5
Human population growth

This lecture will help you understand:
•
Human population growth
•
Demography
• Affluence, technology, the status of women, and the environment
•
Population control programs
• Demographic transition theory
• Consumption and the ecological footprint
• HIV/AIDS and human population

Key Words age pyramid age structure
AIDS epidemic demographic transition demography doubling time ecological footprint family planning greater-than-exponential growth rate human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) industrial stage
IPAT model life expectancy population density population distribution population size post-industrial stage pre-industrial stage replacement fertility sex ratio total fertility rate (TFR) transitional stage

Central Case: China’s One-Child Policy
• Unfettered population growth posed challenges for
China’s environment, economy, and political stability.
• China tried to control its growth with a system of rewards and punishments to encourage one-child families.
•
The program decreased population growth, but meant government intrusion in private reproductive choices.

“Baby Six Billion”
The world’s population now exceeds 6 billion people.
The UN marked this symbolically by declaring a child born in 1999 in war-torn Sarajevo as the six-billionth baby.
Figure 7.1

World population has risen sharply
• Global human population was <1 billion in 1800.
•
Population has doubled just since 1963.
• We add 2.5 people every second (79 million/year).
Figure 7.2

Population growth rates, 1990-1995
•
Growth rates vary from place to place.
•
Growth peaked at 2.1% in the 1960s; it has now declined to 1.3%.
Figure 7.3

Is population growth really a problem?
Some say NO : Some say YES :
•
People can find or manufacture additional resources to keep pace with population growth.
• Nations become stronger as their populations grow.
• Not all resources can be replaced.
•
Even if they could, quality of life suffers.
•
Nations do not become stronger as their populations grow.

Modeling population and its consequences
•
Some models show population growth leading to resource depletion, which can result in declining food production, industrial output, and population.
Figure 7.4

Increasing our carrying capacity
• Technology has allowed us to raise Earth’s carrying capacity for our species time and again.
• Tool-making, agriculture, and industrialization each enabled humans to sustain greater populations.
Figure 7.5

Demography
Demography is the study of human populations.
Human populations exhibit the same fundamental characteristics as do populations of all other organisms.

Population size: National populations
Nations vary from China’s 1.3 billion down to Pacific island nations of 100,000.
Shown are the 15 most populous countries, and selected others; 2002 data.
Figure 7.6

Population size: Future projections
Demographers project population growth trends to estimate future population sizes.
Different fertility rate scenarios predict global population sizes in 2050 of 7.4 billion, 8.9 billion, or 10.6 billion.
All these projections assume fertility rates below today’s; at today’s rate, the population would reach 12.8 billion.
Figure 7.7

Population density and distribution
Humans are unevenly distributed, living at different densities from region to region.
Figure 7.8

Age structure
Age structure can influence population growth rates.
Figure 7.9

Age structure: Age pyramids
Canada (left) has a much slower growing population than does Madagascar (right).
Figure 7.10

Age structure: “Graying populations”
Demographers project that China’s population will become older over the next two decades.
Figure 7.11a,b

Age structure: “Graying populations”
China’s aging population will mean fewer working-age citizens to finance social services for retirees.
Figure 7.11c

Age structure: “Baby booms”
The United States’ “baby boom” is evident in age bracket
40–50. U.S. age structure will change as baby boomers grow older.
Figure 7.12

Sex ratios
A population’s sex ratio can affect its growth rate.
Figure 7.13

Factors affecting population growth rates
Population growth depends on rates of birth, death, immigration, and emigration.
(birth rate + immigration rate)
– (death rate + emigration rate)
= population growth rate

Migration can have environmental effects
Immigration and emigration play large roles today.
Refugees from the 1994 Rwandan genocide endured great hardship, and deforested large areas near refugee camps.
Figure 7.14

Natural rate of population change
Change due to birth and death rates alone, excluding migration
Is often expressed in % per year

China’s natural rate of change has fallen
China’s rate has fallen with fertility rates. It now takes the population 4 times as long to double as it did 25 years ago.

Global growth rates have fallen
The annual growth rate of the world population has declined since the
1960s.
(But the population size is still rising!)
Figure 7.15

Fertility rates affect population growth rates
Total fertility rate (TFR) = average number of children born per woman during her lifetime
Replacement fertility = the TFR that keeps population size stable
For humans, replacement fertility is about 2.1.

Total fertility rates by region
African nations have the highest TFRs.
European nations have the lowest TFRs.

Demographic transition theory
Demographic transition = model of economic and cultural change to explain declining death rates, declining birth rates, and rising life expectancies in Western nations as they became industrialized
Proposed by F. Notestein in the 1940s-1950s

Demographic transition: Stages
Figure 7.18

Demographic transition: Stages
The demographic transition consists of several stages:
Pre-industrial stage : high death rates and high birth rates
Transitional stage : death rates fall due to rising food production and better medical care. Birth rates remain high, so population surges.
Industrial stage : birth rates fall, as women are employed and as children become less economically useful in an urban setting. Population growth rate declines.
Post-industrial stage : birth and death rates remain low and stable; society enjoys fruits of industrialization without threat of runaway population growth.

Female education and TFR
Female literacy and school enrollment are correlated with total fertility rate:
More-educated women have fewer children.
Figure 7.16

Family planning and TFR
Family planning, health care, and reproductive education can lower TFRs.
A counselor advises African women on health care and reproductive rights.
Figure 7.17b

Family planning and TFR
Nations that invested in family planning
(green) reduced
TFRs more than similar nations that did not
(red).
Figure 7.17a

TFR decline in Bangladesh
Bangladesh reduced TFR from 7.1 to 4.6 in 25 yr, and is at 3.3 today.
Family planning, education, and outreach were responsible.
From The Science behind the Stories

HIV/AIDS and human population
AIDS cases are increasing rapidly worldwide.
Figure 7.26

HIV/AIDS and human population
Infects 1 in 5 people in southern African nations
Infects 5 million new people each year
Kills babies born to infected mothers
Has orphaned
14 million children
Has cut 15 years off life expectancies in parts of southern Africa
Figure 7.27

Poorer countries will experience most future population growth
98% of the next billion people born will live in developing nations.
Figure 7.20

Population and the environment
Population growth can lead to environmental degradation.
Overpopulation in Africa’s Sahel region has led to overgrazing of semi-arid lands.
Figure 7.21

Affluence and the environment
Poverty can lead to environmental degradation…
BUT wealth and resource consumption can produce even more severe and far-reaching environmental impacts.

The ecological footprint
The cumulative amount of Earth’s surface area required to provide the raw materials a person or a population consumes and to dispose of or recycle the waste that is produced

Ecological footprints
Residents of some countries consume more resources—and thus use more land— than residents of others.
Shown are ecological footprints of an average citizen from various nations.
Figure 7.23

The wealth gap
Residents of developed nations have larger houses, more possessions, and more money than residents of developing nations.
The richest 20% of the world’s people consumes
86% of its resources, and has >80 times the income of the poorest 20%.
Figure 7.25

Demographic fatigue and demographic transition
Many governments of developing countries are experiencing “demographic fatigue,” unable to meet the social, economic, and environmental challenges imposed by rapid population growth.
This raises the question:
Will today’s developing countries successfully pass through the demographic transition?

The “IPAT” model
Shows how P opulation, A ffluence, and T echnology interact to create I mpact on our environment.
I = P

A

T
Further factors can be added to the original equation of Holdren and
Ehrlich to make it more comprehensive.

Conclusions: Challenges
Human population is rising by 79 million people annually.
Many more people are born into poverty than into wealth.
Rich and poor nations are divided by a “wealth gap.”
HIV/AIDS is taking a heavy toll.
Population growth has severe environmental effects.

Conclusions: Solutions
Expanding women’s rights is crucial to encourage the demographic transition.
Health and reproductive education and counseling can reduce fertility rates.
Education, medicine, and policies can lessen the toll of
HIV/AIDS.
New “green” technologies can help reduce population growth’s environmental impacts.

Viewpoints: Population control?
Timothy
Cline
“Access to reproductive health care, including family planning, is a basic human right.”
Douglas
Sylva
“Governments do not have an interest in further reducing fertility. Nor should they have the authority to do so.”
From Viewpoints

QUESTION: Review
Using the I = P

A

T equation , what would happen if the population doubled?
a.
Affluence and technology would decline.
b.
The environment would become more sensitive.
c.
The environmental impact would double.
d.
Nothing, because Earth can compensate.

QUESTION: Review
What has allowed us to increase Earth’s carrying capacity for our species?
a.
Agriculture b.
Industrialization c.
Tool-making d.
All of the above

QUESTION: Review
Which statement is FALSE?
a.
The global population growth rate is decreasing.
b.
The global population is increasing.
c.
At a TFR of 2.4, a human population grows.
d.
Populations with age distributions skewed toward young people grow more slowly.

QUESTION: Review
Women who are more educated tend to… ?
a.
Have higher TFRs.
b.
Live in developing nations.
c.
Have fewer children.
d.
Contract HIV/AIDS.

QUESTION: Weighing the Issues
Should the United States fund family planning efforts in other nations?
a.
Yes, without reservation b.
Yes, in nations whose programs it approves c.
Only if it can influence the nations’ policies d.
Never under any circumstances

QUESTION: Interpreting Graphs and Data
What happens during the
“transitional stage” of the demographic transition?
a. Birth rates rise; death rates drop; population increases
b. Birth rates drop; death rates drop; population decreases
c. Death rates drop; birth rates are stable; population increases
Figure 7.18

QUESTION: Viewpoints
Do you believe that national governments should implement policies, subsidies, or other programs to reduce birth rates?
a.
No, not at all b.
Yes, but only positive incentives for fewer children c.
Yes—penalties for too many children d.
Yes, both incentives and penalties