1. The Human Population and Its Impact6
The Human Population and Its Impact

2. Core Case Study: Planet Earth: Population 7 Billion
The evolution of Homo sapiens and a total population of 2 billion has taken 200,000 years
It has taken less than 50 years to reach the second 2 billion
It took 25 years to add the third 2 billion
Twelve years later, the population topped 7.1 billion
What is a sustainable human population?

3. Industrial revolution
Core Case Study: Planet Earth: Population 7 Billion
2011 (7 billion)
Billions of people
1999 (6 billion)
1987 (5 billion)
1974 (4 billion)
1960 (3 billion)
Figure 6.1 The human population has grown exponentially—showing slow growth throughout most of history and shooting up at a rapid rate within the last 200 years. This graph also shows projections to 2100 that range from 8 billion to 16 billion. (This figure is not to scale.)
1930 (2 billion)
1800 (1 billion)
Time
Hunting and gathering
Agricultural revolution
Industrial revolution
Fig. 6-1, p. 122

4. 6-1 How Do Environmental Scientists Think about Human Population Growth?
The continuing rapid growth of the human population and its impacts on natural capital raise questions about how long the human population can keep growing

5. Human Population Growth Shows Certain Trends
Rate of population growth has slowed in recent decades
Human population growth is unevenly distributed geographically
People are moving from rural to urban areas

6. Annual Growth Rate of World Population, 1950-2010
Figure 6-2: The annual growth rate of world population has generally dropped since the 1960s, but the population has continued to grow (Figure 6-1).
Fig. 6-2, p. 123

7. Where Population Growth Occurred, 1950-2010
World population (in billions)
Figure 6-3: Most of the world’s population growth between 1950 and 2012 took place in the world’s less-developed countries. This gap has been projected to increase between 2012 and 2050.
Population in less-developed countries
Population in more-developed countries
Year
Fig. 6-3, p. 123

8. Human Population Growth Impacts Natural Capital
As the human population grows, so does the global total human ecological footprint
Cultural carrying capacity
Total number of people who could live in reasonable freedom and comfort indefinitely, without decreasing the ability of the earth to sustain future generations

9. Natural Capital Degradation
Altering Nature to Meet Our Needs
Reducing biodiversity
Increasing use of net primary productivity
Increasing genetic resistance in pest species and disease-causing bacteria
Eliminating many natural predators
Introducing harmful species into natural communities
Figure 6-4: We humans have altered the natural systems that sustain our lives and economies in at least eight major ways to meet the increasing needs and wants of our growing population (Concept 6-1). Questions: In your daily living, do you think you contribute directly or indirectly to any of these harmful environmental impacts? Which ones? Explain.
Using some renewable resources faster than they can be replenished
Disrupting natural chemical cycling and energy flow
Relying mostly on polluting and climate-changing fossil fuels
Fig. 6-4, p. 125

10. 6-2 What Factors Influence the Size of the Human Population?
Population size increases through births and immigration, and decreases through deaths and emigration
The average number of children born to women in a population (total fertility rate) is the key factor that determines population size

11. The Human Population Can Grow, Decline, or Remain Fairly Stable
Population change =
(births + immigration) – (deaths + emigration)
Crude birth rate
The number of live births/1000/year
Crude death rate
The number of deaths/1000/year

12. Different Species Have Different Reproductive Patterns
Some species:
Have many small offspring
Little parental involvement
Other species:
Reproduce later in life
Have small number of offspring

13. Reproductive Patterns: Opportunists and Competitors
Large number of smaller offspring with little parental care (r-selected species).
Fewer, larger offspring with higher invested parental care (K- selected species).
Figure 8-9

14. Reproductive Patterns
r-selected species tend to be opportunists while K-selected species tend to be competitors.
Figure 8-10

15. Little or no parental care and protection of offspring
r-Selected Species
Cockroach
Dandelion
Many small offspring
Little or no parental care and protection of offspring
Early reproductive age
Most offspring die before reaching reproductive age
Small adults
Adapted to unstable climate and environmental conditions
High population growth rate (r)
Population size fluctuates wildly above and below carrying capacity (K)
Generalist niche
Low ability to compete
Early successional species
Figure 8.10
Natural capital: generalized characteristics of r-selected (opportunist) species and K-selected (competitor) species. Many species have characteristics between these two extremes.
Fig. 8-10a, p. 168

16. Fewer, larger offspring High parental care and protection of offspring
K-Selected Species
Elephant
Saguaro
Fewer, larger offspring
High parental care and protection
of offspring
Later reproductive age
Most offspring survive to reproductive age
Larger adults
Adapted to stable climate and environmental conditions
Lower population growth rate (r)
Population size fairly stable and usually close to carrying capacity (K)
Specialist niche
High ability to compete
Late successional species
Figure 8.10
Natural capital: generalized characteristics of r-selected (opportunist) species and K-selected (competitor) species. Many species have characteristics between these two extremes.
Fig. 8-10b, p. 168

17. No Population Can Grow Indefinitely: J-Curves and S-Curves
There are always limits to population growth in nature
Environmental resistance – factors that limit population growth
Carrying capacity
Maximum population of a given species that a particular habitat can sustain indefinitely

18. No Population Can Grow Indefinitely: J-Curves and S-Curves (cont’d.)
Exponential growth
At a fixed percentage per year
Logistic growth
Population faces environmental resistance

19. Growth of a Sheep Population
Population overshoots carrying capacity
Environmental resistance
2.0
Carrying capacity
1.5
Population recovers and stabilizes
Number of sheep (millions)
Population runs out of resources and crashes
1.0
Exponential growth
Animated Figure 5.16 Growth of a sheep population on the island of Tasmania between 1800 and After sheep were introduced in 1800, their population grew exponentially thanks to an ample food supply and few predators. By 1855, they had overshot the land’s carrying capacity. Their numbers then stabilized and fluctuated around a carrying capacity of about 1.6 million sheep. .5
1800
1825
1850
1875
1900
1925
Year
Fig. 5-16, p. 115

20. When a Population Exceeds Its Carrying Capacity It Can Crash
A population exceeds the area’s carrying capacity
Reproductive time lag may lead to overshoot
Subsequent population crash
Damage may reduce area’s carrying capacity

21. Population Crash Population overshoots carrying capacity 2,000 1,500
Population crashes
Number of reindeer
1,000
Figure 5.18 Exponential growth, overshoot, and population crash of reindeer introduced onto the small Bering Sea island of St. Paul in 1910.
500
Carrying capacity
1910
1920
1930
1940
1950
Year
Fig. 5-18, p. 116

22. Humans Are Not Exempt from Nature’s Population Controls
Ireland
Potato crop in 1845
Bubonic plague
Fourteenth century
AIDS
Current global epidemic

23. Women Are Having Fewer Babies, But the World’s Population Is Still Growing
Fertility rate
Number of children born to a woman during her lifetime
Replacement-level fertility rate
Average number of children a couple must have to replace themselves
Approximately 2.1 in developed countries
Up to 2.5 in developing countries

24. The World’s Population Is Still Growing (cont’d.)
Total fertility rate (TFR)
Average number of children born to women in a population
Between 1955 and 2012, the global TFR dropped from 5 to 2.4
However, to eventually halt population growth, the global TFR will have to drop to 2.1

25. Total Fertility Rates Total Fertility Rate Births per woman
Baby boom (1946–64)
Replacement level
Figure 6-5: The graph shows the total fertility rates for the United States between 1917 and Question: The U.S. fertility rate has declined and remained at or below replacement levels since So why is the population of the United States still increasing?
Fig. 6-5, p. 127

26. Case Study: The U.S. Population – Third Largest and Growing
Population still growing and not leveling off
76 million in 1900
314 million by 2012
Drop in TFR in U.S.
Rate of population growth has slowed
What have been some changes in lifestyle in the U.S. during the 20th century?

27. Married women working outside the home 8% 81%
77 years
Life expectancy
47 years
1900
2000
Married women working outside the home 8%
81%
High school graduates
15%
83%
Homes with flush toilets
10%
98%
Homes with electricity 2%
99%
Living in suburbs
10%
52%
Figure 6-7 Some major changes took place in the United States between 1900 and Question: Which two of these changes do
you think had the biggest impacts on the U.S. ecological footprint?
Hourly manufacturing job wage (adjusted for inflation) $3
$15
Homicides per 100,000 people
1.2
5.8
Stepped Art
Fig. 6-7, p. 132

28. Case Study: The U.S. Population – Third Largest and Growing (cont’d.)
Immigration
U.S. has admitted almost twice as many immigrants and refugees as all other countries combined

29. Legal Immigration to the United States
1907
1914 New laws restrict immigration
Number of legal immigrants (thousands)
Great Depression
Figure 6.6 Legal immigration to the United States, 1820–2006 (the last year for which data are available). The large increase in immigration since 1989 resulted mostly from the Immigration Reform and Control Act of 1986, which granted legal status to certain illegal immigrants who could show they had been living in the country before January 1, 1982.
Year
Fig. 6-6, p. 127

30. Several Factors Affect Birth Rates and Fertility Rates
Children as part of the labor force
Cost of raising and educating children
Availability of private and public pension
Urbanization
Educational and employment opportunities for women

31. Several Factors Affect Birth Rates and Fertility Rates (cont’d.)
Average age of a woman at marriage
Availability of legal abortions
Availability of reliable birth control methods
Religious beliefs, traditions, and cultural norms

32. Several Factors Affect Birth Rates and Fertility Rates (cont’d.)
Figure 6-9: This young girl is breaking granite into gravel in the Kerala State of India.
Fig. 6-9, p. 129

33. Several Factors Affect Death Rates
Life expectancy
Infant mortality rate
Number of live births that die in first year
High infant mortality rate indicates:
Insufficient food
Poor nutrition
High incidence of infectious disease

34. Several Factors Affect Death Rates (cont’d.)
Less-developed countries
(deaths per 1,000 live births)
Infant mortality rate
World
Figure 6-10: Infant mortality rates for the world’s more-developed countries and less-developed countries, 1950–2012, with projections to 2050 based on medium population projections.
More-developed countries
Year
Fig. 6-10, p. 129

35. Migration Affects an Area’s Population Size
The movement of people into and out of specific geographic areas
Causes:
Economic improvement
Religious and political freedom
Wars
Environmental refugees

36. 6-3 How Does a Population’s Age Structure Affect Its Growth or Decline?
The numbers of males and females in young, middle, and older age groups determine how fast a population grows or declines

37. A Population’s Age Structure Helps Us Make Projections
Age structure categories
Prereproductive ages (0-14)
Reproductive ages (15-44)
Postreproductive ages (45 and older)
Seniors are the fastest-growing age group

38. A Population’s Age Structure Helps Us Make Projections (cont’d.)
Male
Female
Male
Female
Male
Female
Male
Female
Animated Figure 6-11 Generalized population age-structure diagrams for countries with rapid (1.5–3%), slow (0.3–1.4%), zero (0–0.2%), and negative (declining) population growth rates. Question: Which of these diagrams best represents the country where you live?
Expanding Rapidly Guatemala Nigeria Saudi Arabia
Expanding Slowly United States Australia China
Stable Japan Italy Greece
Declining Germany Bulgaria Russia
Prereproductive ages 0–14
Reproductive ages 15–44
Postreproductive ages 45–85+
Fig. 6-11, p. 131

39. A Population’s Age Structure Helps Us Make Projections (cont’d.)
Figure 6-12: Population structure by age and sex in less-developed countries and more-developed countries for Question: If all girls under 15 were to have only one child during their lifetimes, how do you think these structures would change over time?
Fig. 6-12, p. 132

40. Case Study: The American Baby Boom
79 million people added from
36% of adults
Affect politics and economics
Now becoming senior citizens
Graying of America

41. Case Study: The American Baby Boom (cont’d.)
Animated Figure 6-13 Age-structure charts tracking the baby-boom generation in the United States, 1955, 1985, 2015 (projected), and 2035 (projected).
Fig. 6-13, p. 132

42. Populations Made Up of Mostly Older People Can Decline Rapidly
Slow decline
Manageable
Rapid decline
Economic problems
Proportionally fewer young people working
Labor shortages

43. Some Problems with Rapid Population Decline
Can threaten economic growth
Labor shortages
Less government revenues with fewer workers
Less entrepreneurship and new business formation
Less likelihood for new technology development
Figure 6-14: Rapid population decline can cause several problems. Question: Which two of these problems do you think are the most important?
Increasing public deficits to fund higher pension and health-care costs
Pensions may be cut and retirement age increased
Fig. 6-14, p. 133

44. Populations Can Decline due to a Rising Death Rate: The AIDS Tragedy
AIDS has killed more than 30 million people
Many young adults die – loss of most productive workers
Sharp drop in life expectancy
International community
Reduce the spread of HIV through education and health care
Financial assistance and volunteers

45. The AIDS Tragedy (cont’d.)
Figure 6-15: In Botswana, more than 25% of people ages 15–49 were infected with HIV in This figure shows two projected age structures for Botswana’s population in 2020—one including the possible effects of the AIDS epidemic (red bars), and the other not including those effects (yellow bars). Question: How might this affect Botswana’s economic development?
Fig. 6-15, p. 134

46. 6-4 How Can We Slow Human Population Growth?
We can slow human population growth by reducing poverty, elevating the status of women, and encouraging family planning

47. The First Step Is to Promote Economic Development
Demographic transition
As countries become industrialized
First death rates decline
Then birth rates decline
Four stages
Preindustrial
Transitional
Industrial
Postindustrial

48. Birth rate and death rate
Population
grows very
slowly because
of a high
birth rate
(to compensate
for high infant
mortality) and a
high death rate
Stage 1
Preindustrial
Growth rate over time 80 70 60 50 40 30 20 10
(number per 1,000 per year)
Birth rate and death rate
Low
Death rate
Total population
Birth rate
Population grows rapidly because birth rates are high and death rates drop because of improved food production and health
Decreasing
Stage 2
Transitional
Increasing
Very high
Population growth slows as both birth
and death rates drop because of improved food production, health, and education
Stage 3
Industrial
Low
Population growth levels off and then declines as birth rates equal and then fall below death rates
Stage 4
Postindustrial
Negative
Zero
Animated Figure 6-16 The demographic transition, which a country can experience as it becomes industrialized and more economically developed, can take place in four stages. Question: At what stage is the country where you live?
Stepped Art
Fig. 6-16, p. 135

49. Empowering Women Can Slow Population Growth
Factors that decrease total fertility rates:
Education
Paying jobs
Ability to control fertility
Women:
Do most of the domestic work and child care
Provide unpaid health care
2/3 of all work for 10% of world’s income
Discriminated against legally and culturally

50. Empowering Women Can Slow Population Growth (cont’d.)
Figure 6-17: This woman in Nepal is bringing home firewood. Typically, she spends 2 hours a day, 2 or 3 times a week, on this task.
Fig. 6-17, p. 135

51. Family Planning Can Provide Several Benefits
Family planning in less-developed countries
Responsible for a 55% drop in TFRs
Financial benefits – money spent on family planning saves far more in health, education costs

52. Family Planning Can Provide Several Benefits (cont’d.)
Two problems
42% pregnancies unplanned, 26% end with abortion
Many couples do not have access to family planning
How can family planning programs be expanded?

53. Case Study: Slowing Population Growth in India
Population: 1.26 billion people in 2012
Problems
Poverty, malnutrition, and environmental degradation
Causes
Bias toward having male children
Poor couples want many children
Only 47% of couples use family planning

54. Case Study: Slowing Population Growth in India (cont’d.)
Figure 6-20: Homeless people in Kolkata, India in 2011.
Fig. 6-20, p. 137

55. Case Study: Slowing Population Growth in China: A Success Story
World’s most populous country
Threat of mass starvation in the 1960s
Government established a strict family planning and birth control program
Reduced number of children born per woman from 5.7 to 1.5

56. Growth rate
Growth rate = (New population – Old population)/Old Population X 100
If a population of 10,000 experiences 100 births, 40 deaths, 10 immigrants and 30 emigrants in a year, what is the net annual percentage growth rate?

57. Rule of 70’s 70/ growth rate = doubling time
If a population of a country grows at a rate of 5% a year, the number of years required for the pop to double is what?

58. Environmental Impact Equation (Paul Ehrlich Formula)
Population X affluence X technology = Environmental impact

59. High rates of resource use
Developed Countries
High rates of resource use
Result in high levels of pollution and environmental degradation per person
These are believed to be the key factors determining overall environmental impact.
(Cont….)

60. It is estimated that a US citizen consumes 35 X’s as much as the average citizen of India and 100 X’s as much as the average person in the world’s poorest countries.
(Cont…)

61. Thus, poor parents in a developing country would need kids to have the same lifetime environmental impact as 2 typical US kids.

62. What happens? Slums, fecal snow, disease
Urbanization
What happens? Slums, fecal snow, disease
This problem doesn’t exist too much in the US because of better working & housing conditions & air and water quality being improved.
(Cont….)

63. Urban areas must import most of its food, water, energy, minerals, & other resources.
They produce enormous quantities of wastes that can pollute the air, water & land.
44% of the world’s people live in urban areas that occupy only 5% of the world’s land & they consume 75% of the world’s resources.

64. Reasons for World Hunger Issues
Unequal distribution of available food
Loss of arable land
Increasing population growth rate
Increasing poverty in developing countries

65. Reasons the human population has been so dramatic in the last century
The Industrial Revolution
Modern Medicine

66. Strategies for ensuring adequate nutrition for a growing population:
Increase the number of new food crops from a diversity of plant species
Distribute food more equitably
Increase land are that is dedicated to grain production rather than meat production
Assist developing countries in efficient crop irrigation systems.

67. Fertility rates & reduction
Environmental pressures of urbanization from population growth are reduced because birth rates in urban areas usually are 3-4 X’s lower than in rural areas.
Cities provide education opportunities.

68. Three Big Ideas
The human population is increasing rapidly and may soon bump up against environmental limits
Increasing use of resources per person
Expanding the overall human ecological footprint and putting a strain on the earth’s resources

69. Three Big Ideas (cont’d.)
We can slow population growth by reducing poverty through economic development, elevating the status of women, and encouraging family planning

70. Tying It All Together: World Population Growth and Sustainability
Exponential growth is unsustainable in the long run
Employing solar and other renewable technologies can help cut:
Pollution
Emissions of climate-changing gases
Reuse and recycle materials
Focus on preserving biodiversity