The human core of the shared socioeconomic pathways: Population scenarios by age, sex and level of education for all countries to 2100
Samir KC *, Wolfgang Lutz
WittgensteinCentreforDemographyandGlobalHumanCapital(IIASA,VID/O¨AW,WU),InternationalInstituteforAppliedSystemsAnalysis,Schlossplatz1, 2361Laxenburg,Austria
1. Introduction
Thenumberofhumanbeingsonthisplanethaschangedgreatly overthepastmillenniaandwasinmanyaspectslinkedtochanges in the natural environment—both in terms of being driven by changesintheenvironmentandalsoofinducingsuchchanges—as wellastheevolution of technologiesand humancultures. Itis estimatedthatfromtheappearanceofmodernHomosapienssome 200,000yearsagoinAfricauntilaround35,000yearsagothetotal worldpopulationwaswellunderonemillionandourspecieswas seriouslythreatenedbyextinction(Biraben,2002).Onlyafterthe Neolithic revolution which introduced agriculture the world populationsurpassed100millionroughly7000yearsago.Butit wasonlyinthe19thcenturythatpopulationgrowthreallystarted totakeoffinthenowindustrializedcountriesasaconsequenceofa declinein death rates whichwastheresult ofbetternutrition,
improvementsinhygieneandpublicfreshwatersupplyandother advancesinearlypreventivemedicine.RightaftertheendofWorld WarIIdeathratesthenstartedtofallprecipitouslyinalmostall partsoftheworldwhichatthistimewasalsotheresultofmodern medicine includingthe inventionof antibiotics. Butfor several decadesbirthratesremainedveryhigh(andinsomecaseseven increased due to a better health status of women) since high fertility norms had been deeply imbedded in most traditional culturesandreligionsandsuchnormstendtochangeonlyslowly.
Asaconsequence,worldpopulationsizestartedto‘‘explode’’from 2.5billionin1950tosomewhatabove7billiontoday.Butoverthe pastdecadesbirthrateshavealsostartedtodeclineinmanyparts oftheworld—mostdramaticallyinpopulousEastAsia—givingrise totheexpectationthatoverthecourseofthe21stcenturythereisa highprobabilitythatworldpopulationwillreachapeakandthen starttodecline(Lutzetal.,2001).
Thescientificdisciplineofdemographyhasaratherelaborate and powerful toolbox for studying population dynamics and producesdetailedpopulationprojectionsaccordingtodifferent assumptions about the future trend in fertility, mortality, ARTICLE INFO
Articlehistory:
Received31January2013
Receivedinrevisedform12May2014 Accepted7June2014
Availableonlinexxx
Keywords:
Worldpopulation Education Agestructure Scenarios Countrylevel
Sharedsocioeconomicpathways
ABSTRACT
Thispaperappliesthemethodsofmulti-dimensionalmathematicaldemographytoprojectnational populationsbasedonalternativeassumptionsonfuture,fertility,mortality,migrationandeducational transitionsthatcorrespondtothefivesharedsocioeconomicpathways(SSP)storylines.Indoingsoit goesasignificantstepbeyondpastpopulationscenariosintheIPCCcontextwhichconsideredonlytotal populationsize.Bydifferentiatingthehumanpopulationnotonlybyageandsex—asisconventionally doneindemographic projections—but also bydifferentlevels ofeducational attainment themost fundamentalaspectsofhumandevelopmentandsocialchangearebeingexplicitlyaddressedthrough modelingthechangingcompositionofpopulationsbythesethreeimportantindividualcharacteristics.
ThescenarioshavebeendefinedinacollaborativeeffortoftheinternationalIntegratedAssessment ModelingcommunitywiththemediumscenariofollowingthatofamajorneweffortbytheWittgenstein CentreforDemographyandGlobalHumanCapital(IIASA,OEAW,WU)involvingover550expertsfrom aroundtheworld.Asaresult,intermsoftotalworldpopulationsizethetrajectoriesresultingfromthe fiveSSPsstayveryclosetoeachotheruntilaround2030andbythemiddleofthecenturyalreadya visibledifferentiation appears with the range betweenthe highest (SSP3) and the lowest (SSP1) trajectoriesspanning1.5billion.TherangeopensupmuchmorewiththeSSP3reaching12.6billionin 2100andSSP1fallingto6.9billionwhichislowerthantoday’sworldpopulation.
ß2014TheAuthors.PublishedbyElsevierLtd.ThisisanopenaccessarticleundertheCCBY-NC-SA license(http://creativecommons.org/licenses/by-nc-sa/3.0/).
* Correspondingauthor.Tel.:+432236807424;fax:+43223671313.
E-mailaddresses:kc@iiasa.ac.at(S.KC),lutz@iiasa.ac.at(W.Lutz).
ContentslistsavailableatScienceDirect
Global Environmental Change
j ou rna l hom e pa ge : w w w. e l s e v i e r. c om/ l o ca t e / gl oe n v cha
http://dx.doi.org/10.1016/j.gloenvcha.2014.06.004
0959-3780/ß2014TheAuthors.PublishedbyElsevierLtd.ThisisanopenaccessarticleundertheCCBY-NC-SAlicense(http://creativecommons.org/licenses/by-nc-sa/3.0/).
migrationandotherdriversofchangingpopulationcomposition.
Whilepopulationgrowthhasbeena topicofscientificenquiry anddiscussionforcenturiesandatleastsinceThomasMalthus entered the field of structured quantitative analysis, early population projections only applied an assumed growth rate to the population total. Only after World War II it became standardtoproduceprojectionsthatexplicitlyconsidertheage- and sex-structure of the population (the so-called cohort component method). Hajnal(1955) provides a goodoverview oftheseearlypopulationprojections.Between1951and2011, the UN published 22 sets of estimates (past and current conditions) and projections (future) for all countries and territories of the world. Before 1978 these projections were revisedapproximatelyevery5 years;sincethennewrevisions (called assessments and published in their World Population Prospectsseries)havebeenmadeevery2 years.SofartheUN assessments have provided projections by age and sex for a mediumscenario, andalternative scenarios that are based on alternative fertility assumptions combined with identical mortalityandmigrationassumptions.
The WorldBankstartedtoproduceindependentpopulation projections in 1978. These were always meant primarily for internal use in the Bank’s development planning and were publishedaspartoftheWorldDevelopmentReportseries.After 1984,the WorldBankprojectionswererevised approximately every2yearsandin mostcasesonlyoneupdatedvariantwas publishedbutwithalongtimehorizonto2150. Around1995, the World Bank stopped publishing separate projections but presumablycontinuedtousethemfor internal purposesfor a numberof years. TheWashington-based Population Reference Bureau(PRB) publishes independentworld population projec- tions(populationsizeonlyandasinglescenario)everyyearas partofits annualWorldPopulationDataSheet. TheUSCensus Bureau(USCB)alsoproducessinglescenarioprojectionsforall countriesintheworldsince1985withavaryingtimehorizon.
TheWorldPopulationProgramoftheInternationalInstitutefor AppliedSystemsAnalysis(IIASA)basedoutsideVienna(Austria) beganproducingglobalpopulationprojectionsatthelevelof13 world regions in 1994. One of the purposes was to produce populationprojectionsaspartoftheSpecialReportonEmissions Scenarios (SRES)(Nakicenovic et al., 2000) that underlie the globalemissionscenariosusedbytheIntergovernmentalPanel forClimateChange(IPCC).Thiswasfollowedbythreeroundsof probabilisticprojectionsatthelevelof 13worldregions(Lutz etal.,2008b,2001,1997).
2. Keydimensionsconsideredinpopulationprojections
For most users of population projections clearly the most important piece of information is the future total size of the population. For this reason population size was the only demographic/social variable considered in the SRES scenarios complementedonlybyGDPpercapitaasaneconomicvariable.
Hence, for many practical purposes population size served primarilythe function of a scaling factor in the calculation of percapitaindicators.
Therearetwoimportantreasonsforpopulationprojectionsto go beyond the consideration of population size alone, one methodologicalandtheother substantive.Humanpopulations arenothomogeneousandthisheterogeneitygreatlymattersfor thelikelyfuturegrowthofthepopulation.Populationsthatare selective in a way that they haveonly a small proportion of womenormore elderlypeoplethan youngadultsarelikelyto havelower birthratesthanpopulationofcomparablesizebut witha largerproportionof womeninreproductiveage.Inthis sense future population growth is a direct function of the
age-andsex-structureofthepopulationandforthisreasonall modernpopulation projectionsdo explicitlyincorporatethese two sources of population heterogeneity and define their assumptionsintheform ofage-specificfertility,mortalityand migrationsrates.
The age- and sex-composition of the population is also of interestinitsownright.Populationagingisconsideredahighly importantsocioeconomicissuewhichcanonlybequantitatively addressed if the age-structure of populations is explicitly incorporatedin theprojection model. But thesame is truefor otherhighly relevant individualcharacteristics suchas level of education and rural/urban place of residence.Both areof dual significance:Theyareimportantsourcesofpopulationheteroge- neity,influencingitsdynamics,andtheirchangingcompositionin thepopulationisdirectlyrelevantforanticipatingsocioeconomic challenges for mitigation as well as adaptation tounavoidable climate change. In this paper we will explicitly address the changingeducationalstructureofpopulationswhilethefollowing paper will deal with the modeling of urbanization (Jiang and O’Neill,inpress).
Themethodsofmulti-dimensionalpopulationdynamicsare able to deal with populations that are stratified by further demographic dimensions in addition to age and sex. The International Institute for Applied Systems Analysis (IIASA)—
where these methods were originally developed during the 1970s—has recently applied them to produce reconstructions and projections of populations by age, sex and level of educational attainment for most countries in the world (KC etal.,2010;Lutzetal.,2007).Likeageandsex,educationisalso an important source of population heterogeneity and bears a significantweightofitsown.Almostuniversallymoreeducated peoplehavelowermortality,andthereissufficientevidencethat thisis a realeffectandnot justowingtoselectivity. Lutzand Skirbekk(2013)discuss theissueofcausality inthe effectsof education and bring together many studies based on natural experiments, instrumental variable models and other approachesthatclearlydemonstratethatthisalmostuniversal association is not a spurious effect. They coin the notion of
‘‘functional causality’’ to indicate that—while it is nearly impossible to proof causality for all times and all different cultural settings—there are good reasons to assume that the effectofeducationonloweringmortalityandfertilitycanindeed beassumedtoholdovertheprojectionperiodcoverhere.Finally, itneedstobestressedthattheindicatorofhighesteducational attainmentthatisbeingusedhereastheindicatorofchoicefor allcountriesisonlyaproxyforskillsandhumancapital.Itdoes not include the quality dimension of education (because empiricaldataonthistendtobelimitedtorichcountries)nor does it cover informal education which also contributes to human capital and for which even less reliable statistical information exists. In this sense the choice of educational attainment distribution was primarily driven by pragmatic considerations as the only indicator available in a rather consistentwayforalmostallcountriesoftheworld.Whilethe baseline data distinguish between six educational attainment categories and the multi-dimensional projections have been carriedoutforthesesixcategories,forthepurposeofthispaper wecollapsethemintofourcategoriesfortheeaseofpresenta- tions (for more information about the base line data and assumptionsseeKCetal.,2013).
Theempiricaldatashowthat,invirtuallyallpopulations—and in particular thosethat are still in theprocess ofdemographic transition—more educated women have lower fertility. These educationaldifferentialscanbeverysignificant.TheDemographic andHealthSurveyforEthiopia,forinstance,showsthatwomen without any formal education have on average six children,
whereas thosewith secondary education haveonlytwo (DHS Ethiopia,2012).Becauseofthestrongassociationbetweenfemale educationandfertility,futurechangesinthecompositionofthe female population by educational attainment make a big difference. Lutz and KC (2011) have recently shown that alternativeeducationscenariosalone(assumingidenticaleduca- tion-specificfertilityandmortalitylevels)leadtoadifferenceof more than one billion people in the world population sizes projectedfor2050.
Inadditiontoitseffectsonpopulationdynamics,thechanging educational composition of the population is also of great importanceforabroadrangeofsocialandeconomicdevelopment concerns. Based on a newly reconstructed set of educational attainmentdistributionsbyageandsex(Lutzetal.,2007)formost countriesbackto1970,ithasrecentlybeenshownthatindeedthe improvement of educational attainment in the working age population hasbeenthe mostconsistent and significantdriver ofeconomicgrowtharoundtheworld(Lutzetal.,2008a).Inthe context of the Shared Socioeconomic Pathways (SSPs) this empiricallyestablished relationshipwill alsobe usedto define GDP growth scenarios that are consistent with the education- specificpopulationscenariosdescribedhere.Aswillbedescribed inthefollowingsectionthedifferentSSPsweredesignedtocover alternativesocio-economicpathwayswithrespecttothedifferent levelsofsocietalcapacitiestodealwithclimatechangemitigation andadaptationchallenges.
Beyond economic growth, education as a basic force of empowering people and providing access to information has beenshowntomattertoalargerangeofimportantaspectinthe context of sustainable development. There is overwhelming evidence that education is a key determinant of both infant mortality(Pamuketal.,2011)andadulthealthandmortality(KC andLentzner,2010).Butbeyondindividualbenefits,improving education by age andsex hasalso been shown tomatter for countriesintransitiontomoderndemocraciesandtheruleoflaw (Abbasi-Shavazietal.,2008;Lutz,2009;Lutzetal.,2010).Forthe questionoffoodsecurity,ithaslongbeenshownthatthebasic education of the agricultural labor force is a key factor in agriculturalproduction(HayamiandRuttan,1971).Asthesetof Population–Education–Development–Agriculture (PEDA) mod- elscommissionedbytheUNEconomicCommissionforAfricafor anumberofAfricancountriesshows,whenincludingeducation inanagriculturalproductionfunction,itturnsouttobeoneof the key determinants in reducing malnutrition and food insecurity(Lutzetal.,2004).Finally,inthecontextofadaptation toclimate change, a seriesofempirical studiesondifferential vulnerability to various kindsof natural disastersin different parts of the world have confirmed the dominating role of education as an empowering factor that tends to reduce vulnerabilityandenhancetheadaptivecapacitytothenegative consequences of climate change (Frankenberg et al., 2013;
Helgesonetal.,2013;KC,2013;Sharmaetal.,2013;Striessnig et al., 2013; Wamsler et al., 2012). Hence, it seems very appropriate for socioeconomic scenarios, which are supposed tocapturethesocioeconomicchallengesofbothmitigationand adaptation, to enrich the conventional demographic focus on populationsizeaswellasontheage-andsex-structureofthe populationthroughaddingeducationattainmentasanaddition- al demographic dimension. Since these dimensions together comprehensively describe key characteristics of people, with respect totheir mitigative andadaptive capacities, thisset of scenarios may appropriately be called the human core of the SSPs.
TheWittgenstein Centre (WIC)for Demography andGlobal HumanCapital(a collaborative effortamong theInternational Institute for Applied Systems Analysis, IIASA, the Austrian
Academy of Sciences, OeAW, and the Vienna University of EconomicsandBusiness,WU)recentlycarriedoutamajorexpert inquiryfordefiningnewassumptionsforacomprehensivenew setofpopulationprojectionsbyage,sexandlevelofeducation forallcountriesintheworld(underanERCAdvancedGranton
‘‘ForecastingSocieties’AdaptiveCapacitiestoClimateChange’’).
More than 550 population experts from around the world participatedinthiseffort.Itconsistedofanonlinequestionnaire thatassessedinpeerreviewmannerthevalidityofalternative arguments that would impact the future trends of fertility, mortalityandmigration.Inaseriesoffivemeta-expertmeetings held on five different continents the survey findings were evaluatedandultimatelytranslatedintonumericalassumptions fortheactualprojectionsforallcountries.Thiselaborateprocess was concluded in late 2012—just in time to inform the final populationscenariosfortheSSPsthatarebeingpresentedinthis paper. Allthe parameterchoicesandjustificationsof assump- tions that underlie the projections presented here as well as detailed country-specific results are documented in the forth- coming Oxford University Press book ‘‘World Population and HumanCapitalin the21stCentury’’ (Lutzetal.,2014).Earlier versionsofsomeofthechaptershavebeenpublishedasonline WorkingPapers(BarakatandDurham,2013;Bastenetal.,2013;
Casellietal.,2013;FuchsandGoujon,2013;GarberoandPamuk, 2013; KCet al., 2013;Lutz and Skirbekk,2013; Sanderet al., 2013).
Thismajor neweffortin establishingthescientificbasisfor new world population projections by age, sex and level of education directlyfed into the definition of theSSP scenarios presentedhere.Mostimportantlytheexpertsolicitationmostly focused onthemedium future trajectoriesof all demographic components (fertility, mortality, migration and education) andthismediumscenariowasbydefinitionsettobeidentical toSSP2(the‘‘middleoftheroad’’ SSPasdiscussedbelow). All the other SSPs were defined through another process of intensive consultations (at meetings in Utrecht, Boulder, The Hague and the International Institute for Applied Systems Analysisaswellascountlessteleconferences)amongscientists from the leading Integrated Assessment Modeling groups in ordertoassurethatthespecificdemographicassumptionsmade areconsistentwiththesubstantivenarrativesoftherespective SSPs.
Theresultingage,sex,andeducationcomponentsoftheSSPs astheywerefinalizedinJanuary2013andarepresentedinthis paper and in the SSP onlinedata sethave been labeled WIC- SSPs1.0. They are different from earlier education-specific projections produced for a smaller number of countries and basedonolderbaselinedatabythesameauthors(LutzandKC, 2011; Lutz et al., 2007). More recently (in October 2013) a slightlydifferentupdated versionhasbeen producedwhichis based on more recent information on migration and fertility trends in somecountries(whichis labeled WIC-SSPs1.1).But since it is the WIC-SSPs1.0 that served as input to the other groupscalculatingGDPandothercomponentsoftheSSPswewill onlypresentthisversioninthispaper.
3. TranslationofSSPstorylinesintopopulationandeducation scenarios
ThegeneralSSPrationaleaswellasthestorylinesunderlying the individual SSPs have been extensively discussed and documentedinthepreviouspapers(CrespoCuaresma,inpress;
Dellinketal.,inpress;Leimbachetal.,inpress;O’Neilletal.,in press)andneednotberepeatedhere.Inthefollowing wewill only focuson thespecific way these storylines are translated into alternative fertility, mortality, migration and education
scenarios for different groups of countries. Three groups of countrieshavebeendistinguished:‘‘Highfertilitycountries’’as definedbyaTotalFertilityRateofmorethan2.9in2005–2010;
‘‘Low fertility countries’’ including all countries with a total fertilityrateof2.9andbelowthatarenotincludedinthethird categoryof‘‘Rich-OECDcountries’’,thelatterbeingdefinedby OECDmembershipandtheWorldBankcategoryofhighincome country(seeTableA.1).Itisimportanttonotethatforthissetof generalSSPscountriesareassumedtostayinthegroupingthat theystartout.Thismaybeunsatisfactoryforcountriesthate.g.
areinthemidstofa fertilitydeclineandareexpectedtosoon moveinthelowfertilitygrouporcountriessuchasSingapore thata very richbutat thismomentnot partoftheOECD.But sincethereisan almostinfinitenumberof waysandtimesat whichcountriescouldchangethegroupingsitwasdecidedthat thisshouldbe lefttouserswho wanttodefinetheir country- specificSSPs.
ThetranslationofthefivebroaderSSPnarrativesintospecific demographic assumptions reflects the following logic. Table 1 summarizestheseassumptionsaccordingtotheirimplicationsfor fertility,mortalityandmigration.
SSP1: This assumesa future that is moving toward a more sustainablepath.Inparticularthestoryassumesthateducational and health investments accelerate the demographic transition, leadingtoarelativelylowworldpopulation.Also,inthisstoryline theemphasisshouldshifttostrengtheninghumanwellbeing.This definitionclearlyimpliesforallthreecountrygroupslowmortality and high education assumptions. With respect to fertility assumptionsthestoryismorecomplex.ForrichOECDcountries theemphasison qualityoflifeisassumedtomakeiteasierfor womentocombine workand family, and hencemakes further fertilitydeclinesunlikely.Forthisreasonforthisgroupofcountries the medium fertility assumption was chosen. For all other countriesthelow fertility assumptionswerechosen asimplied by the assumed rapid continuation of demographic transition.
Migrationlevelswereassumed tobemedium for all countries underthisSSP.
SSP2:Thisisthemiddleoftheroadscenariothatcorresponds exactly to the medium variant of the new IIASA-VID-Oxford projections.Itcombines for allcountries medium fertility with medium mortality and medium migration and the Global EducationTrend(GET)educationscenario.
SSP3: This scenario refers to a fragmented world with an emphasis onsecurityat theexpenseof internationaldevelop- ment.Population growth is assumedto behighin developing countries and low in industrialized countries. Accordingly, this scenario assumes high mortality and low education for all three country groupings. Fertility is assumed to be lowin the rich OECD countries and high in the two other country groups. Due to the emphasis on security and barriers to internationalexchange, migrationis assumedtobelowforall countries.
SSP4:Thisreferstoaworldofhighinequalities,bothbetween andwithincountries.Thereisincreasingstratificationbetweena well-educatedinternationallyconnectedsocietyontheonehand andapoorlyeducatedsocietythatworksinlaborintensivelow- techindustries.Intermsofeducationthisisreflectedinaspecial scenariothatdiffersfromthestandardlow-highinthesensethat in every country it produces a more polarized education distributionwithacertaingroupofveryhighlyeducated(which isbiggerintherichOECDcountries)andlargegroupswithlow education. In terms of fertility at the national averages this impliescontinuedhighfertilityintoday’shighfertilitycountries and continued low fertility in both groups of low fertility countries.Formortalitythehighfertilitycountriesareassumed tosufferfrom highlevelswhereas theother twogroupshave mediummortality.Migrationis assumedtobeat themedium levelforallcountries.
SSP5: This refers to a world that stresses technological progress and where economic growth is fostered by rapid developmentofhumancapital.Thisisreflectedinhigheducation assumptionsandlowmortalityassumptionsacrossallcountries.
For fertility again the pattern is strongly differentiated, with relativelyhighfertilityassumedfortherichOECDcountries(asa consequenceofhightechandaveryhighstandardoflivingthat allowsfor easiercombinationofworkandfamily,andpossibly forimmigrantdomesticassistants)andlowfertilityassumedfor all other countries. The emphasis on market solutions and globalizationalsoimpliestheassumptionofhighmigrationfor allcountries.
InTable1thesechoicesforscenariodefinitionsaresummarized the specific choices made result from a lengthy interactive discussionprocessamongthepersonsandinstitutesinvolvedin this SSP effort. Asdiscussed above, only SSP2was taken tobe identical in terms of the fertility, mortality and migration assumptionstothe‘‘medium’’scenarioofthenewWittgenstein Centerprojections(WIC-SSPs1.0called‘‘IIASA-WICPopulationV9’’
in the SSP-Database https://secure.iiasa.ac.at/web-apps/ene/
SspDb/). These assumptions aredescribed in detail in KCetal.
(2013). The data and assumptions used for the projections presentedinthispaperarelabeledWIC-SSPs1.0reflectourwork asofJanuary2013anddifferslightlyfromthemorerecentWIC- SSPs1.1thataredescribedintheKCetal.(2013).Onedifference liesinthemigrationbaselinewhichisduetothefactthattheUN releasedanewupdateonglobalmigrationstocksthatwasusedto re-estimate theearlierratesof migration flows.Differences are onlysizeableforsmallislandsandfordevelopingcountrieswith previouslyunreliabledata.Inadditiontomigration,assumptions forfertilitytrendsinthenearterminafewlow-fertilitycountries were adjusted with newevidence of postponement of fertility among young women due to recent economic recession that startedin2008.Lastly,baselineeducationdistributionsforthree countries(Bolivia, Guinea,and Portugal)werecorrected.Bolivia and Guineahad veryminorchanges however,for Portugal,the proportions withno education or incomplete was too highin Januaryversion.Duetothemarginalnatureoftheseadjustments the results for longer term population aggregates differ only marginally.
Table1
Matrixwithsharedsocioeconomicpathwaysdefinitionsforthedemographicand humancapitalcomponent.
Countrygroupings Fertility Mortality Migration Education SSP1
HiFert Low Low Medium High(FT-GET)
LoFert Low Low Medium High(FT-GET)
Rich-OECD Medium Low Medium High(FT-GET)
SSP2
HiFert Medium Medium Medium Medium(GET)
LoFert Medium Medium Medium Medium(GET)
Rich-OECD Medium Medium Medium Medium(GET)
SSP3
HiFert High High Low Low(CER)
LoFert High High Low Low(CER)
Rich-OECD Low High Low Low(CER)
SSP4
HiFert High High Medium CER-10%/GET
LoFert Low Medium Medium CER-10%/GET
Rich-OECD Low Medium Medium CER/CER-20%
SSP5
HiFert Low Low High High(FT-GET)
LoFert Low Low High High(FT-GET)
Rich-OECD High Low High High(FT-GET)
With respect to fertility, the assumed country-specific trajectoriesresultfromamodelthatsamplesfromthecollective experienceofallcountriesthatoncewereinasimilarstanding, withrespect to thefertility transition, and thenadjuststhese modeledvalues somewhat throughthe country-specific infor- mation,derivedfrom theexpertargumentevaluationexercise andtheconclusionsofthemeta-expertmeetings.Whiletypically the resulting trajectories are not very different from those assumedintheUN2010assessment,asignificantdifferencelies inthefactthatthelongtermconvergencelevelforlowfertility countriesis assumed to be1.75 (ratherthan 2.1as in United Nations, 2011). The ‘‘high’’ and‘‘low’’ fertility scenarios were essentially defined as being 20% higher and lower than the medium by 2030 and 25% different by 2050 and thereafter.
Differentials in education-specific fertility levels started with thoseempiricallyobservedinindividualcountriesandthenwere generally assumed to converge to a global pattern over the comingdecades.
‘‘Medium’’mortalityassumptionsweremadeonthebasisofa global conditional convergence model, under which it was assumed that life expectancies in all countries progressively approachthose inregionalforerunnercountries.These regional championsthemselveswouldslowlyapproachtheglobalforerun- ner(Japan),whichisassumedtoexperienceaconstantincreaseof twoyearsinlifeexpectancyperdecade.Forthe‘‘high’’and‘‘low’’
scenarios it was generallyassumed that life expectancywould increaseoneyearperdecadefasterorslowerthaninthe‘‘medium’’
case. For AIDS effected countries in Sub-Saharan Africaspecial assumptionsweremadewithlargeruncertaintyintervalsinthe nearerterm.Again, thespecificnumericalassumptionsforeach countryresultfromextensiveexpertargumentationasdocumen- tedinGarberoandPamuk(2013),Casellietal.(2013)andKCetal.
(2013).
Themigration assumptions are basedon a newgloballevel estimate of the full matrix of in- and out-migration flows as derived primarily from migrant stock data (Abel, 2013). The mediumscenario thenassumesconstant in- and out-migration ratesforthecominghalfcenturyfollowedbyaslowconvergence tozeronetmigration.Itisworthnotingthattheassumptionof constantrates,ratherthanconstantabsoluteflows,canovertime producechangesintheabsoluteflowsasafunctionofchanging nationalpopulationsize(forout-migration)orworldpopulation size(forin-migration).The highmigration scenarios essentially assume50%higherandthelowmigration 50%lowermigration thaninthemediumscenario.
Finally, the different education scenarios require a word of clarification.TheGlobalEducationTrend(GET)scenarioisbasedon aBayesianmodelthatestimatesthemediumfuturetrajectoryin education-specific progression rates to higher levels from the cumulativeexperienceofallcountriesoverthepast40years.The resulting education trajectories for each country are not only considered to bethe ‘‘medium’’,but they arealso used as the standardagainstwhichallthefutureeducation-specificfertility andmortalitytrajectoriesarebeingderivedfrom,assumptionsof overall fertility and mortality levels. There are two other benchmark scenarios with respect to future education trends:
TheConstantEnrollmentRates(CER)simplyassumesthatineach countrythemostrecentlyobservedlevelofschoolenrollment,and henceeducation progression,are frozen at their current levels.
Sinceinmanycountriestheyoungeragegroupsaremuchbetter educatedthantheolderones,eventhisscenariocanleadtosome improvementsinadulteducationlevelsoverthecomingdecades, butinthelongerrunimpliesstagnation. Ontheotherextreme, there is the Fast Track (FT) scenario which assumes that the country will shift gears and follow the most rapid education expansion experienced in recent history, namely that of South
Korea.SomeoftheeducationscenariochoicespresentedinTable1 fordifferentSSPsarecombinationsoftheabovedescribedstylized scenarios:FT-GETforSSP1andSSP5hasbeencalculatedforeach countrybytakingthearithmeticmeanoftheeducationprogres- sionratesimpliedundertheGETandFTscenarios.ForSSP4amore complexcombinationwaschoseninordertoreflecttheincreasing within-country inequality that storyline implies: ‘‘CER-10%/
GET’’implies that the educational attainment progression ratio (EAPR)isfurtherreducedby10%,ascomparedtoCER(andhence still morepessimistic), forthetransitions fromnoeducationto incomplete primary, incomplete primary to completedprimary andfromcompletedprimarytocompletedlowersecondary.The GET transition ratios are assumed for the higher educational categories which will produce larger groups of elites in these countries. Under ‘‘CER/CER-20%’’, for the high income OECD countries, it is assumed thatfor thesehigher educationgroups thetransitionratesare20%lowerthanunderCERandhencealso produceamorepolarizedsociety.
4. Results
In terms of total world population size the trajectories resultingfromthefiveSSPsstayveryclose toeachotheruntil around 2030 (see Fig. 1). This is due to the momentum of population growth and the fact that the differences in the assumedtrajectoriesofthecomponentsonlyphaseingradually.
By the middle of the century already a visible differentiation appears with the range between the highest (SSP3) and the lowest (SSP1) trajectories spanning 1.5 billion. As expected, duringthesecondhalf ofthe21stcenturytherangeopens up muchmorewiththeSSP3reaching12.6billionin2100andSSP1 falling to 6.9 billion which is lower than today’s world population.The mediumSSP2comestolieat themiddlewith 9.2 billion in 2050 and 9.0 in 2100. SSP4and 5 have greatly differingassumptionsindifferentsetsofcountriesandtherefore atthegloballevelfallinbetweentheextremes,withSSP4being slightlyaboveSSP2andSSP5aboveSSP1.
But as discussed above these SSPs produce much more information thanjust totalpopulation size.Theygiveforevery country and for every point in time for each SSP complete distributionsbyage,sexandlevelofeducationalattainment.This richdataisconvenientlysummarizedvisuallyintheformofage pyramids by level of education as shown in Fig. 2. All the underlying numerical information is available online under https://secure.iiasa.ac.at/web-apps/ene/SspDb/.
6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00
2010 2020 2030 2040 2050 2060 2070 2080 2090 2100
Population (in Billions)
Total Worl d Population Si ze
SSP1 SSP2 SSP3 SSP4 SSP5
Fig.1.Trendsintotalworldpopulationsizeto2100accordingtothefiveSSPs.
Fig.2showstheempiricallygivenage-andeducationpyramid forIndiafor2010.Tomakethepictureclearer,thesixunderlying educationalattainmentcategorieswerecombinedintofour,which refertonoeducation,someprimary,completedjuniorsecondary andpost-secondaryeducation.Forchildrenbelowtheageof15no attainmentdistributionisgivenbecausemostofthemarestillin theprocessofeducation.Duetothepasthighfertilityratesandthe resulting young age distribution the shape of the Indian age pyramidstilllooksroughlylikeapyramid,althoughduetorecent fertilitydeclinesthestepsfortheagegroupsbelowage20have becomeprogressivelymorenarrow.Withrespecttotheeducation distribution,thefigureclearlyindicatesthatatallageswomenin Indiaarelesseducatedthanmen,butforyoungerage-groupsthis gendereducationgaphasbeensomewhatreduced.Forallwomen aboveage40themajorityiswithoutanyformaleducation.For younger cohorts the educational attainment has gradually improved.Inparticularfortheagegroups15–24alreadyaround halfofallwomenhavereceivedatleastjuniorsecondaryeducation as a result of recent government efforts to expand education particularlyinruralareas.Formentheeducationalattainmenthas
always beenhigher in any given agegroup and over time the averageeducationhasalsosignificantlyimproved.
Fig.3givestheage-andeducation-pyramidsasprojectedfor IndiaunderthethreescenariosasdefinedforSSP1,SSP2andSSP3.
Since most of the scenario assumptions (except for mortality) affecttheyoungeragegroupsandthetimehorizonisonly40years, thethreepyramidsareverysimilarfortheelderlypopulationbut differgreatlyfortheyoungerones.Mostsignificantly,theshapeof thepyramidvariesgreatlyfromSSP1wheremuchhigherfemale educationtogetherwithlowerassumededucation-specificfertility ratesresultinmuchlowerbirthrateswhichleadtoanarrowingof thebaseoftheagepyramid. SSP2referstothescenariothatis consideredasmediumscenariowithsomemoderateexpansionof educationtogether withmore moderatedeclines in education- specificfertilityrates.SSP3incontrast,givesthepictureofastalled development bothwithrespecttoeducationas wellas fertility declines.Asa consequencethepyramid ismuchbroaderatthe bottomand thetotalpopulationof Indiaismuchhigher.Aside fromthedifferentageandeducationstructuresofthesescenarios overthecoming40yearsthedifferencebetweenSSP1andSSP3is already more than 400 million additionalpeople. Asshown in Table2below,bytheendofthecenturythisdifferencebetween SSP1and SSP3forIndiaalonewillincreasetoanincredible1.5 billionpeople,whichismuchhigherthanIndia’stotalpopulation today.
Thefollowingfiguresandtablesprovidesummary indicators forthedifferentSSPsanddifferentpointsintimethathavebeen derivedfromthefullerage–sex–education-specificprojectionsas describedabove.Thisinformationwillbepresentedintheformof aggregatesformajorworldregions,theworldasawholeaswellas for12selectedcountries,twofromeachworldregion.Themore detailed informationfor allcountriesis providedin theon-line data base.The presented indicatorof Mean Years of Schooling (MYS)asasummaryindicatorfortheaveragelevelofeducationof theadultpopulationthatispopulationamongeconomistsbutdoes notreflectthedistributionofeducationalattainment.Themethod ofcalculatingMeanYearsofSchoolingpresentedinthispaperis describedinKCetal.(2010)andreflectourworkasofJanuary2013 (WIC-SSPs1.0)whichdifferfromthemorerecentWIC-SSPs1.1 thataredescribedinKCetal.(2013).
Table2aswellasFigs.4and5showthatfortheworldasa whole thedifferent SSPs cover a broad range ofnot only total populationsizesbutthattheyarealsoassociatedwithdifferentage andeducationdistributions.Asdescribedabove,SSP2,whichalso Fig.2.Exampleforanage-andeducation-pyramid:India2010.
Fig.3.PopulationofIndiabyage,sexandeducationalattainmentunderSSP1,SSP2andSSP3scenario.
is considered as a medium scenario for population trajectory, showsacontinuedincreaseofworldpopulationsizeresultingin 9.17billionin2050,thenpeakingaround9.4billioninthe2070s and declining somewhat to 9 billion by 2100. This medium trajectoryofworldpopulationgrowthreachingapeakduringthe second half of the century is consistent with earlier world populationprojectionsbytheInternationalInstituteforApplied SystemsAnalysis(Lutzetal.,2008b)aswellastheUnitedNations projections up to 2010 (United Nations, 2009). The UN 2010 assessment(UnitedNations,2011)doesnotprojectsuchpeaking becauseitmodifieditsassumptionofthelongtermconvergence
leveloffertilityfrompreviously1.85to2.1.SSP2aspresentedhere assumes this long term level to be at 1.75, as is extensively discussed and justified as a result of the expert solicitation in Bastenetal.(2013).
Themostrecent2012UNassessment(UN2013)alsodoesnot resultinapeakingduringthiscenturypredominantlybecauseit assumeshigherfertilitytrajectoriesinAfricathanitdidinprevious assessments. Since in several big African countries (such as Nigeria)thereisevenhugeuncertaintyaboutthecurrentlevelsof fertility,expertstendtodifferconsiderablyaboutthelikelyfuture fertilitylevels.
Table2
Totalpopulationsizeandmeanyearsofschoolingamongadultpopulationaged15yearsandaboveformajorworldregionsandselectedcountries.
Region Year Population(inmillions) MYS
SSP1 SSP2 SSP3 SSP4 SSP5 SSP1 SSP2 SSP3 SSP4 SSP5
World 2010 6871 6871 6871 6871 6871 8.6 8.6 8.6 8.6 8.6
2050 8461 9166 9951 9122 8559 12.1 11.2 9.0 8.7 12.1
2100 6881 9000 12,627 9267 7363 14.1 13.4 8.3 8.1 14.2
Africa 2010 1022 1022 1022 1022 1022 5.8 5.8 5.8 5.8 5.8
2050 1764 2011 2333 2251 1737 11.0 9.7 6.3 5.7 11.0
2100 1865 2630 3947 3622 1808 13.7 12.7 6.4 5.8 13.7
Asia 2010 4141 4141 4141 4141 4141 7.9 7.9 7.9 7.9 7.9
2050 4734 5140 5656 4965 4721 11.8 10.9 8.8 8.5 11.8
2100 3293 4417 6712 4076 3300 14.0 13.3 8.4 8.2 14.1
Europe 2010 738 738 738 738 738 12.0 12.0 12.0 12.0 12.0
2050 769 762 681 716 847 13.7 13.5 13.0 12.8 13.7
2100 657 702 543 535 915 14.5 14.1 12.8 12.9 14.5
LatinAm.&
theCaribbean
2010 590 590 590 590 590 9.0 9.0 9.0 9.0 9.0
2050 679 746 859 710 655 12.6 11.9 10.2 9.6 12.6
2100 487 673 1085 567 453 14.7 14.1 10.3 9.9 14.6
NorthernAmerica 2010 344 344 344 344 344 13.8 13.8 13.8 13.8 13.8
2050 460 450 372 424 535 14.8 14.6 14.3 14.1 14.8
2100 521 513 290 406 801 15.3 15.1 14.4 14.2 15.2
Oceania 2010 36 36 36 36 36 12.1 12.1 12.1 12.1 12.1
2050 56 57 51 56 64 14.2 13.7 12.8 12.7 14.2
2100 59 65 50 61 87 15.2 14.9 12.4 12.6 15.3
China 2010 1341 1341 1341 1341 1341 8.8 8.8 8.8 8.8 8.8
2050 1225 1263 1307 1183 1225 12.1 11.7 10.9 10.5 12.1
2100 644 767 1028 555 645 13.9 13.5 11.2 11.3 13.9
RepublicofKorea 2010 48 48 48 48 48 12.6 12.6 12.6 12.6 12.6
2050 48 46 41 44 51 15.0 15.0 14.9 14.8 14.9
2100 32 30 18 24 42 15.5 15.5 15.2 15.0 15.5
India 2010 1225 1225 1225 1225 1225 6.0 6.0 6.0 6.0 6.0
2050 1550 1734 1971 1601 1547 11.6 10.1 7.1 6.8 11.6
2100 1138 1603 2609 1169 1134 14.4 13.7 7.3 7.4 14.4
Indonesia 2010 240 240 240 240 240 8.5 8.5 8.5 8.5 8.5
2050 271 288 307 261 269 12.4 11.8 10.3 9.8 12.4
2100 184 228 292 152 180 14.8 14.3 10.6 10.7 14.8
Germany 2010 82 82 82 82 82 15.6 15.6 15.6 15.6 15.6
2050 82 79 67 75 92 16.6 16.4 16.2 16.0 16.6
2100 67 67 38 52 99 17.2 17.0 16.3 16.1 17.1
RussianFederation 2010 143 143 143 143 143 10.6 10.6 10.6 10.6 10.6
2050 131 137 134 127 138 11.3 11.1 10.8 10.3 11.3
2100 93 123 149 88 102 11.5 11.3 10.8 10.2 11.5
Kenya 2010 41 41 41 41 41 9.2 9.2 9.2 9.2 9.2
2050 70 78 96 92 68 13.6 12.8 9.2 8.4 13.6
2100 72 96 161 145 67 15.0 14.5 9.3 9.0 15.0
SouthAfrica 2010 50 50 50 50 50 9.6 9.6 9.6 9.6 9.6
2050 62 63 62 56 65 12.7 11.7 10.4 9.9 12.7
2100 49 58 71 39 52 13.9 13.3 10.4 10.6 13.9
Egypt 2010 81 81 81 81 81 7.6 7.6 7.6 7.6 7.6
2050 113 125 141 112 111 12.3 11.8 9.8 9.3 12.3
2100 97 131 198 91 94 14.1 13.7 10.1 10.1 14.1
Turkey 2010 73 73 73 73 73 7.3 7.3 7.3 7.3 7.3
2050 87 96 109 92 87 11.3 10.4 8.1 7.6 11.3
2100 66 90 149 73 66 13.7 13.1 8.2 7.9 13.7
UnitedStatesofAmerica 2010 310 310 310 310 310 13.7 13.7 13.7 13.7 13.7
2050 411 402 334 379 476 14.8 14.5 14.2 14.1 14.7
2100 467 459 262 365 713 15.3 15.1 14.3 14.2 15.2
Brazil 2010 195 195 195 195 195 8.1 8.1 8.1 8.1 8.1
2050 215 232 254 215 213 11.5 10.9 9.7 9.2 11.5
2100 141 188 276 135 139 13.7 13.1 10.0 9.9 13.7
In a nutshell, the uncertainty range of future world population size (from 6.9 billion under SSP1 to 12.6 under SSP3in2100)reflectsaverysignificantuncertaintyaboutfuture fertility, mortality and education trends which translate not onlyintodifferentworldpopulationsizesbutalsoverydifferent ageandeducationstructures.Thesescenarioscannotbedirectly comparedtotheUNhighandlowpopulationvariantsbecause thoseare onlybased on alternative fertility assumptions (0.5 children higherandlower than in themedium variant)while assuming identical mortality and migration patterns and not explicitlyaddressingthepopulationheterogeneitywithrespect toeducation.
Asdiscussedinthesectiondescribingthescenarioassump- tions above, these differences in total world population size result predominantly from two forces: different assumed trajectories in female educational attainment and different levels of education specific fertility. Since almost universally moreeducated womenhavelowerlevels offertility—an effect that is particularly strong for countries in the midst of demographictransition—thechangingeducational composition ofyoungwomenaloneisamajorfactorinfluencingpopulation growth.LutzandKC(2011)haverecentlyshownthatevenwhen assumingidenticaleducation-specific fertilitytrends, different scenariosaboutfuturefemaleeducationlevelsalreadycanlead toa difference of more than1 billionin world population by 2050.Wheneducation-specificfertilitylevelsarealsodifferent acrossscenarios(asisthecasefortheSSPs)theinter-scenario differences are evenlarger. Alternative mortalityassumptions areofsecondaryimportancewhenitcomestopopulationsize butaredominatingthepicturewithrespecttothefuturenumber ofelderlypeopleunderdifferentscenarios.Alternativemigration assumptionsalso can makemajor differences with respect to projected national and to a lesser extent regional population sizes.
Fig.5showsthetimetrendinpopulationsizesbyeducational attainmentunderallfiveSSPs.Inallcasestheabsolutenumberof peoplewithsecondaryortertiaryeducationwillincreaseoverthe comingdecades.Thisisatrendthatisalreadypre-programmedin today’seducationstructureswherealmostuniversallytheyounger agegroupsarebettereducatedthantheolderones.Thismaybe calledthemomentumofeducationalimprovementwhichleadsto betterfutureeducationoftheelderlyevenunderthescenariosthat assumeno further increasein schoolenrollmentrates (suchas underSSP3).UnderSSP1andSSP5theglobalproportionofpeople
withhighereducationwillincreasedramatically andtheglobal meanyearsofschooling(MeanYearsofSchoolinginTable2)ofthe totaladultpopulationwillalreadyby2050reach12years,whichis aboutthecurrentlevelinEuropeandonlysomewhatbelowthatin NorthAmerica.Inotherwords,underthesescenariosthewhole worldin40yearswillbeaswelleducatedasEuropetodayandwill most likely experience all the positive consequences that are associatedwithhighereducation,aswillbediscussedinSection2 above. Evenunderthe mediumSSP2 scenario theglobal Mean YearsofSchoolingwillreach11.2yearsbymid-century.ButSSP3 andSSP4drawamuchmorepessimisticpicturethatisbasedon the assumption of a stagnation of the increase in school enrollment. In both cases the average education of the world populationwillevendeclineslightlyduringthesecondhalfofthe century,followingaminorincreaseinthenearerfutureduetothe abovedescribedmomentum.WhileunderSSP3thereisaparallel stagnation for all education groups, SSP4 shows an interesting polarizationasissuggestedinthestorylineforthatSSP:Boththe groupofcompletelyuneducatedpeopleaswellasthegroupwith tertiary education are increasing in size while the middle categories becomeless frequent. While the overall meanyears ofschoolingofthesetwodifferentscenariosarequitesimilarthe fulleducationdistributionsareverydifferent.Thisisanotherpoint incaseforrepresentingandanalyzingthefulldistributionsandnot onlytheMeanYearsofSchoolingasis doneinmany economic growthmodels.
AsimilarpolarizationisshownwithincountriesinFig6.with theexampleof Kenya.WhileSSP1showsthatwithsignificant further investments in education over the coming decades, Kenyaby 2050could already reachaneducation structure(of theyoungeradultpopulation)thatissimilartothatin Europe today,SSP3andSSP4showthecasesofstalleddevelopmentthat are associatednotonlywith muchlower educationlevels but also with significantly more rapid population growth. While under SSP1 Kenya’s population will ‘‘only’’ increase from currently 41million to 72million by the end of the century, underSSP3itwillincreasebyafactoroffourtoanincredible161 million.Again,SSP4showsaclearlymorepolarizeddevelopment than SSP3 although the mean years of schooling are quite similar.
Finally, several ofthe studiesabouttheeffects of education discussed in Section 2 show that the educational attainment distributionofyoungeradultwomen(aged20–39)isofspecific critical importance. This is evidently the case with respect to Fig.4.PopulationoftheWorldin2010byage,sexandeducationalattainmentandin2050underSSP1andSSP3scenario.
Fig.5.PopulationoftheWorldin2010–2100bybroadage-groupandeducationalattainmentunderSSP1–SSP5scenarios.
Fig.6.PopulationofKenyain2010–2100bybroadage-groupandeducationalattainmentunderSSP1,SSP3,andSSP4scenarios.
Table3
Proportionoffemalepopulationaged20–39byregion,year,levelofeducationalattainmentandSSPscenario(in%).
Region Year SSP1 SSP2 SSP3 SSP4 SSP5
No Edu
Prim Sec Tert No Edu
Prim Sec Tert No Edu
Prim Sec Tert No Edu
Prim Sec Tert No Edu
Prim Sec Tert
World 2010 15 21 49 15 15 21 49 15 15 21 49 15 15 21 49 15 15 21 49 15
2050 2 8 43 47 4 14 53 29 20 26 42 11% 28 24 33 16 2 7 43 47
2100 0 2 35 63 0 5 49 46 24 28 38 9 35 27 21 18 0 2 34 64
Africa 2010 32 31 31 6 32 31 31 6 32 31 31 6 32 31 31 6 32 31 31 6
2050 3 14 47 36 6 25 51 17 33 35 28 5 40 32 21 8 3 14 47 36
2100 0 4 39 57 0 9 56 35 33 35 27 5 41 33 15 11 0 4 39 57
Asia 2010 16 22 49 13 16 22 49 13 16 22 49 13 16 22 49 13 16 22 49 13
2050 2 6 44 48 4 12 55 29 20 25 44 10 28 22 32 17 2 6 43 48
2100 0 2 34 64 1 3 48 49 24 26 41 10 35 22 20 23 0 2 34 64
Europe 2010 0 5 67 28 0 5 67 28 0 5 67 28 0 5 67 28 0 5 67 28
2050 0 1 38 61 0 2 52 46 0 6 67 27 4 5 64 27 0 1 38 61
2100 0 1 30 69 0 1 39 60 0 6 69 25 3 6 60 31 0 1 30 69
LatinAm.andtheCaribbean 2010 4 28 52 17 4 28 52 17 4 28 52 17 4 28 52 17 4 28 52 17
2050 0 5 42 52 0 10 56 33 4 29 53 15 14 26 38 22 0 5 42 52
2100 0 1 34 65 0 2 46 52 4 29 52 15 16 31 25 28 0 1 34 65
NorthernAmerica 2010 0 4 54 42 0 4 54 42 0 4 54 42 0 4 54 42 0 4 54 42
2050 0 1 33 66 0 2 43 55 0 4 57 39 0 4 65 31 0 1 34 65
2100 0 1 28 71 0 1 33 66 0 4 57 39 0 4 65 31 0 1 28 71
Oceania 2010 3 14 51 33 3 14 51 33 3 14 51 33 3 14 51 33 3 14 51 33
2050 0 5 37 58 1 10 46 44 4 21 48 27 7 18 51 24 0 4 36 59
2100 0 1 30 69 0 2 39 58 6 28 45 21 9 22 45 24 0 1 29 70
