# Chapter 7 The Human Population.

## Presentation on theme: "Chapter 7 The Human Population."— Presentation transcript:

Chapter 7 The Human Population

Background Info Earth is ~4.6 billion years old
Modern humans have been on Earth ~200,000 yrs For most of human history, limiting factors kept population levels low (scarce food, disease, etc) High human birth and death rates If we reduce the amount of time life has existed on Earth to one year, from Jan to June all that has existed is bacteria. Animals with heads appeared in Oct and humans appeared on Dec 31st at midnight

History of Human Population Growth:
Early period of hunter/gatherers Total population < a few million Rise of agriculture Allowed for increase in population density and increase in human population Industrial revolution Improvements in medicine, sanitation and agriculture led to rapid increase in population Today Rate of growth slow in industrialized nations but high in less developed nations Earth’s population has doubled several times since 1600 Industrial Revolution begins Agriculture begins Bubonic plague Plowing and irrigation

Factors That Influence Human Population Growth
Demography = study of human populations and their trends Changes in Population Size View population as system with inputs and outputs If inputs > outputs = growth rate is positive If inputs < outputs = growth rate is negative

Global population growth rate = (CBR - CDR) / 10
Crude birth rate (CBR)= the number of births per 1,000 individuals per year Crude death rate (CDR)= the number of deaths per 1,000 individuals per year Global population growth rate = (CBR - CDR) / 10 In 2009 there were 20 births per 8 deaths = %? National population growth rate = (CBR + immigration) - (CDR + emigration) / 10 Doubling time is # of years it takes for population to double = 70 / growth rate (if growth rate remains constant) “Rule of 70” Math Behind the Rule of 70 The use of natural logs arises from integrating the basic differential equation for exponential growth: dN/dt = rN, over the period from t=0 to t = the time period in question, where N is the quantity growing and r is the growth rate.

Examples of Doubling Time
Nicaragua w/ a growth rate of 2.7%, doubling time = 26 yrs US w/ a growth rate of 0.6%, doubling time = 117 yrs Northern Europe w/ a growth rate of 0.2%, doubling time = 350 yrs “Rule of 70”

Fertility Total fertility rate (TFR) = estimate of the average number of children that each woman in a population will bear Current TFR for women in US is 2.06 To gauge changes in population size, look at replacement level fertility (RLF) = TFR required to offset the average number of deaths in a population and for the current population size to remain stable In developed countries RLF is typically 2.1 (one child to replace each parent) In developing countries RLF is above 2.1 Low levels of industrialization Income of <\$3/day High mortality among young (TFR needs to be higher than 2.1 to achieve RLF) Uneducated (especially women) When TFR = RLF and immigration = emigration, a country’s population is stable (zero population growth) 2 babies per couple (one t replace each person)

Projected World Population Growth

The 12 Most Populous Countries in the World

Life Expectancy Average number of years that an infant born in a particular year in a particular country can be expected to live, given the current average life span and death rate of that country Generally higher in countries with better health care Good predictor of high resource consumption rates and environmental impacts Often reported in three ways: overall, males, females: In US, ALE is men 75, 78 women

Infant and Child Mortality Rates
Determined by access to health care, good nutrition and potable water, and exposure to environmental pollutants Infant mortality rate = # of deaths under age 1 per 1,000 live births Child mortality rate = # of deaths under age 5 per 1,000 live births In 2009, global infant mortality rate 46; Europe was ; U.S. 6.6; Bolivia 50, Liberia 99

Aging and Disease Dependent upon standard of living Disease is important regulator of human populations According to World Health Organization (WHO), infectious diseases are the 2nd biggest killer worldwide after heart disease e.g. HIV, AIDS, malaria and tuberculosis

Age Structure Population growth depends upon number of people of different ages Age-structure diagram (population pyramids) = displays a population by ages, used to predict future growth

Migration Country with low CBR, but high immigration rate may still experience population growth U.S. is estimated to grow 44% by 2050 Net migration rate = difference between immigration and emigration per year/per 1,000 people U.S. gains about 1 million people per year with current population of 300 million = 3.3 per 1,000 Canada = 7 per 1,000 people Movement of people around the world affects ecological footprint, and humanitarian and health issues (if displaced) Despite Canada’s 1.6 TFR and US 2.06 TFR, both populations will grow due to immigration

Demographic Transition
As a country moves from a subsistence economy to industrialization and increased affluence, it undergoes a predictable shift in population growth.

Stages of Demographic Transition
Phase 1: Slow population growth because there are high birth rates and high death rates which offset each other. Phase 2: Rapid population growth because birth rates remain high but death rates decline due to better sanitation, clean drinking water, increased access to food and goods, and access to health care. Phase 3: Stable population growth as the economy and educational system improves and people have fewer children. Phase 4: Declining population growth because the relatively high level of affluence and economic develop encourage women to delay having children.

Affluence and Fertility

Zero Population Growth – can it be achieved?
Possible approaches Delay age of first child bearing – simplest and most effective Higher 1st reproduction age = fewer children In South Asia and Sub-Saharan Africa, 50% of women marry between 15-19; Bangladesh average age is 16; Sri Lanka average age is 25 World Bank estimates that if Sri Lanka model were used, families would average 2.2 fewer children

Family Planning Regulating the number and spacing of offspring through the use of birth control Increase education of women = increase women’s incomes = decreased birth rates National programs to reduce birth rates Information (education) Increase access to birth control

Population Size and Consumption, Impact the Enviroment
Human impact on the environment is a result of several factors: Number of people Amount of resources each person uses Each person has an impact on the environment by eating, drinking, producing waste, consuming products, etc. = “Ecological footprint”

Affluence More affluence = more environmental impact Gross domestic product (GDP) = the value of all products and services produced in a year in that country. Made up of consumer spending, investments, government spending, and exports minus imports. A countries GDP often correlates with its pollution levels.

Impact = Population x Affluence x Technology
IPAT Equation To estimate the impact of human lifestyles on Earth we can use the IPAT equation: Impact = Population x Affluence x Technology Modern technology increases the use of resources and enables us to affect the environment in new ways (CFC’s, cars, etc) (T = P x I) equation reveals irony: Improving standard of living increases P, countering the benefits of declining I Thai family vs Japanese family

Human Carrying Capacity
Background Info Every 5 days, the global population increases by about 1 million people In 1798, Thomas Malthus proposed: Human population grows exponentially, while food supply grows linearly Humans will eventually exceed food supply Consequences will be famine, disease, massive human die-off Malthus –English professor and clergyman

How many people can the Earth support?
Limiting Factors Short Term - affect population immediately (food shortages) Intermediate Term - affect population for 1-10 years (e.g. desertification, dispersal of pollutants, etc.) Long Term - effects not apparent until after 10 years (e.g. soil erosion, decline in groundwater supply, climate change) Earth’s long term carrying capacity Wood production peaked in 1967 Fish production peaked in 1970 Beef and cereal crop production peaked in 1977

Estimation methods Extrapolation from past growth (assuming populations follow S- curve) Packing problem approach – how many people can be packed onto the Earth? (50 billion!) Deep Ecology – sustaining the biosphere (few million people) Depends on the quality of life people desire and are willing to accept