

The authors thank the students and their science teachers who participated in theinterviews. Also, we thank Ms. Donna Dorough for the assistance she provided incompleting this study.

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Concepções Alternativas Sobre o Efeito Estufa Por Estudantes

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