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The Twenty-First Century: The World at Carrying CapacityAuthor(s): Gary W. Barrett and Eugene P. OdumSource: BioScience, Vol. 50, No. 4, Integrating Ecology and Economics (Apr., 2000), pp. 363-368Published by: American Institute of Biological SciencesStable URL: http://www.jstor.org/stable/1313713

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RoundtableT h e Twenty-Firstentury: T h eWor ld a t CarryingCapacityBY GARYW. BARRETT NDEUGENE ODUM

Much has been written n recentyearsregardingthe need to live within a societythat sustains itsresources for the future, a goal that requiresimplementingplansfor the futurebased on the conceptofsustainable development (e.g., Lubchenco et al. 1991,Huntley et al. 1991,NCR 1991, Heinen 1994, Goodland1995).A forum on "Perspectives n Sustainability,"hichappeared in Ecological Applications(November 1993),attemptedto summarizemany of the earlierperspectivessurroundingthis topic. Unfortunately,considerablecon-fusion remains,especiallyamongthe citizenry,as to whatis meant by sustainabledevelopment.Dictionariesdefine"to sustain"as "to hold,""to keep in existence," to sup-port,""to endorse without failing or yielding,""to main-tain,"or "tosupplywith necessitiesor nourishmentto pre-vent from falling below a given threshold of health orvitality."Given these definitions,the businesspersonoftenviews sustainabilityas sustaining profits based on ever-increasingconsumption of limited natural resourcesorsustainingrapid economic growth forever!At the otherextreme, the definition in the widely cited Brundtlandreport (WCED1987)-namely, that "sustainable evelop-ment is developmentthat meets the needs of the presentwithout compromisingthe abilityof futuregenerations omeet their own needs"(p. 8)-is so vagueas to be impos-sible to quantifyor implement.In terms of human affairsover the long term, sustain-ability maymore effectivelybe understood and dealtwithin terms of a two-dimensionalcarryingcapacityconcept,which considers not only numbers but also per capitaimpactat the ecosystemand ecosphere evels(EhrlichandHoldren1971,Catton1987)."Carrying apacity"s a con-ceptthat wasoriginallydevelopedby ecologistswith refer-ence to the number of animalsof a givenspeciesthat canbe supportedwithout injury to the habitat (i.e., carriedoverlong periodsof time without reducing he capacityofthe habitat o supportthatmanyanimals n the future; ordetails,see Pulliam and Haddad1994).When referring ohumans, however,just consideringnumbers (density) isnot enough because individuals can differ greatlyin theintensityof their impact on the environment.An Ameri-can citizen,for example, mayconsume 100 or more times

as much energyand resourcesas a citizen of a developingcountry.In other words,affluence reducesthe numberofpeople that can be supportedby a given resourcebase.Thus, ecologistshave to be concernednot only with den-sity but also with per capitademands.From anotherviewpoint,ecosystemdevelopmentparal-lels societaldevelopmentin that both will inevitablyendup in a non-equilibrium pulsingstable state (Odum et al.1995) in which respiration(R; i.e., maintenance)on theaveragedoes not exceed production (P). If the energy,money,or technologyavailable o maintain a complexsys-tem are inadequate,then the system becomes disorderlyand soon defaultsor dies. From this functional or ener-getic viewpoint, carryingcapacity s reachedwhen P/R isapproximately1.To use carryingcapacityas an index for sustainability,two majorconcerns must be addressed: he tendencyforgrowthto overshootcarryingcapacityand the possibilitythat the optimum carryingcapacity s less than the maxi-mum. Figure1 depictsthe two contrastinggrowthforms:the sigmoid, in which growthlevels off as limits (K) areapproached,and the exponential,in which the momen-tum results n overshooting imits,creatinga "boom-and-bust" pattern.As pointed out by Wiegert (1974), theseformsrepresent he slowest andfastestgrowthforms,withmany populations exhibiting intermediate patterns ofgrowth.The overshootpatternoccursin natureand,increasing-ly, in human affairs(Catton 1980). For example, Barkleyand Seckler 1972) listedfour factorsthatforce or encour-age urbandevelopmentto overshoot the optimum:detri-mental self-crowdingeffects (e.g., pollution, congestion,and rising costs of schools, taxes, and police protection)are not felt until sometime after the optimum densityhasbeen exceeded; money is seldom made available forgrowth managementor land-use planning until conges-tion andtrafficbecomemajorproblems;politicalpower sconcentratedwithin a few wealthyor "keystone"groupswho benefit more from growth in size or quantitativegrowththan the average-income itizen;andthe mystiqueof growth persists from the pioneer days, when rapidgrowthand developmentwerenecessaryand desirable.Althoughthe self-crowdingproblemsthatlarge,rapidlygrowing cities are experiencingare generallyblamed onpoor fiscal management, n realitysuch cities have over-shot not only their economic supportbase but also theirregional life support base.Wackernageland Rees (1996)present several regional examples of populations that

Gary W. Barrett (e-mail: gbarrett@sparrow.ecology.uga.edu)sOdum Professorof Ecology,and EugeneP. Odum is DirectorEmeritus, t the InstituteofEcology,University f Georgia,Athens,GA30602-2202.@2000American nstituteofBiologicalSciences.

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Maximum arryingCapacity(Km)

OptimumCarryingCapacityKo)

gSigrnoid (S-Shaped)rowth

ExponentialJ-Shaped) rowth Pointofnflection

i -

I I ITime - -

requirean area that is much larger han their home terri-tory to support their present consumer lifestyles. Forexample, he"ecological ootprint"of Vancouver panstheLowerFraserValleyand is 19 times larger han the area ofVancouver itself. With rapid urbanization occurringthroughout the world, these predicamentsare becomingglobal in extent. Thus, land-use planners,policymakers,economists,and resourceecologistsneed to consider themeritsof downsizingbased on a carrying capacitythat ismore sustainableover the long term.In Figure1,we show the overshoot followedby a down-sizing to a lower carrying capacitylevel (Ko),which weterm"optimumcarryingcapacity."Wepresent his patternas an optimistic predictionfor the future.In otherwords,after experiencing the trauma and disorder of manybooms and busts, societal thinking and planning willreorient to emphasize qualitativeratherthan quantitativedevelopment (Odum 1975). Qualitative developmentwould preventthe kind of livingon the edgein which,forexample,a 1-yearregional crop failurewould cause wide-spreadstarvation,as is now occurring n North Africa.

A relatedconcept,"safecarryingcapacity,"omes out oflong-term studies of animal populations. For example,PaulErrington,who is well known for his lifelongstudiesof muskrat and mink populations in Iowa freshwatermarshes,observed hat muskrats hathad securedensnearfeeding areas were much less vulnerable to predationbymink than muskrats that did not have such high-qualityhousing (Errington1963).The numberof muskratswithsafe dens representedthe safe carrying capacity (Ko),which was almost always ess than the maximumnumberthat couldbe supportedby the food supplyin the absenceof predators i.e., the maximumcarryingcapacity,Km).

Figure1. Thecontrasting igmoid(S-shaped)and exponential (I-shaped)growth orm modelsinrelationto the maximum (KI)and optimum (Ko) carryingcapacityconcepts. n thiscase,growth refers o increase nnumbersof humans.

Such examples from naturalpopulations could serve as modelsfor human population growth aswell. Indeed, not too long ago,politicians used to talk about "thegreatestgood for the greatestnum-bers"as a goal for society.But thisslogan is rarelyheardnow becausesocietyis findingout by experiencethat the greatest good, in terms ofquality of life for the individual,comes when the numbers are notas high as they can possiblybe-and when the per capita

impactsarenot maximized,either.Fortunately,human population growth seems to be

beginningto level off in sigmoid fashion,with a projectedplateauat 9.4 billion by the year2050 and 10.4 billion bythe year2100 (Bongaarts1998,UN 1998).Currentworldhumanpopulationdensitymay, n fact,be just beyondthepoint of inflectionin the sigmoid growthmodel (see Fig-ure 1). The earth can probablyfeed more than 10 billionpeople, even with increasingaffluence,althoughif such adensity proves to exceed the optimum carryingcapacityfor a quality ifestyle,as many ecologistsbelieve will be thecase (e.g.,Smail 1999),then there will haveto be a periodof negative growth in population and per capita con-sumption. It seems likely that such a period of negativegrowthand per capitaconsumptionwill come soon. Peo-ple in developedcountriesareincreasinglybecomingcon-cerned about overconsumption,waste, unwantedbabies,and the increasinggapbetweenrich and poor worldwide.However,the momentum of rapid population growth issuch that downsizingis not likelyto occur until aftertheovershoot.Of course, some "cornucopianoptimists"believe thatdeveloping technologies (hydrogen economy, wastelessindustries, andlessagriculture)will enable10 billion peo-ple to coexistwith enoughnaturalenvironment o providefor the necessary ife support,preservationof endangeredspecies,and enjoymentof nature(seeAusubel1996).Newtechnologieswill certainlyincrease the carryingcapacityof the earth for humans, but, as PaulGray, ormerpresi-dent of the MassachusettsInstitute of Technology,hassaid, "A paradox of our time is the mixed blessing ofalmost every technologicaldevelopment"(Gray 1989, p.

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Roundtable192). Many technologies, such as fissionatomic energy or deep-sea drilling for oil,cost more than they are worth (i.e., theyhaveprovidedlittle or no net energy).EvenDonella Meadows and colleagues, whose1972book Limitsof Growthpredictedover-shoots unless economic policies changed(Meadowset al. 1972), are now somewhatoptimisticthat the worst "boomsand busts"can be avoided,eventhough they documentcases where limits have been exceeded(Meadowset al. 1992).We contend, therefore, that there existlimits (e.g., net energy and feedback con-trols) to human population growth, espe-ciallyasrelated o the qualityof human exis-tence, and that these limits and regulatoryprocessesareincreasinglycoming into play.Ratherthan expecting continuing unregu-lated human population growth well intothe new century,society should plan for afuturebasedon a sustainableoptimum car-rying capacity (Ko). Such planning wouldbenefit from a better understandingof howto integrateeconomic capitalwith nature'scapital.Thecarryingcapacityconceptasrelated to economicsThe urgentneed to integratenonmarketgoods and ser-vices (naturalcapital)into mainstreameconomic systems(see Barrettet al. 1998)is the focus forthis special ssue ofBioScience.Thisneedhas long been recognizedbut poorlyimplemented.For example, n the 1960s,economist Ken-neth Bouldingwrote about the need to move from quan-titative(getting bigger)to qualitative gettingbetter)eco-nomics. Although his books (e.g., A Reconstruction fEconomics;Boulding 1962) and papers (Boulding 1966a,1966b) were admired and he was one of the first econo-mists to be elected to the NationalAcademyof Sciences,mainstreameconomistspaidlittle attention. The time wasnot yet rightto implementhis ideas.In the 1970s, Howard and Eugene Odum suggestedusing energy as a common denominator to evaluate andcombine both marketandnonmarketvalues(Odum 1971,1973, Odum and Odum 1972, Gosselink et al. 1974).Because t takesenergywithin an economyto makemon-ey, energeticvaluescan be convertedto monetaryvalues.Dollar values for wetlands calculatedon this basis wereimpressiveenough to the citizenryto playa majorrole incoastalmarsh protection legislation of Atlantic and GulfCoastwetlands n the early1970s.However,economistsofthattime objectedstrenuously o the conversionof energyvaluesto monetaryvalues.Theycontendedthat value andpricewere determinedbypeople's"willingnesso pay"andnot by the amount of energyrequired o producea prod-

140

Ecomonic130 Growth

120

110 Thresholdo" (Carrying Capacity)o 100

o0Economic Welfare(Quality of Life)

80

70

601945 1950 1955 1960 1965 1970 1975 1980 1985 1990Year

Figure2. Recenttrends n thegrossnationalproduct(GNP)indexand theIndexof SustainableEconomicWelfare ISEW) n the UnitedStates,with thethreshold uggestedas theoptimum carryingcapacity.Opencircles,GNPindex;solid boxes,ISEW ndex.Figure modified romMax-Neef(1995),withterms in parentheses(on thecurves)addedby theauthors.

uct or service (a quantitynow labeled"eMergy";Odum1996).The OdumsandeconomistsLeonardShabmanandSandraBatieengagedin a point-counterpoint discussionof this difference n the pagesof the CoastalZoneManage-ment Journal(Shabman and Batie 1978, Odum 1979a,Odum 1979b).Again,the time had not yet come for anykind of reconstruction of economics. A weak ecologicaleconomics infrastructureduring the 1970s most likelyimpededthe integrationof ecologyand economicsat thattime.However, during the 1980s and 1990s, the time wasrightfor a seriousdialoguebetweenecologistsand econo-mists. EcologistRobertCostanzaand economist Herman

Daly collaboratedwith manyothersto establish he Inter-nationalSocietyforEcologicalEconomicsand a newjour-nal, EcologicalEconomics.For example,economist Man-fred Max-Neef (1995) compared trends in the grossnationalproduct(GNP)index with the Daly-Cobb(1989)Index of SustainableEconomic Welfare(Figure2). Thetwo indexes trackone anotherand then separateat a timeknown as the economic welfare hreshold.Figure2 repre-sents the United States'situation, but Max-Neef (1995)presented graphs depicting similar trends for all of thecountriesin westernEurope,althoughthe thresholdpointcomes a bit laterin time in some of these countries.We suggest that the economic welfare threshold isequivalent o optimum carryingcapacitybecause t repre-sentsthe point at which increasingreturnsof scale (biggeris better)changesto decreasingreturnsof scale (bigger s

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..........?..........~~Ki. . . . . . . . . . . 2 + . . ? = ? ;............:~~:~:~:~::2 . ? r

:~:::::. .. . . .. . . ..( : : : ? : a ' O ' ECOLOGY~;

H U M A K I N D S G O D S A T U E ' S O O DS E R V I C E S A N D S E R V I C E S

C O E V O L U T I O N A R Y : ~ : ~ ~ ? ? ~ : ~ ? ~( U R B A N - R U R A L )L A N D S C A P E D E V E L O P M E N T ? '~-~

no longerbetter).It wouldseem, therefore, hateconomicgrowthmeasuredby GNP is beginningto overshoot whatmight be called"qualityof life carrying capacity" n thedevelopedcountries.It is importantto distinguishbetween economicgrowthand economic developmentif society is to achieve a qual-ity of life carryingcapacity.A 1991reportfrom the Unit-ed NationsEducational,Scientificand CulturalOrganiza-tion (Goodlandet al. 1991) makes a distinction betweeneconomicgrowth,which involvesgettinglarger(quantita-tive growth),and economic development,which involvesgettingbetter (qualitativegrowth)without increasing hetotal consumptionof energyand materialsbeyonda levelthatis reasonably ustainable.Thereportconcludesthat"afive-to-tenfold expansion of anything remotely resem-blingthe presenteconomy [whichsome economistssayisnecessary to reduce poverty worldwide] would simplyspeedus from today's ong-run unsustainability o immi-nent collapse" pp. 10-11). Therefore, he report goes on,the economic growth required for poverty reduction(especially n the less-developedcountries)"mustbe bal-

Figure3. Convertinga bifurcatedaestheticperspectiveof nature'scapitaland human marketcapital to an integrative andscapeperspective nwhicha coevolutionary urban-rural)systememerges hat includesall goodsand servicesnecessary o sustain a quality life for all of Earth'sinhabitants.

anced by negative throughput growth for therich."A noteworthyroundtablediscussionof carryingcapacityand ecologicaleconomicsby Daly (1995)and Mark Sagoff (1995) has helped to continuethis dialogue among ecologists and economists.Costanzaet al. (1997) have estimatedthat the val-ue of the total biosphericnaturalecosystemser-vices in monetaryterms is greaterthan the valueof the total world market goods and services.Although mainstream economists were quick tochallenge the Costanza et al. (1997) initial esti-mate,it is encouraging hattherenow exists a seri-ous discussionfocusingon the quantitative mon-etary)value of nature'sgoods and services.It is also encouragingthat during the past 5years there has been a flood of new books thatmight be classified under the heading of "thegreeningof business."A good exampleis Ander-son (1998).RayAnderson s CEOof acarpetcom-panynamedInterface hatleases,rather han sells,carpets. Carpetstaken back to the factorywhenthey are worn out are completely recycled andreconstituted into new carpets with almost nowaste and pollution. Anderson says that he wasinspiredto makehis "mid-coursecorrection" fter

readingPaul Hawken'sEcology fCommerce: Declarationof SustainabilityHawken1994).Overview:An integrated(ecologic/economic) apitalismHuman society is rapidly approaching, and in someaspects already overshooting, global carrying capacity,whichwe define as two dimensional(densityand intensi-ty of percapitause).We have made a casefor the proposi-tion that the optimum carryingcapacity(Ko)is less thanthe maximum (Km),and that carryingcapacity s reachedwhen the P/R ratio approximates1. Accordingly,thereexists an urgent need to bring together essentialproce-dures andapproaches hatin the pastwere considered ep-arate and unrelatedoperations (the "one problem-onesolution"mind set). Some of these needs or strategiesareas follows:

A need to bring togethermarketand nonmarketgoodsand servicesas a basis for a more holistic economicandecosystem/landscapemanagement perspective.Odum

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Roundtable(1997a, 1998) suggests creating an integrated"dualcapitalism"i.e.,naturaland marketcapital;Figure3) as a way to capture the substantial benefits that,as summarizedby Daily et al. (1997), naturalecosys-tems supply to human societies. Cairns (1997)expresses this need in terms of promoting acoevolutionary, mutualistic relationship betweenhuman society and natural systems, rather than anindividualistic, competitive view of ecology andeconomics.* A need to promote appreciationof the aesthetics,as wellas the utility,of a diverse andscapethat includes natur-al areas,clean streams and lakes,well-managedfarm-land,and attractivevillages,towns,and citiesall operat-ing together to maintain a high quality of life(i.e., an integrative andscapeperspective;Barrett1985,1992, Barrett et al. 1998). Many people viewheavily fertilized and watered gardens,mowed lawnsor clipped grasses, and yards of carefully sweptsoil (i.e., something to be weeded, manicured, ormanaged for the short term in accordance with atraditional economic purpose or a cultivatedtaste) as"beautiful" nd natural,self-sustainingmeadows,grass-lands, or woodlands as "ugly."Figure3 illustrateshowthis previouslybifurcated aesthetic perspectiveis nowbeing integrated into a holistic, coevolutionaryland-scape perspective.An informed and educated societythat understands he goods and servicesprovidedby anintegratedurban-rural andscapewill likelyconduct itsbusinessbased on an educationalincentive rather thana regulatorymandate(Barrett1989).* A need to bridgethe communication gap between sci-ence and society,whichrequires mprovingthe dialoguebetween decision-makers (politicians, corporatemanagers,economists,lawyers)-who are,by and large,not scientists-and research cientists,who are increas-ingly more specialized(reductionist)and isolatedfromthe realitiesof public policy.* Reorganizing ollegesand universities o promotemoreinterdisciplinarycourses, including an integrativesci-ence approach (Barrettand Odum 1998), as is nowunderwayin many collegesand universities,will helptodevelop C. P. Snow's "third culture,"in which thecommunication gap between the humanities andthe sciences would be closed (see Odum 1997b).For this concept to come to fruition, a closerliaison must be establishedbetween basic and applieddisciplines (Barrett1984, 1994), which are often segre-gated in separate schools in academia, with littlecommunicationamongthem.* A need to unite ruralandurbanplanninginitiatives ntocomprehensive andscape-levelplanning (Barrettet al.1998) that acknowledges the interdependenceof the low-powered, rural, natural life-supportingecosystems and the high-powered, urban, techno-ecosystems (term suggested by Naveh 1982). This

task is difficult because political lines often sep-arate city from country. Ian McHarg pioneeredthis approach to planning three decades ago (e.g.,McHarg 1969), but society was not as ready for thisapproachas it is now.* Finally, ocietycould learn from the studyof the pioneerto mature naturalecosystemdevelopment(r to K selec-tion). (Resourcesare diverted to high growth rate andfecundity,rather than persistence, n r-selectedspecies;resources are directedto persistence,ratherthan highgrowth rate,in K-selectedspeciesunder carryingcapa-city conditions.) Natural selection favorsopportunistic,r-selected species in pioneer or early successionalcommunities but K-selectedspeciesin maturesystems,where survival and quality of the individual are moreimportant than the quantity of production. Societycould find waysto makea similar transition.

In additionto developingthese strategies o bringtogeth-er scholars and practitionersof ecologyand economics,itis importantto do so quickly.Unfortunately,manyof theideas and concepts about sustainability and carryingcapacitybeing espousedin recent reviewsand books haveremained traditional and disciplinary in concept andimplementation.The time has come to findwaysto devel-op truly ntegrativedeas aboutsustainabilityandcarryingcapacityand to implement these as soon as possible, inview of the increasing hreatsto the healthof the cohabi-tants of Earth.Indeed,Lester Brown recentlynoted thathuman society appears to be approachinga thresholdregardingan environmentalawakening,ncluding shiftingviews concerning energy,urbantransportationand plan-ning,materialuse,and humanpopulation growth(Brown1999). We sense that human society is readyto usher innew integrative(transdisciplinary)and ecologicaldefini-tions of carryingcapacityand sustainablegrowth as weenter the twenty-firstcentury.AcknowledgmentsG. W. B. thanksAlmo Farinafor invitinghim to co-chairthe plenary roundtable discussion entitled "IntegratingEcologyand Economics"at theVIIInternationalCongressof EcologyduringJuly1998in Florence, taly.Thisplenarysession servedas the catalystfor this specialissue of Bio-Science.We areindebted to TerryBarrettand threeanony-mous reviewers or their critical review of the manuscriptand to RebeccaChasan,editor-in-chiefof BioScience,orher editorial skillsin bringingthis issue to fruition.References itedAndersonRC.1998. Mid-courseCorrection:Towarda SustainableEnter-

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