a decision-analytic framework for impact assessment

8/12/2019 A Decision-Analytic Framework for Impact Assessment

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L C A M e t h o d o lo g y I m p a c t A s s e s s m e n t

LC MethodologyA Decision A nalytic Fra m ew ork for Imp act AssessmentP a r t 2 : M i d p o i n t s , E n d p o i n t s , a n d C r i t e r i a f o r M e t h o d D e v e l o p m e n tE d g a r G . H e r t w i c h 1 a n d J a m e s K . H a m m i t t 2i Industrial Ecology Program and Institute for Product Design, Norwegian University of Science and Technology, 7491 Trondheim, No rwa y2 Center for Risk Analysis, Ha rvard School of Public Health, Boston, MA , USACorresponding author: Edgar G. Hertwich; e-maih [email protected]

D OI : h . t t D : fl dx do i . o rg / 10 . 1065 / LC A2001 . 07 . 058Abstract In the first part of this paper, we showed how life-cycle impact assessment can be described as an exercise in deci-sion analysis. We developed a structure for how to decide onthe relative importance o f different environmental stressors. Inthis second part, we offer criteria fo r the grouping o f stressorsinto impact categories and for the development of impact indi-cators. Facts to be included in a characterization method shouldbe selected according to their relevance and combined follow-ing established scientific models. Facts should be included onlyif they are informative, that is, if sufficient and sufficiently cer-tain info rmation is available for all stressors that should be evalu-ated by this method. Abstract, constructed indicators at themidpoint level are better suited to compare similar impactsthan indicators reflecting observable environmental endpointsif there is a large uncertainty about the effects on observableendpoints. W e argue tha t midpoint m odeling should be retained.The additional evidence introduced by endpoint methods shouldbe used to support judgments about facts needed to evaluatethe importance of different impact categories (or means objec-tives) in the means-ends objectives network.Keywords : Acidification potential; dam age functions; environ-mental themes; integrated assessment of climate change; ISO14042; life-cycle m pact assessment; multicriteria decision analy-sis; weight o f evidence

I n t r o duc t i o nLife -cyc le imp ac t a ssessment requ i res the comp ara t ive eva lu -a t i o n a n d a g g r e g a t i o n o f t h e v a r i o u s e m i s s i o n s , r e so u r c e s ,a n d o t h e r d i s t u r b a n c e s s u c h a s l a n d u s e a n d n o i s e , c o n n e c t e dt o p r o d u c t i o n , u s e , a n d d i s p o s a l o f a p r o d u c t . A n a g g r e g a -t i o n o f t h e s e s t r e s s o r s i n v a r i a b l y c o n t a i n s a p p l e s - a n d - o r -a n g e s c o m p a r i s o n s ( H o l d r e n e t a l . 1 9 8 0 ) . S t r e s s o r s c a u s eu n l i k e e f f e c ts t o d i f f e r e n t p e o p l e o r e c o s y s t e m s a c c o r d i n g t od i f f e r e n t m e c h a n i s m s o f a c t io n a n d a t d i f f e re n t ti m e s . E v e ni f t h e m e c h a n i s m s o f a c t i o n a r e t h e s a m e , a s f o r g r e e n h o u s eg a s e s , t h e i r d y n a m i c b e h a v i o r a n d t h e r e f o r e t i m e h o r i z o nd i f fe r s ( H e r t w i c h e t a l . 2 0 0 0 ) . T h e d e t e r m i n a t i o n o f t h e c o m -p a r a t i v e d e t r i m e n t o f o n e e n v i r o n m e n t a l i n s u l t r e la t i v e t oa n o t h e r i s h e n c e n o t p r i m a r i l y a q u e s t i o n o f m e a s u r e m e n t ,i t i s o n e o f j u d g m e n t . T h e d e c i s i o n o f h o w b a d o n e i n s u l t i sc o m p a r e d t o o t h e r s c e r t a i n l y d e p e n d s o n t h e s c i e n t i f i c d e -s c r i p t i o n o f t h e r e s u lt i n g d a m a g e , b u t i t a l so d e p e n d s o n o u r* Part 1 LCA and De cis ion Analysis, in: Int J LCA 6 (1) 5-12 (2001)

c o n c e r n s , o u r a t t it u d e s t o w a r d s u n c e r t a i n t y , a n d o n w h e t h e rd a m a g e s a r e b o r n e b y t h o s e w h o o b t a i n t h e b e n e f i ts .In the f ir s t pa r t o f th is a r t ic le , we have d i scussed how LC Ai m p a c t a s s e s s m e n t c a n b e d e s c r ib e d a n d s t r u c t u re d a s a p r o b -lem in deci s ion ana lys is (Her tw ich an d H am mi t t 20 01) . 1 Ca t -e g o r y i n d i c at o r s i n L C A , s u c h a s t h e g l o b a l w a r m i n g p o t e n -t i al , a re ca l l ed a t t r ibu tes in dec i s ion ana lys i s . The p reven t iono r m i n i m i z a t io n o f t h e c o r r e s p o n d i n g i m p a c t s , e . g. t e m p e r a -ture increase and sea-level r ise , is the related object ive. Ourinves t iga t ion o f the use o f dec i s ion ana lys i s to s t ruc tu re andjus t ify impac t a ssessment i s mo t iva ted by the recogn i t ion th a tLC A can be de fended as a r a t iona l too l on ly th ro ugh i ts use indec i s ion making , and no t a s a sc ien t i f i c measurement dev ice .I t i s des i rab le to do LCA because i t i s the on ly dec i s ion sup-por t too l tha t a l lows fo r a compreh ens ive inc lus ion o f env i -r o n m e n t a l i m p a c t s t h r o u g h o u t t h e p r o d u c t l if e as w e ll a s t h esys temat ic compar i son o f r e leases a t d i f fe ren t po in t s and tod i f fe ren t med ia (Her twich e t a l . 2000) . The deve lopment o fgener ic impac t a ssessment methods and a genera l ly ava i lab lepub l ic se t o f ind ica to r s i s jus t i fi ed because i t p resen t s a c lea rimpro vem ent over the cur ren t s i tua t ion where assessments a red i f f i cu lt o r imposs ib le . G iven the an a tom y of the dec i s ionm a k i n g p r o b l e m i n L C A , c h a r a c t e r i z e d b y t h e n e c e s s i t y o fva lue judgments and the need fo r sc ience to desc r ibe the re l -evan t f ac t s , we h ave de r ived c r i t e r ia fo r ob jec t iv i ty wh ich im -pac t a ssessment me thods sh ou ld sa t i s fy (Her twich e t a l. 2000) .In the second p a r t o f th i s a r ti c le , we inves t iga te the i s sue o fm e t h o d c h o i c e i n m o r e d e r a i l. W e a r e s p e c i f i c al l y in t e r e s t edi n h o w d e c i s i o n a n a l y s i s c a n h e l p u s d i s c r i m i n a t e a m o n gc o m p e t i n g m e t h o d s . T h e r e i s a w i d e r a n g e o f c o m p e t i n gm e t h o d s b o t h i n t e r m s o f t h e o v e r a l l a s s e s s m e n t a p p r o a c ha n d f o r s i n g l e i m p a c t c a t e g o r i e s ( P e n n i n g t o n e t a l . 2 0 0 0 ) .W e d i s t in g u i s h m e t h o d s t h a t f o l l o w th e env i ronmen t lthemes a p p r o a c h f r o m t h o s e b a s e d o n a d m ge funct iona p p r o a c h , z T h e environment l themes a p p r o a c h w a s d e f i n e d1A similar approach has also been taken by Sepp&l& (1999).2A recent UNEP workshop (Bare et al. 2000b) f ramed the discussion as'midpoint' vs. 'endpoint' . Since there is no agreement among the pa rt ic i-pants as to which m ethods are midpoint or endpoint , we do not adopt histerminology. According to the pre-workshop m aterial for the UNE P work-shop (Bare et al. 2000b), endpoint modeling refers to assessment de-scribing observable environmental endpoints, and midpoint modeling isassessment that stops short of describing observable endpoints. In theterms introduced in pa rt 1, endpoint indicators are natural at t r ibutes a tthe end of the cause-consequence chain, such as years of l i fe ost , whereasmidpoint indicators are constructed at t r ibutes located somewhere alongthe cause-consequence chain, such as the global warming potent ial.

Int J LCA 6 (5) 265 - 272 (2001)9 eco me d publishers, [3-86899 Landsberg, Germany an d Ft. Worth/TX, USA ~ Tokyo, Japan , , Mumbai, India ~ Seoul, Korea2 6 5


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Impact Assessment LCA MethodologySO~ NO~ HCI s t r e s s o r

H2SO4 HNO3 AttributeAcid precipitation i n s u l t

~ Means-Acidification Acidification endsof lakes of soils s t r e s s objective/ / networkFish death Forest die-back c o n s e q u e n c e

Recrea/~;onalX \ educedBiodiversity timb er arvest v l u e l o s tlossFig. 1 : S t r u c t u r in g o f o b j e c t i v e s a n d s p e c i f ic a t i o n o f a t t r i b u t e s i n l i fe cycleimpact assessment: S e v e r a l i m p a c t c h a i n s c a n be grouped t o g e t h e rbecause there is a common mechanism of ac t ion go ing from the insu l t tothe value lost.The com mon ly used attr ibute for the acidification c a t e g o r y -[ H l o a d i n g o r S O 2 e q u i v a l e n t s - d e s c r i b e s a n i n su lt ; the remainder of thec a u s a l chain is then le f t to be e v a l u a t e d b y v a l u a t i o n . I t c a n be descr ibedb y a means-ends ob jec t ives n e t w o r kb y th e p ro m in en t C M L -g u id e (H e i ju n g s e t a l. 1 9 9 2 ) . I t w asa d o p t e d b y t h e S o c i e ty o f E n v i r o n m e n t a l T o x i c o l o gy a n dC h em is t ry , S E T A C (F av a e t a l. 1 9 9 3 ) an d in IS O 1 4 0 4 2 ( IS O2 0 0 0 ) . S im i l a r ap p ro ach es h av e b een u sed b e fo re , e . g . i n t h eas ses sm en t o f en e rg y t ech n o lo g ies (H o ld re n e t a l. 1 9 8 0 ) . I na f i r s t s t ep , c l a s s i f i ca t i o n , s t r e s so r s a r e g ro u p ed in to sep a -r a t e im p ac t ca t eg o r i e s su ch a s g lo b a l w arm in g o r ac id i fi -cat ion (F ig . 1 ) . In a second s tep , character izat ion , the re la-t i v e co n t r i b u t io n o f s t r e s so rs t o each ca t eg o ry i s ev a lu a t ed .In a t h i rd s t ep , v a lu a t i o n o r w e ig h t in g , t h e im p o r t an ce o fd i f f e r en t im p ac t s i s ev a lu a t ed . A l t e rn a t i v e ly o r a s a p rep a ra -t i o n fo r w e ig h t in g , t h e ca t eg o ry i n d i ca to r s can b e n o rm a l -i zed b y d iv id in g i t b y t h e ch a rac t e r i zed en v i ro n m en ta l s t r e s -so r s i n a co u n t ry , an d /o r g ro u p ed acco rd in g t o im p o r t an ce(F in n v ed en e t a l. 2 0 0 1 ) . T h e ca t e g o ry i n d i ca to r s w ere ch o -sen a t t h e l o w es t l eve l a t w h ich a co m m o n a l i t y b e tw een th es t r e s so r s i n each ca t eg o ry can b e e s t ab l i sh ed , e . g. t h e i n f r a -r ed ab s o rp t io n cap ac i ty o f g r een h o u s e g ases o r t h e p o t en t i a lt o d o n a t e H * io n s fo r ac id i c co m p o u n d s (F ig . 1 ).Damage unction modelingg o es b ack to t h e eco n o m ic ev a lu -a t i o n o f e n v i r o n m e n t a l d a m a g e s a n d , t o o u r k n o w l e d g e , w a sf i r s t i n t ro d u ced to L C A th ro u g h th e E n v i ro n m en ta l P r io r i t y

System, EPS (S teen and Ryd ing 1991) . I t requ ires an assess-m en t o f t h e w h o le cau se -e f f ec t ch a in d esc r ib ed i n t h e f i r stp a r t ( H e r t w i c h a n d H a m m i t t 2 0 01 , F i g . 1) . D a m a g e f u n c-t ion methods, such as EPS (S teen 1999 an d th e E co - In d i ca -to r 99 ( G o e d k o o p a n d S p r i e n s m a 1999 , d o n o t fo l l o w th ee n v i r o n m e n t a l t h e m e s a p p r o a c h ; t h e y a t t e m p t t o p r e d i c td a m a g e a n d t h e n a g g r e g a t e p re d i c t e d d a m a g e s i n t e r m s o fan i n d i ca to r t h a t a l r ead y in c lu d es ex p l i c i t v a lu a t i o n .T h e d ec i s io n -an a ly t i c s t ru c tu re d esc r ib ed i n t h e f i r s t p a r t( H e r t w i c h a n d H a m m i t t 2 0 0 1 ), d i s ti n g u is h i ng b e t w e e n a t -t r i b u t e s ( ca t eg o ry i n d i ca to r s ) an d th e t r ad e - o f f o f o b j ec t iv es(w e ig h t in g ) , co r r e sp o n d s t o t h e en v i ro n m en ta l t h em es ap -p ro ach . T ab le I co m p ares t h e t e rm in o lo g y u sed in o u r d ec i-s i o n - a n a l y t i c f r a m e w o r k w i t h t h a t o f L C A i m p a c t a s s e s s -m en t . W e w i l l re f i n e th i s s t ru c tu re fu r th e r t h ro u g h th e i n t ro -d u c t io n o f c r i t e r i a fo r w h a t w e ca l l t h e co n s t ru c t i o n o f a t -t r i b u t e s . W e w i ll f i rs t ad d res s t h e g ro u p in g o f im p ac t s i n to al im i t ed n u m b er o f ca t eg o r i e s . T h en w e w i l l f o cu s o n t h e d e -v e lo p m en t o f ca t eg o ry i n d i ca to r s . I n t h e l a s t p a r t , w e w i l lad d res s t h e cu r r en t m id p o in t v s . en d p o in t d eb a t e an d d i s -c u s s th e s t r e n g t h s a n d w e a k n e s s e s o f t h e e n v i r o n m e n t a lt h e m e s a n d d a m a g e f u n c t io n a p p r o a c h e s .1 E s t a b l i s h m e n t o f I m p a c t C a t e g o r i e sF o l lo w i n g t he e n v i r o n m e n t a l t h e m e s a p p r o a c h , U d o d e H a e s(1 9 9 6 ) r eco m m e n d ed a l i s t o f 1 4 im p ac t ca t eg o r i e s , i n c lud -in g l an d u se , o zo n e d ep l e t i o n , eco sy s t em to x i c i t y , an d r ad i a -t i o n . S u ch g ro u p in g o f im p ac t ch a in s i n to im p ac t ca t eg o r i e sis a mat ter o f analy t ical conven ience and heur is t ic necess i ty .T h e re a r e t o o m an y s t r e s so r s - each o f w h ich h as m u l t i p l eim p a c t ch a in s an d a f f ec t s d i f f e r en t en d p o in t s - t o an a ly zeeach an d ev e ry o n e o f t h ese ch a in s . T h e l im i t a t i o n s o f h u -m a n j u d g m e n t a r e w e l l d o c u m e n t e d a n d s u g g e s t t h a t t h en u m b e r o f f a c t o r s t h a t w e c a n c o n s i d e r a t a n y o n e t i m e i sv e ry l im i ted (K le in d o r fe r e t a l. 1 9 9 3 ) . H en ce w e a re t ry in gto f i n d co m m o n a t t r i b u t e s an d o b j ec t i v es t h a t a l l o w u s t og r o u p i m p a c t s .T h e g ro u p in g o f cau sa l ch a in s i n to im p ac t ca t eg o r i e s i s b asedo n s im i l a r i t i e s am o n g th ese ch a in s . T h e u l t im a te r eq u i r e -m e n t fo r t h e s t r e s so r s i n an im p a c t ca t eg o ry i s t h a t t h ey a l ln e e d to f i t t h e s a m e c h a r a c te r i z a t io n m e t h o d . T h e e x a m p l ein F ig . 1 i l lu s t ra tes the causal chain o f acid i f icat ion . In th iscase , th e im p ac t ca t eg o ry i s s e lec t ed b ecau se t h e sam e m ech a-

Table 1: Re la t ionsh ip between the t e r m i n o l o g y s u g g e s t e d b y d e c i s i o n a n a l y s i s and traditional LCA termino logy . Mod i f i ed f rom U d o d e H a e s a n d L i n d e i je r ( 2 0 01 )T e r m s u s e d i n d e c i s i o n a n a l y s i s C o r r e s p o n d i n g te r m s u s e d i n L C I A

attr ibutemeans-ends objective networkfundamental objectives networkstressorinsultstressconsequencevalue loststructuring the assessmentconstructing attr ibutestrade off am ong objectives valuation)

c a t e g o r y indicatorr e l a t i o n s h i p o f c a t e g o r y i n d i c a t o r s to endpointsr e l a t i o n s h i p o f e n d p o i n t s t o safeguard subjectse n v i r o n m e n t a l i n t e r v e n t i o nmidpointmidpointe n d p o i n t( d a m a g e )c a t e g o r i z a t i o nd e v e l o p m e n t o f characterization methodsweighting of category indicators

66 In t J LCA 6 (5) 2001


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LC Me thodolog y Impa ct ssessment

n i s m o f a c t i o n l e a d s f r o m t h e i n s u l t o f a c id p r e c i p i t a t i o n t ov a r i o u s c o n s e q u e n c e s , i n d e p e n d e n t o f t h e s t re s s o r t h a t c a u s esa c i d p r e c i p i t a t i o n .T h e f o l l o w i n g c r i t e ri a p r o v i d e g u i d a n c e f o r t h e g r o u p i n g o fi m p a c t c h a i n s i n t o a s i n g l e i m p a c t c a t e g o r y :1 . T h e i m p a c t c h a i n s g r o u p e d i n t o o n e c a t e g o r y s h o u l d b e

s i m i l a r e n o u g h s o th a t t h e y c a n b e d e s c r i b e d b y th e s a m ep i e c e s o f i n f o r m a t i o n . H e n c e , a c o n s t r u c t e d a t t r i b u t ec o m b i n i n g i n d i v i d u a l p i e ce s o f i n f o r m a t i o n s h o u l d a p -p r o p r i a t e l y r e f l e c t t h e h a z a r d o f a s t r e ss o r a t a g i v e n d e p t h- c o m p a r e d t o o t h e r s t r e s s o r s in th e s a m e c a t eg o r y . T h eg r o u p i n g o f i m p a c t s m a y b e j u s t if i e d in t e r m s o f a s im i -l a r m e c h a n i s m o f ac t i o n , a si m i l a r e n d p o i n t , o r t h e s a m et o o l s b y w h i c h w e u n d e r s t a n d a n d a n a l y z e th e im p a c t sg r o u p e d i n a c a t e g o r y .

2 . T h e i m p a c t c a te g o r y sh o u l d c a p t u r e th e m o s t i m p o r t a n tc o n t r i b u t i o n s o f a c e r t a in s t r e s s o r t o t h e e n d p o i n t v a l u el o s t) t h a t t h e c a t e g o r y i s m e a n t t o c o v e r . F o r e x a m p l e , i fw e j u d g e t h e d i r e c t e f f e c t o f S O 2 o n t r e e s t o b e s i g n i f i -c a n t c o m p a r e d t o t h e a c i d i f ic a t io n c a u s e d b y s u lf u r ic a c i dt h e n w e n e e d t o f i n d a w a y t o i n c l u d e t h i s e f f e c t . T h i sm a y e i t h e r b e i n a s e p a r a t e i m p a c t c a t e g o r y e .g . , p h y t o -t o x i c i t y ) o r t h r o u g h a c h a n g e o f t h e p r e se n t c a t e g o r y .

T h e f i rs t c r it e r i o n i s d i c t a t e d b y t h e r e q u i r e m e n t o f te c h n i -c a l v a l id i t y . I f t h e s a m e p i e c e s o f i n f o r m a t i o n h a v e a d i f f e r -e n t m e a n i n g f o r d i f f e re n t i m p a c t s c h a i n s i .e ., i f d i f f e r e n tm o d e l s n e e d t o b e a p p l i e d c o n t a i n i n g t h e s a m e p a r a m e t e r s )t h e n t h e e q u i v a l e n t t r e a t m e n t o f t h e s e p i e c es o f i n f o r m a t i o ni s i n c o r r e c t . T h e s e c o n d c r i t e r i o n a r i s e s f r o m t h e d e s i r e t ob e c o m p r e h e n s i v e . I f t h e m o s t i m p o r t a n t i m p a c t c h a in s a r en o t c o v e r e d b y t h e a s s e s s m e n t , t h e a s s e s s m e n t w i l l n o t a p -p r o p r i a t e l y r e f le c t th e i s s u e o f c o n c e r n a n d h e n c e w i l l p r o -d u c e m i s l e a d i n g r e s u l t s .1.1 Gro uping of toxic impactsT o e a r l y L C A p r a c t i t i o n e r s i t m a y h a v e s e e m e d t o b e a no b v i o u s c h o i c e t o g r o u p a l l t o x i c e f f e ct s i n h u m a n s i n t o as i n g l e c a t e g o r y . T h i s c h o i c e i s n o t o b v i o u s t o a r i s k a s s e s s o r ,m u c h l e s s t o a t o x i c o l o g i s t . T o x i c c h e m i c a l s a c t a c c o r d i n gt o d i f f e re n t m e c h a n i s m s o f a c t io n i n d i f fe r e n t o r g a n s a n dr e s u l t i n d i f f e r e n t e f f e c t s . T o x i c c h e m i c a l s m a y i m p a c t t h ep o r t a l o f e n t r y l u n g , in t e s ti n e , e tc . ) a n d t h e n b e r a p i d l yd e t o x i f i e d , o r t h e y m a y b e r e l a t i v e l y h a r m l e s s a t t h e e n t r ya n d r e q u i r e m e t a b o l i c a c t i v a t i o n i n t h e l i v e r o r t h e k i d n e y .T o x i c o l o g i s t s d i s t in g u i s h b e t w e e n l o c a l e f f ec t s t h a t f o c u s o na s in g l e o r g a n a n d s y s t e m i c e ff e c ts in t h e w h o l e b o d y . T h e yd i s t in g u i s h a m o n g a c u t e , r e p e a t ed , a n d c h r o n i c e x p o s u r e a n da m o n g p e r s i s t e n t , t r a n s i e n t , c u m u l a t i v e , a n d l a t e n t e f f e c t s .C h e m i c a l s m a y c a u s e s e n s i t iz a t i o n a n d a l le r g ic e f f e ct s , t h e ym a y a f f e c t a w h o l e p o p u l a t i o n o r o n l y t h o s e g e n e ti c a l ly p r e -d i s p o s e d . T o x i c e f f e c t s d i f f e r i n t h e i r s e v er i t y , t h e i r p o t e n t i a lf o r m e d i c a l t r e a t m e n t , a n d t h e a g e g r o u p s t h a t a r e a f f ec t e d .S o m e h a v e s u g g e s t e d t h a t t h e s a m e m e c h a n i s m o f a c ti o n i sr e q u i r e d t o g r o u p e f f e ct s i n t o a s i n g le c a t e g o r y ; th i s c o n d i -t i o n i s c l e a r l y n o t f u l f i l l e d i n t h e c a s e o f t o x i c e f f e c t s . S ow h y a r e t h e y s t i l l g r o u p e d t o g e t h e r ?

D e s p i t e t h e d i s s i m i l a r m e c h a n i s m s o f a c t i o n a n d d i s s i m i l a re f f e ct s o f t o x i c c h e m i c a l s , w e h a v e d e v e l o p e d a s i n g l e c o g n i -t i v e s t r a t e g y t o l e a r n a b o u t t h e s e c h e m i c a l s a n d t o d e c i d e a b o u tp r e v e n t i v e a c t i o n . W e r e c o g n i z e t h a t , f o r a n a d v e r s e e f fe c t t oo c c u r , a c h e m i c a l n e e d s t o p o s s e s s a p r o p e r t y w e c a ll t o x i c i t ya n d t h a t h u m a n s n e e d t o b e e x p o s e d . T o x i c o l o g y h a s d ev e l -o p e d a s e t o f t o o l s t o a s s e s s t o x i c i ty . T h e s e i n c l u d e t r a d i t i o n a lt e s t s l i k e a n i m a l b i o a s s a y s , i n v i t r o te s t s, a n d e p i d e m i o l o g i c a li n v e s ti g a t io n s . W i t h t h e a d v e n t o f m o l e c u l a r b i o l o g y a n d b i o -c h e m i s t r y t h e s e t o f t o o l s h a s b e e n g re a t ly e x p a n d e d . T h e m o s tw i d e l y a v a i l a b l e a n d f r e q u e n t l y u s e d t e s t s r e s u l t s , h o w e v e r ,a r e s t i l l t h e e f f e c t i v e o r l e t h a l d o s e m e a s u r e s i n a n i m a l t e s t s .E x p o s u r e a n a l y s i s h a s d e v e l o p e d m e a s u r e m e n t m e t h o d s a n dm o d e l s t o a s s e ss w h e t h e r i n d i v i d ua l s a r e o r h a v e b e e n e x p o s e dt o c h e m i c a l s a n d t o e s t i m a t e t h e m a g n i t u d e a n d d u r a t i o n o ft h e e x p o s u r e . S o c i e t y h a s d e v e l o p e d a u n i f o r m r e s p o n s e m e c h a -n i s m t o t o x i c c h e m i c a l s ; r i s k a n a l y s i s c o m b i n e s t h e r e s u l t s o ft o x i c o l o g y a n d e x p o s u r e a s s e s s m e n t t o e v a l u a t e t h e m a g n i -t u d e o f a r is k , a n d r i s k m a n a g e m e n t t a k e s t h e a p p r o p r i a t ea c t i o n t o m i t i g a t e r i s k s t h a t a r e d e e m e d t o b e u n d e s i r a b l e .R i s k a n a ly s i s a n d m a n a g e m e n t h a v e b e e n a d o p t e d a s r e s p o n s es t r a t eg i e s i n a w i d e s e t o f la w s a n d r e g u l a t i o n s t h a t d e a l w i t hi ss u es r a n g i n g f r o m f o o d s a f e ty to a i r q u a l i ty N R C 1 9 9 4 ) . W h i l em o s t o f t h e s e la w s a n d r e g u l a t io n s d o n o t e x p l i c i tl y c o m p a r er i sk s , t h e i n t e n t i s t o a p p l y t h e s a m e c r it e r ia a n d s t r in g e n c y t oa l l t he c he m ic a l s c ov e re d b y a spe c i f i c p ie c e of l e g i s l a t ion .T h e j u s t i f i c a t io n f o r c r e a t in g a c a t e g o r y o f h u m a n t o x i c i t yi s t h a t w e u s e t h e s a m e c o g n i t i v e s t r a t e g i e s a n d s c i e n t i f i ct e s ts t o u n d e r s t a n d a n d e v a l u a t e t o x i c c h e m i c a l s , in s p it e o ft h e i r d i s s im i l a r i ti e s . W e u s e t h e s a m e p i e c e s o f i n f o r m a t i o n

d o s e - r e s p o n s e r e l a t i o n s h i p a n d e x p o s u r e e s t i m a t e - t o a s-s e s s t h e r i s k o f a c h e m i c a l a n d t o d e c i d e a b o u t w h a t t o d o .T h e C o n s t r u c t i o n o f A t t r i b u t e s

T h e m o s t i n t e r e s t in g q u e s t i o n i n t h e m e t h o d o l o g i c a l d e v e l -o p m e n t o f i m p a c t a ss e ss m e n t m a y b e h o w t o c o n s t r u c t m e a n -i n g f u l a t t r i b , t e s . A n a l o g o u s t o t h e i ss u e o f t h e o r y c h o i c e i nt h e e p i s t e m o l o g y o f s c i en c e K l e e 1 9 9 7 , H e r t w i c h e t a l .2 0 0 0 ) , t h i s q u e s t i o n c a n a l s o b e p h r a s e d a s o n e o f m e t h o dc h o i c e . T w o i s s u e s a r i se in a t tr i b u t e c o n s t r u c t i o n : 1 ) w h a ti n f o r m a t i o n s h o u l d b e i n c l u d e d , a n d 2 ) h o w s h o u l d th i si n f o r m a t i o n b e c o m b i n e d ? C o m p e t i n g m e t h o d s m a y d if fe ri n w h a t i n f o r m a t i o n t h e y in c lu d e a n d h o w t h e y c o m b i n e i t.I f t h e a t t r i b u t e i s m e a n t t o d e s c r i b e a t l e as t p a r t o f a n i m -p a c t c h a i n , i t c a n b e i n t e r p r e t e d a s a p h y s i c a l q u a n t i t y . I nm a n y c a s e s a s c i e n t i f i c m o d e l d e s c r i b i n g p h y s i c a l o r e c o -n o m i c r e l a t i o n s h i p s w i l l b e t h e m o s t s u i t a b l e b a s i s f o r a t -t r i b u t e c o n s t r u c t i o n . I n d e e d , p h y s i ca l m o d e l s h a v e b e e n u s e de x t e n s i v e l y i n t h e d e v e l o p m e n t o f L C A i m p a c t i n d i c a t o r s .T h e g l o b a l w a r m i n g p o t e n t i a l G W P ) , f o r e x a m p l e , i s b a s e do n m o d e l s o f t h e a t m o s p h e r i c f a te o f g r e e n h o u s e g a s e s a n dt h e r a d ia t i o n b a l a n c e o f t h e a t m o s p h e r e . T h e G W P r e p r e -s e n t s t h e t i m e - i n t e g r a t e d i n f r a r e d a b s o r p t i o n . T h e o z o n ed e p l e t i o n p o t e n t i a l O D P ) i s b a s e d o n a m o d e l o f a t m o s p h e r i cf a t e a n d c h e m i s t r y d e s c r i b i n g o z o n e d e p l e t i o n i n t h e s t r a t o -s p h e r e . T h e O D P r e p r e s e n t s t h e s t e a d y s t a t e d e c r e a s e i ns t r a t o s p h e r i c o z o n e r e s u l t i n g f r o m a m a r g i n a l i n c r e a s e i ne m i s s i o n s o f t h e o z o n e d e p l e t i n g g a s W u e b b l e s 1 9 9 5 .

I nt J L C A 6 5 ) 2 0 0 1 2 6 7


4/8

I m p a c t A s s e s s m e n t L C A M e t h o d o l o g y

S c ient i fi c m o d e l s a r e a t t r ac t i v e b ecau se t h ey em b o d y sc i en -t i fi c k n o w led g e a b o u t t h e r e l a t i o n sh ip o f th e s t r e s so r t o o u rco n ce rn s . T h e y can b e v a l id a t ed an d im p ro v e d acco rd in g t oes t ab l i sh ed p ro ced u re s , an d th ey can se rv e a s a r a l l y ing p o in tfo r ach i ev in g ag reem en t . S c i en t i f i c m o d e l s s eem l e s s a rb i -t r a ry t h an t h e co n s t ru c t i o n o f m o re a r t i f i c ia l i n d i ca to r s . W esh o u ld k eep in m in d , h o w ev er , t h a t t h e p u rp o s e o f t h e a t -t r i b u t e i s t o r e f l ec t co n ce rn s , n o t t o r ep resen t p h y s ica l q u an -t i t i e s . I n d eed , t h e m o d e l p a ram e te r i za t i o n s an d co n d i t i o n su sed fo r t h e d ev e lo p m en t o f i n d i ca to r s a r e o f t en n o t r ea l i s -t i c . T h e G W P i s b ased o n a p resen t -d ay a tm o sp h ere , i t d o esno t ta ke in to acc oun t the p ro jected increase in g reenhouse gasco n cen t r a t i o n s . I n ad d i t i o n , so m e o f t h e f eed b ack m ech an i sm so f i n c reased g reen h o u se g as co n cen t r a t io n s w ere n eg l ec ted ,resu l t ing in s ign if ican t ly smal ler GW Ps fo r the n on-C O 2 g reen-house ga ses (Wu ebb les e t a l . 1995) . The cho ice to ignore somem ech an i sm s m ay h av e b een d r iv en b y t h e d es ir e t o av o id b as -in g t h e G W P o n u n ce r t a in a n d th e re fo re m o re eas il y co n tes t edin fo rmat ion . S imilar ly , the use o f s teady-s ta te cond i t ions fo rthe OD P do es no t ref lect the expected s i tuat ion . These cho icesre f l ec t n o rm a t iv e a n d ep i s tem ic j u d g m en t s o n p a r t o f t h e i nd i-ca to r d ev e lo p e r s , w h o see th ese s im p li f ied m o d e l s a s a m o readequate basis fo r decis ion mak ing .B ased o n t h e p rev io u s d i scu ss io n o f L C A an d d ec i s io n an a ly -s i s, w e w o u ld l i k e t o o f f e r a n u m b er o f c r i t e ri a fo r t h e co n -s t ru c t i o n o f a t t r i b u t e s . T h ese c r i t e r i a a r e m ean t t o g u id ed ec i s io n s ab o u t w h a t k in d o f i n fo rm a t io n t o u se i n co n s t ru c t-i n g a t tr i b u t e s a n d h o w t o c o m b i n e t h i s i n f o r m a t i o n.1 . I n f o r m a t i o n m u s t b e m e a n i n g fu l t o th e p r o b l e m . T h ed a t a t h a t a r e i n c lu d ed in t h e a t t r i b u t e m u s t h av e a r e l a -t i o n sh ip t o t h e o b j ec t i v e t h a t t h e a t t r i b u t e i s su p p o se d to

re f l ec t . A b as i c s c i en t i fi c u n d e r s t an d in g o f t h e p ro b l emis r eq u i r ed t o d ec id e w h e th e r i n fo rm a t io n i s r e l a t ed t oth e o b j ec t i v e . T h i s c r i t e r i o n i s m o s t d i r ec t l y j u s t i fi ed b yK ee n ey s (1 9 9 2 ) d em an d th a t t h e o b jec t i v e r ep resen t edb y th e a t t r i b u t e sh o u ld b e e s sen t ia l , I t is f u r th e rm o re su p -p o r t ed b y r eq u i r em en t s fo r an a ly t i ca l e ff i c ien cy an d t ech -n i ca l v a l id i t y . I n IS O 1 4 0 4 2 , t h i s c r it e r i o n i s t e rm ed en -v i r o n m e n t a l r e l e v a n c e .2 . T h e c o m b i n a t i o n o f t h e in f o r m a t i o n s h o u ld r e f le c t o u ru n d er s t an d in g o f t h e r e l a t io n sh ip b e tw een th e s t r e s so ran d th e su b j ec t o f co n ce rn . In m an y cases , a m o d e l d e -sc r ib in g a p a r t o f t h e cau se -co n seq u en ce ch a in w i l l b eu sed . S u ch m o d e l s a r e b ased o n an u n d e r s t an d in g o f t h ep h y s i ca l r e l a t i o n sh ip am o n g d i f f e r en t v a r i ab l e s . T h e u seo f m o d e l s i s n o t r eq u i r ed b y d ec is io n an a ly s is , b u t i t r e -f l ec t s o u r d es i r e t o ap p ro p r i a t e ly u n d e r s t an d th e r e l a -t i o n sh ip b e tw een s t r e s so r s an d im p ac t s an d to i n c lu d eth i s u n d e r s t an d in g in o u r a s ses sm en t . T h i s c r i t e r i o n h en ceh e lp s t o en su re n o rm a t iv e r e l ev an ce an d t ech n ica l v a l i d -i t y . I n ad d i t i o n , t h e p h y s i ca l i n t e rp re t a t i o n p o t en t i a l l yp r o v i d e s f o r a m o r e u n d e r s t a n d a b l e a t t ri b u t e , b a s e d o ni n f o r m a t i o n a n d m o d e l s t h a t c a n b e v a li d a te d .3 . A n a l y t i c a l r e f i n e m e n t m u s t b e i n f o r m a t i v e: A d d i t i o n a ld a t a o r a n a l y s i s m u s t b e i n f o r m a t i v e e n o u g h s o t h a t i tsv a lu e -o f - in fo rm a t io n o u tw e ig h s t h e h ig h e r co s t s o f an a ly -s is . S u f f i c i en t d a t a m u s t b e av a i l ab l e an d th e av a i l ab l ed a t a m u s t b e c e r t a i n e n o u g h t o b e i n f o rm a t i v e a b o u t t h ea t t a i n m e n t o f t he o b j e c ti v e. T h e i de a o f i n f o r m a t i v e -

n e s s ( H a m m i t t a n d S h l y a k h te r 1999) w as in sp i r ed b yv a l u e - o f - i n f o r m a t i o n a n a l y s i s ( M o r g a n a n d H e n r i o n1 9 9 0 ) . H er tw ich 1999) su g g es t ed a m ea su re o f r e so lu -t ion serve as a tes t fo r th is cr i ter ion .T h i s c r i t e r i o n su g g es t s t h a t i n fo rm a t io n sh o u ld o n ly b eincluded i f i t actual ly has the po ten t ia l to in f luence adecis ion . Th is i s in the in tere s t o f an aly t ic ef f ic iency andp rac t ica l i ty . I t i s a l so su p p o r t e d b y K e en ey s ca ll f o r i n -c lu d in g o n ly e s sen t i a l p ro p e r t i e s . I n sev e ra l ca ses , an a -ly s t s h av e su g g es t ed t o i n c lu d e p i eces o f i n fo rm a t io nw h ich m ay , i n p r in c ip l e , b e r e l ev an t t o t h e p ro b l em b u tw h ich a r e n o t av a i l ab l e fo r m o s t o f t h e im p ac t ch a in s o fco n ce rn . I f d a t a fo r p a r t o f t h e im p ac t ch a in a r e n o t av a i l -ab l e an d w e h av e t o u se t h e sam e u n ce r t a in ty d i s t r i b u -t i o n s fo r m o s t o f t h e im p ac t ch a in s t h en t h e ad d i t i o n a lan a ly s i s o r i n fo rm a t io n c lo u d s t h e p i c tu re ; i t d o es n o tco n t r i b u t e t o o u r k n o w led g e an d can b e o m i t t ed .

2 1 The a ppropria t e de p t h o f a na ly s isI f s ci en ti f ic m o d e l s a r e u t i l i zed i n t h e co n s t ru c t i o n o f a t -t r ibu tes , the quest ion o f wh at in f o rm at ion shou ld be includedcan b e sp ec if i ed a s : w h a t i s t h e ap p ro p r i a t e d e p th o f an a ly -s is , and what i s the level o f deta i l wi th which each s tep inth e cau se -co n seq u en ce ch a in i s d esc r ibed ? A s p rev io u s ly in -d icated , the depth o f analysis expresses the level in the im-p ac t ch a in a t w h ich t h e m ean s o b j ec t i v e is l o ca ted ; e l em en t sup to th is level are included in the calcu lat ion o f the a t -t r i b u t e , a A m o re d e t a i l ed an a ly s i s sh o u ld b e ab l e t o g iv e am o re r ea l is t i c p i c tu re o f t h e p o t en t i a l en v i ro n m en ta l co n se -q u en ces b ecau se i t i n c lu d es m o re i n fo rm a t io n . W h i l e t h i sw o u ld a rg u e i n f av o r o f an i n c reased d ep th , t h e co s ts o fan a ly s i s an d th e l ack o f i n fo rm a t io n f av o r l e ss d ep th .T h e q u es t i o n o f t h e ap p r o p r i a t e d ep th o f an a ly si s f r eq u en tlyo ccu r s i n en v i ro n m en ta l p o l i cy an a ly s i s . T h e ch o ice o f an a -ly t ica l d ep th r eq u i r e s m a k in g t r ad e o f f s b e tw een d es i r ed c r i -t e r i a , n o t ab ly t h e r e l ev an ce o f t h e i n d i ca to r ( t h e ex t en t t ow h ich i t cap tu res co n seq u en ces t h a t a r e o f d i r ec t i n te r e s t t op o l i cy m ak er s ) a n d th e accu r acy w i th w h ich fu tu re l eve ls o fth e i n d i ca to r can b e p ro j ec t ed u n d e r a l t e rn a t i v e p o l i c i e s( H a m m i t t 1 9 9 9 ) . T h e c o m p a r i s o n o f a l t e r n a t iv e e v a l u a ti o n so f c l im a te ch an g e p o l i cy i l l u s t r a t e s t h a t t h e ch o ice o f t h eev a lu a t i o n en d p o in t can h av e im p o r t a n t im p l i ca t i o n s fo r t h ech o ice o f a lt e rn a t i v e p o l i c ie s . T h e s t a n d a rd ev a lu a t i o n en d -p o in t fo r r e sp o n se s t r a t eg i e s t o c l im a te ch an g e i s t h e l eve l a tw h ich C O 2 co n ce n t r a t i o n i s s t ab i li zed . I f s t ab i li za t i o n w a sth e g o a l, em i s sio n s r ed u c t io n s co u ld b e p o s tp o n ed . H a m m i t t(1 9 9 9 ) sh o w s th a t i f i n s t ead t h e m ax im iza t io n o f t h e n e tb en e f i ts o f em i s s io n co n t ro l i s th e g o a l , an ea r l ie r r ed u c t io no f g reen h o u se g as em is s io n s is d es i r ab l e . I n o th e r w o rd s , t h el a rg es t n e t b en e f i ts can b e o b t a in ed f ro m a p o l i cy o f ea r ly ,g rad u a l em i s s io n s co n t ro l . T h e d i f f e r en ce b e tw een ev a lu a -t i o n en d p o in t s p a ra l l e l s o u r co m p ar i so n o f t h e eco n o m icd am ag e in d i ca to r (E D I ) an d th e g lo b a l w arm in g P o ten t i a l(H er tw ich e t a l . 2 0 0 0 ) .3 n the terminology of the UNI=p workshop Bare et al . 2000b), this couldbe rep hrased as the qu estion of how close to the ultimate, observableendpo int he category indicator should be.

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car accidents or smoking. Being closer to our concerns, theyform a m ore solid basis for valuation. This may be the rea-son why valuatio n results are readily available.An assessment based o n 'obse rvable consequences', however,requires a prediction of the damages resulting from variousstressors. A predic ted dam age, such as years of life lost, con-stitutes a factual truth claim. It should fulfil the requirementof scientific validity. D amag e mod eling makes much stron gertruth claims and thus has to meet tougher standards of evi-dence than an evaluation following the environmental themesapproach. Such requirements are necessary because damagemodeling m akes statements not on ly about the relative impor-tance o f srressors but also abo ut their absolute scale, that is,their im porta nce relative to health care, traffic safety, and edu-cation. Th e question is , given the complexity of environmen-tal, physiological, and economic processes, can LCA deliversuch scientifically valid predictions?In ou r op inion , the scientific credibility of damage mod els canonly be maintained if uncertainty is fully expressed and car-ried through in the analysis. Based on a Baysian statisticalperspective, unc ertain ty distributions for dose-response rela-tionships for chemicals lacking specific evidence can b e basedon d ata from che micals that have such data. For cases such asclimate change, fo r which no prior experience exists, the con-nection between insult and en dpoint can based on expert judg-ment (Morgan and Kei th 1995). In other words, data gapscan be replaced by highly uncertain data that represents theentire ran ge o f possible outcom es (Fig. 2). This is the on lyway in which we can assure that factual claims, such as theyears of life lost due to an insult, remain valid.If such a practice is established, the danger is that uncer-tainty swaps out all othe r inform ation included in the analy-sis, so that no meaningful differences between alternativesinvestigated by LCA can ever be established. It is easier toestablish a relative difference between two alternative thantheir absolute impact . Uncerta inty about factors that are

Fig. 2: The uncertainty in our knowledge of different steps in the impactchain differs significantly. The largest uncertainty exists in the connectionbetween increased infrared absorption and changes in weather patterns

common to both will affect estimates of the absolute im-pacts much more than estimates of the relative impact, un-der reason able assumptions. For exa mple, if one factor l ikea dose-response slope enters the impact calculation for bothtechnologies, error in the estimated coefficient will affectthe estimated impact in a proportional way, but will notreverse any ranking between the technologies. Thus, a com-parative LCA may yield inconclusive results even if there isa meaningful difference between alternatives. The hypotheti-cal example in Fig. 3 illustrates such a case. In Fig. 3, thetwo life cycle inventories contain only tw o emissions each.One stressor each contributes to global warming, the otherto human health. Assume that, using the global warmingpotential and the human toxicity potential (or any of theircomp etitors), we find that LC1 is clearly worse than LC2. Ifwe go directly to the endpoint, however, quantifying the largeuncertainty about the human and ecological effects of cli-mate change or toxic compounds, we find a large overlapbetween LC1 and LC2. LC1 will still be statistically domi-nant, but if we calculate the reliability of our conclusionsfollowing Steen (1997), i t will be very low. Ho w serious theproblem of uncerta inty and data gaps int roduced in damagemodeling is and how strongly it affects the reliability of LCAresults remains to be investigated. While EPS, Eco-Indicator99, and the ExternE project (European Commission 1999,Eyre et al. 1999) all contain data on the un certainty of theeffects, this dat a d oes no t easily lend itself to such an inves-tigation. Only p art of the uncertainty is quantified, and theevaluations h ave significant data gaps.In ou r search for a suitable example to specify the impact ofthe additional uncertainty introduced by damage functioncalculations, we found two problems with the existing stud-ies. One, investigations neglect possible but unproven ef-fects. Shrader-Frechette 1996) calls this effect framing un-certainty. She argues that there is a difference between thetruth or falsity of a scientific hypothesis (the concern of sci-entists) and the acceptability of risk decisions with regardsto environmental impacts. Scientists are interested in mini-mizing false positives (type I errors) rather than false nega-tives (type II errors). In situations of unce rtainty, scientists

Climate[ c h a n g e [

Ecosys tem1damage /

Acidification

Humanheal th--...

Fig. 3: A comparison of two life-cycles LC1, LC2) m ay be conclusive atthe midpoint level but result in overlapping probability distribution at theendpoint level because of common uncertainties about how climate changeand acidification affect the endpoints

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p lace th e g rea t e r b u rd en o f p ro o f o n th e p e r so n w h o p o s tu -l a t e s so m e , r a th e r t h an n o , e f f ec t . T h e r e su l t i s a t en d en cyto unde rest im ate r i sks (Shrader-Freche t te 1996) . 4T h e seco n d p ro b lem i s t h e w e l l -d o cu m en ted t en d en cy b yb o th sc i en t i s ts an d l ay p eo p le t o u n d e res t im a te u n ce r t a in ty( M o r g a n a n d H e n r i o n 1990, Shlyakh ter e t a l . 1994) . Basedo n o u r o w n ex p e r i en ce w i th u n ce r t a in ty an a ly s i s , w e v i ewth e r ep o r t e d u n ce r t a in t i e s w i th su sp i c io n . T o ad ju s t fo r t h eo v e rco n f id en ce o f ex p e r t s , m e th o d s su ch a s t h a t p ro p o sedby Sh lyakh ter e t a l . (1994) can be used . Ano ther consequ enceo f t h e t en d en cy to u n d e res t im a te u n ce r t a in t i e s , h o w ev er , i st h a t p eo p le a r e n o t u sed t o t h e l a rg e u n ce r t a in t i e s t h a t ex i s tin real i ty . I t is no t c lear ho w the y wi ll resp ond to a fu l l quan-t i f icat ion o f uncer ta in ty .T h e cu r r en t d am ag e m o d e l s r ep resen t w o r th w h i l e a t t em p t s t oaddress the d i f f icu lt quest ion abo u t the abso lu te env iron men -ta l impacts o f p roducts . Their approaches deserve to be pur-sued fu rther . Given the p rob lem s wi th the ex is t ing m ethods aswell as the principal difficulties regarding the complete ac-coun t ing fo r a l l re levan t impacts and the t reatmen t o f uncer-ta in t ies in the analysis , we th ink i t wou ld be unwise to aba n-don the env ironmental themes approach . Ins tead , in the nex tsect ion we wou ld l ike to suggest a wa y in which som e to theresu l ts o f dam age m odel ing cou ld be used to ass is t the valua-t ion s tep in the env ironmental themes approach .4 F r o m I n d i c a t o r s t o V a l u es : t h e m e a n s e n d s o b j e c t i v e s

n e t w o r kIn the f i rs t par t o f th is pape r (section 4 ) , we have descr ibed themea ns-end s objectives netwo rk as a decision-analytic a ppr oac htowards es tab l ish ing a connect ion between the in termed iate'me ans ob ject ives ' and the funda men tal ' ends ob ject ives . ' The' judgm ent abo u t facts ' (Keeney 1992) necessary to es tab l ishthe means-ends ob ject ives network needs to s tar t wi th a de-scrip tion of these facts. Th e addition al evidence util ized byendpo in t methods is c lear ly re levan t fo r decid ing abou t theimpo rtance o f d i fferen t category ind icato rs . A judgmen t abo u tthese facts , however , shou ld no t on ly be based on the num eri -cal resu l ts o f the midpo in t - to -endpo in t calcu lat ions bu t a lsotake in to accou n t the qual i ty o f the under ly ing ev idence, theequ i ty o f the d is t r ibu t ion o f ef fects in society , and whetherr isks are impo sed o r accep ted vo lun tar ily .W ha t we are suggesting is hence a new approac h to valuat ionwhich do es no t m erely ask ind iv iduals o r g roups ab ou t thei rp re fe ren ce r eg a rd in g d i f f e r en t en v i ro n m en ta l im p ac t s , b u twhic h uses quan titative and qualitative in form ation to describewhat we know abou t the possib le o r l ikely effects re la ted toth e im p ac t ca t eg o r i e s . W e th in k t h e m ean s -en d s o b j ec t i v esnetw ork o ffers a good co ncep tua l basis fo r u ti liz ing the ev i -d en ce ab o u t d am ag es i n t h e en v i ro n m en ta l th em es ap p ro ac h .

This i s a lso the case in LCA-re late d s tudies . Assessments of climatechan ge, e.g. thos e par t o f the Exte rnE pro jec t Eyre et a l. 1999) , o f tenneglect the expected far - ranging effects on ecosystems because theirimpact on human wel fare is d i f f icu l t to predict. T h e E c o - l n d ic a t o r 9 9G oed k oop and S p r i ens m a 1999 ) i nc ludes on l y ca r c inogen ic and r es p i -r a t o r y hea l t h e f fec ts o f t ox i c c hem ic a l s bec aus e dos e - r es pons e c u r v esa r e unav a i l ab le for other toxic ef fec ts . LCIs of ten neglec t process es forwhich no d a t a was f ound .

5 C o n c l u s i o n sL i fe -cy c l e a s ses sm en t can b e d esc r ib ed a s a p ro b l em o f d ec i-s ion analysis . Th is o ffers an a l ternat ive termino logy , as d is-p lay ed in Tab le 1 , wh ich in i t se l f i s no t ye t a benef i t , as therei s a l r ead y an ab u n d an ce o f t e rm in o lo g y in L C A . T h e b en -ef i t s ar ise , however , f rom the access to a r ich l i tera tu re ond ec i s ion m ak in g th a t i s r e l ev an t t o L C A . T h i s l i t e r a tu re i s o fin t e r e s t i n a t l ea s t t h r ee a r eas . T h e f i r st i s p ro b l em s t ru c tu r-i n g , ex p lo red i n t h i s p ap e r . T h e seco n d i s m e th o d s t o t r ad e -o f f co m p e t in g o b j ec t iv es , u se fu l fo r t h e w e ig h t in g p ro cess .T h ese m e th o d s o f p re fe ren ce e li c i t a ti o n h av e b een ex p lo redby F innveden et a l . (2001) . The th i rd area i s the evaluat iono f t h e e f f ec t i v en ess o f d ec i s io n su p p o r t m e th o d s an d co m -p u te r t o o l s , y e t l a rg e ly u n ex p lo red i n L C A (M o n tazem i e ta l . 1 9 9 6 ) . T h e d ec i s io n an a ly t i c f r am ew o rk r eco n s t i tu t e s t h echarac ter izat ion s tep o f LCA as the const ruct ion o f a t t r ibu tes .At t r ibu tes are const ructed to ref lect speci f ic ob ject ives o rco n ce rn s . T h e im p a c t w eb se rv es a s a g u id e t o t he d es ig n o fat t r ibu te s . O ften i t i s conve n ien t to use scien ti f ic mod els thatr ep resen t a t l ea s t p a r t o f t h e cau sa l ch a in f ro m s t r e s so rs t oconsequences . In th is case , a t t r ibu tes wi l l have a physicali n t e rp re t a t i o n . T h e d ec i s io n an a ly t i c f r am ew o rk a l so p ro -v id es a m o re d e t a i l ed g u id an ce t o v a lu a t i o n , o r t h e t r ad e -o f fam o n g o b j ec t i v es . T h e m ean s -en d s o b j ec t i v es n e tw o rk r e -l a t e s a t t r i b u t e s ( im p ac t i n d i ca to r s ) t o fu n d am en ta l o b j ec t iv eor safeguard sub jects . Factual , sc ien t i f ic in fo rmat ion can beim p o r t an t t o b e t t e r u n d e r s t an d th i s co n n ec t io n . E s t im a teso f t h e m ag n i tu d e o f ex p ec t ed en v i ro n m en ta l im p ac t s p ro -v id ed d am ag e fu n c t io n s sh o u ld b e i n c lu d ed , t o g e th e r w i thm o re q u a l i t a t i v e co n s id e ra t i o n s , i n t h e v a lu a t i o n s t ep .The key d if ference between env ironm ental themes approache san d d a m ag e fu n c t io n ap p ro a ch es l i e s n o t i n t h e i r d ep th o fanalysis , bu t in the factual t ru th c la ims emb odied in the cho-sen i n d i ca to r . T h e eco n o m ic d am ag e in d i ca to r fo r c l im a tech an g e (H am m i t t e t a l. 1996 has the sa me de p th o f analysisa s t h e ca l cu l a ti o n s o f th e h u m an h ea l th an d eco sy s tem d am -age embodied in EPS o r the Eco lnd icato r 99. T h i s i n fo rm a-t ion is on ly used to assess the re la t ive importa nce o f d i f feren tg reenhous e gases , however , no t the abso lu te resu l t ing dam agee.g. f rom ch anges in d isease vecto rs o r tem peratu re ex t remes.Given the unpred ictab le consequences o f c l imate change andma ny relevan t qual i ta t ive con siderat ions tha t are on ly insu ffi -c ien t ly (o r no t a t a l l ) cap tu red in in teg rated assessment mod -els o f c l imate change impacts , i t may be wiser to leave theu l t im a te ev a lu a t i o n o f t h e im p o r t an ce o f c l im a te ch an ge t oh u m an ju d g m en t . R i sk p e rcep t io n s tu d i e s h av e sh o w n th a tind iv iduals do no t a ccep t expe r t evaluat ions o f r i sk in termsof p robab i l i ty and consequences , especial ly when unfamil iaro r po ten t ia l ly catas t roph ic impacts are invo lved (S tern andFineberg 1996 . S u ch im p o r t an t j u d g m en t s sh o u ld b e d eb a t edas j u d g m en t s , n o t a s m a t t e r s o f an a ly ti ca l m e th o d s .We have developed cr i ter ia fo r the g roup ing o f s t resso rs andthe construc tion of attributes. For the constructio n of attributes,w e h av e su g g est ed t h a t t h e L C A c r i t e ri o n o f ' en v i ro n m en ta lre levance ' can be more exact ly descr ibed as the re levance o fth e i n fo rm a t io n i n c lu d ed in a ch a rac t e r i za t i o n m e th o d an dval id i ty o f the wa y i t i s included , ref lect ing our unders tand ingof the cause-consequence re la t ionsh ip . In add i t ion , we sug-gest that good e nough da ta needs to be avai lab le that an analy t i-ca l re f i n em en t i n d eed ad d s m o re i n fo rm a t io n t h an n o ise . T h e

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c r i t e r i o n i s in s p i r e d b y t h e d e c i s i o n - a n a l y t i c c o n c e p t o f v a l u e -o f - i n f o r m a t i o n . T h e s e c r i t e r i a s e r v e n o t o n l y a s a g u i d a n c e ,t h e y c a n b e u s e d t o f o r m u l a t e a r g u m e n t s a b o u t t h e m e r i t o fc o m p e t i n g i m p a c t a s s e s sm e n t m e t h o d s . T h e d e v e l o p m e n t o fs u c h c r i t e r i a e n a b l e s a m o r e s y s t e m a t i c d e s i g n a n d s e l e c t i o n o fi m p a c t a s s e s s m e n t m e t h o d s a n d m a y e s p e c i al l y b e u se f u l f o rm e t h o d d e v e l o p m e n t a n d s t a n d a r d i z a t i o n e f f or t s l ik e I S O a n dt h e e m e r g i n g U N E P / S E T A C L i f e C y c l e I n i t i a t i v e .

Ac kno wled gem ent s . Mater ia l in th is ar t ic le was f irs t presented at theUNEP workshop on midpoint vs. endpoints in Brighton (Bare et al.2000a). We have benef ited f rom discussion with num erous col leaguesat the workshop a nd cri t ical comments f rom three reviewers and a num-ber of co l leagues.

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Received: January 28th, 2001Accepted: July 7th, 2001OnlineFirst: July 10th 2001

7 Int J LCA 6 (5) 2001

a decision-analytic framework for impact assessment

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