Tracking the ecological overshoot of thehuman economyMathis Wackernagel*†, Niels B. Schulz‡, Diana Deumling*, Alejandro Callejas Linares§, Martin Jenkins¶, Valerie Kapos¶,Chad Monfreda*, Jonathan Loh!, Norman Myers**, Richard Norgaard††, and Jørgen Randers‡‡*Redefining Progress, 1904 Franklin Street, 6th Floor, Oakland, CA 94612;‡Institute for Interdisciplinary Studies of Austrian Universities, Department ofSocial Ecology, Schottenfeldgasse 29, 1070 Vienna, Austria;§Centro de Estudios para la Sustentabilidad, Obreros Textiles 57 Departamento 6, ColoniaMarco Antonio Mun˜ oz, 91060 Xalapa, Veracruz, Mexico;¶World Conservation Monitoring Centre, 219 Huntingdon Road, Cambridge CB3 0DL, UnitedKingdom;!World-Wide Fund for Nature International, Avenue Mont-Blanc, 1196 Gland, Switzerland; **Green College, Oxford University,Oxford OX2 6HG, United Kingdom;††Energy and Resources Group, 310 Barrows Hall, University of California, Berkeley, CA 94720-3050;and‡‡Norwegian School of Management BI, Elias Smiths vei 15, Box 580, N-1302 Sandvika, NorwayEdited by Edward O. Wilson, Harvard University, Cambridge, MA, and approved May 16, 2002 (received for review January 17, 2002)Sustainability requires living within the regenerative capacity ofthe biosphere. In an attempt to measure the extent to whichhumanity satisfies this requirement, we use existing data totranslate human demand on the environment into the area re-quired for the production of food and other goods, together withthe absorption of wastes. Our accounts indicate that humandemand may well have exceeded the biosphere’s regenerativecapacity since the 1980s. According to this preliminary and explor-atory assessment, humanity’s load corresponded to 70% of thecapacity of the global biosphere in 1961, and grew to 120% in 1999.Accounting for Humanity’s Use of the Global BiosphereThe hum an economy depends on the planet’ s natural ca pital,which pro vides all e cological services and natural resources.Drawing on natural capital beyond i ts regenerative capacityresults in depletion of the cap ital stock. Through comprehensiveresource accounting that compares huma n demand to th e bio-logical ca pacity of the globe, it should be pos sible to detect th isdepletion to help prepare a pa th toward sus tainability.The purpose of this study is to develop such an accountingframew ork, and to measure the e xtent of humanity’s currentdemand on the planet’s bioprodu ctive capacity. We build o nmany earlier attempts to create comprehensive measures ofhuman impact on the biosphere. For examp le, Vitousek et al. (1)used consumption estimates to calculate humanity’s appropria -tion of the biosphere’s Net Primary Produc tivity (NP P). Theyconclu ded that th e human eco nomy co-opted organic materialequivalent to 40% of the NPP of terr estr ial ecosystems in 1980 .Odum developed a conceptua l basis for accounting for energyfl ows t hrough ecosystems and human eco nomies, but did notproduce overall accounts (2). Fischer-Kowalski and Hu¨ttler (3)advanced the concept of ‘‘societal metabolism,’’ using materialfl ow analysis as a macro ind icator for the environmental per-forman ce of societies. The Global Environment Outlook 2000 (4)and World Resources 2000 –2001 (5) describe human im pacts onvarious ecosys tem types in detail, but both reports lack anaggregat ed summary of the impacts. Others have analyzed th eintegrity of subcomponents of the biosphere, su ch as carboncycles (6), freshwater use (7, 8), and the nitrogen cycle (9), haveassigned approximate monetary va lues to the ecological servicesthat humanity depe nds on (10), or established frameworks formoneta ry natural capital accounts for nations (11).This pr eliminary a nd exploratory study demonstrates an ag -gregated approach to natural capital accounti ng in biophysica lunits. A wide variety of hum an uses of nature are identified,measured, and expressed in units that enable direct comparisonof human dem ands with nat ure’s supply of ecological services.The calculation results an d annotated spreads heet for 1999 arepublished as supporting inform ation on the PNAS web site,www.pnas.org.Our global accounts build on assessments of the ‘‘ecologicalfootprint’’ of humanity (12, 13). Such assessments are b ased onsix assumpti ons:1. It is possible to keep track of most of the resources humanityconsum es a nd the wastes humanity generates.2. Most of these resource and waste flows can b e measured interms of the biologically productive area necessary to main-tain these flows (those resour ce and waste flows t hat cannotare excluded from the assessment).3. By weighti ng each area in proport ion to its usable biomassproductivity (that is, its potential production of biomass thatis of economic interest to people), t he different areas can beexpressed in standar dized hectares. These standardized hect-ares, which we call ‘‘globa l hectar es,’ ’ represent hectares withbiomass productivity equal to the world average productivitythat year.4. Because these areas stand for mutually exclusive uses, a ndeach glo bal hectare represents the same amount of usablebiomass pr oduction for a given year, they can b e added up toa tota l repr esen ting the aggregate human demand.5. Nature’s supply of ecological services can also be expressedin global he ctares of biologically product ive space.6. Area demand ca n exceed area supply. For examp le, a forestharvested at twice its regeneration rate appears in ouraccounts at twice its area. Th is phenomenon is called ‘‘eco-logical over shoot’’ (14, 15).Thus, the ecological impact of humanity is measured as the areaof biologically productive land a nd water required to produce theresources consumed and to assimilate the w astes generated byhumani ty, under the predo minant management and produc tionpractices in any given year. No t only human demand on nature,but also n ature’s supply changes over time because of in nova-tions in technology and resource management, changes in landuse, and cum ulative damage of past impacts.We recognize that reducing the com plexity of humanity ’simpact on nature to appropriated biomass offers only a partialassessment of global sustainability. It is a necessary, but notsuffic ient, requirement that human demand does not exceed theglobe’s biol ogical capacity as measured by o ur accounts.The Impact ComponentsOur accounts i nclude six h uman activities that require