Env-107 - Lecture noteProf. Dr. Md. Anisur Rahman Khan (ARK)

Human Population and Environment

According to the data from the “United Nations Population Division, World Population Prospects, 1998"

World Population Reached1 billion in 18042 billion in 1927 (123 years later)3 billion in 1960 (33 years later)4 billion in 1974 (14 years later)5 billion in 1987 (13 years later)6 billion in 1999, ((12 years later)

World Population May Reach7 billion in 2013 (14 years later)8 billion in 2028 (15 years later)9 billion in 2050 (22 years later)

Between 1950 and 2002, the world's population increased from 2.5 billion to 6.2 billion. Unless death rates rise sharply, it may reach 8 billion by 2028, 9 billion by 2050, and 10-14 billion by 2100.

In many ways , this reflected g ood n ews for humanity : Child mortality rates decreased, life expectancy increased, people were on average healthier and better nourished than at any time in the history.

However, there are b ad news, because, during the same period: Changes in the global environment began to accelerate, pollution heightened, resource depletion continued, green house gases emission continued and the threat of rising sea levels increased.

Growth of Human Population – Different societies and their impacts on the environment:The history of human population can be viewed in four major periods:

Stage 1: Hunter and Gatherer Societies: An early period of hunters and gatherers (before 9000 B.C., population between 250,000 to 2 million). Hunter-Gatherers are people who obtain their food by collecting plants and killing wild animals and survived by the use of tools for hunting, gathering, preparing foods etc. In the early period of hunters and gatherers, the world's total human population was probably less than a few million.Population density was : 1 person/ 130-260 Km2

Rate of growth was: 0.00011% per year.

1

Stage 2: Early,Pre-industrial, Agricultural Societies: A second period beginning with the rise of agriculture, which allowed a much greater density of people and the first major increase in human population. Beginning sometime between 9000 B.C. and 6000 B.C. and lasting approximately until the sixteenth century A.D. (1 A.D., population about 100 million; 1600 A.D., population 500 million. Population density was : 1-2 person/ Km2

Rate of growth was: 0.03% per yr.

Stage 3: The machine age (Industrial Societies): The industrial revolution is the change that spreads through societies as they start to use fossil fuels as energy sources to power their technology - with improvements in health care and the supply of food, leading to a rapid increase in the human population. Beginning about 1600 A.D. with the Renaissance in Europe and lasting until 1960 A.D. (1600 A.D., population 500 million; 1800 A.D., population 900 million; 1900 A.D., population 1600 million; 1960 A.D., population 3 billion). Industrial effects on the environment are the vast migration of people from the countryside into cities and the pollution of air, land, and water.Rate of growth was 0.1% per yr.

Stage 4: The Modern Era: The present situation, where the rate of population growth has slowed in wealthy, industrialized nations but population continues to increase rapidly in poorer, less developed nations. The growth rate of the human population reached 2% in the middle of the twentieth century and has declined slightly, to 1.4%. The modern era begins in 1960 A.D. (1960 A.D., population 3 billion; 1998 A.D., population 5.9 billion; 2007 A.D., population 6.7 billion). Use of technology has altered much of the nature in a number of ways and caused significant damage to the environment: increased air pollution, water pollution, waste production, soil depletion and degradation, groundwater depletion, habitat destruction and degradation, biodiversity depletion.

Population Growth in Bangladesh:Bangladesh is an over populated country The rapid growth of Bangladesh's population following devastating storms vividly illustrates the human population's great capacity for growth and suggests the problems that this growth poses threat for the environment.

Bangladesh is one of the poorest nations in the world, and this poverty affects human survival. Less than half the population has access to safe drinking water, and less than a fifth has access to adequate modern sanitation. Average life expectancy is about 60 years. With inadequate resources for each individual and a rapid growth rate, Bangladesh struggles to maintain even its existing poor standard of living. The low-lying coastal areas that make up most of this nation are fundamentally uninhabitable at high population densities for extended periods and are only inhabited now because of the huge numbers of people living in the country. Already the need for food for the increasing numbers of people has led to overuse of the land for grazing and crop production. Almost all the usable agricultural land is already being used. For Bangladesh it is difficult to talk about

2

solving major environmental problems, conserving biological diversity, or optimizing production of fisheries and vegetation when people barely have sufficient resources to survive and the growth of the human population erases any advances

How Populations Change Over Time

The central question: What would make it possible for the human population to cease to grow? This question can be answered only if we understand basic ideas about any population.

A population is a group of individuals of the same species living in the same area or interbreeding and sharing genetic information. A species is all individuals that are capable of interbreeding. A species is made up of Populations. Five key properties of any population are: abundance which is the size of a population-now, in the past, and in the future; birth rates; death rates; growth rates, and age structure; How rapidly a population changes depends on the growth rate, which is the difference between the birth rate and the death rate.

Human Population Terms:

Crude birth rate: number of births per 1,000 individuals per year; "crude" because population age structure is not taken into accountCrude death rate: number of deaths per 1,000 individuals per yearCrude growth rate: net number added per 1,000 individuals per year; also equal to crude birth rate minus crude death rateTotal fertility rate (TFR): average number of children expected to be born to a woman throughout her child bearing yearsMorbidity: general term meaning the occurrence of disease and illness in a populationRate of natural increase (RNI): birth rate minus death rate, implying annual rate of population growth not including migrationDoubling time: number of years it takes for a population to double, assuming a constant rate of natural increase. A concept used frequently in discussing human population growth, is the time required for a population to double in size. A useful role of thumb is that if you divide 70 by the annual percentage growth—that will give approximately doubling time for anything growing exponentially. If the growth rate of a human population of any country is 5% per year then its population will double in every 14 years. Life expectancy at birth: average number of years a newborn infant can expect to live under current mortality levels GNP per capita: gross national product (GNP), which includes the value of all domestic and foreign output.

Major Characteristics of a PopulationPopulations are dynamic and change in response to environmental stress or changes in environmental conditions. Populations change over time and over space. The general study of population changes is called population dynamics. They change in (1) size (number of individuals), (2) density (number of individuals in a certain space), (3) dispersion (spatial pattern such as clumping, uniform dispersion, or random dispersion, depending mostly on resource availability, and (4) age distribution (proportion of

3

individuals of each age in a population). These changes, called population dynamics,

The following features characterize a population:

1. Population size: The size of a population is the number of individuals making up a population. For example, the human population of Bangladesh is comprised of over 14 million individuals.

2. Population growth: This refers to the increase in the number of individuals in a population. The factors that affect growth in a population are birth, immigration, death and emigration.

3. Population density: This is the number of individuals of a population per unit area at a given time. Thus, to calculate the population density of Bangladesh for the year 1997, divide 150 million or 150,000,000 (population size) by 58000 sq km (total land area of Bangladesh).

4. Population dispersion or distribution: This refers to the general pattern in which the members of a population exist in their habitat. Population distribution may be random, clumped, regular, or may show a gradient. For example, in a crop -land, the crop population is usually distributed in a regular pattern with similar distance between two plants, whereas in a natural forest, the same plant may be dispersed in clumps in those areas where there is no tree shade and where suffi-cient sunlight is available for their growth. Thus, population dispersion depends on various factors like availability of food, shelter or protection.

5. Age structure: The proportion of individuals in each age group in a population is its age structure. Common age categories are pre-reproductive, reproductive and post-reproductive. A larger percentage of individuals in the pre-reproductive and reproductive categories means greater population growth. Understanding the age structure of human populations is important for framing development policies and plans. The age structure helps to make future projections of the na-tion's population growth. Natural populations maintain a balanced age structure because, in nature, there is always the survival of the fittest. However, human actions may drastically change such balances.

Factors affecting the population growth :

How is population size affected by Birth Rates and Death Rates?Four variables-births, deaths, immigration, and emigration-govern changes in population size. A population gains individuals by birth and immigration and loses them by death and emigration. Population change is calculated by subtracting the number of people leaving a population (through death and emigration) from the number entering it ( through birth and immigration) during a specified period of time (usually a year):

4

Population change = (Births + Immigration) - (Deaths + Emigration)

These variables depend on changes in resource availability or on other environmental changes. Populations vary in their capacity for growth, also known as the biotic potential of the population. Unlike other kinds of organisms, humans are also influenced by social, political, economic, ethical factors.

When births plus immigration exceed deaths plus emigration, population increases; when the reverse is true, population declines.

Instead of using the total numbers of births and deaths per year, demographers use the birth rate, or crude birth rate, and the death rate, or crude death rate.The rate of the world’s annual population change (excluding migration) usually is expressed as a percentage: Birth rate – Death rate Annual rate of natural population change (%) = ------------------------- x 100 1,000 persons Birth rate – Death rate = ------------------------------- 10

Kinds Population Growth

Resources are very important in the population dynamics of biologic systems. The growth and reproductive success of organisms depend on the availability of life-supporting resources. In an environment where unlimited resources are available and where nothing interferes with growth or reproduction, exponential growth can occur.

In exponential growth, population increases geometrically a given rate of increase per unit of time-the growth rate. This is also called geometric growth. It differs from arithmetic growth, in which the amount of growth per unit of time, rather than the rate, is a constant.

The mathematic equation that describes exponential growth is dN/dt = rN, where N is the number of individuals, t is the unit of time, and r is the growth rate (like the interest rate in a bank account). The term d is a mathematic term that means "change." Therefore, the equation can be read as "The change in the number of individuals per change in unit of time is equal to the number of individual times the growth rate."

If you plot the results of the penny or bacteria calculations on a graph using N as the vertical axis and t as the horizontal axis, you will see that a graph of exponential growth is shaped like the letter J. This J-curve is characteristic of exponential growth. (If you plot an arithmetic increase, however, you should get a straight-line graph.)

5

An obvious oversight in the calculation is that we have only considered growth as a function of birth rate, the number of births (new individuals added to the population) per unit of time. However, organisms also die. The death rate (or mortality) in a population represents the number of individuals that have died during the same period and must be subtracted from the population. In the natural environment, organisms can also enter a population through immigration or leave through emigration. These adjustments to population must also be made.

The growth that a population theoretically could experience in the absence of any limitations is called the biotic potential of the population. As a population grows, however, many factors begin to place limitations on its growth.

Some of these are related to population density, the number of individuals per unit of space. If a system is very densely populated, individuals may have a difficult time gaining access to the resources they need, such as light, water, food, shelter, or living space. Resources may become depleted or run out altogether.

In a community with more than one species, additional factors come into play. For example, with increasing population density, an individual might be more likely to encounter a predator. Environrnental risk factors, such as drought, a cold winter, or a population explosion among predators, also influence the growth of a population.Anything that acts to limit or control population growth is called a limiting factor.

Limiting Factors:

A population that exceeds the carrying capacity (the maximum population size that can be sustained indefinitely by the environment) will change the environment in a way that will decrease future population size. Clearly, no population can sustain an exponential growth rate indefinitely. Eventually the population will run out of food and space. That is, eventually human population will be limited by some factor or combination of factors, called limiting factors.

These include: disruption in the distribution of food within a country due to political events, local loss of current crops, abrupt change in weather (e.g. drought), major world catastrophes, such as outbreak of a new disease, energy shortages that affect food production and distribution, desertification, wide dispersal of certain pollutants into waters and fisheries, disruption in the supplies of nonrenewable resources, soil erosion; a decline in groundwater supplies, climatic changes, such as global warming; and wide dispersal of certain pollutants, such as acid rain.

Short-term factors: Effect apparent with a year. Examples: loss of current crops, drought, sudden wars etc.

Intermediate-term factors: 1-10 years. Examples: climate changes, pollution, energy shortages that affect food production.

Long-term factors: may take decades to affect the environment. Example: Soil erosion, global warming, acid rain etc.

6

These factors provide environmental resistance to unlimited growth in biologic populations. Typically, a population will start out growing rapidly on an exponential J-curve. As population density increases, environmental resistance comes into play, and the population will begin to level off, resulting in a curve that is S-shaped. The leveling-off point represents the maximum number of individuals in a population that can be supported by the ecosystem on a long-term basis; it is called the carrying capacity (K).

Difference Between Expo nential and Logistic Population Growth

A population that has few if any resource limitations grows exponentially. Exponential growth starts out slowly and then proceeds faster and faster as the population increases. If number of individuals is plotted against time, this sequence yields a J-shaped exponen-tial growth curve.

Logistic growth involves exponential population growth when there is a steady decrease in population growth with time as the population encounters environmental resistance and approaches the carrying capacity of its environment and levels off. After leveling off, a population with this type of growth typically fluctuates slightly above and below the carrying capacity. A plot of the number of individuals against time yields a sigmoid, or S-shaped logistic growth curve.

Technological, social, and other cultural changes have extended the earth's carrying capacity for the human species. We have increased food production and used large amounts of energy and matter resources to make normally uninhabitable areas of the earth habitable. However, there is growing concern about how long we will be able to keep doing this on a planet with (1) a finite size and resources and (2) a human population whose size and per capita resource use are growing exponentially.

Zero population growth, or ZPG :A population that is stable with a growth rate of zero-neither increasing nor decreasing-is said to have achieved zero population growth, or ZPG. It takes a couple of generations of reproduction at or below replacement levels for a population to stabilize to ZPG.

The effect of age distribution can be seen in population pyramids for fast-growing and slow-growing populations. In a fast-growing population, a large proportion of the population is under the age of fifteen; in a slow-growing population, the age distribution of the population is more even. Some economists worry that ZPG will mean that the population will age too quickly and there will be too many old people and not enough young, working people to support the nation's productivity. Others argue that ZPG and the demographic transition are necessary to stabilize the world's population and keep it within the carrying capacity of the planet.

7

8

Age Structure

So, An important factor in population growth is the population age structure, the proportion of the population in each age class. The age structure of a population affects current and future birth rates, death rates, and growth rates; has an impact on the environment; and has implications for Current and future social and economic status.

We can picture an age structure as if it were a pile of blocks, one for each age group, where the size of each block represents the number of people in that group. Although age structures can take many shapes, four generel types are most important to our discussion: a pyrainid, a column, an inverted pyramid (top-heavy), and a column with a bulge.

The pyramid age structure occurs in a population with many young people and a high death rate at each age -and therefore a short average lifetime. A column shape occurs where the birth rate and death rate are low and a high percentage of the population is elderly. A bulge occurs if some event in the past caused a high birth rate or death rate for some age group but not others.

Age structure provides insight into a population’s history, its current status, and its likely future. Age structure varies considerably by nation. The overall shape of an age structure diagram indicates whether the population is increasing, stable, or shrinking. Demographers typically construct age structure diagram by plotting the percentages or numbers of males and females in the total population in each of three age categories: prereproductive (ages 0-14), reproductive (ages 15-45), and postreproductive (ages 45

9

and up). The age structure diagram of a country with a very high growth rate is shaped like a pyramid In developing countries about 37% of the populations are under 15 years old (e.g. Kenya). Any country with many people below age 15 has a powerful built-in momentum to increase its population size unless death rates rise sharply. A positive population growth momentum exists because when all these children mature, they will become the parents of the next generation, and this group of parents will be larger than the previous group. Thus, even if the fertility rate of such a country has declined to a replacement level (that is, couples limit themselves to two children), the population will continue to grow for some time.

Worldwide, 30% of the human population is under age 15. When these people enter their reproductive years, they have the potential to cause a large increase in the growth rate. Even if the birth rate does not increase, the growth rate will increase simply because there are more people reproducing.

The age structure diagrams of countries with slowly growing, stable, or declining populations indicate that a smaller proportion of the population will become the parents of the next generation. The age structure diagram of stable population, one that is neither growing nor shrinking, demonstrates that the numbers of people at pre-reproductive and reproductive ages are approximately the same. Also, a larger proportion of the population is older—that is, post-reproductive—than in a rapidly increasing population. Many countries in Europe have stable populations.

In a population that is shrinking in size, the pre-reproductive group is smaller than either the reproductive or post-reproductive group. Russia, Bulgaria, Austria and Germany are examples of countries with slowly shrinking populations. Most of the world population increase since 1950 has taken place in developing countries as a result of the younger age structure and the higher-than-replacement-level fertility rates of their populations. Most of the population increase that will occur during the 21st

century will also take place in developing countries, largely the result of their younger age structures. These countries are least able to support such growth.

Projecting Future Population GrowthWith human population growth a central issue, it is important that we develop methods to forecast what will happen to our population in the future. One of the sim-plest approaches is to calculate the doubling time.

10

.

11

Demography

The study of human population trends is called demography. Demographers analyses the factors that influence human population growth, such as total fertility rates, rates of natural .increase, migration patterns, population age structures, demographic transitions, and environmental factors. These data are used to project future population trends and to analyse, alternative scenarios aimed at solving population-related environmental problems.

The first important predictions about human population were made more than two hundred years ago by Thomas Malthus. He concluded that the human population inevitably will overwhelm available food resources, resulting in famine, disease, and

12

war over resources.Thomas Malthus published “An Essay on the Principle of Population”. His Theory was that Human population tends to grow geometrically, while the resources available to support it tend to grow arithmetically. He postulated that population growth was already outpacing the production of food supplies in 18th-century England. He predicted that population growth would lead to degradation of the land, and eventually massive famine, disease and war. Malthus presented his theory in response to optimists of his day who thought that mankind's ability to master the environment was limitless. Improvements in agriculture and the industrial revolution postponed the disaster that Malthus thought was imminent. But his ideas are even more applicable today. Modern population theorists who predict catastrophes and conflicts as a result of uncontrolled population growth are sometimes referred to as neo-Malthusians.

What is a neo-Malthusian? A population theorist who, like Malthus, argues that human population growth is out of control and will eventually exceed available resources, resulting in catastrophes such as famine, war (competition for resources), and disease.

The Demographic TransitionExamining the birth and death rates of western European countries that industrialized during the 19th century, demographers (people who study population) developed a hypothesis of population change called the Demographic Transition. This transition occurs in four phases:

1. In the pre-industrial stage, living conditions are harsh and the birth rate is high (people have more children to replace children who die from infectious diseases, malnutrition, etc.), but the death rate is also high. Thus, there is little population growth.

2. In the transitional stage, when industrialization begins, food production rises and health improves. Death rates drop, but birth rates remain high, so the popu-lation grows rapidly.

3. In the industrial stage, industrialization is widespread. The birth rate drops and eventually approaches the death rate. This is because people in cities realize that children are expensive to raise. Having too many children also hinders them from taking advantage of job opportunities. Population growth continues, but at a slower and fluctuating rate, depending on the economic conditions.

4. In the post-industrial stage, the birth rate declines even further to equal the death rate, thus reaching zero population growth. Subsequently, the birth rate falls below the death rate, and the total population size slowly decreases.

Total Fertility Rate and Replacement-Level Fertility:An important factor that can delay changes in population growth is the average number of children expected to be born to a woman during her lifetime, known as the total fertility rate, or TFR. A population that maintained a TFR of 3.8 over a long time would increase

13

rapidly, whereas a population that had a TFR of 2.0 over a long time would decline.

Replacement-level fertility (RLF) is the TFR required for a population to remain constant. A total fertility rate of 2.1, that is, replacement-level fertility will not necessarily immediately result in a stable population with zero growth for several reasons. First, the death rate may fall as living conditions improve and people live longer. If the death rate falls faster than the birthrate, there will still be an increase in the population even though it is reproducing at the replacement rate.

A comparison of nations suggests that the TFR declines as income increases. Bangladesh, which has an average income per person of a few hundred dollars per year, has a high fertility rate—approximately 4.3 children born to each woman.

Future Population Trends:World Bank, from the logistic growth curve has made critical assumptions which are (1) mortality will fall everywhere and level off when female life expectancy reaches 82 years; (2) fertility will reach replacement levels everywhere between 2005 and 2060; (3) there will be no major catastrophe. Even assuming a rapid achievement of RLF, this approach projects an equilibrium world population of 10.1 to 12.5 billion. Developed countries would only increase from 1.2 billion today to 1.9 billion, but developing countries would increase from 4.5 billion to 9.6 billion. Bangladesh would reach 257 million. In these projections, the developing countries contribute 95% of the increase.

How Can We Stop Population Growths:The simplest and one of the most effective means of slowing population growth is to delay the age of first childbearing by women. As more women enter the work force and as education levels and standards of living increase, this delay tends to occur naturally. Social pressures that lead to deferred marriage and childbearing can be very effective.Countries with high growth rates have early marriage. In Bangladesh, women marry at age 16 on the average, whereas in Sri Lanka the average age for marriage is 25. The World Bank estimates that if Bangladesh adopted Sri Lanka’s marriage pattern, families could average 2.2 fewer children. Increases in the marriage age could account for 40% to 50% of the drop in fertility required to achieve zero population growth for many countries.Reduction in birth rates requires a change in attitude, knowledge of the means to control birth, and the ability to afford these means. Changes in attitude can arise simply with an increase in the standard of living.By bringing about more equitable relationships between men and women, with emphasis on improving the status of women and expanding education and job opportunities for young women can help reduce the number to a great extent.The best way to slow population growth is a combination of investing family planning, reducing poverty, and elevating the status of women.

14