Human Population Envi 201 Spring 2004

Key Concepts n Exponential Growth – Rule of 70 n Demographic transition n Age structure and population momentum n Causes of fertility decline n Links between fertility decisions and environment (Dasgupta article)

Exponential Growth n Quantity grows by the same relative amount (g) each year n P (next year) = P (this year) * (1+g) n At time t, P = P 0 x (1+g) t

Exponential Growth n Quantity grows by the same relative amount each year n Doubling time d is constant

Rule of 70: n Doubling time x growth rate = 70 n Examples: r, growth rate, % per year d, doubling time, years

World Population Growth

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

Trends in Population Growth Worldwide Population Increase and Growth Rate, Five-Year Periods Millions Percent increase per year Source: United Nations, World Population Prospects: The 2002 Revision (medium scenario), 2003.

Growth Rates have Peaked…

Alaska Population: Average Annual Rates of Growth (due to births, deaths, and net migration)

The Demographic Transition n Stage I: high birthrates and death rates n Stage II: continued high birthrates, declining death rates n Stage III: falling birthrates and death rates, eventually stabilizing

Replacement Rate would be 2 children per woman

Population Momentum n Lots of young people n Although each woman may have total fertility = 2 children, n There are many more future mothers than current mothers

Native Age Structure Does Alaska have Population Momentum?

Replacement Rate would be 2 children per woman

Testing the Relationship: n Bangladesh fertility dropped from 7.0 to 3.8 between 1970 and 1998 n Bangladesh income per capita in 1998 is supposed to be $2200 in 1980$…. n Latest HDR says $1602 year 2000$ n Fertility has dropped faster than curve predicts