Human Population

Envi 201 Spring 2004

Key Concepts

Exponential Growth – Rule of 70 Demographic transition Age structure and population

momentum Causes of fertility decline Links between fertility decisions and

environment (Dasgupta article)

Exponential Growth

Quantity grows by the same relative amount (g) each year

P(next year) = P(this year)* (1+g)

At time t, P = P0 x (1+g)t

Exponential Growth

Quantity grows by the same relative amount each year

Doubling time d is constant

Rule of 70:

Doubling time x growth rate = 70 Examples:

r, growth rate, % per year

d, doubling time, years

10 7

1 70

2 35

World Population Growth

World Population Grew Slowly Through 1945…Then accelerated…Then slowed

Trends in Population Growth WorldwidePopulation Increase and Growth Rate, Five-Year Periods

7987

82 79 77 75 7369

0

10

20

30

40

50

60

70

80

90

1980-1985

1985-1990

1990-1995

1995-2000

2000-2005

2005-2010

2010-2015

2015-2020

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Net population added per year Annual population growth rate

Mill

ions

Per

cen

t in

crea

se p

er y

ear

Source: United Nations, World Population Prospects: The 2002 Revision (medium scenario), 2003.

Growth Rates have Peaked…

0%

1%

2%

3%

4%

5%

6%

1950-60 1960-70 1970-80 1980-90 1990-2000

Alaska Population: Average Annual Rates of Growth

(due to births, deaths, and net migration)

The Demographic Transition

Stage I: high birthrates and death rates Stage II: continued high birthrates,

declining death rates Stage III: falling birthrates and death

rates, eventually stabilizing

Replacement Rate would be 2 children per woman

Population Momentum

Lots of young people Although each woman may have total

fertility = 2 children, There are many more future mothers

than current mothers

Native Age Structure

-1500 -1000 -500 0 500 1000 1500

Age

4

9

14

19

24

29

34

39

44

49

54

59

64

69

74

79

84

89

Male

Female

Does Alaska have Population Momentum?

Replacement Rate would be 2 children per woman

Testing the Relationship:

Bangladesh fertility dropped from 7.0 to 3.8 between 1970 and 1998

Bangladesh income per capita in 1998 is supposed to be $2200 in 1980$….

Latest HDR says $1602 year 2000$ Fertility has dropped faster than curve

predicts