Human Population Dynamics and Growth

• Chapter discusses the science behind human population dynamics and its effects on the environment

Human Population Growth

• Human population growth is a key issue in environmental science, with a focus on demography, demographic transition, and factors influencing population growth
• In 1970, China faced starvation with 790 million people, prompting the government to institute a one-child policy
• China's one-child policy, though now less strict, has led to killing of female infants and black-market trade in teenaged girls

China's One-Child Policy

• The policy has resulted in a shrinking workforce and has created an aging population
• Populations continue to rise in most countries, especially in poverty-stricken developing nations
• The rate of growth may be slowing, but population size is still on the increase
• India is projected to soon surpass China as the most populous nation

Population Growth Rate

• The world population grows by over 80 million each year
• Reaching 1 billion people took until 1800
• Another 130 years was all it took to get to 2 billion
• It only took 30 years to reach 3 billion

Exponential Growth

• Human population growth continues to grow exponentially and added 3 billion in the last 12 years
• At the current global growth rate of 1.2%, the world population will double in 58 years
• Developing countries have the highest growth rates

Limits to Growth

• Technology, sanitation, medication, and food increase population by reducing infant mortality rates, causing death rates to drop further than birth rates
• The Earth's carrying capacity is estimated at 1–2 billion prosperous people or 33 billion very poor people
• Thomas Malthus predicted that war, disease, and starvation would reduce populations

Differing Views on Population

• Paul Ehrlich's "The Population Bomb" (1968) predicted that population growth would lead to famine and conflict
• Intensified food production has averted this catastrophe for now
• Economists believe depleted resources will be replaced, new resources may be found/created
• Environmental scientists point out that many resources, such as species, cannot be replaced if depleted
• Unchecked growth will decrease quality of life, reducing space, food, and wealth per person
• Population growth is a problem when it depletes resources, stresses social systems, and degrades the environment

IPAT Model

• IPAT model indicates that total impact (I) on the environment results from population (P), affluence (A), and technology (T)
• Population includes individuals needing space and resources (P)
• Affluence is per capita resource use (A)
• Technology increases or protects the use of resources (T)
• Sensitivity (S) is a fourth factor showing how sensitive an area is to human pressure
• Further model refinements include the effects of education, laws, and ethics

China and IPAT Model

• China exemplifies the IPAT formula, where elements of the equation combine, causing tremendous impact in a very short time
• Modern China's rapid development is causing unprecedented environmental challenges
• Intensive agriculture is eroding farmland and overuse has dried up the Yellow River
• Increasing vehicles are causing urban air pollution and traffic jams
• China's current trajectory indicates what the rest of the world can become

Demography

• Demography applies population ecology principles to the study of change in human populations
• Demographers study population size, density and distribution, age structure, sex ratio, and birth/death/immigration/emigration rates
• The UN predicts 9.3 billion humans by 2050
• The prediction is based on women having just 0.5 child fewer than the medium scenario

Population Density and Distribution

• Humans are unevenly distributed globally; most populated areas have temperate, subtropical, and tropical climates, and are near seacoasts and rivers
• Unpopulated areas such as deserts and arid grasslands are environmentally sensitive with a high S value in the modified IPAT equation
• Unpopulated areas are vulnerable to humans, agriculture and ranching etc.

Age Structure

• Age structure describes relative numbers of individuals in each age class within a population, often shown by age structure diagrams (population pyramids)
• A wide base indicates many young individuals who have not yet reproduced, signaling rapid population increase
• Even age distribution indicates a stable population, where births are nearly equal to deaths
• Canada has a balanced age structure with a growth rate of 0.4%, while Nigeria's age structure is heavily weighted toward the young with a 2.8% growth rate

Social Aspects of Population Studies

• Global mean age is currently 28, projected to be 38 in 2050
• China's age structure is changing: the median age was 20 in 1970, but is projected to be 45 by 2050
• The number of those working to support social programs will decrease, meaning that retirees will need to volunteer more
• Human sex ratios at birth slightly favor males for every 100 females, 106 males are born
• Chinese females are selectively aborted, with 120 boys reported for 100 girls
• Undesirable social consequences include teenaged girls being kidnapped and sold as brides

China's Reproductive Policy

• China's former reproductive policy resulted in several issues
• Now, alternatives to China's policy can be more conducive to dealing with the resource demands of a rapidly growing population by targeting social and economic factors
• Rates of birth, death, and migration determine whether a population grows, shrinks, or remains stable
• Birth and immigration add individuals, where death and emigration remove individuals

Technological Advances and Birth Rate

• Technological advances decrease death rates and the increased gap between birth and death rates resulted in population expansion
• Decrease in infant mortality is due to better nutrition, prenatal care, and presence of medically trained practitioners during birth
• Infant mortality rates are closely tied to level of industrialization and are highest in poorer nations in Africa

Fertility Rates

• Decreasing global growth rates doesn't mean decrease on population size
• Total fertility rate (TFR) is the average number of children born to each female during her lifetime
• Replacement fertility is the TFR that keeps the population size stable (about 2.1)
• Europe's rate 0.0-0.1%
• In 2013, 18 of 45 European nations declined populations
• By 2013, around 77 counties were below the 2.1 fertility rate

Demographic Transition

• Demographic transition is a model of economic and cultural change from a pre-industrial state of high birth and death rates to a post-industrial state of low birth and death rates
• Industrialization decreases mortality rates, resulting in less need for large families and parents investing in quality of life, not quantity of kids
• Death rates fall before birth rates, resulting in temporary population growth

Demographic Transition Stages

• Pre-industrial stage has low population growth due to high death (disease, starvation, few medicines) and birth (compensation for mortality) rates
• Transitional stage yields high population growth due to industrialization, increased food, and medical care
• Mortality rates decrease, however birth rates are still high
• Industrial stage causes population growth to decrease as women get jobs and use birth control
• In the post-industrial stage the population stabilizes due to low birth and death rates

Population and Society

• Factors affecting fertility in a society include public health, culture, and economic factors
• Contraception involves deliberate prevention of pregnancy through a variety of methods, hindered by religious and cultural influences
• Rates of contraception use range from below 10% (Africa) to 86% (China)
• A key factor is the amount of time when women can become pregnant

Policies and Standards

• Funding and policies that encourage family planning lower population growth rates
• Many programs provide education and healthcare to lower birth rates and address social needs
• Empowering women reduces fertility rates as a nation's fertility rates drop when women gain access to contraceptives, family-planning programs, and educational opportunities
• Educated women reduces fertility rates, delays childbirth, and gives them a voice in reproductive decisions

Affluence

• Poor societies have higher population growth rates, worsening poverty and population growth
• 99% of the next billion people added will be born in poor, less developed regions that are least able to support them
• Affluent societies have enormous resource consumption, severe environmental impacts, and huge ecological footprints
• Developed nations must slow their consumption as the global ecological footprint is already 50% more than the Earth can support
• To guarantee a high standard of living and quality of life for all, developing nations must slow their population growth
• Developed nations must also slow their consumption to make an impact

General Conclusions

• The human population is larger than ever
• Rates are decreasing, but populations are still rising
• Most developed nations have passed through the demographic transition
• Expanding women's rights slows population growth
• The future of population levels is tied to the demographic transition, governmental intervention, or disease and social conflict