【麦肯锡】依赖和人口减少？直面新的人口现实的后果-2025.1

Mcsey

GlobalInstitute

Dependencyanddepopulation?

Confrontingtheconsequencesofanewdemographicreality

Authors

AnuMadgavkar

MarcCanalNoguerChrisBradley

OliviaWhite

SvenSmit

TJRadigan

Editor

StephanieStrom

Datavisualization

JuanM.Velasco

January2025

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Copyright©2024McKinsey&Company.Allrightsreserved.

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MGIDirectors

SvenSmit(chair)

ChrisBradley

KweilinEllingrud

SylvainJohanssonNickLeung

OliviaWhiteLareinaYee

MGIPartners

MekalaKrishnan

AnuMadgavkarJanMischke

JeongminSeong

Dependencyanddepopulation?1

Dependencyanddepopulation?2

Contents

Ataglance3

Introduction4

1.Theageofyouthscarcity6

2.Alower-growth,higher-dependencyfutureinfirstwaveregions24

2.1.Demographicshifts,slowereconomicgrowth2

5

2.2.Moreworkers,morehours,andmoreproductivityneeded35

2.3.Agrowingsocietalbillfordependency44

2.4.Olderworkers,olderconsumers55

3.Anticipatingdemographicshiftsinlaterwaveregions62

4.Respondingtoanewdemographicreality71

Acknowledgments75

Glossary76

Endnotes7

7

Dependencyanddepopulation?3

Ataglance

—Fallingfertilityratesarepropellingmajoreconomiestowardpopulationcollapseinthiscentury.Two-thirdsofhumanitylivesincountrieswithfertilitybelowthereplacementrateof

2.1childrenperfamily.By2100,populationsinsomemajoreconomieswillfallby20to50percent,basedonUNprojections.

—Agestructuresareinverting—frompyramidstoobelisks—asthenumberofolderpeoplegrowsandthenumberofyoungerpeopleshrinks.ThefirstwaveofthisdemographicshiftishittingadvancedeconomiesandChina,wheretheshareofpeopleofworkingagewillfallto

59percentin2050,from67percenttoday.Laterwaveswillengulfyoungerregionswithinoneortwogenerations.Sub-SaharanAfricaistheonlyexception.

—Consumersandworkerswillbeolderandincreasinglyinthedevelopingworld.Seniorswillaccountforone-quarterofglobalconsumptionby2050,doubletheirsharein1997.Developingcountrieswillprovideagrowingshareofgloballaborsupplyandofconsumption,makingtheirproductivityandprosperityvitalforglobalgrowth.

—Thecurrentcalculusofeconomiescannotsupportexistingincomeandretirementnorms—somethingmustgive.InfirstwavecountriesacrossadvancedeconomiesandChina,GDP

percapitagrowthcouldslowby0.4percentannuallyonaveragefrom2023to2050,andup

to0.8percentinsomecountries,unlessproductivitygrowthincreasesbytwotofourtimesor

peopleworkonetofivehoursmoreperweek.Retirementsystemsmightneedtochannelas

muchas50percentoflaborincometofunda1.5-timeincreaseinthegapbetweentheaggregateconsumptionandincomeofseniors.Laterwavecountries,takenote.

—Inconfrontingtheconsequencesofdemographicchange,societiesenteruncharted

waters.Absentaction,youngerpeoplewillinheritlowereconomicgrowthandshoulderthecostofmoreretirees,whilethetraditionalflowofwealthbetweengenerationserodes.Long-standingworkpracticesandthesocialcontractmustchange.Morefundamentally,countrieswillneedtoraisefertilityratestoavertdepopulation—asocietalshiftwithoutprecedentinmodernhistory.

Dependencyanddepopulation?4

Introduction

Familiesacrosstheglobearehavingfewerandfewerchildren.Inmuchoftheworld,fertilityrateshavefallenbelowthereplacementraterequiredtomaintainastablepopulation,and,despite

increasinglongevity,somecountrieshavealreadystartedtoseepopulationdecline.Othersmayfollowinthenot-so-distantfuture

.1

Fallingfertilityratesshiftthedemographicbalancetowardyouthscarcityandmoreolderpeople,

whoaredependentonashrinkingworking-agepopulation.Longerlifespansacceleratetheshift.

ThisphenomenonhasbeguntoplayoutacrossadvancedeconomiesandChina,whereinthree-fifthsofcountriesannualdeathsalreadyexceedbirths.

2

Emergingeconomieshavemorerunway,buttheyfacetheneedtogetricherbeforethedemographictransformationsetsin.

Ourcurrenteconomicsystemsandsocialcontractshavedevelopedoverdecadesofgrowing

populations,inparticularworking-agepopulationsthatdriveeconomicgrowthandsupportandsustainpeoplelivinglongerlives.Thiscalculusnolongerholds.

Acombinationofhigherproductivity,moreworkperperson,effectivemigration,andhigherfertilityratescanensureglobalprosperityforthefuture.Thatsaid,nooneofthoseleversalonewillbe

enough,andeachpresentschallenges.Bendingthetrajectoryofthedemographicshiftwillrequiresocietytorethinkexistingsystemsforworkandretirementinwaysthatmaycompelachangeinoursocialcontract—noeasyfeat.

Thisreportfirstexploresthedemographicshiftsdrivenbyfallingfertilityrates,untilrecentlya

trendprimarilyofinteresttodemographersandactuariesbutnowatopicofglobalconversation.

3

Chapters2and3provideacomprehensiveanalysisofthepotentialeconomicconsequencesof

fallingfertilityratescombinedwithlongerlifespans.Thefirstwaveofagingeconomieshasstartedtofeeltheimpactsoneconomicgrowth,labormarkets,consumption,andpublicfinances.Later

wavesofagingwillhitemergingeconomies,whichareexpectedtofaceasimilarfatejustonetotwogenerationslater.Weconcludewithimplicationsandrecommendationsforpolicymakers,businesses,andsociety.

WhiletheglobalpopulationlastdeclinedsignificantlyduringthebubonicplagueoftheMiddle

Ages,whichisbelievedtohavekilledroughlyhalfofEuropeans,thedemographicshiftwearelivingthroughtodayisinmanywaysaresultofvastimprovementsinglobalhealth,welfare,andprosperity

.4

Humanityhasdemonstratedincredibleresourcefulnessthroughoutitshistory,andnodoubtwillfindopportunitiestothriveamidthechallengesthataworldwidechangeindemographicsposes.

©IcyMacload/GettyImages

Dependencyanddepopulation?6

1.Theageofyouthscarcity

Aswell-beingandprosperityincreasearoundtheworld,twooutcomes—fewerchildrenandlonger

lives—arereshapingglobalpopulations.Overthepastseveraldecades,familieshaveshrunkinsize

virtuallyeverywhere.Inmuchoftheworldtoday,thetotalfertilityrate,whichwerefertoasthefertilityrate,isbelowthereplacementrateof2.1,whichisthenumberofchildrenneededtoreplacetheir

parents.

5

(Demographictermsusedinthisreportaredefinedintheglossary.)Asaresult,theglobalagemixisshifting.Whilemanypeoplecallthisphenomenon“aging,”infactthedecliningnumber

ofyoungpeople—ayouthdeficit—isdrivingthebulkofthedemographicshift,aphenomenonweexploreinthischapter.

Whiledecliningfertilityratesandchangingpopulationpatternsareoccurringeverywhere,afirst

waveofregions,generallyhigher-incomeones,hasalreadybeguntoexperiencetheeffectsofthedemographicshiftoverthepastseveraldecades.Laterwavesofthesamechallengewillwashovermanyemergingeconomiesinthenextonetotwogenerations.

Fallingfertilityisreshapingpopulations—everywhere

Todayinmorethanhalfoftheworld’scountries,hometotwo-thirdsofhumanity,thefertilityratehasdroppedbelowthereplacementrateof2.1childrenperwoman.Globally,thefertilityrate

averaged2.3childrenperwomanin2023,justoverthereplacementrate.

6

Overthepastquartercentury,thefertilityratehasdeclinedin90percentoftheworld’scountries(seesidebar“Whatisthefertilityrate?”).

ThestoryofcollapsingdemographicsstartsinLuxembourg,thefirstcountrytheUnitedNations

recordedashavingafertilityratebelowreplacementin1950,whenitfirststartedcollectingdata

(Exhibit1).Thecountry’sfertilityratereboundedinthe1950s,however,makingSerbiaandCroatia,

bothpartofYugoslaviaatthetime,thefirstcountrieswherefertilitypermanentlydroppedbelowthereplacementthreshold,in1963andin1968,respectively.Withinayear,fertilityratesinDenmark,

Finland,andLuxembourghadfollowedsuit.Noneofthesecountrieshashadafertilityrateequaltoorabovereplacementsincethen.

Twentyyearslater,mostcountriesinAdvancedAsia,Europe,andNorthAmericahadcrossed

thereplacementfertilitythreshold,andChinajoinedthemin1991.Subsequently,fertilityrates

incountriesatvaryinglevelsofeconomicdevelopmentaroundtheworldhavefallenbelow

replacement—inThailandin1989,Mexicoin2015,andIndiain2019.Sub-SaharanAfricaistheone

regionoftheworldtodaywherefertilityratesremainhighandarelikelytostayabovethereplacementratebeyondthenextquartercentury.

Dependencyanddepopulation?7

Sidebar:Whatisthefertilityrate?

Theword“fertility”hasadifferentmeaninginthevernacularcomparedwithitsuseamongdemographers.Colloquially,fertilityoften

referstowhetherapersonisabletoconceiveachild.Butdemographersfocusonfertility

rates,ameasureoftheaveragenumberofchildrenwomenhavethroughouttheirlife.

Measuringtheaveragenumberofchildren

perwomaninanygivengenerationis

straightforwardoncethatgenerationhas

passedchildbearingage.Forexample,the

calculationtodayiseasyforanycohortof

womenbornbeforeabout1970.However,

thisreflectsonlyoldinformationratherthanprovidinganindicationofhowmanychildrenfamiliesarehavingtodayorarelikelytohaveovertheirlives.

Tocharacterizethefertilityrateinanygivenyear,demographersmeasurethetotal

fertilityrate,whichisaso-calledperiodmetric.TheUnitedNationsmeasures

totalfertilityrateastheaveragenumber

ofchildrenthatwouldbebornalivetoa

womanduringherlifetime,assumingshe

weretopassthroughherchildbearingyearsconformingtotheage-specificfertilityratesinthatyear.1Age-specificfertilitymeasuresthenumberofchildrenthatwomenineach

agebrackethaveinthereferenceperiodandistypicallycollectedforfive-yearbrackets

rangingfrom15to50years.

Thetotalfertilityratemaydifferfromwhat

cohortfertilityratesultimatelyendupbeingformanyreasons—age-specificfertilityrateschangeovertime,forexample.Fertilityratescouldbeunderestimatedifyoungerwomentodayenduphavingthesamenumberof

childrenasyoungerwomen15yearsago,

onlylater.Inthiscase,themeasuredfertilityratewillfalltoday,eveniftheeventual

numberofchildrenbornperwomanisthe

same.Conversely,fertilityratesmaybe

overestimatedfortoday’schildbearing

cohortifthenumberofchildrentheyhaveinlateradulthoodcontinuestofallrelativeto

oldercohorts.Nonetheless,thetotalfertilityrateprovidesasetofharmonizedestimatesthatcanbecomparedacrosssocieties,

tracedovertime,andusedtopredictpopulationsize.

Populationsizeisexpectedtoremain

flatifthefertilityrateisatreplacement

level,definedbytheUnitedNationsas

approximately2.1childrenperwoman.This

representstheaveragenumberofchildren

awomanwouldneedtogivebirthtoinordertoensurethatsheisreplacedbyadaughterwhosurvivestochildbearingage.Thetrue

replacementratealsovariesacrosscountries

andmaybeslightlyhigherorlowerbasedondifferencesinchildmortalityandsexratiosatbirth.2

Inthelongrunandsettingmigrationaside,thepopulationofasocietywithafertility

rateabovereplacementisexpectedtogrow,whilethepopulationofonewithafertility

ratebelowreplacementisexpectedto

shrink.However,thisruleofthumbdoesn’tnecessarilyholdintheshortterm,since

populationsizealsodependsonthenumberofwomenofchildbearingageandlife

expectancy.

Therearemyriadcausesforfertilitychangesaroundtheworld,rangingfromsocietal

shiftstodeeplypersonaldecisions.Inthis

report,wedonotexplorethecausesof

decliningfertilityratesbutratherexamine

theirpotentialeconomicconsequences.

Foradiscussionofthecausesofdeclining

fertilityrates,see,forexample,PabloAlvarez,“Whatdoestheglobaldeclineofthefertility

ratelooklike?”WorldEconomicForum,

June2022;NicholasEberstadt,“Theageofdepopulation:Survivingaworldgonegrey,”ForeignAffairs,November/December2024;andAliceEvans,“Whyisfertilitycollapsing,globally?”TheGreatGenderDivergence,

November1,2024.

1Handbookonthecollectionoffertilityandmortalitydata,UnitedNationsDepartmentofEconomicandSocialAffairs,2004.

2Alternatively,newresearchmeasurestheeffectivefertilityrate,whichaccountsforchildmortalityandbringsthereplacementrateto2.Theresearchfindsthataportionofdecliningtotalfertilityratescompensatesforhighersurvivalrates—althoughsincethe1990s,thishasonlybeenthecaseinSub-SaharanAfrica,wherechildmortalityratesremainedhigh.SeeAnupMalaniandAriJacob,Anewmeasureofsurvivingchildrenthatshedslightonlong-termtrendsinfertility,NationalBureauofEconomicResearchworkingpapernumber33175,November2024.

Dependencyanddepopulation?8

Exhibit1

Fertilityratesaredecliningeverywhere.

19501965

Totalfertilityratebycountry,livebirthsperwoman

Luxembourg:2.0

1

1

1

1

1

1

Belowreplacementrate

8

11.52.134567

2010

1995

1980

1

1

1

1

1

1

1

1

1

2023

WesternEurope

Centraland

EasternEurope

AdvancedAsia

x.x

NorthAmerica

2.4

EmergingAsia

Middle EastandNorthAfrica

2.5

2.0India

1.8

Latin

Sub-

SaharanAfrica

Americaand

Caribbean

Totalfertilityratebyregion,livebirthsperwoman,1950–2023

FirstwaveLaterwaves

LatinAmericaandtheCaribbean

8

6

4

2

0

8

6

4

2

0

MiddleEastand NorthAfrica

CGhreater

China

AdvancedAsia

Central

Western

Europe

NorthAmerica

andEastern

Europe

Sub- Saharan

Africa

India

EmergingAsia

5023

1950202350235023502350235023502350235023

Note:Theboundariesandnamesshownonthismapdonotimplyo代cialendorsementoracceptancebyMcKinsey&Company.1TheUnitedNationsreportsthatthestatusofbordersinthisareahasnotbeenagreeduponbytheparties.

Source:WorldPopulationProspects2024,UnitedNations;McKinseyGlobalInstituteanalysis

McKinsey&Company

Dependencyanddepopulation?9

Atthesametime,lifeexpectancyhasincreasedalmosteverywhere.7

Butgreaterlongevityexplainsjust20percentofthechangeintheageprofilesofpopulationsindevelopedcountriessince1960;

fallingfertilityratesexplaintherest(Exhibit2).

ConsiderthecombinedimpactofthesetwoforcesinGermany.From1960to2021,26millionfewerbabieswereborn,anumberequivalentto31percentoftheGermanpopulationattheendofthat

period,thaniffertilityrateshadremainedconstantatthe1960level.Sevenmillionmoreseniors,orabout8percentofthecountry’spopulation,werealiveattheendoftheperiodduetoincreasedlifeexpectancyoverthesameperiod.Net-net,thecountry’spopulationin2021was23percentsmallerthanitwouldhavebeenhadbothfertilityandlifeexpectancyratesremainedconstant,equivalenttoroughly19millionfewerpeople.

Japanistheonlydevelopedcountryinourresearchwherelifeexpectancyhadroughlythesame

impactasfertility.Thisunusualpatternwasduetotwofactors.First,Japanalreadyhadaverylow

fertilityratein1960—1.98comparedwith,forexample,2.7intheUnitedKingdomatthattime.Andlifeexpectancyat65increasedmoreinJapanthaninothercountries—bynineyearscomparedwithsix

yearsintheUnitedKingdom.

Inemergingeconomies,fertilityratesfellevenmoredramaticallyfrom1960to2023.Forinstance,awomanhadanaverageof6.1babiesinBrazilin1960,whereastoday,shehas1.6children.

Exhibit2

Fallingfertilityratesexplainabout80percentofthechangesintoday’stotalpopulationresultingfromthedemographicshiftsweepingtheworld.

Impactofchangesinfertilityrateandlifeexpectancyontotalpopulation,1960–2021,%of2021population

UnitedUnitedGreaterSouth

StatesKingdomSpainChinaGermanyItalyAustraliaFranceJapanKorea

61

0%

95

MORESENIORS

Additionalseniorswhowouldnotbealivetodayhadlifeexpectancynotincreased,%of2021

9

population1

FEWERYOUNGPEOPLEAdditionalpeoplewho

wouldhavebeenbornhadfertilityratesnotdeclined,%of2021

population

76

Shareof

demographicshiftexplainedbydeclining

fertility,%

100%

79

50

78

81

82

83

87

72

77

30

30

31

39

52

44

27

18

16

13

10

15

6

8

8

8

8

157

1Seniorsdefinedasindividualsaged65yearsandolderin2021.

Source:WorldPopulationProspects2024,UnitedNations;McKinseyGlobalInstituteanalysis

McKinsey&Company

Dependencyanddepopulation?10

Globallifeexpectancyhasextendedbysevenyearsonaveragesince1997,reaching73yearsin2023andsettohit77yearsby2050.Centenarians,orthose100yearsandolder,arethefastest-growingagegroupinpercentageterms,accordingtotheUnitedNations.Yetforalltheattentionpaidtorisinglongevity,decliningfertilitymorepowerfullydeterminesglobaldemographics.

Populationsmorphfrompyramidsintoobelisks

Duetothedemographicshiftswe’vedescribed,whatdemographerscallpopulationpyramidsare

shapedlessandlesslikepyramidstoday.Toanalyzehowpopulationstructuresareshiftingovertime,we’vegroupedtheworld’scountriesintotenregions:AdvancedAsia,CentralandEasternEurope,

EmergingAsia,GreaterChina,India,LatinAmericaandtheCaribbean,MiddleEastandNorthAfrica,NorthAmerica,Sub-SaharanAfrica,andWesternEurope(formoreonourclassificationanddata,

seesidebar“Pyramidfoundations:Demystifyingtheapproach”).Inmostregions,thesestructuresnowresembleshallots,andinmoreeconomicallyadvancedones,theyaretakingontheshapeofobelisks(Exhibit3).

Exhibit3

Populationpyramidswillturnintoobelisksby2100.

Populationbreakdownbygenderandagegroup,1960–2100

1960202320502100

Firstwaveregions

MaleFemale

Population

Age

100+

90-94

80-84

70-74

60-64

50-54

40-44

30-34

20-24

10-14

0-4

AdvancedAsia

North

America

WesternEurope

GreaterChina

Centraland

EasternEurope

Laterwaveregions

Age

100+

90-94

80-84

70-74

60-64

50-54

40-44

30-34

20-24

10-14

0-4

Emerging

LatinAmerica

MiddleEast

Sub-Saharan

Asia

India

andCaribbean

andNorthAfrica

Africa

MaleFemale

Population

Note:Pyramidsaredrawntoscalewithineachregionbutnotbetweenregions.

Source:WorldPopulationProspects2024,UnitedNations;McKinseyGlobalInstituteanalysis

McKinsey&Company

Dependencyanddepopulation?11

Societiesareshapedinlargepartbytheiragestructures,andtheireconomicprioritiesshiftastheirpopulationpyramidsinvert.Theamountofphysicallyintensiveworkdoneversusthenumberof

physicaltherapistsneeded,orthenumberoffamiliesaddingnurseriestotheirhomesratherthanaddingaccessorydwellingunitstohouseagingparents,dependsonthemixofyoungerandolderpeopleinapopulation.

Crucially,pensionentitlementskickinbetween60and67yearsofageinmanyeconomies,

particularlyinadvancedones.Atthatpoint,seniorsbecomerecipientsof“support”providedbytheworking-agepopulation,thoseaged15to64,whogeneratemostoftheincomeandpaymostofthetaxesthatsupportolderpeople.Withoutsignificantchanges,theworld’sagingpopulationmeansagrowingnumberofolderpeoplewhoaren’tworkingwillrequirethesupportofashrinkingnumber

ofyoungerpeoplewhoare.Evenifglobalfertilityratesweretojumpovernighttothereplacementrate,itwouldtake20years,giveortake,forthoseadditionalbabiestobecomeadultsandbegincontributingtoeconomicgrowththroughwork.

Sidebar:Pyramidfoundations:Demystifyingtheapproach

Inthisreport,weexploretheimplications

ofchangingdemographicsbyanalyzing

projectedpopulationshiftsbasedonUnitedNationsforecasts.Weexaminetheoutcomesacrossdifferentwavestounderstandthe

impactovervarioustimehorizons.

Wehaveconsolidatedtheworldintoten

regionstopresentourfindings,andeachofthe237countriesandareasintheUNWorldPopulationProspects2024isindividually

accountedforsothatglobalpopulations

sumtothetotal.Ourfirstwaveregions

includeAdvancedAsia(Australia,Japan,

NewZealand,Singapore,andSouthKorea),WesternEurope,GreaterChina,Central

andEasternEurope,andNorthAmerica.

LaterwavesencompassLatinAmericaandtheCaribbean,India,theMiddleEastand

NorthAfrica,EmergingAsia(economiesnotincludedinAdvancedAsia,India,orGreaterChina),andSub-SaharanAfrica.

Throughoutthereport,werelyon20

countriesforexamples.Forfirstwaveregions,thosecountriesareAustralia,China,France,Germany,Italy,Japan,SouthKorea,Spain,

theUnitedKingdom,andtheUnitedStates.Together,thesecountriesaccountfor28

percentofglobalpopulationandgenerate

65percentoftheworld’snominalGDP.The

examplecountriesfromlaterwaveregions

areBangladesh,Brazil,Egypt,Ethiopia,

India,Indonesia,Mexico,Nigeria,Thailand,

andTürkiye.Thesecountriesaccountfor35

percentofglobalpopulationand12percentofnominalGDP.

Mostofourdatasourcesarepubliclyavailableandstandardized.Thefuturepopulation

projectionsinthisreportarebasedon

themediumscenariofromtheUNWorld

PopulationProspects2024,whichcovers237geographicentities,mostlycountries.The

reportincludespopulationestimatesfromthe1950stothepresent,aswellasprojections

through2100.Additionally,wehave

supplementedouranalysiswithincomeandconsumptiondatafromtheNationalTransferAccountsProject;labormarketdatafromtheInternationalLabourOrganization’sILOSTATandTheConferenceBoard;andadditional

informationfromEurostat,theOECD,and,

whereapplicable,nationalstatisticaloffices.WealsouseconsumptiondatafromWorld

DataLabandsupplementoureconomic

analyseswithOxfordEconomicsdata,whicharenotpubliclyavailable.

Throughoutthereport,ouranalysistakesa

ceterisparibusapproach,holdingallvariables

constantexceptdemographicchange,to

isolateitseffect.Ourapproachhastwo

keylimitationstohighlight.First,ceteris

paribusoutcomesthroughoutthisreport

arenotpredictions;rather,theyarethought

experimentstoexploretowhatdegree

currenteconomicsystems“addup”infuturedemographicrealitiesandtounderstandthewaysinwhichtheydonot.Thesecalculationsarenotdynamic,butwereadilyacknowledgethatceterisparibusneverholdsinpractice.

Forexample,wedonotconsidertheimpactofagingdirectlyonproductivitywithincountries,onpersonalsavingsrates,andsoforth.1

Societiesarehighlyadaptable,andtheymustandwilladaptinwaysthatourcalculationsdonotattempttoanticipate.Infact,thesizeof

therequiredadjustmentiswhatweattempttoapproximatewithourmethodology.

Second,oursourcesofdata,whilerobust,

havelimitations.Insomeinstances,differentsourcesdonotagree,andsomegapsinthedatarequireinterpolation.Insomecases,

datasourcesarethemselvesestimating

quantitieswithahighdegreeofuncertainty.EventheUNpopulationscenarios,whiletheclosestassessmentsavailabletoaglobal

consensusview,havetheircritics(see

sidebar“Predictingthefutureishard,anddemographersdon’tagree”).

1SeeNicoleMaestasetal.,“TheEffectofPopulationAgingonEconomicGrowth,theLaborForce,andProductivity,”AmericanEconomicJournal:Macroeconomics,April2023.

Dependencyanddepopulation?12

Sidebar:Predictingthefutureishard,anddemographers

don’tagree

Thecomplexinterplaybetweenfertility,

lifeexpectancy,migration,andexisting

populationstructuresthroughouttheworldnotsurprisinglycreatesuncertaintyabouthowpopulationswillevolveinthefuture.

Manyorganizationsforecasttrajectories,

whichoftenvarywidely.Theprojectionsin

thisreportarebasedontheUNmedium

scenariofrom2024.1TheUnitedNationsis

keenlyawareoftheinherentuncertaintyin

itscalculations:itslowandhighscenariosforglobalpopulat