2 Background Info Earth is ~4.6 billion years old Modern humans have been on Earth ~200,000 yrsFor most of human history, limiting factors kept population levels low (scarce food, disease, etc)High human birth and death ratesIf 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
3 History of Human Population Growth: Early period of hunter/gatherersTotal population < a few millionRise of agricultureAllowed for increase in population density and increase in human populationIndustrial revolutionImprovements in medicine, sanitation and agriculture led to rapid increase in populationTodayRate of growth slow in industrialized nations but high in less developed nationsEarth’s population has doubled several times since 1600IndustrialRevolutionbeginsAgriculturebeginsBubonicplaguePlowingandirrigation
4 Factors That Influence Human Population Growth Demography = study of human populations and their trendsChanges in Population SizeView population as system with inputs and outputsIf inputs > outputs = growth rate is positiveIf inputs < outputs = growth rate is negative
5 Global population growth rate = (CBR - CDR) / 10 Crude birth rate (CBR)= the number of births per 1,000 individuals per yearCrude death rate (CDR)= the number of deaths per 1,000 individuals per yearGlobal population growth rate = (CBR - CDR) / 10In 2009 there were 20 births per 8 deaths = %?National population growth rate = (CBR + immigration) - (CDR + emigration) / 10Doubling 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 70The 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.
6 Examples of Doubling Time Nicaragua w/ a growth rate of 2.7%, doubling time = 26 yrsUS w/ a growth rate of 0.6%, doubling time = 117 yrsNorthern Europe w/ a growth rate of 0.2%, doubling time = 350 yrs“Rule of 70”
7 FertilityTotal fertility rate (TFR) = estimate of the average number of children that each woman in a population will bearCurrent TFR for women in US is 2.06To 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 stableIn developed countries RLF is typically 2.1 (one child to replace each parent)In developing countries RLF is above 2.1Low levels of industrializationIncome of <$3/dayHigh 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)
10 Life ExpectancyAverage 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 countryGenerally higher in countries with better health careGood predictor of high resource consumption rates and environmental impactsOften reported in three ways: overall, males, females: In US, ALE is men 75, 78 women
11 Infant and Child Mortality Rates Determined by access to health care, good nutrition and potable water, and exposure to environmental pollutantsInfant mortality rate = # of deaths under age 1 per 1,000 live birthsChild mortality rate = # of deaths under age 5 per 1,000 live birthsIn 2009, global infant mortality rate 46; Europe was ; U.S. 6.6; Bolivia 50, Liberia 99
12 Aging and DiseaseDependent upon standard of livingDisease is important regulator of human populationsAccording to World Health Organization (WHO), infectious diseases are the 2nd biggest killer worldwide after heart diseasee.g. HIV, AIDS, malaria and tuberculosis
13 Age StructurePopulation growth depends upon number of people of different agesAge-structure diagram (population pyramids) = displays a population by ages, used to predict future growth
14 MigrationCountry with low CBR, but high immigration rate may still experience population growthU.S. is estimated to grow 44% by 2050Net migration rate = difference between immigration and emigration per year/per 1,000 peopleU.S. gains about 1 million people per year with current population of 300 million = 3.3 per 1,000Canada = 7 per 1,000 peopleMovement 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
15 Demographic Transition As a country moves from a subsistence economy to industrialization and increased affluence, it undergoes a predictable shift in population growth.
16 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.
18 Zero Population Growth – can it be achieved? Possible approachesDelay age of first child bearing – simplest and most effectiveHigher 1st reproduction age = fewer childrenIn South Asia and Sub-Saharan Africa, 50% of women marry between 15-19; Bangladesh average age is 16; Sri Lanka average age is 25World Bank estimates that if Sri Lanka model were used, families would average 2.2 fewer children
19 Family PlanningRegulating the number and spacing of offspring through the use of birth controlIncrease education of women = increase women’s incomes = decreased birth ratesNational programs to reduce birth ratesInformation (education)Increase access to birth control
20 Population Size and Consumption, Impact the Enviroment Human impact on the environment is a result of several factors:Number of peopleAmount of resources each person usesEach person has an impact on the environment by eating, drinking, producing waste, consuming products, etc. = “Ecological footprint”
21 AffluenceMore affluence = more environmental impactGross 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.
22 Impact = Population x Affluence x Technology IPAT EquationTo estimate the impact of human lifestyles on Earth we can use the IPAT equation:Impact = Population x Affluence x TechnologyModern 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 IThai family vs Japanese family
23 Human Carrying Capacity Background InfoEvery 5 days, the global population increases by about 1 million peopleIn 1798, Thomas Malthus proposed:Human population grows exponentially, while food supply grows linearlyHumans will eventually exceed food supplyConsequences will be famine, disease, massive human die-offMalthus –English professor and clergyman
24 How many people can the Earth support? Limiting FactorsShort 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 capacityWood production peaked in 1967Fish production peaked in 1970Beef and cereal crop production peaked in 1977
25 Estimation methodsExtrapolation 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