Human Population History, Projections, Modeling, and Limits to Growth

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Human PopulationHistory, Projections, Modeling,
and Limits to Growth
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Estimates of Human Population
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Estimates of Human Population
Green revolution
Industrial revolution
Fire, tool-making
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Population Estimates 10,000 BC to 2050
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Population Estimates 1 AD to 2050
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Population Estimates 1850 to 2050
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Where the People Are
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Where the People Are
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How Many Humans Have Ever Lived?

• Answer depends entirely on when we start counting
  humans
• Lower limit assume two modern Homo sapien
  sapiens in 50,000 BC
• 50 billion born before 1 AD
• 60 billion born after 1 AD, of which
• 6.2 billion alive today

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UN Population Scenarios
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UN Population Scenarios
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Birth/Death Rates UN Medium Variant
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UN Population Scenarios
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Births/Deaths UN Medium Variant
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Population Growth Rates
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Most Growth in LDCs
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Most Growth in LDCs
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Most Growth in LDCs
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Distribution of PopulationUN Medium Variant
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World Population by Region
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Increment to Population (million/y)
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Area Proportional to Population
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Area Proportional to Population
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Projections Trending Downward
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Total fertility rates in 2000
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Total Fertility, UN Medium Variant
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Fertility Declining Faster Than Expected
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Fertility Declining Faster Than Expected
Latin America
Europe
World
China
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Infant Mortality Rates
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Life Expectancy UN Medium
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Life Expectancy Increasing
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Life Expectancy
Africa
N. America
World
India
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Life Expectancy in 7 Countries with Highest
Incidence of AIDS
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Effect of AIDS on Growth Rate Botswana
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Effect of AIDS Sub-Saharan Africa
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IIASA Population Scenarios
10.6 billion
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Most Developed Countries
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Eastern Europe and European FSU
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IIASA Fertility Scenarios
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Low IIASA Fertility Scenario
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Central IIASA Fertility Scenario
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High IIASA Fertility Scenario
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Age Structure Population Pyramids (2000)
Major Reproductive Ages
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TFR ? RF Squares Off the Pyramid
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Total fertility rates for the US
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Baby Boom in the U.S.
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Dependency Ratios
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Demographic Transition
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Demographic Transition Sweden
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Demographic Transition Mexico
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Demographic Transition China
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Beginning of Demographic Transition
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Fertility Transition, 1962-2000
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Demographic Transition

• Decline in death rates well understood
• nutrition, hygiene, food handling, clean water
  supply, sewage, antibiotics
• Decline in fertility well known, poorly
  understood
• increased affluence, industrialization/urbanizatio
  n?
• increased cost of raising children, children less
  necessary for agriculture, support in old age
• decline in infant mortality?
• availability of birth control?
• decrease in unwanted fertility
• improved status of women?
• education provides women with other options

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Decline in Death Rates in Europe Preceded Modern
Medicine
Tuberculosis
Measles
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Fertility and Affluence
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Fertility and Affluence
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Birth, Death Rates and Affluence
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Birth, Death Rates and Affluence
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Fertility and Infant Mortality
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Fertility and Childhood Mortality
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Infant Mortality and Affluence
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Fertility and Contraception
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Fertility and Female Education
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Fertility and Education of Women
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Fertility and Female Illiteracy
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Basic Math
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Growth Rate and Fertility

• TFR total fertility rate (live births per
  woman)
• f fraction of children born who are girls
• ? fraction who survive to age of reproduction
• ? average age at reproduction
• RFR replacement fertility
• NRR net reproduction rate

Assuming TFR, death rates constant over ?
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Growth Rate and Fertility
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Zero Population Growth

• ZPG occurs when birth rate death rate
• If dP/dt 0 (zero growth), then
• ZPG does not occur when TFR RF!
• population momentum age pyramid must fill out
  for growth to stop, even after TFR RF
• TFR RF for ? 2-3? (50-75 y) to achieve ZPG
• If TFR 2.1 today, world population would level
  off at 7.5 billion by 2050

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TFT 2.1 beginning in 1980
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One time step of the cohort-component method for
a female population
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• Pt total population in year t
• Pm male population, Pf female population
• Si,t proportion who survive year i
• Fi,t fertility rate for women aged i in year t
• fm fraction of male births

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Population and the Environment

• Impact (Population) x (Affluence) x
  (Technology)
• Migration to high-affluence areas
• small net effect on global population
• immigration decreases death, fertility rates
• large effect on global consumption, emissions
• effect of US population growth on global problems
  (e.g., climate change) greater than effect of
  growth in China, India

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US population growth is driven by immigration,
not fertility
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Effect of Future Migration
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Population and the Environment

• Migration to high-affluence areas
• Increased urbanization in LDCs (4/y)
• at medium incomes, local pollution increases
  impacts increase rapidly as more people exposed
  to higher concentrations
• damage to sensitive coastal ecosystems,
  consumption of prime farmland
• in the long run, urbanization decreases direct
  pressures on natural ecosystems, facilitates
  water/sewage supply, health care, education

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Urban Environmental Problems in LDCs

• Water pollution
• 220 million (13) without access to clean water
  420 million (25) without access to sanitation
• 2 million children die from diarrhea each year
• Air pollution
• 1.1 billion in cities with unhealthful air
  indoor air pollution acute in areas using coal,
  dung stoves
• 300,000 to 700,000 premature deaths per year
• 50 million cases of childhood respiratory
  infections
• millions exposed to high lead levels, IQ loss
• Waste disposal
• 20 to 50 percent of solid waste is uncollected
• uncontrolled dumping of hazardous, toxic wastes

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Increasing Urbanization
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Urbanization and Affluence
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Mega-cities
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Population and the Environment

• Migration to high-affluence areas
• Increased urbanization
• High growth in high biodiversity regions
• least developed countries are predominately in
  highest biodiversity areas
• urbanization is not increasing fast enough to
  offset pressures on natural ecosystems for food
  and fiber
• Limits to growth?

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Biodiversity Hotspots and Major Tropical
Wilderness Areas
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Population Density (1995) and Global
Biodiversity Hotspots
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Population and Biodiversity

• In 2000, about 1.2 billion people were living in
  the 25 biodiversity hotspots
• Hotspots cover 12 percent of global land area but
  are home to 20 percent of global population
• Population growth in hotspots (1.8/y) is more
  rapid than the world average (1.2/y)
• Very rapid growth in major tropical wilderness
  areas (3.1/y)
• Population density in the hotspots (80/km2) is
  greater world average (45/km2)

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Population and the Environment

• Migration to high-affluence areas
• Increased urbanization
• High growth in high biodiversity regions
• Limits to growth?
• carrying capacity
• resources land, water, energy, minerals
• pollution
• net human material well-being
• nature
• habitat destruction and loss of biodiversity

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Carrying Capacity

• Scientists have traditionally argued that any
  natural system has a fixed, maximum sustainable
  population or carrying capacity, S8
• Economists note that carrying capacity is a
  function of technology, which improves with time,
  S8(t). This can be modeled as follows
• No analytical solution, but we can use Excel

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Fixed Carrying Capacity (c 0)
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Carrying Capacity Increases
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Faster (c 0.9)
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As Fast As Population (c 1)
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Large r Produces Chaos!
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What Determines Carrying Capacity?

• Standard of living (what kind of life?)
• Technology
• Food and fiber (land, nutrients, fisheries)
• Water
• Energy (fossil, nuclear, solar?)
• Metals, minerals, other resources
• Waste assimilation
• Disease
• War

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Estimates of Carrying Capacity
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Land for Food

• Area Cultivated for Grain
• 1.5 Gha arable, 1.0 Gha cultivated, 70 grain
• Also 0.5-2.5 Gha potentially arable (most in
  Sub-Saharan Africa, Latin America), depending on
• conversion of forests and wetlands
• minimum acceptable productivity
• other land uses (settlements, non-food crops
  (fiber, biofuels), grazing, energy (solar))

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Average Grain Yield

• world average 3.1 t/ha-y at 1960-2000 rate of
  improvement, average in 2100 todays best 7.6
  t/ha

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Per-Capita Grain Consumption

• world average 0.35 t/y Ethiopia 0.16 US
  0.9

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Carrying Capacity Grain
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Water Supply

• Renewable freshwater (km3/y or Gm3/y)
• 113,000 precipitation
• 71,000 evaporation and transpiration
• 42,000 runoff and groundwater recharge
• 28,000 flood runoff
• 14,000 stable runoff
• 5,000 uninhabited areas
• 9,000 usable runoff

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Water Demand

• Per-capita consumption (1990s)
• United States 1800 m3/y
• Japan, Italy 750
• World average 650
• India, Netherlands, Russia 500
• China 400
• Israel, Austria 300
• Irrigated agriculture 250 grain only
• Ethiopia, Nigeria 35

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Carrying Capacity Water
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Other Limits?

• Wood, fiber, energy, minerals, waste
  assimilation
• Ecological footprint concept
• 11.5 Gha of productive land
• excludes 3.3 Gha ice, rock, sand, tundra
• specify diet, shelter, transportation, good and
  services
• calculate area needed to provide food, fiber,
  shelter, fuel, roads, etc.
• Me 9-13 ha 11.5 Gha/9 ha 1.3 billion