Uh-oh, it looks like your Internet Explorer is out of date.
For a better shopping experience, please upgrade now.
Foundations of Environmental Physics: Understanding Energy Use and Human Impacts available in Hardcover
Foundations of Environmental Physics is designed to focus students on the current energy and environmental problems facing society, and to give them the critical thinking and computational skills needed to sort out potential solutions. From its pedagogical approach, students learn that a simple calculation based on first principles can often reveal the plausibility (or implausibility) of a proposed solution or new technology.
Throughout its chapters, the text asks students to apply key concepts to current data (which they are required to locate using the Internet and other sources) to get a clearer picture of the most pressing issues in environmental science. The text begins by exploring how changes in world population impact all aspects of the environment, particularly with respect to energy use. It then discusses what the first and second laws of thermodynamics tell us about renewable and nonrenewable energy; how current energy use is changing the global climate; and how alternative technologies can be evaluated through scientific risk assessment. In approaching real-world problems, students come to understand the physical principles that underlie scientific findings.
This informative and engaging textbook offers what prospective scientists, managers, and policymakers need most: the knowledge to understand environmental threats and the skills to find solutions.
|Product dimensions:||7.20(w) x 10.10(h) x 1.10(d)|
Read an Excerpt
Foundations of Environmental Physics
Understanding Energy Use and Human Impacts
By Kyle Forinash
ISLAND PRESSCopyright © 2010 Kyle Forinash
All rights reserved.
Population Growth and Environmental Impacts
It has often been asserted that a particular generation has a special place in history, and names such as The Greatest Generation, Baby Boomers, Gen Xers, and Generation Y have been given to specific groups. But although each generation has its own claim to fame, in terms of population statistics, people born in the past 50 years have a unique place in recorded history. For the first time, the world's population has doubled in a person's lifetime. It took 650 years for the global population to grow from a quarter of a billion to half a billion, 125 years to grow from 1 billion to 2 billion, but only 39 years to double from 3 billion to 6 billion in 2000. The world population increased in the last 5 years by half a billion, more than the total number of people living in 1600. However, if current fertility projections made by the United Nations Population Division hold, no one born after 2050 will live through another doubling of the human population. Demographic changes are not limited to the total number of people. The year 2000 marked the first time in history that the number of people older than 60 outnumbered the population younger than 10. In 2008, the number of urban people passed the number of rural people.
These facts make the current era unique in human experience and have critical implications for the natural world. As we will see in Chapter 7, the global emission of carbon dioxide is directly linked to the number of people in the world, as are the availability of clean water and the concentration of pollutants in the atmosphere and soil. In this chapter we will look at population trends, examine a simple model of population growth, and consider the environmental impacts of these profound changes.
1.1 Population Growth
Figure 1.1 shows the historical rise of the global population and projections of future population growth out to the year 2150 made by the United Nations Population Division. There are several things to notice in the graph. Asia, which includes India and China, has historically contained almost half the world's population, and this trend is expected to continue for the next 150 years. Sections of Asia, Africa, and to a lesser extent South America and the Caribbean are experiencing a steep population increase, whereas Europe and northern America (not including Central America) are experiencing stable or decreasing populations. The world's population is projected to begin leveling off after 2050, reaching about 9 billion people by 2150. Because of uncertainties about fertility rates, the actual global population in 2150 may be as low as 7.9 billion or as high as 10.9 billion.
Many of the terms used to describe population and demographic changes have specific definitions. Population increase is the net population increase due to births, deaths, and migration in a specified period of time. The population growth rate is the percentage change per year in the population due to births, deaths, and migration. The general fertility rate is the number of live births per 1,000 women of childbearing age (assumed to be either 15 to 44 or 15 to 49, depending on the agency reporting the figure) per year. Because the yearly rate may change during a person's lifetime, another term is used more often: The total fertility rate is the number of live births per 1,000 women of childbearing age, based on age-specific birth rates during childbearing years. These rates are not equivalent to the birth rate, which is the number of live births per 1,000 people (the age of the women is not taken into account). Net migration is the total effect on an area's population due to immigration and emigration over some specified period of time. The net migration rate is the net migration per 1,000 people per year. Finally, it should be pointed out that life expectancy varies with age. Life expectancy at birth is generally lower than life expectancy in middle age, for example. This is because you are much more likely to die in the first few years of life; once this critical time has passed, your life expectancy is longer.
Table 1.1 shows a snapshot from the years 1995 to 2000 of other pertinent population data. From the table we see that approximately three quarters of the world's population lives in developing regions of the world. Average life expectancy at birth in developing regions is approximately 12 years less than in developed regions and is about 24 years lower in Africa. Fertility rates are highest in West, Middle, and East Africa and Melanesia, and these rates correspond roughly to the use of contraceptives; regions with lower fertility rates show higher use of contraceptives. This is an important indicator of how population growth rates have changed in recent history. Fertility rates decrease when women have access to contraceptives, and this tends to occur when women are better educated and have higher standards of living.
A fertility rate of two children per woman is said to be the replacement rate and, if maintained, would eventually lead to a growth rate of zero if both children lived to adulthood and there were no migration. Because of infant mortality, the United Nations Population Division assumes the actual replacement rate to be 2.1 children per woman, a number that varies somewhat depending on access to infant health care services. Even after the replacement rate has been reached, a population will continue to grow for some time as youth born before the replacement rate is reached attain childbearing age. Only if this new generation maintains the replacement birth rate will the population level off. Fertility rates are the strongest indicator of population change, but migration can also play a significant role. In Table 1.1 we see that the fertility rate in developed countries is less than 2 (1.6 children per woman), but the annual growth rate is greater than zero (0.3). A few economically mature countries have growth rates less than zero and are therefore experiencing a decline in population. But on average, developed countries are gaining population through immigration and young women coming of childbearing age, which results in the positive growth rates shown.
The effects of regional differences in population growth rates on the local political environment can be seen by comparing recent population increases in Central America with that in the United States. The population of Mexico has increased fivefold in the past 60 years, whereas the U.S. population doubled in this time frame, a figure that includes immigration. The stress on available food, land, and water resources in Central America caused by this more rapid increase in population is one of several factors leading to increased migration, both legal and illegal, into the United States.
Whether through immigration or births, we often hear that a particular population is growing exponentially. The word exponential sometimes is used colloquially to simply mean a rapid increase, but in fact it has a specific meaning. When an amount increases (or decreases) over time in proportion to the current amount, the growth (or decline) is said to be exponential. Stated differently, a growth rate is exponential if, for equal time intervals, the increase is a fixed percentage of the current amount. An important example of exponential growth from economics is a fixed percentage return on an investment; each year the amount increases by a fixed percentage of the previous year's total. There are other types of growth; for example, in linear growth a fixed amount is added for each time period. Given enough time, exponential growth always leads to a larger final quantity than linear growth. In Chapter 4 we will consider a different kind of increase governed by the logistic equation; in the following we consider exponential growth.
Intuitively we expect population to increase exponentially; the more people there are, the more people are having children, so the increase in the number of people depends on the number of people of reproductive age. Obviously reproductive age does not extend over a woman's entire lifetime, so we expect population growth to be slightly different from exponential because the growth rate is a percentage of only the number of reproductive-aged women. The population figures mentioned earlier reflect total annual growth, which takes into account the fact that women do not have children throughout their lives. Despite these complications, on average the assumption holds: For the last several hundred years world population growth has been exponential although at varying rates for different time intervals.
In Example 1.1 we show how to model exponential growth. It is important to realize that growth rates larger than zero (i.e., a stable fertility rate greater than 2.1 and zero migration) if they remain constant will always lead to exponential growth. Negative growth rates lead to exponential decline; only a sustained growth rate of zero will lead to a stable population. From Table 1.1 we see that Europe is the only region with a stable population. All other regions in the world are undergoing exponential growth, although at significantly different rates and sometimes for different reasons (e.g., immigration).
Exponential laws in nature are fairly common. In Chapter 4 we will see examples of exponential decay; here we look more closely at the global growth rate using an exponential growth model.
The world population growth in Figure 1.1 is obviously not linear (it is not a straight line). However, we may wonder whether it is exponential with a constant rate or perhaps with a constant rate along some part of the curve. A quantity N(t) is said to increase exponentially if at time t we have
(1.1) N(t) = N(0)erf,
where N(0) is the original quantity at t = 0 and r is the (constant) growth rate. Here time is in years, so the growth rate represents the fraction of increase per year. The growth rate is positive for exponential growth and negative for exponential decay. A value of zero for r means an initial magnitude that does not change over time.
It is difficult to compare data with exponential curves, so a useful trick is to turn this expression into a straight line. We can do that if we take the natural logarithm (1n) of both sides, in which case we have ln[N(t)] = ln[N(0)] + rt. If we plot ln[N(t)] versus t we should have a straight line with slope r and y-intercept equal to ln[N(0)]. In Table 1.2 the year, the population in billions, and the log of the global population are shown.
From Figure 1.2 we see that a plot of ln[N(t)] versus year is approximately straight. A linear equation can be fit to the data that has the form y = 0.014x - 5.073, as shown in the graph. The slope of this linear graph gives a growth rate constant of 0.014 or 1.4% per year, which is the value shown in Table 1.1 for the global growth rate between 1995 and 2000.
One thing that should be noted is that our model shows a constant growth rate of 1.4% between 1900 and 2000. However, closer examination of the graph reveals that the slope changed somewhat during this 100-year period. The data have a slightly lower slope (and lower growth rate) between 1900 and 1930 and a higher rate between 1950 and 1980. In fact, the growth rate was about 0.7% between 1900 and 1930 and about 1.8% between 1950 and 2000. It is also obvious that this equation cannot apply to the real population before 1900 because the y-intercept indicates a population of zero in the year 360.
If the current fertility rates shown in Table 1.1 remained fixed, the world population would reach 244 billion people by 2150 and 134 trillion by 2300 . Obviously the world population cannot continue to grow exponentially forever. It is very doubtful that a global population equivalent to that of a densely populated city such as Calcutta, India, would be sustainable because no land would be left for growing food. However, the growth rate and subsequent population increase are very sensitive to fertility rates. As shown in Figure 1.3, fertility rates are falling and may possibly reach two children per woman by about 2050, resulting in a stabilization of the global population by about 2150. However, if the actual fertility rate falls only to two and a quarter children per woman, the global population will reach 36.4 billion by 2300. If the rate falls to 1.75 the world population in 2300 is projected to be only 2.3 billion. From this we see that because of the exponential nature of population increases, small changes in fertility rates have a large effect over time, much larger than death rates due to HIV/AIDS and other pandemic illnesses, for example.
The current decline marks the first time in history that fertility has fallen voluntarily. The only time the global population has declined was during widespread plagues such as the Black Death in Europe during the fourteenth century, when two thirds of the population is thought to have died. Despite the declining fertility rates shown in Figure 1.3, the total population is expected to continue to grow for the near future. This is because even when the fertility rate falls to two children per woman (the replacement rate), the greater-than-replacement rate experienced before this time has generated a disproportionate number of young people who will grow up to have offspring. It takes at least a generation after the replacement rate is reached for the population to stop growing. Even then, longevity often increases as countries become more developed, leading to a slower decline in the number of people living.
Declines in fertility and subsequent changes in projected population growth are occurring for several reasons. The single largest factor affecting fertility is women's education, a factor that is also positively correlated with higher economic status. In developing countries a larger part of the population has traditionally lived in rural areas where farming, much of which is done by women, is the main occupation. This mode of subsistence is changing, however, as the world's population moves into cities. Urban living often means higher economic status for women because they can work for wages, which offers the opportunity to purchase medicine, contraceptives, and better access to education, whereas an economy based solely on agriculture does not. It is also the case that farming techniques in developing countries are based on manual rather than mechanical methods, so large families are needed in order to supply workers. As societies move from rural to urban areas, there is less need for a large family; in fact, it can often be a detriment because it means more mouths to feed. Women who have moved to urban areas and have a choice and access to affordable birth control generally decide to have fewer children. This trend is widespread in developing countries and is often actively supported by government agencies in those countries. The United States is one of the few countries where subsidized family planning services and national population planning do not play a significant role in public policy.
Because fertility rates are generally higher in developing countries, the majority of the population growth in the next 50 years is expected to occur in the less economically developed countries of Asia and Africa. A handful of countries—India, Pakistan, Nigeria, Democratic Republic of Congo, Bangladesh, Uganda, and China—will account for most of the increase in the next 50 years. Other African countries such as Botswana, Swaziland, and Zimbabwe are also expected to grow significantly in population despite the fact that the HIV and AIDS epidemic is widespread in these countries. Because of low fertility rates in the United States, the population would level off by 2020 if there were no immigration. As a result of low fertility and lack of immigration, some developed countries such as Germany, Japan, and the Russian Federation are expected to continue losing population in the next 50 years. The difference in fertility rates between developed and developing regions means that the number of people living in developing regions will increase relative to the number of people in developed areas of the world. Today the population in more developed countries makes up about 20% of the world's total. The UN Population Division projects that by 2050 the number of people living in developed regions will be only 10% of the global population.
Excerpted from Foundations of Environmental Physics by Kyle Forinash. Copyright © 2010 Kyle Forinash. Excerpted by permission of ISLAND PRESS.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Table of Contents
Chapter 1. Population Growth and Environmental Impacts
Chapter 2. Efficiency and the First Law of Thermodynamics
Chapter 3. Efficiency and the Second Law of Thermodynamics
Chapter 4. Nonrenewable Energy
Chapter 5. Renewable Energy
Chapter 6. Energy Storage
Chapter 7. Climate and Climate Change
Chapter 8. Risk and Economics
Appendix A: Useful Constants and Conversions
Appendix B: Error Analysis