Factors Affecting Population Growth: Exponential vs. Linear - Prof. John M. Pratte, Study notes of Physics

Download Factors Affecting Population Growth: Exponential vs. Linear - Prof. John M. Pratte and more Study notes Physics in PDF only on Docsity! Population Introduction On October 12, 1999, the Earth welcomed a newborn child that brought our planet's population up to the 6 billion mark, according to the U.N. Population Fund. While this is an astoundingly large number of people to have on Earth, what makes this figure even more remarkable is that as recent as 1960, there were only a little over 3 billion people on the planet. For the last century, we have been averaging a rate of increase in the world's population that would double it about every 50 years. If this continues, it means that we will have close to 12 billion people on the planet by the middle of this century. By some people's estimates, this would amount to complete environmental devastation if it were to happen. While the world's population has been growing at a staggering pace, it has not been a homogenous, global growth. Some areas of the world are not experiencing any growth at all. In fact, some areas of Europe are actually experiencing a decline in their population. Other areas of the world offset these declines by growing at a rapid clip. Both of these situations bring about their own unique set of problems. In this chapter, we will look at the factors that affect population and discuss how global population might change over the coming century. Before we do that, we need to define a few terms and formulae that are important to this discussion. Demographic Basics Demography is the study of populations, whether they be human, plant, or animal. Human demography is that subdiscipline that looks specifically at humans, and it relies very heavily on statistics, geography, psychology, and sociology. Like any area of study, it has its own unique terms that, while they exist in everyday language, describe something very specific that might be different from their everyday definitions. For example, demographers have several terms that they use to describe how a population can change. The terms that they use are birth rate, death rate, natural growth rate, growth rate, replacement-level fertility, and total fertility rate. The first two of these are quite simple and are what you would expect. Birth rate: Commonly used as the crude birth rate, this is the number of births per 1,000 people within a certain population. Death rate: Commonly used as the crude death rate, this is the number of deaths per 1,000 people within a certain population. The formulae for determining crude birth rate and crude death rate for a given time interval, such as a year, are as follows: total number of births in a population x 1,000 = crude birth rate total population total number of deaths in a population x 1,000 = crude death rate total population The next two terms are not quite as obvious, but are easily explained. The natural growth rate is just the crude birth rate minus the crude death rate, i.e. the number of people who are born minus the number that died per 1,000 people. Many people who read this think “Well, that is obvious. The growth is just how many new babies are born minus the number of people who die.” However, this neglects the effect of immigration and emigration, and it is why this term is called the natural growth rate. The term growth rate includes the effects of immigration (people entering a country) and emigration (people leaving a country) and is defined as the natural growth rate plus the migration rate (immigration minus emigration). To explain this another way, let us look at an example. Suppose that a country of 100,000 people has 15,000 births in a year in which 10,000 people die. At the same time, 540 people move into the country to settle and 780 leave the country live in the Arctic tundra of Canada. With these values, the terms we have defined so far are: 150000,1 000,100 000,15 == xbirthrate deathrate = 10,000 100,000 x1,000 =100 naturalg rowthrate =150 −100 = 50 migrationrate = 540 − 780 100,000 x1,000 = −2.4 growthrate = natrua lg rowthrate + migrationrate = 50 + (−2.4) = 47.6 Thus, this country has a total growth rate of 47.6 people for every 1,000 citizens that it has. At this rate of growth, it would take 21 years for the population to double, as 47.6 people per year times 21 years is equal to 1,000 people (actually, 999.6 people, but there is no such thing as .6 of a person). We must recognize that this way of expressing the growth is a little different than some other ways of expressing it. In some instances, we express the growth as a percentage of the population. It is easy to convert between the two, as all one needs to do is to divide the crude growth rate by 1,000 people and then multiply by 100%. In our example, this is percentagegrowth = 47.6people 1,000people x100% = 4.76% We need to note, though, that if the population continues to grow at this percentage, then the amount of time to double will not be 21 years; it will be less. The reason for this is quite simple, as growth at a fixed percentage means that each year sees greater overall growth than the year before. In our example, growth at 4.76% means that 4,760 people are added to the country the first year. The next year, the number of people who are added will be 4.76% of 104,760, or 4,762. While this is only 2 people more, this will continue to grow in succeeding years, which means that doubling will be reached sooner, as we will show below. Replacement-level fertility: This is the average number of births that couples in a population must have in order to keep the population stable. At first glance, one might think that this number is 2.0, as it is a simple matter of each member of a couple replacing himself or herself. However, not all children will survive until they reach puberty when they could legitimately take part in producing the next generation of children. For this reason, replacement-level fertility (RLF) is higher than 2.0 and depends greatly upon the infant and childhood mortality rates of a country. In more developed countries, this number is approximately 2.1, while in developing countries with poor medical care, the number can be as high as about 2.3. Total fertility rate: This is the average number of children a woman in a population has in her lifetime. Excluding immigration and emigration from the equation, if the total fertility rate exceeds the replacement- level fertility in a population, then the population is growing. If the total fertility rate is below the replacement-level fertility, then the population is reducing. Germany in 2007, for example, had a total fertility rate of 1.4, which is well below the RLF. With this rate, the population of Germany should be shrinking; yet, it is actually stable. The reason for this is in two parts. First of all, Germany is These two reasons, along with the basic instinct to procreate, are probably the two strongest reasons for growth in the U.S. and some other developed countries. In developing countries where growth rates are the largest, there are often many other very important reasons. For instance, a lack of education and economic opportunity for women has been very strongly correlated to increased birth rates. Women in these situations generally do not have information about birth control. The lack of economic opportunities further compounds the problem as their only “job” is to be married and have children. This is a double- edged sword. If they are able to find employment, then there is pressure not to have more children, as each child means that they will have to be away from work, and thus, decrease the earnings for the family. If there are no economic opportunities available, then the only way for women to provide for themselves later in life is to have children who will take care of them as they age. Hence, if there are economic opportunities, there is pressure to decrease family size while a lack of them causes pressure to increase it. Another very important factor in determining growth is the age at which women get married. The average woman has about 30 years in which she can have children. If she starts having children at an early age, then she is much more likely to have a lot of children. This factor is also tied to economic opportunities and education, as these two things often delay the age at women get married. Developed Countries and Immigration When George Washington started the first Presidency of the United States of America, he was governing less than 4 million people who occupied an area of 2,300,000 square kilometers1. It was an agrarian society, with 95% of the population living on farms and only 5% in cities or towns of more than 2,5002. There was plenty of land, and a vast array of natural resources, just waiting to be tapped. Today, we live in a country of over 300 million people3. While we are one of the major food producers in the world, it is no longer due to us being an agrarian society. Today, most people live in towns and cities, with less than 25% of the population living in rural areas. And even though we have grown to a physical size of over 9.8 million square kilometers, our population density has increased from the 2 people per square kilometer of Washington’s day to almost 30 people per square kilometer today. From where did all of these people come? The increase in territory that we experienced over that time did increase the number of people in the U.S. from the simple fact that there were already people living there. We have also expanded by immigration, with wave after wave of people entering this country to find new life and new opportunity. Neither of these, though, accounts for the largest segment of growth. Both put together still account for less than 80 million people4. The largest sector of people is here due to birth. Fig. 2: Historical U.S. Population (Data: U.S. Census) This same thing is true of most countries. Immigration is often a small factor to the overall growth of the country. However, it can have a powerful effect on the growth of a country, as the birthrate can be greatly affected by it. In the early days of the U.S., the growth from births came from all sectors of society. However, as the following story shows, the growth of a developed country can come mostly from the descendents of immigrants. Karen’s Story by Matt Laposata It had been a bad day for Karen Christini. After enduring paralyzing rush-hour traffic following a miserable day at work, she was ready for some hard-earned relaxation. But no such opportunity availed itself, for tonight was decision night. While in college, Karen had joined the Sierra Club, a national organization dedicated to environmental preservation, with her boyfriend Andrew. Andrew lasted less than a semester, but her Sierra Club membership was still going strong as she entered her mid-thirties. And on this chilly April night it was the Sierra Club that demanded her attention. The Sierra Club's budget, political lobbying, policy stances, and preservation efforts are directed by a group of 15 elected board members. Board elections were typically not national news, but this election was anything but typical. For some time, the membership of the Sierra Club had been divided on the issue of U.S. immigration and its relationship to human population growth. In 1998, a movement within the organization put forth a proposal to replace the Sierra Club's historic "no position" stance on U.S. immigration with one that advocated reductions in the number of immigrants admitted to the United States to reduce environmental impacts associated with growing populations. Sixty percent of members rejected the proposal and the Sierra Club continued advocating controls on global human population growth with a neutral policy towards U.S. immigration. In the following years, however, three members that advocated a stance towards reduced immigration were elected to the board. There were five open seats this year, so the election of five reduced-immigration candidates would give the group a majority on the board and the power to steer the organization. Karen had not come to a decision on her votes and the ballot had to be in the mail tomorrow. As she had done many times over the past few weeks, she sat at the kitchen table hunched over her Sierra Club ballot and began running her fingers through her hair, trying to use the rhythmic motions to force a decision from her head. She reviewed the major points of view one last time, hoping yet another analysis would yield a conclusion. On the one hand, she thought, the advocates of reduced immigration had a point. The United States absorbs around one million legal immigrants and several hundred thousand illegal immigrants a year, and these immigrants have average birth rates about double that of U.S.-born citizens. Unlike most industrialized nations, the population of the United States is expected to grow from around 292 million (in 2003) to about 422 million in 2050 – and up to 70% of this growth is attributable to immigration. Given the highconsumption lifestyle in modern America, this population growth will lead to increased impacts on the local and global environment, exactly the things the Sierra Club aims to reduce. Proponents of immigration reduction also argue that international immigration causes talented and educated citizens of developing nations to leave for industrialized countries, slowing the industrialization that leads to lower birth rates. They further contend that immigration has economic costs when wages earned in the United States are sent home by immigrant workers. But, she thought, those that support current immigration policies make several convincing arguments. They argue that while international immigration increases the U.S. population, it slows the growth of the global human population as the children of immigrants have birth rates like that of other U.S. born citizens – rates likely far lower than those in the immigrant’s native country. Immigration proponents also claim that immigration improves cultural awareness in the United States, thereby promoting environmental sustainability in these countries through foreign aid initiatives. Immigration advocates say that the United States should always be a "safe harbor" for victims of human rights abuses or armed conflict around the world. They also claim that immigrants infuse skills and labor into the workforce and improve the economy of the host country. Karen’s family was a classic example. Her grandparents emigrated from Sicily to the vibrant Italian-American community in New Haven, Connecticut, in the early 1900s and prospered in subsequent generations through a dedication to education and hard work. Karen sat back in the chair and sighed heavily. The epiphany, the tiebreaker, or the revelation she sought had once again eluded her. This wasn't going to be easy. She sat forward, propped her elbows on the table, stared at her ballot, and began running her fingers through her hair… If you were Karen, what would you do? Describe how your family’s immigration history in the United States. Did an understanding of this history affect your views on the subject? Do you think the current U.S. immigration regulations are appropriate? Explain why or why not. If you think current immigration policies are inappropriate, provide specific suggestions on how they should be modified. Predicting the Future For all of its futuristic stylings, the television show Star Trek was, like most science fiction, a commentary on the state of society at the time it was written (late 1960’s). One of the more famous episodes of that series was the one entitled The Mark of Gideon, which dealt with a planet that was so overpopulated that people did not have anywhere to sit down. At the time of the show, the Earth’s population was at about 3.5 billion, and was increasing at an incredible rate. The effects of such a large population on the environment were beginning to become abundantly clear, and people had begun to wonder just how many more people the Earth could hold. This Star Trek episode was just one of a number of television shows, movies, and books at that time (ex. Soylent Green) that foretold of an ominous future if we did not begin to do something. All of these shows were predicated on predictions made by demographers at the time of what the world’s population would be at some point in the future. Each generation has done this, sometimes with startling accuracy, and sometimes missing the mark completely. For example, in 1798, Thomas Malthus, an English demographer and economist, predicted that the world’s population would one day outstrip mankind’s ability to feed itself, and that this would be reached when the population was 1 billion people. Of course, Malthus could not foresee the introduction of the internal combustion engine and the production of artificial fertilizers that have increase our capacity to feed. We now have more than 6.5 billion occupants of Earth, and we are continuing to grow. As previously stated, at current rates of growth, we will reach 12 billion by the year 2050. However, this prediction is most assuredly wrong, as it relies on everything going along just as it is. As Malthus shows us, one cannot assume this. In order to make a more sophisticated prediction, we need to look deeper at the