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Human Population - Human Population The Next Half Century...

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Unformatted text preview: Human Population: The Next Half Century joel E. Cohen By 2050, the human population will probably be larger by 2 to 4 billion people, more slowly growing (declining in the more developed regions), more urban, especially In less developed regions, and older than' In the 20th century Two major demographic uncertainties in the next 50 years concern international migration and the structure of families Economies, nonhuman environments. and cultures (including values, religions, and politics) strongly influence de- mographic changes Hence, human choices, individual and collective, will have demographic effects, intentional or otherwise. It is a convenient but potentially dangerous fiction to treat population projections as exogenous in- puts to economic, environmental, cultural, and political scenarios, as if population processes were autonomous. Belief In this fiction is encouraged laws, family structure, domestic and international order, and the physical and biological environ- ment. Odler biological species are recognized ex- plicitlyonlyintherecentinnovationofquantify- mgflredevasmtingdenrographicirripactsoflfiv 'andAIDSXIheabsencefl'ompopulationprejec— tion algorithms of influential external variables indicates scientific ignorance of howexternalvari— ables influence demographic rates ratherthan any lack of influence (1). Demographic projections stimulate fears of ovemopmadmmmfmsofdemognphh r mohne andculuuflmaimhroflmm, Earth’spopnlatiargi'ewaburllfl-fnldfiutiifim ”mutanpeqflfld '5).‘ '1 "WWW ‘ mflhonpeqicthOOtoflSlilfiunmmm Theseandarlduimuphicmatamahmém; '4 ' mummies: 0&me inimimghrymnrpeopie mamwmmwtr l927toputthefirst2billionpeoplerfillnM-F’ WWW “It! repeatedqualificdimsuf tedlttookfimrtho lessthanSOyearstoaddflrenethlillmpemh any prior experience with such rapid growth and large numbers of its own species. From 1750 to 1950, Europe and the New World experienced the most rapid population growth of any region, while the populations of most of Asia and Afi'ica grew very slowly. Since 1950, rapid population growth shifted flom Western countries to Africa, the Middle , tory occurred around 1965—70. The global popua lafiongrowtlr rate nabbed its all-time peak of about 2.1% per year (pa). It then gradually fell to 12% paby 2002 (4). The global total fertility rate fellfiemSchildrenperwomanperlifetimein 1950—55 to 2.7 children in 2000—05. The abso- lute annual increase in population peaked aroimd l990at86millionandhasfallento77million ' Concurrent trends included worldwide efforts to hflfcenunywmuimanpt-fimhh-w .. . immmfim phcatrons or iiinniy W with - lawn-Minnow bin-minty hmlhnumjampahy. Wham-1 '-: ,_- Mhmndgrdaand . my, the phyiflLchmfiuluflthghlfl' 'Eh‘flgww'dm.‘ “’3‘“? "' I vironment, ammomnuuniecin animal; 1960, £113 mil-ii inai reality mismesmm-m-z .. .frt- Liiiiflaéfrfifimuwmfldbmplaoe ' ‘I " _“ nifiélmsimt'Bymmiere Past Population ' ' '»'=‘=--'-'==-'-'Fm= 0' fim-fi‘m- ' iii-ch'Emma. ' " wilhabout " WWW for W'W ' g‘i‘e‘allyin 15‘1”. Imam r'r‘riluthan Wfitommimmleurlngia Between 'iosibruinnebiiyirwenmm -' Rockefeller University (by iwqmmzsmomdndflm mwimmmmwmpifiwmwmrsmmmm mmwmmmmmm honbeiweenimnamntfiurerarw dummwfiywmm dwellersmseanotherl4—foldormore,fiom200 adelohalmmNowmm millionto 29 brlhon. In 1900, no cifieshad 10 lrvedthrwghatriphng'lhehinnanspecreslacks millionpeopleorr‘nore. By 1950, Wong citydid: ' .,,r. ({ .ycwngln and Columbia Unlvers .1230 * PM”? NewYogk’ijlvenneJoxzo New Yorlr. NY 100% us»; (Joya, 0's- _.., New York, and Les Angeles) mi' it'fl M ltlérhhfli‘tr hfdty' dwfllr‘n roan ~ ‘ V population would grow to 12.8 billion by 2050, :more than double its' present size. The medium w reams J) million; ; Airlines, 91in four ' "behaviors related to AIDS Will become less (frequent and chances of infection among those 7-7): mwmiffllégmw rel-{mi «Hear Demographic Projections of the Next 50 Years Projections of future global population prepared by the United Nations Population Division, the World Bank, the United States Census Bureau, and some research institu- tions assume business as usual (7—9). They include recurrent catastrophes to the extent that such catastrophes are reflected in past trends of vital rates, but exclude catastrophes of which there is no prior experience, such as thermonuclear holocaust or abrupt, severe climate change. The following summary relies mainly on the United Nations Population Divi- sion’s urbanization forecasts (6) and World Population Prospects: The 2002 Revision (4 ). Alternative projections prepared by the UN in- clude low, medium, high and constant—fertility variants. Estimates of present levels of demo- graphic variables are projections based on mea- surements in recent years, rather than global current measurements. 1 According to the medium variant, the world’s population is expected to grow from ' 6.3 billion today to 8.9 billion in 2050. Whereas the first absolute increase by 1 billion people took fi'om the beginning of time until about 1800, the increase by one billion people from 6.3billionto7.3billionisprojectedtorequire 13 to 14 years. The anticipated increase by 2050 of 2.6 billion over today’ 5 population exceeds the tall pnpnlnflrm of the world in 1950, which was 2,5 Current absolute gird relative global popula- ,tiongrowthrauucfitlfighu'than any expe- rienwd before World War II .The annual addi- 3~tion of 77 million people poses formidable '.:cha11engraoffood,hmaing.edneatinn.healtll, employment, polifidl «genitalia: and public 0' order. Virtuallyallofdreincreascisandwillbe "in the economically less-developed regions. ‘ More than halfof the annual Increase currently occurs in six countries: India, China, Pakistan, Bangladesh, Nigeria, and the United States. Of the total annual increase, the United States accounts for 4%. ‘ Were fertility to remain at present levels, the projection of 8.9 billion people in 2050 assumes that efforts to make means of family planning available to women and couples will continue and will succeed, and that after 2010 high-risk in high risk behaviors will decline. “it xii-,1 », a @0602 SCENE wwsciencemagorg The UN’s 2002 estimate of 8.9 billion people in 2050 is 0.4 billion lower than that in their 2000 medium variant. About half of the decrease in the projection for 2050 is due to fewer projected births and about half to more projected deaths, notably from AIDS. Global statistics conceal vastly different sto- ries in different parts of the world. In 2000, about 1.2 billion people lived in the economi- cally rich, more developed regions: Europe, Northern America, Australia, New Zealand, and Japan. The remaining 4.9 billion lived in the economically poor, less developed regions. The current annual growth rate of global population is 1.22%. Rich regions’ population currently increases 0.25% annually. Poor re- gions’ population grows 1.46% annually, near- ly six times faster. The population of the least developed regions, the 49 countries where the world’s poorest 670 million people lived in 2000, annually increases 2.41%. By 2050, the projected annual growth rate of global popula- tion is 0.33%. The poor ecunties’ population will still be increasing 0.4% annually, whereas the population of the rich countries will have been helining for 20 years and will then be falling at —0.l4% annually. Thirty of the more developed counties are expected to have lower populations in 2050 than today, including Japan (14% smaller), Italy (22% smaller), and the Russian Federation (29% smaller). By contrast, the population of today’s poor counties is pro- jected to rise to 7.7 billion in 2050 fiorn 4.9 billion in 2000. Fertility in the less developed regions is expected to fall to replacement level ‘ in 2030—2035 but to remain above 2 children per woman by 2050 because some of the least developed countries will still have total fertility rates well above replacement level. The popu- lation of these high- -fertility poor counties will beanincreasingproportionofthepopulationof the less developed regions. The world‘s m population dnsity of 45 people/km” hm ismujectedmfiuumfifi people/km2 by 2050. actually. perhaps 10% of landisarable, npohulafiaudmflfiuupuamitof arable land are roughly-IO times higher. In the rich counties, the population density was 23 people/km2 in 2000 ——half the global average— and was projected not to change at all by 2050. Intrupucrooumiar, thepopulation density‘was BWnMandwaspmjectedtorise h 93 purrplulfknra km 2050. For comparison, the population density of Liechtenstein was 204 people/km: in 2000 and that of the United mm'.30-Apopulltiunr-dunnityof93 peoplethn’ovnrflstmtim-duvulching Iwnrhjnfillpounnnprnedurtedwnblunsof " .J'alltli r; hurry“: “J Induiniudi' ' admire-u W114: nth Nmmh dimmer: ‘ 'thatinthe n'éh countries is projected to rise m from 2.6 in 2000 to 4.0 in 2050. Over the same interval, while the population density of Europe is projected to drop from 32 to 27 people/kmz, that of Africa is projected to rise from 26 to 60 people/km? The ratio of pop- ulation density in Africa to that in Europe is projected to rise from 0.8 in 2000 to 2.2 in 2050. It seems plausible to anticipate increas- ing human effects on the natural environment in Africa and increasing pressure of migrants from Africa to Europe. The difference in population growth rate between rich and poor countries affects both population size and age structure. If a popula- tion grows slowly, the number of births each year nearly balances the number of deaths. As most deaths occur at older ages, the numbers of individuals in different age groups are roughly equal up to older ages. The so—called population pyramid of a slowly growing population resem- bles a column (Fig. 1, middle row left) (10). If a population grows rapidly, each birth cohort is larger than its predecessor and the population pyramid is triangular (Fig. 1, middle row right). The projected difference in age structures be- tween the European Union versus North Afiica and western Asia (Fig. 1, bottom) has obvious implications for the supplies of military person- nel and ratios of elderly to middle-aged Inequality in the face of death between rich and poor will decrease but remain large if sur- vival improves everywhere as anticipated in the coming half century. Global life expectancy in 2000—05 is estimated at 65 years; in 2045—50, at 74 years. Over the same interval, life expect- ancy in the rich countries is expected to rise ficm76yearsto82yearsandinthepoor counties tom 63 years to 73 years. The aver,- age infant born in a poor country had a chance of dying before age 1 that was 8.1 times higher than that in a rich country in 2000—05; the . same ratio is projected to be 5.2 in 2045—50. Despite higher death rates, poor counties’ ,\ populations grow faster than those of rich because birth rates in poor countries are much higher. At current birth rates, during her life- time, the average woman in the poor coun- tries bears nearly twice as many children (2.9) as in the rich counties (1.6). By 2050, according to the medium variant, the total fertility rate in today’s poor counties will drop to 2.0. The total fertility rate in today’s more developed countries is projected to rise to almost 1.9 children per woman, as timing effects that currently depress the total fertility rate cease to operate. In the coming decade, more than halfof all peoplewill live incities, firflmufirflthne-in humanhistory. Aixnostaumnnmmhh," thenexthalfcenturywill he hchinsinpqu counties while the world‘s null population willremainflat,near3billionpeople 1g ,1 ‘ wwwsclenoemagorg SCIENCE VOL 302 14 NOVEMBER 2003 - The United Nations Population Division projects urban population only as far as 2030 (6). Its figures on urbanization disguise major ambiguities and variations among countries in definitions of “cities” and “urban.” Never— theless, the trend toward urbanization is clear. Of the projected 2.2-billion increase in pop- ulation from 2000 to 2030, 2.1 billion will be in urban areas, and all but 01 billion of that urban increase will be in developing coun- ties. The annual rate of increase of urban population over the next 30 years, 1.8%, is nearly twice the projected annual rate of in— crease of global population during that peri— od. The urban population of developing re- gions will grow rapidly as people migrate from rural to existing urban areas and trans- form rural settlements into cities. The rural population of the rich counties peaked around 1950 and has slowly declined since then. The rural population of the presently poor countries is expected to peak around 2025 and then gradually decline. Urbaniza- tion of the rich counties will continue, rising from 75% of people in 2000 to 83% in 2030. Over the same period, urbanization of the poor countries will rise from 40% to 56%, similar to the level of urbanizationjn the rich counties in 1950. The coming half century will see dramatic population aging, which means a higher pro- portion of the population in elderly age groups. The proportion of children aged 4 years and under peaked in 1955 at 14.5% and gradually declined to 10.2% in 2000, By contrast, the fraction of people aged 60 years and older gradually increased from a low of 8.1%in1960to 10..0%i.n2000 Eaehyoup constitutes about 10% of hunnrty today The 20th century-willmbe lhulut In which younger people «incubated older ones Childrenagudomiifinmuctndtn decline to 6. 6% of global population by 2050, 7 . whereas people aged 60 years and older are projected to more than double to 21 .4%. By 2050, there will be 3.2 people land 60 years or older for every child 4 your; 'old oi: young- er. This reversal in the numerical dominances . of old and young reflects improved survival and reduced futilrty impound survival raised the global W Burgh oflifu from perhaps 30 years ulflsubcgrmingofflluZOth 'centuryto 65 yematthnhummgufflme ‘mé fiactcnsmlldrcpto21%and 216% in *zpomandfichmrmtiarespectively. Theglobal 1173 fraction of the elderly population (aged 65 years or more) will rise from 7% in 2000 to 16% by 2050. Over the same period, the elderly fraction will rise from 5 to 14% in the presently poor countries and from 14 to 26% in the rich coun- tries. Though the fiaction of children in the population will decrease by more in the poor countries than in the rich, the fraction of elderly will increase by more in the rich countries than in the poor. Both shifts will have consequences for spending on the young and the old. E Illa sssatmrsrssts " '53 1 950 E iiiiiiiiiiiiiiil ii??:t“"" if ID 'iil' ind‘the ll tarts: ' ' “maternal - -- 111i" 'forme'swat (Nautilus: am mat-am and ma (termite-a mum ‘ persons separately by sex; vertical scale gives age groups in Increments of 5 years. 3 H ' .~ Slowly growing populations have a higher elderly dependency ratio (the ratio of the number of people aged 65 and older to the number aged 15 to 64), while rapidly grow- ing populations have a higher youth depen- dency ratio (the ratio of the number of people aged 0 to 14 to the number aged 15 to 64). The elderly dependency ratio rose from 1950 to 2000 at a rapid rate in the more developed countries, slightly less rapidly in the United States, and still less rapidly in the world as a mmmmmm Wimm Eiliiiiiiiiiiiiii .4 Z In s 312 .- ‘i iiiiiiiiiiiiii gr .. ‘ . insistent: whole. The ratio rose only slightly in the less developed countries, and hardly at all in the least developed countries. Afier 2010, in the more developed countries, the United States, and the less developed countries, the elderly dependency ratio will increase sharply faster; this acceleration will be greater in the more developed countries and the United States. The least developed countries will experience a slow increase in the elderly dependency ratio after 2020 and, by 2050, will be ap- proaching the elderly dependency ratio of the more developed countries in 1950. Demographic Uncertainties: Migration and the Family According to the United Nations Popula- tion Division, “International migration is the component of population dynamics most difficult to project reliably. This oc- curs in part because the data available on past trends are sparse and partial, and in part because the movement of people across international boundaries, which is a response to rapidly changing economic, geopolitical or security factors, is subject to a great deal of volatility” (1 I). The UN’s 2002 medium variant posits migration from less to more developed regions of 2.6 mil- lion people annually during 1995—2000, de— clining to nearly 2.0 million by 2025—30, and remaining constant at that level until 2050. The United States is anticipated to increase annually by 1.1 million of these 2 million migrants, more than five times the number expected to be added annfially to the next largest recipient, Germany (211,000). The major sending countries are expected to be China, Mexico; India, the Philippines, and Indonesia. . International migration is likely to remain important for specific cormtries, including the United States. In the mid-1990s, about 125 mil- lion people (2% of world population) resided outside of their country of birth or citizenship. In 1990, only 11 cormtries in the world had more than 2 million migrants, and-they collectively had almost 70 million migrants. The largest We of misfits were mm ng1 (19.6 mm (SJnfilMWH-fiu nfilfimhFMISHMMmiflm/(fifla million). The countries with the hi'gheét percent: age of international migrants in thetbtal popu- lation were countries with relatively small pop-_ ulations. IntheUnitedArabEmir'atesnAndorra, "Kuwait,Monaco,anantar 64m90%ofthe WWW‘R tiff-niltii n-i ic transition weakened the ties between men 14‘NOVEMBEK2003 VOL 302 SQENCEtL wwwscienoemagmgg , and women based on parenthood and that the rise in divorce and cohabitation is weakening the ties between fathers and children. Non- marital births increased as a percentage of all births in the United States from 5.3% in 1960 to 33.0% in 1999. In 1999, the United States had 1.3 million births to unmarried women (13). In 1998, Iceland, Norway, Sweden, Denmark, France, United Kingdom, and Fin- land all had higher proportions of nonmarital births than the United States. By contrast, in Germany, Italy, Greece, and Japan, less than 15% of births were nonmarital (13). Among United States women aged 15 to 29 years at first birth, when that first birth was conceived before maniage, the fraction who married before the birth fell from 60% in 1960—64 to 23% in 199094 (14). By 1994, about 40% of children in the United States did not live with their biological father (12). In the United States, the number of wid— owed males aged 55 to 64 per thousand mar- ried persons fell from 149 in 1900 to 35 in 2000, whereas the number of divorced males aged 55 to 64 per thousand married persons rose from 7 to 129. Divorced males became more frequent than widowed males between 1970 and 1980. Divorced females became more frequent than widowed females be- tween 1990 and 2000. By 2000, the number of divorced and widowed persons aged 55 to 64 per thousand married persons was 164 males and 426 females (2.6 such females for WW each such male) (15). Remarriages and step- families are becoming increasingly common. Three factors set the stage for further ma- jor changes in families: fertility falling to very low levels; increasing longevity; and changing mores of marriage, cohabitation, and divorce. In a population with one child per family, no children have siblings. In the next generation, the children of those chil- dren have no cousins, aunts, or uncles. If adults live 80 years and bear children be- tween age 20 and 30 on average, then the parents will have decades of life after their children have reached adulthood and their children will have decades of life with elderly parents. The full effects'on marriage, child bearing, and child rearing of greater equality between the sexes in education; earnings; and social, legal, and political rights have yet to be felt o...
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