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IN 1900, THERE WERE 1.6 BILLION PEOPLE ON EARTH.By 2000, that number had skyrocketed to 6.1 billion. This astounding rate

of growth has slowed, but the trend is still heading dramatically upward.

It varies substantially by region, however, with the less developed coun-

tries growing rapidly and the more developed countries growing slowly

if at all. World population is expected to pass 7 billion in late October

and is projected to top 9 billion by 2050; the latest U.N. projections put

it at about 10 billion in 2100. In truth, no one knows exactly how high

population will grow or when it might flat-line. All population projections

are uncertain, as they are entirely dependent on assumptions about the

futurefor instance, how many children a woman will have 20 or 30 years

hence. In that sense, these numbers can be considered best scientific

guesses, not destiny. Whats more, the further out one looks, the cloudier

these projections become. Still, they offer a window into what the world

might look like in 2050. LESLIE ROBERTS9Billion?

NEWS

0

1

2

3

4

5

6

7

8

9

10

India

China

Africa

Other less developed countries

More developed countries

World Population Growth, 19502050 (medium varian

1950 1970 20101990 2030

SOURCES: UNPD, 2

9.3Billio

0

1

2

3

4

5

6

7

8

9

10

Population

(billions)

Historic and Projected Population Growth

13 years

To add the next1 billion people

SOURCES: CARL HAUB, POPULATION REFERENCE BUREAU (PRB), 2010; U.N. POPULATION DIVISION (UNPD), 2011

1+ Million years 6000 B.C.E. 4000 B.C.E. 2000 B.C.E. C.E. 1 C.E. 2000

7Billion 2011

6Billion 1999

5Billion 1987

3Billion 1960

2Billion 1930

4Billion 1974

1Billion 1800

8Billion 2024

1950 1975 2000 2025 2050 2075

0

5

10

15

20

25

U.N. Population Projections, 19502100

SOURCE: UNPD, 20

High-fertility variant, 2.5 children

Medium-fertility variant, 2.0

Low-fertility variant, 1.6

Constant fertility variant

*Total fertility rate: the average number

of children women would bear in their

lifetime if the birth rate of a particularyear were to remain unchanged.

TFR* 2.5

Constant

2.0

1.6Population

(billions)

Population is growingfast ...

Different assumptions,different scenarios.The United Nations has peered outto 2100, but those projections areeven more uncertain than thosefor 2050. The medium variantmost commonly used assumes theaverage woman in 2100 will havetwo children. If she had half a childmore, or less, the picture would

change dramatically. And if fertil-ity remained constant at currentlevels

Trends in Life Expectancy at Birth, 1950 and 2010

Africa Asia Europe N. America WorldLatin Amer. andthe Caribbean

19501955 200520

0

20

40

60

80

47.7

67.9

42.9

69.0

38.2

55.251.3

73.4

SOURCE: UNPD, 2

68.778.2

65.675.4

Years

Behind the growth.Much of the population growthof the past 50 years is due to thespectacular gains in life expec-tancy in developing countries,reflecting advances in publichealth and medicine.

Going up.The world has never seen anything like the population explosion of the past century. Fourbillion people have been added to the planet since 1950, and the time it takes to add 1 billion people hasdropped to 13 years. World population could reach 9.3 billion by 2050, according to U.N. projections.

Published by AAAS

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SPECIALSECTION

Fertility and Education, 2007Percentage of girls enrolled in secondary school

Total fertility rate

100

80

60

40

20

0

0 1 2 3 4 5 6 7 8

Total fertility rate

100

80

60

40

20

00 1 2 3 4 5 6 7 8

Fertility and Poverty, 2007Percentage of population living on

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3%Population 65+,sub-Saharan Africa

LATIN

AMERICA

2010590,082

Population

2050750,956

Projected

NORTH

AMERICA

2010344,529

Population

205446,86

Project

AFRICA

20101,022,234

Population

20502,191,599

Projected

ASIA

20104,164,252

Population

20505,142,220

Projected

EUROPE

2010738,199

Population

2050719,257

Projected

100+

2699

125

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SPECIALSECTION

Percentage Residing in Urban Areas, 19502050100

WorldMore developedLess developed

1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050

90

80

70

60

50

40

30

20

10

0

The Demographic Divide

NIGERIA JAPAN

Population 2010 (millions)

Lifetime births per woman

Annual number of births

Percentage of population below age 15

Percentage of population over age 65

Life expectancy at birth

Infant death per 1000 birthsAnnual number of infant deaths

Population 2050 (millions)

158

5.7

6,700,000

43

3

47

75500,000

326

127

1.4

1,090,000

13

23

83

2.62,830

95

Nigeria2010

15 10 5 0 5 10 15

Population (millions)

04

85+

8084

Age

Japa201

Population (millions)

0-4

85+

8084

Age

Males

Females

15 10 5 0 5 10

City bound.More and more people will be living in cities and towns, with thefastest rate of urbanization occurring in less developed countries.

A tale of two countries.A look at Nigeria and Japan today suggests whats ahead. Given Nigeriashigh birthrate and large number of women of childbearing age, the population is expected to more thandouble by 2050, while the population of Japan is expected to decline.

Higher costs, fewer workers.In 2050, developedcountries will not have enough workers to support thehigher costs of their aging populations. Developing coun-tries with young populations will not have enough jobs.International migration is set to increase.

The World Ahead

By the numbers

6:1 Population of developing to developedcountries, 20502:1 Population of developing to developedcountries, 1950

12 Biggest Cities

1975 2025

26.61

15.88

10.69

9.84

9.61

8.93

8.74

8.56

7.89

7.62

7.56

7.55

Population

(millions)

Tokyo

N.Y.-Newark

Mexico City

Osaka-Kobe

So Paulo

L.A.-Long Beach

Buenos Aires

Paris

Kolkata

Moscow

Rio de Janeiro

London

City

Tokyo

Delhi

Mumbai

So Paulo

Dhaka

Mexico City

N.Y.-Newark

Kolkata

Shanghai

Karachi

Lagos

Kinshasa

37.09

28.57

25.81

21.65

20.94

20.71

20.64

20.11

20.02

18.73

15.81

15.04

City Population

(millions)

0

5

10

15

20

World More developed Less developed Least developed

9

4 4

2

11

4

17

9

Number of Working-Age Adultsper Older Adult, 2010 and 2050

2010

2050

37Million

Number of people that developing coun-tries could be adding each year in 2050

0 Number of people that developed coun-tries could be adding each year in 2050

By the numbers

SOURCE: PRB, 2010

SOURCE: UNPD, 2011

SOURCES: (CHART) PRB, 2010; (POPULATION PYRAMIDS) UNPD, 2011

SOURCE: PRB, 201

SOURCE: UNPD, 2009 SOURCE: UNPD, 200

P bli h db AAAS