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UT ENS 112 - Chapter 6: Human Population

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Environmental Science 112FALL SEMESTER 2018INSTRUCTOR: DR. Adrienne [email protected] 6: Human PopulationOur World at Seven Billion● The current world population is over 7.4 billion, with most of the growth occurring indeveloping nations○ China (1.378 billion)○ India (1.329 billion)The Human Population continues to grow● The human population is currently growing at a rate of 88 million per year; that is 2.8 people added every second○ The human population did not reach 1 billion until after 1800○ A billion people are currently being added about every 12 years● This is an example of exponential growth, where a small percentage growth rate stillproduces a large increase due to the size of the base population● The doubling time of a country's population can be estimated by taking the number 70 and dividing it by the annual percentage growth rate○ Global doubling time is 70/1.2% or 58 years○ China’s doubling time prior to the one-child policy was 70/2.8% or about 25 years. It is now about 140 yearsIs there a limit to human population growth?● Our population growth is largely due to technological, agricultural, and sanitation advances that reduced death rates. Can this growth continue?● British Economist Thomas Malthus argued that the number of people would 1eventually outgrow the available food supply○ Paul and Anne Ehrlich made similar warnings in the 1968 book, The Population Bomb● Despite a quadrupling of the human population, these predictions have not fully materialized○ Food production has intensified as a result of the “Green Revolution”● Despite these improvements, population growth still depletes resources, stresses social systems, and degrades the natural environmentPopulation is one of several factors that affect the environment● The IPAT model represents how our total impact (I) on the environment results fromthe interaction of population (P), affluence (A), and technology (T)○ I=PxAxT● Increased population = less space, less resources, and more waste● Affluence = greater per capita resource consumption● Technology = increase impact by enhancing our ability to exploit resources or decrease impact by improving efficiencyDemography● Principles of population ecology can be applied to the study of statistical changes…Demography is the study of the human population● Demographers study several characteristics of the human population○ Size ○ Distribution○ Age Structure○ Sex Ratio○ Rates of birth, death, emigration, immigration● The current population size is about 7.4 billion, spread among 200 nations○ The United Nations predicts that by 2050, the global population will surpass 9.7 billion2● Many other demographic aspects determine environmental impact besides size● Age structure diagrams, also called population pyramids describe the relative numbers of individuals at each age class within a population● Wide base denotes a large population of pre-reproductive age people and the potential for rapid future growth● Even age distribution indicates a stable population● High proportion of post-reproductive age adults indicates a shrinking population● For example, Nigeria’s large concentration of individuals in young age groups predicts a much greater population growth than Canada● The global population is older than in past years○ The median age today is 28; in 2050, it is predicted to by 35○ This creates strain in social welfare programs in some countries● The naturally occuring sex ratio at birth for human populations is 106 males born to every 100 females born.○ This is likely an evolutionary adaptation to the increases mortality rate face by males at all ages● In China, age distributions have become increasingly skewed● The cultural gender preference for male children coupled with the one-child policy, has resulted in roughly 116 Chinese boys born for every 100 girls○ The leading hypothesis is that many parents are using ultrasounds to determine the gender of their unborn fetus, and then selectively aborting femalesPopulation change results from birth, death, immigration, and emigration● Births and immigration add individuals to a population● DEath and emigration remove individuals from a population● Global decreases in infant mortality rates, the frequency of children dying in infancy,have played a large role in population growth● Infant mortality rates are closely tied to a nation’s level of industrialization3● In recent decades, falling growth rates in many countries has led to an overall decline in the global growth rate○ This is primarily due to a steep drop in birth rates● Immigration and emigration also significantly impact the population of individual nationsTotal fertility rate influences population growth● Total fertiity rate is the average number of children born per woman during her lifetime○ Replacement fertility is the TFR that keeps the size of a population stable. Forhumans, this is 2.1● Industrialization, improved women’s rights, and health care have decreased TFR in many nations in recent years.○ Nearly European nation has a TFR below replacement level○ Europe's rate of natural increase, which only includes birth and death rates, was between 0% and 0.1% in 2015● Worldwide, by 2015, 84 countries have fallen below that replacement fertility level● Europe;s rate of natural increase, which only includes birth and death rates, was between 0.0% and 0.1% in 2015Many nations have experienced the demographic transition● Industrialized countries tend to have the highest life expectancy (average number of years a person in an age group is expected to live) increases due to a drop in infant mortality● Countries still industrializing will pass through a series of stage of economic and cultural change called the demographic transition● During the pre-industrial stage, death rates are high due to widespread disease, rudimentary health care, and unreliable food supplies● People compensate for high infant mortality by having many children. Birth control is not available4○ Population growth, overall, is stable● DEath rates decline during the transitional stage, due to improved food production and health care● Birth rates remain high as society has not yet adjusted to the new economic conditions○ Overall, population growth rate is very high● During the industrial stage, employment opportunities increase for women and birth


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