© 2012 Pearson Education, Inc. Lecture Presentations prepared by Heidi Marcum Essential Environment: The Science Behind the Stories 4th Edition Withgott/Laposata

© 2012 Pearson Education, Inc.

Lecture Presentations prepared by Heidi Marcum

Essential Environment:The Science Behind the Stories 4th Edition

Withgott/Laposata

Chapter 6

Human Population


This lecture will help you understand:

• Human population growth• Population, affluence, and technology’s effects• Demography • Demographic

transition• Factors affecting

population growth


Central Case Study: China’s One-Child Policy

• In 1970, China’s 790 million people faced starvation

• The government instituted a one-child policy– The growth rate plummeted

• The policy is now less strict but has unwanted consequences:– Killing of female infants

– Black-market trade in teenaged girls


Our world at seven billion

• Populations continue to rise in most countries– Particularly in poverty-stricken developing nations

• Although the rate of growth is slowing, we are still increasing in numbers

Counting to 1 billion (1/second) would take 31 years—it would take 221 years to count to 7 billion!


The human population is growing rapidly

• Our population grows by over 80 million each year• It took until 1800 to reach 1 billion• We added 6 more billion in 130 years• We added the most

recent billion in 12 years

Because of exponential growth (increase by a fixed %), even if the growth rate remains steady, population will continue to grow


Growth rates vary from region to region

• At today’s 1.2% global growth rate, the population will double in 58 years (70/1.2 = 58)

• If China’s rate had continued at 2.8%, it would have had 2 billion people within 25 years


Is there a limit to population growth?

• Technology, sanitation, medication, and food increase population

– Death rates drop, but not birth rates

• Earth’s carrying capacity for people?

– 2 billion prosperous people

– 33 billion very poor people

• Thomas Malthus’ An Essay on the Principles of Population (1798)

– War, disease, starvation will reduce populations


Different views on population growth

• Paul Ehrlich’s The Population Bomb (1968) predicted that population growth would lead to famine and conflict– But intensified food production fed more people

• Many economists think depleted resources will be replaced or new resources created– But many resources (e.g., species) cannot be replaced

• Quality of life will suffer with unchecked growth– Less space, food, wealth per person

• Population growth is a problem if it depletes resources, stresses social systems, and degrades the environment


Population growth: causes and consequences


Several factors affect the environment

• The IPAT model: I = P A T• Our total impact (I) on the environment results from:

– Population (P): individuals need space and resources

– Affluence (A): per capita resource use

– Technology (T): increases use of, or protects, resources

• Sensitivity (S): a fourth factor showing how sensitive an area is to human pressure

• Further model refinements include the effects of education, laws, and ethics on the formula


China is an example of the IPAT formula

• Elements of the IPAT equation can combine

– Causing tremendous impact in a very short time

• Modern China’s rapid development is causing unprecedented environmental challenges

– Intensive agriculture is eroding farmland

– Overuse has dried up the mighty Yellow River

– Increasing vehicles are causing urban pollution and massive traffic jams

• China shows us what the rest of the world can become


Human population growth and regulation-Effects of human activity

Animation: Population Growth RegulationRight-click slide / Select “Play”



Human population growth and regulation-Carrying capacity


Demography

• Demographers study: – Population size – Density and

distribution– Age structure– Sex ratio – Birth, death,

immigration, and emigration rates

• Demography: applying the principles of population ecology to the study of change in human populations


Population size and density

• The UN predicts 9 billion humans by 2050• Highest density: temperate, subtropical, tropical biomes

– Coasts, rivers, cities

• Lowest density: extreme climates (desert, rainforest, tundra)– Also, areas away from water

If women have just 0.5 child fewer than the medium scenario, there will be 8, not 9.15, billion by 2050


Population distribution

• Humans are unevenly distributed around the globe• Many unpopulated areas (e.g., deserts, arid grasslands) are

environmentally sensitive – High S value in the modified IPAT equation

– Vulnerable to humans (agriculture, ranching, etc.)


Age structure affects population size

• Age structure: describes relative numbers of individuals in each age class– Shown by age structure diagrams (population pyramids)

• Wide base: has many young that haven’t reproduced yet– Population will soon grow rapidly

• Even age distribution:– Remains stable

– Births = deaths


Canada’s age structure is balanced (growth rate = 0.4%)

Madagascar’s age structure is heavily weighted toward the young (growth rate = 2.9%)

Age structures: Canada vs. Madagascar


Many populations are aging

• The global mean age is now 28—in 2050, it will be 38• China’s age structure is changing

– In 1970, the median age was 20

– By 2050, it will be 45

Although fewer people will be working to support

social programs, the elderly can remain productive


Sex ratios affect population dynamics

• Human sex ratios at birth slightly favor males – For every 100 females born, 106 males are born

• Chinese females are selectively aborted– 120 boys were reported for 100 girls

• The undesirable social consequences?– Many single Chinese men– Teenaged girls are kidnapped and sold as brides


Factors in population change

• Rates of birth, death, and migration determine whether a population grows, shrinks, or remains stable– Birth and immigration add individuals

– Death and emigration remove individuals

• Technological advances cause decreased deaths– The increased gap between birth and death rates resulted

in population expansion

• Natural rate of population change: change due to birth and death rates alone, excluding migration


Falling growth rates do not mean fewer people

Despite falling growth rates, the population continues growing by

adding 80 million people each year


Factors affecting total fertility rate

• Total fertility rate (TFR): the average number of children born to each female during her lifetime

• Replacement fertility: the TFR that keeps the size of a population stable (about 2.1)

• Causes of decreasing TFR:

– Medical care reduces infant mortality

– Urbanization increases childcare costs

– Children go to school instead of working

– Social Security supports the elderly

– Educated women enter the labor force


Life expectancy is increasing

• People live longer in countries with good sanitation, health care, and food

• Urbanization, industrialization, and personal wealth reduces rates of infant mortality

– Which increases life expectancy (the time a person can expect to live)

• Demographic transition: a model of economic and cultural change

– Explains the declining death and birth rates in industrializing nations


The demographic transition

• As they industrialize, nations move from a stable pre-industrial state of high birth and death rates

– To a stable post-industrial state of low birth and death rates

• Industrialization decreases mortality rates

– So there is less need for large families

– Parents invest in quality of life, not quantity of kids

• Death rates fall before birth rates

– Resulting in temporary population growth



Human population growth and regulation-Death rate


The 4 stages of the demographic transition

• Pre-industrial stage: low population growth

– High death (disease, starvation, few medicines) and birth (compensation for mortality) rates

• Transitional stage: industrialization, increased food and medical care reduce mortality rates

– High birth rates cause population to surge

• Industrial stage: women get jobs and use birth control

– Kids do not need to help get food

• Post-industrial stage: low birth and death rates stabilize populations


The demographic transition’s four stages

Population growth is seen as a temporary phenomenon


Is the demographic transition universal?

• It has occurred in Europe, the U.S., Canada, Japan, and other nations over the past 200–300 years

– But it may or may not apply to developing nations

• The transition could fail:

– If the population is too large to allow the transition

– In cultures that place greater value on childbirth or grant women fewer freedoms

For people to attain the material standard of living of North Americans, we would need the natural resources of

4.5 more Earths


Family planning: key to controlling growth

• Family planning: efforts to plan the number and spacing of children

– The greatest single factor slowing population growth

– Clinics offer advice, information, and contraceptives

• Birth control: controlling the number of children born by reducing the frequency of pregnancy

• Contraception: deliberate prevention of pregnancy through a variety of methods

– Hindered by religious and cultural influences

– Rates range from 10% (Africa) to 86% (China)


Empowering women reduces fertility rates

• A nation’s fertility rates drop when women gain access – To contraceptives, family planning programs, and

educational opportunities

• Women need control over their reproductive window:– The time in their lives

when they can become pregnant

Educating women reduces fertility rates, delays childbirth, and gives them a voice in reproductive decisions


A woman controls her reproductive window

• Jobs or school delays the birth of a first child • Contraceptives space births• The window is “closed” after the desired number of kids



Human population growth and regulation-Slowing the growth rate



Human population growth and regulation-Decreasing births per woman


Policies and family planning work

• Funding and policies that encourage family planning lower population growth rates in all nations

• Thailand’s education-based approach to family planning reduced its growth rate from 2.3% to 0.6%

– Brazil, Mexico, Iran, Cuba, and other developing countries have active programs

• 1994’s UN population conference in Cairo, Egypt, called for universal access to reproductive health care

– Offer education, health care, and address social needs

– Global funding has fallen 33%, slowing progress


Family planning reduces fertility rates

Blue: with family planning

Red: without family planning


Poverty and population growth are correlated

• Poor societies have higher population growth rates

• Poverty and population growth make each other worse

99% of the next billion people added will be born in poor, less developed regions that are least able to

support them


Poverty causes environmental degradation

• Population growth in poor nations increases environmental degradation– Farming degrades soil in arid areas (Africa, China)

– Poor people cut forests, deplete biodiversity, and hunt endangered species

Poor people hunt “bush meat”—driving even great apes to extinction


Wealth also impacts the environment

• Affluent societies have enormous resource consumption– With severe, far-

reaching environmental impacts

– Ecological footprints are huge

One American has as much environmental

impact as 3.5 Chinese or 9 Indians or 13 Afghans


We must reduce population growth and consumption

Our global ecological footprint is 50% more than the Earth can support

• For a high standard of living and quality of life for all, developing nations must slow their population growth– Their consumption

is also increasing

• Developed nations must slow their consumption


Conclusion

• The human population is larger than it has ever been

• Rates are decreasing but populations are still rising

• Most developed nations have passed through the demographic transition

• Expanding women’s rights slows population growth

• How will the population stop rising?

– The demographic transition, governmental intervention, or disease and social conflict?

• Sustainability requires a stabilized population to avoid destroying natural systems

Documents

© 2012 Pearson Education, Inc. Lecture Presentations prepared by Heidi Marcum Essential Environment: The Science Behind the Stories 4th Edition Withgott/Laposata