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ApproachesforQuantifyingtheMetabolismofPhysicalEconomies:AComparativeSurvey.PartII:ReviewofIndividualApproaches

ArticleinJournalofIndustrialEcology·December2002

DOI:10.1162/108819802320971641·Source:OAI

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� Copyright 2002 by theMassachusetts Institute of Technologyand Yale University

Volume 6, Number 1

Approaches for Quantifyingthe Metabolism of PhysicalEconomies: A ComparativeSurveyPart II: Review of Individual Approaches

Peter L. Daniels

Keywords

industrial metabolismmass balancematerials flow analysis (MFA)physical economysocietal metabolismsubstance flow analysis (SFA)

e-supplement available on the JIEwebsite

Address correspondence to:Peter DanielsSchool of AESGriffith UniversityNathan 4111, BrisbaneAustraliap.daniels@mailbox.gu.edu.au

Summary

This article is the second of a two-part series that describesand compares the essential features of nine “physical econ-omy” approaches for mapping and quantifying the materialdemands of the human economy upon the natural environ-ment. These approaches are critical tools in the design andimplementation of industrial ecology strategies for greater eco-efficiency and reduced environmental impacts of human eco-nomic activity. Part I of the series provided an overview, meth-odological classification, and comparison of a selected set ofmajor materials flow analysis (MFA) and related techniques.This sequel includes a convenient reference and overview ofthe major metabolism measurement approaches in the formof a more detailed summary of the key specific analytical andother features of the approaches introduced in part I. Thesurveyed physical economy related environmental analysis ap-proaches include total material requirement and output mod-els, bulk MFA (IFF (Department of Social Ecology, Institute forInterdiscplinary Studies of Austrian Universities) material flowbalance model variant), physical input-output tables, substanceflow analysis, ecological footprint analysis, environmentalspace, material intensity per unit service, life-cycle assessment(LCA), the sustainable process index, and company-level MFA.

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66 Journal of Industrial Ecology

Introduction

In part I of this article pair, a selected set ofmaterials flow analysis (MFA) and related tech-niques were assessed and compared along a num-ber of key dimensions. MFA approaches focusupon a given geographical area and are charac-terized by the systematic physical measurementof the magnitude and “location” of the mass ofspecific flows of environmentally significant ma-terials for purposes of environmental monitoring,analysis, and management. They are derivedfrom notions of a societal or industrial “metab-olism” where the significant environmental flowsconnecting society and nature are studied as avalid and inevitable biological extension of met-abolic dynamics observed for individual organ-isms, populations, communities, and ecosystems(Fischer-Kowalski 1998). The analysis accom-panying the part I review also suggested thatthere is a need to specify whether MFA is bestconsidered as a general metabolic flow measure-ment procedure (that can be applied from micro-to macrolevels of economic activity) or a morespecific methodology aimed primarily at economy-wide analyses that can depict the overall materialrelations between society and nature.

This second article in the two-part series pro-vides general descriptions of nine existing ap-proaches and evaluates them against the system-atic set of descriptive parameters outlined in partI. The list of approaches surveyed is neither ex-haustive nor mutually exclusive, but covers mostmajor approaches and provides a good cross sec-tion of work in the area.

The review is not intended to provide a com-prehensive description of the design character-istics and existing research associated with eachtechnique. This formidable task has been tack-led, for various individual tools and groups oftools, in a range of other publications. For ex-amples of overviews covering several of the in-cluded approaches, see Eurostat (2001a), Kan-delaars (1999), Uno and Bartelmus (1998),Vellinga and colleagues (1998), and Yenckenand Wilkinson (2000). Key empirical researchand literature containing more detailed descrip-tions are indicated where possible. The purposehere is to provide sufficient detail to compile a

useful reference (for a broad audience) forquickly identifying the key methodological fea-tures of each approach and to facilitate theircomparative analysis by building upon the sys-tematic description outlined in table 2 of part I.

The MFA-related classification of approachesused in this series circumvents many of the prob-lematic issues regarding the definition and scopeof MFA (versus the other approaches) discussedin part I and essentially adopts a schema basedon what appears to be the viewpoint of the ma-jority of researchers in the field.

Definitive forms of MFA are assumed to in-clude the following:

• The total material requirement and output(TMRO) approach based on total materialinputs, material outputs, and related indi-cators

• The bulk internal flow MFA (MFA-BIF)models as represented by work at the De-partment of Social Ecology, Institute forInterdisciplinary Studies of Austrian Uni-versities (IFF), Vienna

• Substance flow analyses (SFAs)1

They are tentatively identified as unequivocalforms of MFA primarily in view of their straight-forward physical measurement of material flowsin mass (or sometimes volume) terms and theirinterest in systemwide features relating to indi-vidual substances or a comprehensive range ofsubstance groups. Induced flows (for a given pe-riod of time) are associated with a particular re-gion. On the basis of these requirements, physicalinput-output tables (PIOTs) appear to fit theclassical MFA mold, but are tentatively excludedbecause of their mixed treatment in the relevantresearch literature. Instead, it is placed in a sec-ond group containing life-cycle assessment(LCA), material intensity per unit service(MIPS), and company-level material and energyaccounting techniques, which adopt a more mi-croeconomic sphere of relevance rather than fo-cusing upon overall descriptions of the materialbasis of wider economic systems. Environmentalspace models, ecological footprint analysis(EFA), and the sustainable process index sharemany similarities with the purpose and method-ology of economywide MFA, but are more

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Daniels, Approaches for Quantifying the Metabolism of Physical Economies: Part II 67

heavily customized versions of the general tech-nique.

MFAs Covering Broad Areasof Economic Activity

Total Material Requirementsand Outputs

Although the TMRO approach is not a stan-dard title, it has been adopted here as a conve-nient label for the MFA research style coordi-nated by the World Resources Institute andWuppertal Institute of Climate, Environment,and Energy in Germany. Arguably, this is becom-ing the core approach in MFA studies under-taken at the (supra-) national or regional systemlevel—the appropriate resolution under the “sys-temwide” definition option presented in part I ofthis pair of articles. TMRO is a materials flowaccounting approach focused upon measuringthe total annual mass flows of a comprehensiverange of environmental inputs and outputs of theentire system of national (or regional) economiesat relatively high levels of material aggregation(i.e., “bulk materials” that can include natural ortechnical compounds). The core of the total ma-terial requirement (TMR) is the direct materialrequirement composed of the weight of importsand material inputs from domestic extraction.An intrinsic feature, however, is the incorpora-tion of domestic and foreign hidden flows of non-marketed inputs associated with imports and do-mestic production that stay outside the economyand have no formal economic value (figure 1)(Adriaanse et al. 1997; Bringezu 2000; Matthewset al. 2000). Material outputs are composed ofthe weight of exports and total domestic output,which also includes domestic hidden flows to-gether with nonmarketed domestic processedoutput emitted to the environmental compart-ments of air, water, and land.2 The techniquemeasures material flows induced at any stage ofthe life cycle of economic output and aims tocapture the “ecological rucksack” or mass of ma-terial physically displaced by humans to produceand utilize a good minus the weight of the gooditself. Upstream or downstream flows associatedwith imports and exports (resource requirements

or emissions) may be considered in differentTMRO indicators (Bringezu 2000). With a fewexceptions, material flows are only measured toand from the economy overall rather than indi-vidual economic sectors.

Together with the MFA-BIF models and, ar-guably, PIOTs, the TMRO studies are forms of“bulk MFA” (b-MFA) that use MFA to revealthe structure of material throughput (or materialbasis) of national or regional economies (Brin-gezu 1997). The induced material flow inputsgenerally fall within several major categories, in-cluding domestic nonrenewables (e.g., energycarriers, metals, and industrial and constructionmaterials) and renewables (e.g., agriculturalplant biomass, forestry biomass), imported non-renewable, renewable, semimanufactures and fi-nal products, and foreign hidden flows. Systemoutputs include materials such as carbon dioxide(CO2), sulfur dioxide (SO2), oxygen, water va-por, fertilizer, and sewage sludge. Domestic hid-den flows of overburden and soil erosion aretreated as both inputs and outputs. Althoughmany studies have been restricted to the inputfocus of TMR calculations, TMRO-related ma-terial accounts have been undertaken for at least19 nations or regions: Amazonia, Australia, Aus-tria, Belgium/Luxembourg, China, Denmark,Egypt, Finland, Germany, Greece, Italy, Japan,the Netherlands, Poland, Portugal, Spain, Swe-den, the United Kingdom, and the UnitedStates.3

The specific approach of the TMRO “school”has been inspired by research into MIPS pio-neered by Schmidt-Bleek (1993, 1994). MIPSinvolves the identification of a single mass-basedmeasure of the total, life-cycle-wide (or “cradle-to-grave”) primary material and energy require-ments of services provided by specified productsor infrastructure. TMRO has also developed fromthe material flow balance (MFB) models imple-mented independently in Austria (Steurer 1992;Fischer-Kowalski and Haberl 1993), Germany(Schutz and Bringezu 1993), and Japan (JEA1992) in the early 1990s. In comparison to theMFB models, TMRO entails a more detailedtreatment of “bulk” material groups and a wideranalytical framework for analyzing ecologicalrucksacks. Although there are numerous research

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Figure 1 The materials cycle in the TMRO approach. DMI � direct material input; TDO � totaldomestic output; TMR � total material requirement.

publications stemming from this general ap-proach, TMRO is best represented by the con-ceptual notions and empirical findings describedin Adriaanse and colleagues (1997) and the later,more elaborate analytical developments reflectedin Matthews and colleagues (2000). More de-tailed methodological guidelines are provided inthose documents and in the Eurostat (2001a)economywide MFA handbook.

For the initial TMR studies that focused onmaterial inputs, a major general aim was to revealthe size and structure of the material flows into(and hidden flows “around”) the national econ-omy. The results permit the assessment and com-parison of absolute and per capita flows, and ma-terial intensity, over time and betweencountries.4 Environmental outputs were onlyconsidered in an indirect manner by the inclu-sion of hidden flows and by assuming that inputsand waste output levels are positively correlated.Input flows were quantified for 30 to 40 individ-ual material types with annual values stretching

as far back as 1965. The primary comparativeindicators relate to the TMR index (measured inmetric tons, which is obtained by summing themass flows for direct material inputs and hiddenflows. Air and water movements were separatedout from this index given their sheer magnitude(and presumed lesser environmental signifi-cance). At this extreme level of aggregation, theTMR for Germany, the United States, and theNetherlands ranged from around 75 to 85 metrictons per capita per year with Japan requiring onlyaround 45 metric tons per capita.5 A large partof the TMR (55% to 75%) was attributed to hid-den flows across the range of countries studied.Furthermore, there appeared to be a gradual risein per capita material requirements over the pastfew decades.

The TMR value can also be weighted by do-mestic output (gross domestic product) to createa macroeconomic analog (in kilograms per dollarunit service) of the MIPS approach. This indi-cator is claimed as an effective measure of a na-

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Daniels, Approaches for Quantifying the Metabolism of Physical Economies: Part II 69

tion’s materials intensity or eco-efficiency cov-ering the full range of induced flows linked toboth direct and hidden sources of domestic pro-duction and imports. Although more precisemeasures would depend upon the disaggregatedand qualitative characterization of input and out-put flows, ratios of TMROs to GDP and popu-lation can reveal much about levels and trendsin economic pressures upon the global environ-ment. Naturally, overall population and GDPlevels must also be included in this evaluation.Unlike the absolute levels of material use, thetrends for materials intensity appear to have lev-eled off and give some conditional hope for thepotential delinking of economic growth and en-vironmental pressure as originally identified byJanicke and colleagues (1989) (Adriaanse et al.1997).

The limitations of only analyzing input flowsand the masking of qualitative variations in theenvironmental significance of flows have led tomore recent extensions of the TMR concept thatincorporate many of the features of the bulk in-ternal flow models discussed in the next section.These extensions include the quantification ofenvironmental outputs and partial adoption ofmaterials balance principles. In addition, initialefforts have been undertaken to distinguish ma-terial flows according to their medium of entryor mode of dispersion, and physical, chemical,temporal, and spatial characteristics (e.g., their“velocity,” “mobility,” and “quality” [Adriaanseet al. 1997]) that configure their respective en-vironmental impacts. In their further develop-ment of the original TMR studies, Matthews andcolleagues (2000) include Austria with the origi-nal sample of nations and present time series dataon around 50 individual material flow outputs.Outputs are measured as the mass of exports andtotal domestic output, the latter being composedof domestic processed outputs and domestic hid-den flows. The domestic processed output flowsare allocated to their respective environmentalgateways (e.g., to air, water, and land).

Some of the major findings of the study in-clude the apparent growth in the physical scaleof waste output (despite greater material effi-ciency), the dominance of fossil fuels as a sourceof waste output, and the dire need for improved

physical accounting systems. Once again, thesefindings are not optimistic with respect to theenvironmental impacts of the metabolism of theglobal economy overall.

The general material flow methodology is in-tended to provide a systematic means of collect-ing quantitative physical measures of materialflows. In order to assess the actual sustainabilityof human production and consumption, it is gen-erally necessary to integrate other informationconcerning critical input and output thresholdsor natural fluxes. As discussed, however, trendsand cross-country comparisons of mass and vol-ume measures do provide a general idea of theexistence and extent of dematerialization. Forexample, the TMRO indices can be used tomonitor resource demands in relation to Factor4 or 10 eco-efficiency improvement targets iden-tified as necessary for sustainable development(Factor 10 Club 1995; Lehmann and Schmidt-Bleek 1993; von Weizsacker and Schmidt-Bleek1994).

Accurate sustainability indicators, however,would require detailed information on individualmaterial flows in order to assess demands in termsof specific thresholds. Effective strategic re-sponses to reduce the socioeconomic metabolismwould also depend upon identifying not just flowsdirectly between the natural environment andthe various sectors of the human economy, butalso analysis of intersectoral material flows aspursued in the MFA-BIF models and (very ex-tensively) in PIOTs.

MFA-BIF: The IFF MFB Models

The national MFA models produced by theDepartment of Social Ecology at IFF have beenadopted as the main representation of the second“economywide” physical economy approach toquantifying the human use of nature in materialterms. In accordance with table 2 (in part I ofthis pair of articles), it is classed with the TMRO,PIOT, and SFA approaches because it examinesmaterial flows induced by the entire economicsystem of a given region. The “systemwide” na-ture of the perspective is consistent with an un-derlying aim of gaining a holistic understandingof the material basis of society-nature relations

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70 Journal of Industrial Ecology

(Fischer-Kowalski 1997; Udo de Haes and vander Voet 1997).

Neatly labeling the approaches in this secondgroup is difficult, and a number of alternative de-scriptors could have been applied. Although thespecific focus has been placed upon the nationalMFA for Austria (published in 1997), this ap-proach builds upon original studies undertakenmore or less independently for Austria (Steurer1992), Germany (Bringezu 1993; Schutz andBringezu 1993), and Japan (JEA 1992) in theearly 1990s.6

The modeling of material flows so that inputsand changes in system stocks match system out-put measures is a key feature of the MFB ap-proach adopted in models such as the IFF(“MFA-BIF”) variant. Naturally, this frameworkrequires the explicit incorporation of outputflows. Although the input-output balance wasless critical in the early stages of work that fo-cused on inputs for calculating TMRs, the MFBmodels can be seen as the precursors to theevolving TMRO mode of analysis.

The IFF approach is presented as a uniquestage in the development of physical economymodels in view of one major distinguishing fea-ture: the identification and quantification ofphysical flows of materials within subsystem com-ponents of the economic system under study. Un-like the PIOT methodology, the pattern of flowsis intentionally restricted to a limited number ofcomponents and “bulk” material types. The IFFapproach thus reveals the fundamental nature ofeconomic system sources of flows without theoverwhelming detail and data problems associ-ated with constructing full physical input-outputrelations between dozens of sectors and for nu-merous materials and commodity groups. Hence,this approach is conveniently termed “bulk in-ternal flow” MFA (MFA-BIF). Although theoutput from the approach is probably still inade-quate for the formulation and implementation ofspecific ecological restructuring policies, it pro-vides more than just a general indication of ma-terial requirements or intensity. It also throwslight on the nature of sectoral-material flow link-ages allowing the identification of areas for moredetailed analysis.

The MFA-BIF model is akin to “bulk-PIOT,”forming a compromise between TMROs and the

highly disaggregated treatment of material inter-dependencies between sectors in the PIOT.7 Inthis regard, the MFA-BIF approach provides agood overview of the structural nature of the ma-terial basis of economies. It is generally appliedon a regional basis, but can be customized to fo-cus on specific industry sectors or activity fields(see Schandl and Huttler 1997; Schandl andZangerl-Weisz 1997).

The original 1992 national MFA for Austriaby Huttler and colleagues (1997) reflects most ofthe key features of the approach. This study wasbased on flows for one year only (1992) and cov-ers five broad materials groups—coal, oil, andnatural gas; mineral materials; biomass; air; andwater. As in the TMRO studies, results for airand water are often treated separately in view oftheir overwhelming magnitude. The total systemflow diagram (figure 2) suggests a similar generalapproach to the TMRO method (with data onlyrelating to the input and output flows across theeconomy-environment system border), but witha higher level of aggregation of material flows. Inaddition, the MFA-BIF analysis does not con-sider domestic and imported hidden flows thatstay outside the economic system boundary. “Im-ports” are confined only to raw materials and ma-terials embodied directly in imported interme-diate and finished products and exclude foreignhidden flows. In contrast to the initial studiesbased on TMR, however, the Austrian MFA-BIFcovers output flows (under five modes—emis-sions, waste, deliberate discharges, exports, anddissipative losses) and changes in stocks withinthe human economy. The approach’s uniquemeasurement of intersectoral flows is apparent inthe MFA subtables for the major material groups(an example for biomass is shown in figure 3) inwhich relevant material type mass flows arequantified between primary extraction, process-ing, and final demand sectors (and several sub-sectors within the production activities), to-gether with stock changes and flows back out tothe environment.

The MFA-BIF models can be distinguishedfrom the TMRO approach on at least threegrounds.8 First, in TMRO, material flows tend tobe only measured at the boundaries between thedomestic economy, environment, and the rest ofthe world.9 The MFA-BIF models, however, have

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Daniels, Approaches for Quantifying the Metabolism of Physical Economies: Part II 71

Figure 2 Total material flows in the IFF bulk internal flow model.

routinely disaggregated or opened up the “blackbox” of the economy to examine and measurematerial flows between major economic sectors.This represents a step toward obtaining the de-tailed sectoral flow patterns provided by PIOTapproaches without the formidable resource re-quirements and time delays involved in compil-ing PIOT data. In addition, it is a means of ex-tracting key material features of the systemsunder study rather than confronting the rich, butbewildering, array of data generated in PIOTs.

Second, MFA-BIF models, unlike the TMROmethodology, do not aim to extend the materialencompass of resource flows “beyond the border”to fully account for the ecological rucksacks. Fi-nally, the TMRO line of research initially con-centrated upon flows of environmental inputs inits calculation of the TMRs of nations and didnot fully embrace materials balance principles.This has been addressed in more recent exten-sions that include material outputs to the envi-ronment and rest of the world’s economy (seeMatthews et al. 2000). Similarly, differences inthe level of analysis of intersectoral material

flows in the economy and coverage of hiddenflows will weaken as the TMRO and MFA-BIFapproaches continue to converge.

One major potential extension of the MFA-BIF information system as a sustainability indi-cator is evident in the research into the humanappropriation of the net primary production ofplants (Whittaker and Likens 1973; Haberl1997; Haberl and Schandl 1999; Vitousek et al.1986). MFA-BIF studies are ideally placed toprovide detailed biomass flow data for augment-ing sustainability research of this genre. Simi-larly, the “raw” data of MFAs can provide a sys-tematic framework for collecting and feedingdata into other, more direct (if customized) sus-tainability indicator approaches such as EFA andthe derivation of the sustainable process index(Haberl and Schandl 1999). The TMRO ap-proach could fulfill this same role, but the “open-ing” of the system to include internal materialflows within the economy provides a better ideaof the sectoral and activity field “pull” and thusthe appropriate nature and intensity of adaptivestrategies.

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Daniels, Approaches for Quantifying the Metabolism of Physical Economies: Part II 73

Physical Input-Output Tables

The PIOT methodology is presented as thethird main physical economy approach con-cerned with economywide material flows. Al-though there are several other related environ-mental extensions to the national accountingframework, PIOTs have been selected as the mostappropriate major approach given the clearphysical basis of measurement. PIOTs are theonly extended national accounting framework toretain physical flow measures in both the eco-nomic sphere and in connections with the nat-ural environment.

The 1993 version of the United Nation’s Sys-tem of Integrated Environmental and EconomicAccounting (SEEA) was heavily concerned withcomplete physical natural resource stock ac-counts and changes in stocks as measures of de-pletion (UNSD 1993; de Haan 1999). Economicvaluation and monetarization were also key goalsseen as helping in aggregating measures of nat-ural resource stocks and human use. The PIOTapproach relates to the SEEA, but focuses onflows (which act as additions or reductions tostocks or assets) to identify complete materialbalances for production sectors and householdconsumption (Stahmer et al. 1998).10

As in the TMRO and MFA-BIF models, theprimary objects of interest in PIOT are environ-mental concerns related to the throughput of aregion (Bringezu 2000). The approach attemptsan exhaustive physical coverage of the move-ment (origins and uses) of most environmentallyrelevant materials induced by an economic re-gion. Within the economy, PIOTs share the con-ceptual basis of older environmental input-output analyses by identifying physical materialflows within the framework of monetary input-output tables and by including “production factornature”—that is, “free” natural resources as asource of inputs and a sink for residuals from theeconomy (Radermacher and Stahmer 1998).Material flows examined vary in aggregationlevel from the bulk materials of b-MFA to inputsand residuals analyzed as elements or simplechemical compounds. Gravgard Pederson (1999,p. 7) describes the aim of PIOTs as showing “howthe natural resources enter, are processed andsubsequently, as commodities are moved around

the economy, used and finally returned to thenatural environment in the form of residuals.”PIOTs have at least two features, stemming fromthe underlying input-output analysis framework,that together distinguish it from the previousTMRO and MFA-BIF approaches, however.They are as follows:

(1) The detailed investigation of intersec-toral physical flows of environmental re-source inputs, commodity weights, andresiduals

(2) Given this intersectoral specificationand transactions matrix structure, theability to evaluate the cumulative en-vironmental burden (total direct and in-direct effect material requirements andpressures) of private consumption andother final demand for the products ofdifferent industries (Tjahjadi et al.1999)

Analogous to the logic of financial account-ing in standard input-output analysis, the calcu-lation of material flow quantities within the sys-tem borders in PIOTs must adhere to thematerials balance principle.11

Although many nations have been develop-ing PIOT-related frameworks to accommodateproposed changes under SEEA in the twenty-firstcentury, the PIOT methodology has been mostextensively applied by Germany (1990) (Stah-mer et al. 1998) and Denmark (1990–1992)(Gravgard Pederson 1999). Other projects areunderway or have been completed on a partialbasis for the Netherlands (1990) (Konijn et al.1995), Finland (1995) (Maenpaa 2000), and Ja-pan (1990) (Moriguchi 2002). As early as the1980s, a developmental PIOT was developed forAustria using 1983 input-output data (Katterland Kratena 1990). All studies examine (1) massflows and the physical accumulation of materialand energy commodities within the economy us-ing standard disaggregation into economic cate-gories covering industry branches (often includ-ing environmental protection and recyclingservices), household consumption, tangible as-sets, and the rest of the world and (2) flows be-tween the economy and natural environmentlinked to these same categories. The exact meth-odological form and coverage of PIOT, however,

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varies considerably across the different nationswhere it has been implemented (Eurostat2001a). In the complete German PIOT, thephysical measurement of product flows in tradi-tional input-output table structures allows thedetermination of material balances for activities,and both German and Danish PIOT also includedetailed NAMEA-type substance accounting.

The format of the 1990 German PIOT pro-vides a good idea of the technique’s approach toidentifying the structural relations of materialflows. This analysis was composed of the follow-ing:

1. Physical input or “use” tables establishingwhich economic categories (explainedabove) use or receive which materials(“materials” are divided into three maingroups: raw materials, products, and resid-uals)

2. Physical output or “supply” tables showingwhich economic categories (includingnonproduced natural assets) produce ordeliver which materials (hence, raw ma-terials from nature would show as an out-put in the supply tables but an input in theuse tables)

3. Material integration tables indicating theuse made of the entire supply of the threemain material types (in rows) by the vari-ous economic categories (in columns)(The material integration tables are com-piled after reconciling inputs and outputsin the economic categories and checkingbalances in tangible assets and the rest ofthe world sectors. Although the separatephysical input and output tables providedetailed information of the flows betweenmaterials and sectors, the integration ta-bles comprise the full input-output link-ages between the PIOT economic catego-ries. At present, the full input-outputrelations are less detailed.)

4. Separate subtables showing the materialcategories of water, energy, and other ma-terials (such as biomass and constructionmaterials) (This step allows assessment ofvery marked differences in flow magni-tudes and environmental significance andaids the reconciliation process.)

Views on whether PIOT should be classed asa form of MFA are mixed. For example, whereasHuttler and colleagues (1997) discuss PIOT as avariation of MFA, Udo de Haes and colleagues(1998) see it as a separate approach sitting along-side MFA as alternative types of the broader fam-ily of environmental accounting techniques. Ar-guments against its treatment as MFA mayinclude its highly disaggregated approach withtoo great an emphasis on specific input-outputcharacteristics and results that tend to obscurethe “bigger picture” required for a systemwideperspective. Similarly, it is often applied with asectoral or problem-theme focus utilizing formaleconomic classifications and procedures inherentto economic input-output methods. PIOTs, how-ever, do exhibit many of the key features thatseem to be required of MFA, including the eco-nomic systemwide nature of material flow sourcesand impacts, national or regional flow extents(and national economy–environment systemboundaries), and the comprehensive coverage ofmaterials. Hence, although PIOTs are framedwithin the standard economic context of mon-etary input-output analysis, these characteristics,together with their purely physical measurementapproach, have led to their classification here asan “MFA2” technique (in table 2 of part I).

Many sources of information can be used inthe ambitious task of compiling PIOTs—fromdetailed records of physical flows (including re-cycling), to input and residual technical coeffi-cient data and energy input-output tables, to theconversion of commodity data from value tomass measures using price-volume ratios. In theDutch PIOTs, monetary supply and use tables areconverted into material balances using physicaland price information, expert knowledge, andwaste flow data (Eurostat 2001a). Aggregation ofthe detailed commodity data facilitates the rec-onciliation of input-output relations. The diffi-cult process of data collection can include theclose examination of observed input-output im-balances to assess or cross-check stock changesand residual output levels. Physical data on tradestatistics can also be very useful in the derivationof PIOT.

In the German approach, PIOTs have beenutilized as the basis for establishing a compre-hensive material and energy flow information

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Daniels, Approaches for Quantifying the Metabolism of Physical Economies: Part II 75

Figure 4 Physical input output tables and the material and energy information system.

system (MEFIS). This system can be conceivedas a “virtual cube” where the horizontal faceshows the matrix of flows between branches ofeconomic activities, changes in the stocks ofphysical and natural capital, and transactionswith the rest of the world (figure 4). The verticalface structures the material flow types coveringenvironmental resource inputs, commodities,and residual outputs. Hence, each horizontalslice would show the economy-environment andintersectoral flows for any specific material flowtype (Radermacher and Hoh 1997). The MEFISis aimed at improving the analysis of individualmaterial flows by identifying the relationships be-tween input, commodity, and residual flows.

The positive features of PIOTs include thehighly detailed information yielded on specificmaterial and commodity flows between very dis-aggregated sectoral activities. The input-output(intersectoral) structure covering a comprehen-sive range of physical material flows facilitatesthe relatively unique ability to apply Leontief in-verse matrix operations to estimate cumulativeenvironmental impacts associated with final con-sumption. This potential can yield a more ac-curate depiction of the true extent of environ-mental burdens of products and processes and theenvironmental quality impact of the nature ofconsumption. Most MFA approaches only mea-sure the direct material requirements into the

economy or, at best, the flows for a few highlyaggregated sectors and material groups.

A number of limitations of PIOTs offset theseadvantages for environmental policy analysis anddesign. In addition to the general problem ofstatic and linear input-output relations shared byall “snapshot” physical economy techniques andmonetary input-output analysis, specific limita-tions of PIOTs include (1) restricted coverage toenvironmental inputs and outputs associatedwith domestic economic sectors and minimalincorporation of domestic and foreign hiddenflows (especially those linked to production) and(2) enormous data requirements, long time lagsin data collection and table preparation, and re-lated problems in discerning key patterns andtrends in the vast array of generated information.In time, many of these weaknesses will be ad-dressed by methodological improvements. Onlya handful of nations currently have informationsystem capabilities to pursue PIOT-styled analy-ses on a cost-effective basis—a situation that isundoubtedly responsible for the limited inter-national implementation of PIOTs to date.

PIOTs present a consistent, thorough, and de-tailed systematic framework with great potentialas an MFA approach. In particular, they can re-veal the relative and absolute material intensityor material efficiency of specific economic sectorsand trends in these measures if data are available

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over time. Given its compatibility with existingeconomic dimensions and national income ac-counting methods, PIOTs have all the potentialapplications of environmental input-outputanalysis (see James 1982; Kandelaars 1999; Pear-son 1989), but with greater precision in terms ofunderlying physical flow relations within theeconomy and hence eco-efficiency assessmentand the formulation of socially efficient strategiesfor sustainable development. These prospectswill undoubtedly strengthen as the various physi-cal economy approaches converge and data col-lection methodologies and techniques becomemore standardized and routine. The systematicapproach of PIOTs and their compatibility withexisting monetary input-output tables suggestthat they will play a key role in the ongoingstructuring and standardization of MFA tech-niques.

Substance Flow Analysis

SFAs are the fourth set of economywidephysical economy approaches and the last of thetechniques that are unambiguously considered asforms of MFA. SFA actually encompasses a num-ber of methodological variations, and the needfor standardization has been recognized by keyresearchers in the field (Udo de Haes et al. 1997).For most purposes, SFA is equivalent to thesubstance-based materials flux analysis approachdeveloped by a core group of researchers in Swit-zerland (Baccini and Brunner 1991). With re-spect to other MFA approaches, the primary dis-tinguishing characteristic of SFA is its focus uponmaterial flows of just one, chemically defined sub-stance, or a limited group of such substancesthrough the metabolism of a relatively extensive,predefined geographic region (Udo de Haes et al.1988; van der Voet et al. 1996). “Substances,” aschemical elements and their compounds, be-come the “material” under study in this variantof MFA. Typical examples in existing researchinclude nutrients such as nitrogen and phospho-rous, chromium, mercury, lead and other heavymetals, carbon, water, and organochlorine com-pounds.12

SFA fits neatly into the MFA family becauseof its emphasis on systemwide flows, accumula-tions, and impacts; integrated chain relations;

and material balance principles in tracking flowsinto, within, and out of the human economy.Furthermore, the economywide regional basis forflow sources would seem to qualify SFA as a clas-sic form of “macro-MFA” (as described in part I).SFA has developed largely as a response to criti-cal environmental pollution problems stemmingfrom a specific (typically toxic) environmentalpollutant source, however, and this singular focusis often associated with a relatively narrow iden-tification of the range of metabolic flows in theoverall human economy. As a result, although acomplete SFA may consider systemwide aspectslinked to the single substance (group) understudy, it may only describe a very small portionof the surrounding metabolism of the wider eco-nomic system. On this basis, SFA is only a “par-tial macro-MFA” that is powerful in terms of itsspecific problem theme, but is limited with re-spect to MFA’s potential strength in providingsystemwide understanding of the nature of soci-ety’s metabolism (as incorporated in the TMROand MFA-BIF approaches).

Although there are exceptions (for example,water and carbon), SFA tends to study the met-abolic pathways of high-impact, low-volumetoxic materials (Wernick 1998). This stands incontrast to b-MFA, which aims to identify theoverall material basis of economies by measuringa comprehensive suite of material group catego-ries composed of major compounds (for example,water and oxygen) and mixtures of compoundsin the form of natural and technical materialssuch as biomass, soil, ores, fossil fuels, and soforth. While the division between SFA and otherforms of MFA is somewhat arbitrary, the disag-gregated nature of materials studied, the environ-mental problem theme focus, and the delimitedextent of coverage in SFA, has led to the for-mulation of a number of distinct methodologicaldimensions. SFA generally begins with a specificenvironmental problem (for example, lead emis-sions and accumulations) and proceeds to di-rectly relate impacts of “problem” substances totheir economic origins by modeling substancepathways and quantifying actual flows. Thesources of the release of the substance to the en-vironment (and hence, how to eliminate or min-imize these sources) is of primary interest in SFA(Hansen 1997). Alternatively, b-MFA ap-

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Figure 5 SFA diagram for nitrogen compounds for the European Union.

proaches tend to be more concerned with theoverall metabolism functions and objectives re-quired for Factor 4, 10 and other related eco-efficiency strategies.

SFAs are usually designed to provide the in-formation basis for overall environmental man-agement and the formulation and implementationof elimination, reduction, dissipation minimiza-tion, and recycling strategies for dealing with aspecific pollutant or other resource substanceflow. This is achieved by identifying (1) existinglevels and trends in substance emissions, accu-mulations, and concentrations in the humaneconomy and various environmental media (e.g.,the lithosphere and biosphere), (2) the contri-bution of specific life-cycle stages and processes,goods, sectors, and activities to anthropogenicflows and emissions (and how these contribu-tions change over time), and (3) the qualitativenature of environmental impacts of certain hu-man economy activities associated with a specificsubstance (figure 5).13 SFA is also useful formonitoring and prediction purposes for evaluat-

ing management strategies and for revealing thelocation, timing, and extent of future problemslinked with specific pollutants or other high-impact substances.

The development of SFA in a number of sepa-rate institutional settings has led to some signifi-cant conceptual and terminological variations.One major example of this diversification is thecoherent accounting framework emphasis of ma-terials flux analysis based on the work of Bacciniand Brunner (1991).14 The aim and mode ofanalysis in material flux analysis is very similar tothe general SFA approach. It includes some ofthe most detailed and comprehensive examplesof existing research and modeling in the identi-fication of substance flows and accumulations as-sociated with what the researchers associatedwith the material flux approach call the “metab-olism of the anthroposphere.” Most of the dis-crepancies between material flux analysis andother SFAs are related to terminology; however,these differences do reflect a degree of conceptualdissimilarity. For example, “material” in material

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flux analysis refers to chemically defined ele-ments and their compounds (Brunner et al.1994). This is basically equivalent to “sub-stances” in the general MFA studies that con-sider “materials” as covering a broad range of nat-ural or technical elements and compounds andeconomically and environmentally relevantmixtures of these chemically defined substances.Furthermore, materials flux analysis utilizes rela-tively precise and specific definitions of “pro-cesses,” “goods,” and “activities,” and aspects ofthis underlying conceptual framework are not al-ways adopted in other SFAs. The basic relationsbetween material fluxes, goods, and processeswithin a study region is schematically depictedin figure 6.

The materials flux analysis model explicitlystresses the need to incorporate flows of goods(as carriers of multiple materials) at the systemlevel to properly assess material or substanceflows.15 The “SFA” label is more consistent withthe acceptance of MFA as a generalized metatoolfor the physical quantification of the metabolismof the human economy, however.

SFA does not generate any inherent referencemeasures for gauging sustainability, but its spe-cific substance focus enables the ready compari-son of current and predicted anthropogenicfluxes (e.g., of nitrogen, carbon, and lead) withnatural, geogenic fluxes in order to assess the sig-nificance, and perhaps sustainability, of human-induced flows and accumulations. Despite thisimmediate appeal, sustainability references basedon comparisons with geogenic fluxes and naturalvariations are often arbitrary, and actual toler-ance or threshold levels or ratios of anthropo-genic to natural fluxes are rarely known (Chad-wick 1998).

Individual SFAs are also limited in providinginformation for overall resource managementgiven their indirect links to monetary data andtheir reliance on a very narrow range of materialflows. This narrow focus means that SFA is gen-erally unable to gauge the net effects of substi-tution by other substances and related shifts inflows and accumulations across environmentalmedia (Udo de Haes et al. 1998). Nevertheless,SFA is an essential member of the MFA familyof techniques and contributes valuablesubstance-specific, intersectoral flow data for as-

sessing the significance of human-induced flows.This role will increase in importance with on-going development of its methodology and datasources and with greater integration with otherforms of MFA.

Other Approaches forQuantifying Material Flowsfrom the Entire PhysicalEconomy (“MFA-Related”Techniques)

Ecological Footprint Analysis

EFA calculates and groups material and en-ergy requirements of nations (or regions) andconverts these metabolic flows into the ecologi-cally productive land area required to producesuch resource categories. These land require-ments are then compared to the “supply” of eco-logically productive areas available at regional,national, or global scales. Existing studies havetypically been restricted to the ecological re-source output potential of terrestrial areas. Theapproach has attracted increasing interest follow-ing initial work in North America, Japan, Aus-tralia, and New Zealand (see Wackernagel andRees 1996; Wackernagel et al. 1997).

EFA was designed as a readily comprehendedindicator of the sustainability of the humaneconomy vis-a-vis the Earth’s remaining “natu-ral” capacity to supply resources (sometimes con-sidered equivalent to the planet’s terrestrial car-rying capacity). Two main interpretiveapproaches to the application of the EFA meth-odology exist. The best-known approach focuseson assessing the sustainability and equity of cur-rent use patterns by comparing (1) total and percapita national or global “footprints” of inducedmetabolic flows with (2) national or global “car-rying capacity” (Bicknell et al. 1998). If currenttotal or average per capita demands exceed avail-able regeneration or assimilative capabilitiesfrom eco-productive land areas, existing meta-bolic needs are deemed unsustainable and areonly maintained in the short term by reducingtotal assets of natural capital (or by imports orunfair consumption if assessing regional pat-terns). Hence, eco-footprints can provide a mea-sure of the extent to which carrying capacity is

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Daniels, Approaches for Quantifying the Metabolism of Physical Economies: Part II 79

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being utilized or overexploited (Yencken andWilkinson 2000).

Alternatively, the ecological footprint meth-odology can be directed toward more policy-oriented purposes by highlighting which con-sumption activities have the greatest impact interms of material and energy requirements andby suggesting the appropriate focus of more de-tailed analysis for metabolic reductions via effi-ciency, recycling, consumption, and other strat-egies.

EFA has been classified here as the first ofthose physical economy approaches that quantifythe metabolism induced by all actions across thehuman economy, without generally being clas-sified as a form of MFAs. It is important to rec-ognize, however, that EFA possesses several ofthe essential characteristics of the MFA meth-odology. For example, EFA has similarities interms of system boundary identification, an over-riding concern with the measurement of meta-bolic flows in physical terms, an economywideanalytical focus that includes all economicsources of resource demands from a political oreconomic geographical entity, and coverage of allmajor material flows. Hence, EFA (and the re-lated “environmental space” and “sustainableprocess index” approaches) are proposed as“MFA-related” techniques.16

On the other hand, EFA has unique differ-ences that set it apart from the general MFAmethod. These include its incorporation of en-ergy consumption as a major metabolic through-put (in thermodynamic terms but converted to a“material” measure in terms of the output fromland); the rather specialized and aggregated setof material flow groups (which are much less de-tailed than the PIOT and TMRO approaches);the emphasis on renewable and surface, terres-trial resource sources; and the restriction of met-abolic flow measures to the intermediate stagesof the analysis (prior to conversion to an ultimatefocus upon land area as the essential sustainabil-ity unit).

The derivation of sustainability reference in-dicators is a critical objective and outcome ofEFA. This is achieved by the translation of hu-man demands and ecological supplies into eco-logically productive land, which is consistent

with the fundamental premise that area (theEarth’s surface) represents the main limiting fac-tor for the scale of human activity (Haberl andSchandl 1999). Metabolic flows are consideredas the total intake of material and energy needs.Mass flow measures are then “lost” in the con-version to six major types of ecologically produc-tive land: energy, built (degraded), garden, crop,pasture, and forestland. Next, the converted ma-terial and energy requirements are attributed tofive types of consumption activities (food, hous-ing, transportation, consumer goods, and govern-ment services).17 The result is an ecological“footprint” matrix (land type–consumption sec-tor matrix), which clearly shows the environ-mental (land) requirements of different con-sumption activities in a nation or region. Agraphic illustration of this matrix, based an eco-logical footprint study for Australia, is shown infigure 7.

Despite good potential for integration withinput-output approaches, current EFA tech-niques do not offer much scope for identifyingflows between specific goods and processes, andcradle-to-grave impacts are only measured in ahighly aggregated manner. Similarly, they arevery limited for measuring recycling, stockchanges, and output from the human economyand hidden flows that occur around the peripheryof “economic” activity.

As a sustainability measure, the values for thesix ecologically productive area types can also besummed together to get a total land requirementfor the nation’s current consumption. This mea-sure (and its per capita derivative) can be com-pared with those for other nations and the totalamount of ecologically productive land availablein the nation under study. The latter comparisonreveals the ecological “deficit” associated withthat nation.18

Environmental Space Models

Environmental space (or eco-space) is the to-tal annual consumption of natural resources towhich each individual is entitled on the basis ofboth the capacity of the natural environmentand equity considerations (Eurostat 2001a; Hille1999). Physical measurement of the socioeco-

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Figure 7 Ecological footprintanalysis matrix for Australia.

nomic metabolism under the environmentalspace concept (and also in the sustainable pro-cess index) has many similarities to EFA. It hasbeen, however, largely a western European un-dertaking developed by Opschoor and Reijnders(1991), Buitenkamp and colleagues (1992), andthe Wuppertal Institute and supported and pro-mulgated by projects by the Friends of the Earth,Europe. As with the other two MFA-relatedphysical economy approaches in table 2 of part Iof this series, the environmental space techniquewas devised as an indicator of the sustainabilityof current resource use by humans. Its primaryfunction is to quantify or track sustainable de-velopment by comparing resource demands anduse with available “environmental space” or thephysical boundaries of the Earth’s supply of en-vironmental services that are available and canbe appropriated sustainably by humans. As inEFA, environmental space rests upon the generalnotion of the carrying capacity of the environ-ment by identifying the “ceilings” or maximumlimits of the renewable resource regeneration andwaste assimilation capabilities of the environ-ment.

EFA estimates a “footprint,” or a measure ofhuman-appropriated carrying capacity, as thesum of various categories of land-type areas

needed to produce the natural resources requiredby a population in a given region. Next, this totalarea required is compared with the ecologicallyproductive capacity of land available. The en-vironmental space approach follows a similarlogic by attempting to identify the quantity ofvarious categories of natural resource servicesthat can be exploited by humans over a giventime period (usually a year) without compromis-ing the quantity and quality that can be accessedby future generations (DEPA 1999). Of course,this requirement is problematic for nonrenew-able resources, and the introduction of substitu-tion possibilities greatly increases the complexityof operationalizing this concept. Unlike the focuson total ecologically productive land area inEFA, the environmental space methodology doesnot attempt to convert all environmental im-pacts into a single unit or statistic. Rather, it sep-arately assesses sustainability for energy and rawmaterials, biological resources, waste assimilationand storage, and fundamental life-support func-tions. A fairly comprehensive coverage of themajor human environmental impacts is under-taken by independently analyzing resource ser-vice function capabilities or sustainability limits(ideally, the global or appropriate regional aver-age per capita maximum consumption levels

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consistent with sustainable development). Theselimits are compared with national per capita uselevels for categories such as energy, forests, nat-ural or agricultural areas, water, and major non-renewable minerals groups (see FEE 1995).

A definitive aspect of the environmentalspace approach, however, is the concern for eq-uity in resource use. This includes the adoptionof sustainable development–related principles ofintergenerational equity and an assessmentframework based upon intragenerational equityacross the existing global population. Hence, thekey indicator in this mode of analysis is environ-mental space expressed as global or regional av-erage per capita consumption levels that can besustained. Thus, it is not surprising that the high-income nations are revealed to have consump-tion levels that greatly exceed their fair share ofthe sustainable output of natural resources fromthe environment. For example, Europe’s CO2

emissions in the mid-1990s have been estimatedas well over 4 times the maximum global averageemissions per capita that can be sustained in viewof the planet’s assimilative capacity and antici-pated population level (Spanenberg 1995; Han-ley et al. 1999).

Such comparisons of environmental spaceand human demands and trends indicate thescale and priority of changes required in each re-source category. The extent of the gap betweensustainable ceilings and current use in per capitaconsumption provides the critical informationfor recommending sustainability targets and ap-propriate strategic policy action.18 Minimum lev-els of per capita consumption for acceptablequality of life (“floors”) can also be considered inthe analysis.

Metabolism Measures ofSpecific Products, Services,and Processes

The previous techniques have been con-cerned primarily with gauging total, highly ag-gregated bulk materials or specific substanceflows associated with the entire sphere of humaneconomic activity within a given region. For pur-poses of comparison, part I of this series includedthree individual models that concentrate uponthe environmental implications of quite specific

areas or types of activities within the overalleconomy. These activities include selectedgoods, services, technologies, or processes. Thegroup is identified as MFA2 in the major divi-sions in the second row of table 2 in part I. Giventhat these approaches are not concerned withthe economywide analysis of physical economiesand the need to economize on the printed lengthof the article, the overviews of these techniqueshave been shifted to the e-supplement section ofthe Journal of Industrial Ecology (mitpress.mit.edu/jie). The enterprise level delineation ofthe human economy labeled “company-levelMFA” is included in the comparison in part I,but its description would introduce a new set ofauxiliary considerations beyond the purview ofthis review.

Conclusions

The measurement of material flow levels inthe economywide approaches that clearly belongto the MFA family (MFA1) do not provide adirect indication of the sustainability of existinglevels of human use of the environment. Ofcourse, substantial reductions in metabolic flowswill, if maintained, contribute toward the poten-tial for sustainable development. Without criti-cal environmental threshold limits that fully ac-count for the temporal and spatial dimensions ofsustainability, however, straightforward physicalmeasures of anthropogenic flows are inadequatefor this task. Arguably, MFA does not claim toprovide the comprehensive evaluation of thepath toward sustainable development. Rather, itcan be envisaged as a methodological approachfor systematically compiling the physical data in-formation base for subsequent development andintegration with other data so that effective de-cisions can be made and policies formulated andapplied to achieve sustainability.

The results of MFA must be evaluated againstsome sustainability reference or “acceptance cri-teria.” These yardsticks can be derived in manyforms—from comparisons with natural geogenicfluxes, to carrying capacity or assimilative capac-ity thresholds, to LCA-style impact assessmentcalculation of percentage contributions to majorenvironmental emission and other problem“themes” (see Udo de Haes et al. 1998 and Wer-

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nick and Ausubel 1995). Furthermore, the highlyaggregated TMR and domestic output and totalmaterial flows of the MFA-BIF models are not asuseful for devising specific sustainability strate-gies as the measures of flows at a more detailed,individual level. The synergistic and complex in-teractions between individual flows ensure thatsystemwide perspectives will play an importantrole in this quest, however.

This article has described and compared ninedifferent models for quantifying the material(and sometime energy) flows that are induced byhuman economic activity. The major aim hasbeen to systematically deconstruct most of thepopular socioeconomic metabolism quantifica-tion approaches and compare their key featuresalong several key methodological parameters.The analysis should help improve understandingof these popular approaches across an ever-growing group of researchers and policy makersconcerned with eco-efficiency (and indeed inter-national competitiveness and economic welfare)gains through the dematerialization of produc-tion and consumption. The article is intended toprovide an effective “primer” rather than an in-depth analysis of individual methodologies.

Although introductory in nature, this articlehas provided more extensive discussion of thespecific features, implementation, and sustain-ability relevance of the definitive notion of MFA(“MFA1”) vis-a-vis the other related physicaleconomy approaches that are not categoricallytreated as MFA. By identifying areas of agree-ment and discord, we hope to stimulate discus-sion and further steps toward the developmentof a more consistent overarching framework forthe physical quantification of metabolic flows.

The tentative comparative analysis has beendifficult in view of the rapidly evolving natureof relevant scientific work that has been directedat the same general goal, but with independentdevelopment spawning distinct methodologicalvariants. Nonetheless, the review of the physicaleconomy approaches demonstrates the need forstandardization and convergence of approachesto help progress toward the development ofclearly defined, if still evolving, techniques thatare appropriate for different functions and at dif-ferent system levels. An understanding of the ap-proaches, and the individual strengths, weak-

nesses, and linkages of their methodologies,reveals a great deal of potential for mutual inter-action and benefit. Building upon the many sim-ilarities in the techniques covered in this surveywill encourage convergence and standardizationand facilitate the realization of this potential.

Acknowledgments

This article is a modified version of a posi-tional article prepared for the inaugural MaterialsFlow Analysis for Sustainable Resource Manage-ment meeting held at the Wuppertal Institute forClimate, Environment, and Energy, November23–25, 2000, under the auspices of the ScientificCommittee on Problems on the Environment ofthe International Council of Scientific Unions.

Notes

1. These three techniques are classified as “MFA1”in table 2 of part I of this article pair.

2. Under the materials balance principle, domesticprocessed output must equal the mass of domesticmaterial input minus the mass of net additions tostock and exports.

3. This list of country studies is derived mainly fromthe work of Bringezu (2000) and Eurostat (2001a;2001b). Most of the country reports are unpub-lished. A partial list of TMRO-based analyses in-cludes studies of the United States, Japan, Neth-erlands, Germany, and Austria (Adriaanse andcolleagues 1997; Matthews and colleagues 2000),Australia (Poldy and Foran 1999), China (Chenand Qiao 2000), Egypt (El-Mahdi 2000), Finland(Maenpaa and Juutinen 2000; Hoffren et al.2000), Italy (Femia 2000; DeMarco et al. 2000),and the United Kingdom (Schandl and Schulz2000). Most other report results are consolidatedin the Wuppertal Institute database described ina report by Eurostat (2001b).

4. The study by Adriaanse and colleagues (1997)presented TMR results for Germany, Japan, theNetherlands, and the United States. Collectively,these nations produce more than 50% of thevalue of Organisation for Economic Cooperationand Development (OECD) economic output.

5. The emphasis of this survey is on comparativemethodological features of the approaches anddiscussion of empirical results is necessarily keptto a minimum. For more detailed results of theTMR studies, see the original report (Adriaanse

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at al. 1997; Berkhout 1998; Yencken and Wilkin-son 2000).

6. Two major representative works for the IFFSchool of Social Ecology approach are by Fischer-Kowalski and Haberl (1993) and Huttler and col-leagues (1997).

7. The School of Social Ecology has also developedthe operating matrix economy-nature (OMEN)tables (see Fischer-Kowalski et al. 1998) as ameans of compiling consistent and internation-ally comparable material input-output balancesgiven the shortcomings and classification diver-sity of material flow data in different national set-tings. In the OMEN method, subtables would becompiled for the various resource input categories(and imports) relevant for each of the five majormaterial groups as used in the 1992 national MFAfor Austria. Outputs are distributed among ex-ports, emissions to air, emissions to water, wastes,and deliberate disposal. The sectoral breakdownis split between primary production, processing,consumption, and stocks.

8. As discussed, materials balancing is becoming astandard feature of the TMRO approach as it pro-gressively includes the analysis of environmentaloutputs and net additions to stock.

9. In extensions of the TMRO approach, the econ-omy has been disaggregated to measure flows fromthe environment to individual economic sectors(for example, see the input-output based analysisof material inputs of industry delivered to finaldemand in Bringezu et al. [1998]).

10. Alternatively, the National Accounting Matrixincluding Environmental Accounts (NAMEA)builds upon earlier environmental input-outputframeworks (for example, Cumberland 1966; Le-ontief 1970; Victor 1972) to provide a consistentextension from existing monetary national in-come accounts by directly connecting environ-mental externality effects, measured in physicalterms, to the monetary statistics in the nationalincome accounting matrix classifications (Keun-ing et al. 1999). These environmental impacts aretypically aggregated into a limited number ofthemes to link to ecological, social, and eco-nomic parameters and make national and sectoralcomparisons in terms of contribution to total en-vironmental pressures and sectoral eco- orenvironment-intensities (for example, CO2 emis-sions per international dollar of value added.)NAMEA has become an integral part of Euro-stat’s environmental accounting approach andthe 2000 version of the international SEEA. TheUnited Nation’s SEEA attempts to integrate en-

vironmental and economic accounting and ex-pands and complements the conventional Systemof National Accounts for national income ac-counting by quantifying the services provided bynatural capital as well as those of human-madecapital (Bartelmus 1994). It covers the use or de-pletion of natural resources in production andconsumption, and negative and positive changesin environmental quality from human interven-tion and natural regeneration or loss.

11. Radermacher and Stahmer (1996) describe theaxiomatic equation for flows (in tons) for eachdomestic activity (production branches andhouseholds) as Extracted Raw Materials � Useof Domestic and Imported Products � Storage orTreatment of Residuals � Products of DomesticProduction � Supply of Residuals from DomesticActivity.

12. Relevant SFA studies include those for chlorine(Kleijn et al. 1994), nitrogen (Febre Domene andAyres 2001), cadmium and nitrogen (van derVoet 1996), and polyvinyl chloride (Tukker et al.1997; Kleijn, Huele and van der Voet 2000). Anextensive list of substances covered by SFAs atthe national level in Denmark can be found inHansen (1997), and a range of analyses of sub-stance flows such as mercury, biotic carbon, lead,and plastics are included in the report by Bringezuand colleagues (1997). More information onchlorine flows can be found on the Web atwww.yale.edu/jie/SpecSeriesChlorine.htm.

13. See the work of Udo de Haes and colleagues(1997) and Berkhout (1997) for detailed over-views of the policy and strategic applications ofsubstance flow and related analyses.

14. A brief overview of the Baccini and Brunner ap-proach and essential steps in its procedure havebeen described in part I of the article pair.

15. While the method is initially very resource in-tensive, its economic viability is being enhancedwith the establishment and compilation of data-bases of goods, and material concentrations invarious goods, together with improved under-standing of the partitioning of materials throughprocesses.

16. In view of space limitations and an emphasis oncore MFA techniques, the remaining approacheswill be described in less detail.

17. When EFA land requirements are totaled, thisanalytical focus on relating ecological availabilityto human appropriation of ultimate renewable re-source supply sources can be seen as similar to thenet primary production (NPP) approach to as-sessing sustainability (Vitousek et al. 1986).

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18. Volume 32 of the journal Ecological Economics hasa special issue (Number 3) with commentary de-voted to this topic. Volume 37 (Number 1) alsocontains relevant articles and a central critiqueof the ecological footprint approach is presentedin van den Bergh and Verbruggen (1999).

19. Hanley and colleagues (1999, 62) actually define“environmental space” in terms of this gap. Forexample, they discuss how the “EnvironmentalSpace measure for any resource i is . . . the per-centage reduction (or increase) in the use of thatresource in country j necessary to reduce (in-crease) per capita consumption in country j to theglobal per capita average for resource i [requiredfor sustainability]”. However, most other re-searchers in the area define environmental spaceas a measure of the (per capita) eco-productiveoutput of the environment and hence the abilityof the environment to supply natural resources tothe human economy over a given period of time.

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About the Author

Peter Daniels is a senior lecturer in the AustralianSchool of Environmental Studies, Griffith University,Nathan, Brisbane, Australia.