P in IPAT Human population

Forecasting population growth

Four evolutions in population growth

1. Hunters and gatherers• Low population density

2. Early, pre-industrial agriculture• Allowed a much greater density of people• The first major increase in human population

3. Machine age• Industrial revolution increased possibility of increased density• Significant increase in EROI

4. The Modern era• Rate of population has slowed in wealthy nations but continues to

increase rapidly in poorer, less developed nations.

Human Domination- History

• Four stages– Hunters gatherers– Pre-industrial

agriculture– Industrial agriculture– Industrial revolution

Hunters and Gatherers

• Taking what nature gives you - hardly any domination

• Omnivorous non-specialist animal• Competed with other species in food-webs• Constrained by available photosynthetic energy• Low life expectancy, low population density

Transition to agriculture

• 12,000 BP in southwestern Asia• 8000 - 9000BP in China and Mexico• Involved:– Domestication of plants and animals

• Initially shifting cultivations (slash and burn) - sustainable?

• Increased population density from 2 persons to 25-1000 persons per sqKM.

Slash and burn agriculture

Transition to Agriculture

• Why did they “go for it”?– Saw the prospects for a better life?– Needed to in order to survive - possible that the

population had increased beyond what the HG systems could sustain

– Gave more reliable food supplies– Provided higher energy return– Enabled higher population densities

Traditional Agriculture

• Cultural Implications of the transition:– Less time devoted to gathering food– Cultural evolution– Increased population density– Beginning of Urbanization– Social stratification

Traditional Agriculture

• Environmental Implications:– Large areas of forest cleared– Increased population density and thus land could not lay

fallow as needed– Soil erosion– Distribution of plants and animals shifted in favor of

domesticates– Diseases - monocultures made the system vulnerable

Intensification of Agriculture

• Slowly progressing domination• Development of irrigation and fertilization– Simple machines such as simple plows and irrigation

systems

• Land did not need to lay fallow• Population density continued to increase• EROI remained relatively low (energy return on

investment)

EROI

• Energy return on investment (EROI)• Describes how much energy is invested in the

system compared to what we get out.

Energy out/energy in

• See Table 3.1• Can be used as an indicator of scarcity

Table 3.1 in Common and Stagl

Industrial revolution - Industrial agriculture

• Began in China ca 1200 with the use of coal• Slowly progressed as various inventions enabled

more efficient use of energy– Steam engine (coal)– Internal combustion engine (oil)– Gas turbines

• Humans became energy slaves!• Possible to link major changes in human history

to changes in energy use, and prime movers.

Implications

• Enabled increased population densities• Urbanization and urban growth• New human enterprises• Increased production in less time:– Increased use of inputs– Increased use of outputs and waste

• Increased pressure on the environment

Theories of population and resources; Malthus vs. Boserup/Simon

• Thomas Malthus 1798 (classical economist) “Essay on the Principle of Population”

• Populations increase in size exponentially• Food supplies increase linearly• Thus population growth will outstrip the food resources,

with catastrophic consequences—mass starvation, poverty, and economic and social collapse.

• True? Why/why not?

Malthus

Theories of population and resources; Malthus vs. Boserup/Simon

• Ester Boserup 1965 “The conditions of Agricultural Growth”

• Population growth is independent of population, but triggers higher productivity through land intensification and innovation of new technology - improving the human condition.

• Julian Simon: More people, more minds

Condition today

• Human population grows exponentially• Economic growth (goods and services

produced), increase as well – and due to the laws of thermodynamics this growth requires material and energy inputs.

• Pressures on resources and the environment mount - BUT how can we know how what the impact on the environment may be if population keeps growing at current rates?

Can we get through the bottleneck?

Population growth per region

How to forecast population growth?

Population Basics

• Formula to represent population change:Pt = Pt-1 + (B – D) + (I – E)P: population at time (t) or at time (t-1)B: BirthsD: DeathsI: ImmigrationE: EmigrationSome Statistics see: http://www.census.gov/ipc/www/idb/

• Current Population: 6,721,318,709

Important concepts

• Crude birth rates: average annual births/1000 population

• Crude death rates: average annual deaths/1000 population

• Total fertility rate: average number of children a woman has from 15-49 yrs old

• Rate of natural increase: birth rate-death rate

• Net growth rates: birth rate-death rate

• Infant mortality rates: Annual number of death of infants under the age of 1 per 1000 life births

• Life expectancy at birth: Average number of years a newborn infant can expect to live under current mortality levels

• Age-specific death and birth rates: Age class effects taken into account

Region specific demographic factors

Iceland

• Current Population: ca. 304,367• Crude Births per 1000 indiv: 14• Crude Deaths per 1000 indiv: 7• Annual growth rate: 0.8%• Infant Mortality per 1000 indiv: 3• Life Expectancy (at birth): 81• Total Fertility Rate: 1.9 per woman

Denmark

• Current Population: ca. 5,468,000• Crude Births per 1000 indiv: 11 Crude

Deaths per 1000 indiv: 10• Annual growth rate: 0.3%• Infant Mortality per 1000 indiv: 5• Life Expectancy (at birth): 77.6• Total Fertility Rate: 1.7 per woman

Finland

• Current Population: ca. 5,245• Crude Births per 1000 indiv: 10 • Crude Deaths per 1000 indiv: 10• Annual growth rate: 0.1• Infant Mortality per 1000 indiv: 4• Life Expectancy (at birth): 79• Total Fertility Rate: 1.7 per

woman

Indonesia

• Current Population(2005): 237,512• Crude Births per 1000 indiv: 19 • Crude Deaths per 1000 indiv: 6• Annual growth rate: 1.2 %• Infant Mortality per 1000 indiv: 31• Life Expectancy (at birth): 70• Total Fertility Rate: 2.3 per

woman

Iraq

• Current Population(2008): 28,221• Crude Births per 1000 indiv: 31 • Crude Deaths per 1000 indiv: 5• Annual growth rate: 2.6 %• Infant Mortality per 1000 indiv: 45• Life Expectancy (at birth): 70• Total Fertility Rate: 4.0 per

woman

Burkina Faso

• Current Population(2008): 15,265• Crude Births per 1000 indiv: 45 • Crude Deaths per 1000 indiv: 14• Annual growth rate: 3.1 %• Infant Mortality per 1000 indiv: 86• Life Expectancy (at birth): 53• Total Fertility Rate: 6.3 per woman

Doubling time

• Nt = (1+ r)Nt-1

r: growth rate

dN/dt = rN

Doubling time2 Nt = Nt-1ert2x

Take natural log at both sides…

t2x = ln(2)/r = 0.693/r (or 70/growth rate in %)

Population Age Structure

• Population age structure:– The proportion of the population in each age class –

also called age cohorts– Affects current and future birth rates, death rates

and growth rates– Has an impact on the environment– Has complications for current and future social and

economic status.– So-called age class effects! – Important for resource

management e.g. deer

Population Pyramids

The Demographic Transition• Demographic transition:

– Three-stage pattern of change in birth rates and death rates.– Occurred during the process of industrial and economic development

of Western nations.– Leads to a decline in population growth.

Stage I: High birth and death rates - death rate declining - Undeveloped

Stage II: High growth rate (high birth rate, lower death rate) - transition

Stage III: Birth rate drops toward the death rate, leading to low or zero growth rate.

Stage IV: same as stage II, but now due to disease….

The Demographic Transition

Disease related parameters

• Cause specific death rate: number of deaths from one cause per 100,000 total deaths

• Incidence rate: Number of people contracting a disease per 100 people per timeperiod

• Prevalence rate: Number of people afflicted by a disease at a particular time

• Morbidity: Occurrence of disease in a population

Forecasting Population Growth

• How can we do this? - three models• Mathematical extrapolation– Linear Growth– Exponential– Logistic growth

• Cohort Component Method (most common for humans)

• Systems Models (more complex, used at e.g. IIASA)

Exponential growth

• Exponential growth• Characterizes anything

that can grow without limit

• Same as compounding formula in economics

• Pt+N = Pt*(1+r)^N

• Pt+1 = Pt*(1+r) ^1

Logistic Growth

• Logistic or density dependent growth

• Upper limit to the ultimate size - carrying capacity– Constant– Can be assessed

Growth determined by:Pt = Pt-1 + r* Pt-1 * (CC - Pt-1)/CC

Carrying Capacity

• Definition: The maximum population of a species an area can support without reducing its ability to support the same species in the future

• Function both of the area and the organism (ex. Ceteris paribus Larger area higher cc)

Carrying Capacity

• Determined by size limiting factors, such as space, food, energy etc.

• Affects birth and death rates. • What determines CC – and can it be

estimated? – Mathematics for assessing this parameter....

Different CC for different species

• Human carrying capacity– Factors:

• Food supply• Land and soil resources• Water resources• NPP• Population density• Technology

– Is it static?

• Biophysical carrying capacity• Social carrying capacity

Estimating CC

• Total area times productivity/ccal needed to survive (e.g.)

• Useful?

Cohort Component

• Breaks population into age cohorts (usually 5 year) by gender, ethnicity

• Cohort specific death and birth rates.

• Cohort specific immigration/emigration

0-4

10-14

5-9

15-19

10-14

5-9

15-19

T1 T2

0-4

B

BD

D

D

DD

D

D

D

Forecasting Population Growth - Possible Futures

• Population expected to reach 10billions in 2050

• GDP/capita to increase 2 - 4 fold

Forecasting Population Growth - Possible Futures

Reason for difference

Total Fertility Rate

What can we do about P?

• If P really is a culprit for environmental degradation - how can it be reduced?

• Should we?

• Ethics?

Zero Population Growth

• Zero population growth (ZPG) is a term indicating the number of births that will simply replace a population, without further growth.

• It takes a total fertility rate of about 2.1 in developed nations or 2.7 in developing nations to maintain a population at a constant size, assuming a stable age structure and no net migration.

Zero Population Growth• The difference is explained by higher mortality rates

in the developing nations, which require a higher birth rate to offset losses.

• A total fertility rate of less than 2.1 would eventually lead to population decline, assuming no net immigration.