Science Guide: The Human Impact on Natural Resources PDF

Section III The Human Impact on Natural Resources THE HUMAN POPULATION In the previous section of the resource guide, we discussed the factors that regulate population abundance and distribution, with a focus on nonhuman species. We will start this section wit...

Section III The Human Impact on Natural Resources THE HUMAN POPULATION In the previous section of the resource guide, we discussed the factors that regulate population abundance and distribution, with a focus on nonhuman species. We will start this section with a focus on the population whose growing exploitation of global resources is the primary impact on all environmental systems—the human population. According to the United Nations World Population Prospects, the global human population reached its first 1 billion Granada Hills Charter High School - Granada Hills, CA people in 1804. It then took 123 years for the population to double to 2 billion in 1927. However, from then, human population growth really took off, taking just thirty-two years to reach 3 billion and only thirty-nine more years to double to 6 billion. Then, sometime in November 2022, the United Nations estimated that we hit a population of 8 billion people. However, while from 1974 to 2022 we added 1 billion people to the population every twelve years, it is estimated that it will take approximately fourteen years to reach 9 billion and that the human population may well peak at a little over 10 billion by around 2100, if not sooner. In the first part of this section, we will look at how some of the density-independent and density-dependent factors that we dealt with in the previous section—that control nonhuman population abundance and distribution—also play a factor in human population growth. We will also touch upon some of the human-specific factors that regulate our population growth. Growth Rate Technically, the growth rate is the percent change that has occurred in a population in a given time period, usually a year. In 1963 the human population of 3.6 billion was growing at 2.1 percent per year; as of 2023, it is estimated to be growing at between 0.83 percent to 0.9 percent.18 Growth rates are currently decreasing in most countries throughout the world. Because of this decline in growth rates, and despite the greater total number of people in the world today, the number of people added each year is smaller now (roughly 70 million additional people per year) than when the growth rate was 2.1 percent and there were 3.6 billion people (76 million additional people per year). Four factors define the growth rate of a country or continent: births, deaths, immigration (the number of people who migrate into a country), and emigration (the number of people who migrate out of a country). The growth rate equals all the additions to the population minus all the subtractions from the population, divided by the total number in the population. This can be represented as: (births + immigration) − (deaths + emigration) 100 = %GR the total population So, a village with 300 people that in one year had 10 births, 3 migrations, 4 deaths, and 2 emigrations has a growth rate of [(10 +3) – (4 + 2)]/300 ≈.02 To obtain the growth rate as a percent, you multiply by 100 ≈ 2% Migration and emigration are important when analyzing an individual country—for example, migration has 2024–2025 Science Resource Guide 93  FIGURE 52 Granada Hills Charter High School - Granada Hills, CA Global human population growth from 1700 to the present and beyond. Source: United Nations, DESA, Population Division accounted for up to one-third of the population increases in the United States in some years. When we consider the entire world, because the numbers are so large, the human birth rate is normally expressed as the number of births per 1,000 individuals per year. This figure is often called the crude birth rate (CBR) because it is the crudest, or most basic, measure of birth rate. The number of deaths per 1,000 individuals in the population per year is the crude death rate (CDR). If we exclude migration, then the growth rate can be calculated based on the birth rate and death rate alone: CBR−CDR = %GR 10 Here we divide by 10 because the CBR and CDR are expressed per 1,000 people in the population. To refer to the 2024–2025 Science Resource Guide 94 growth rate as a percentage (per 100 people), we must adjust the numbers accordingly. The most effective way to see the changes that take place in growth rates over time is to plot the birth rate and death rate versus time for a given country. By looking at the difference between the two, it is possible to see the change in the growth rate on a year-to-year basis. If the birth rate is above the death rate, the country will experience positive growth. The greater the distance between the birth and death rates, the greater the positive growth rate. If there is no difference between birth and death rates, then there is no growth. Lower- and Higher-Income Countries Of the 8 billion human inhabitants on Earth today, 1.3 billion live in higher-income countries (Europe, North America, etc.), and 6.7 billion live in lower-income countries, those countries that haven’t yet or are currently industrializing—in which we will include China and India for now. The population difference between more- and less-developed countries has not always been so large. In recent decades, populations in parts of the world, particularly sub-Saharan Africa, have continued to grow rapidly (an average of 1.5 percent per year) while population growth rates in the higher-income countries have almost leveled off (an average of 0.2 percent per year). FIGURE 53 Granada Hills Charter High School - Granada Hills, CA Population growth divergence: high- versus lower-income countries. Source: United Nations Conference on Trade and Development (UNCTAD), based on United Nations Department of Economic and Social Affairs World Population Prospects 2022 2024–2025 Science Resource Guide 95 Population Size and Resource Use Every one of the eight billion people on Earth eats, drinks, and generates waste products. Provision of even the most basic foods, such as beans or rice, requires energy, water, and mineral resources. To raise beef or catch fish from far offshore requires even greater expenditures. Further, despite differences around the world, people generate a huge demand for wood, paper, plastic, steel, and energy to make homes, automobiles, and consumer products and to give and receive services. The mining and extraction, processing, use, and disposal of all these materials contribute to environmental degradation. The overall impacts of 8 billion people are hard Energy use is a good indicator of the overall environmental to appreciate and even more difficult to quantify. impact of population growth. The larger the human The following equation can be used to estimate population, the greater the consumption of fossil fuels. Granada Hills Charter High School - Granada Hills, CA environmental impact: By Walter Siegmund (talk) - Own work, CC BY 2.5, https://commons. wikimedia.org/w/index.php?curid=3413544 Environmental Impact = Population X Resource Use Per Person X Impact of the Resource Used Energy use is one good indicator of overall environmental impact. In 1960, when the population was 3 billion, world fossil fuel consumption was almost 3,000 million tons of oil equivalents. In 1999, world fossil fuel use was 7,900 million tons of oil equivalents. While the population doubled, the use of fossil fuels more than doubled. And in 2022, our now 8 billion people used approximately 11,500 million tons of oil equivalents, continuing to increase at a rate greater than the human population. The consumption of fossil fuel has numerous environmental impacts, including land and water degradation from extraction and air pollution and carbon dioxide emissions resulting from combustion, so we can safely assume that environmental impacts increased considerably during this time. Factors Affecting Population Growth If we want to predict future trends in the human population, it is important to identify the factors that have caused the human population to grow slowly at times and quickly at other times. FIGURE 54 Crude Birth Rate (CBR) = Total number of live births per 1,000 in population per year Crude Death Rate (CDR) = Total number of deaths per 1,000 in population per year Growth Rate (GR; also called the Rate of Natural Increase) = percent population growth per year = ((Yr 2 − Yr 1)/ Yr 1) × 100 or (CBR−CDR)/10 Total Fertility Rate (TFR) = Average number of children born to a woman during her child-bearing years Doubling Time (Tdouble) = Time in years for population to double at current growth rate Infant Mortality (IM) = Number of infants per 1,000 live births who die before first birthday Life Expectancy (LM) = Average expected lifespan of an infant born in a given year %65 = Percent of population below age 15/above age 65 Factors that affect population growth—terms and brief definitions. Source: United Nations Conference on Trade and Development (UNCTAD), based on United Nations Department of Economic and Social Affairs World Population Prospects 2022 2024–2025 Science Resource Guide 96 Fertility We can consider the human population as a system comprising a pool of 6 billion people with births as inputs and deaths as outputs. In any given time period, the number of births in a population is dependent on the number of individuals in the population and the birth rate, and the number of deaths is dependent on the number of individuals in the population and the death rate. In the United States, the total fertility rate (an estimate of the average number of children that will be born to each woman in the population throughout her child- bearing years) today is 1.84, which means that, on Infant mortality, the number of deaths of infants (children average, each woman of child-bearing age will have a under age one) per one thousand live births, together with life expectancy, can provide an accurate representation of health little less than two children. As you would expect, the care in a given country. growth rate of a population and the total fertility rate By Kimberly Vardeman - CC BY 2.0, https://commons.wikimedia.org/w/ Granada Hills Charter High School - Granada Hills, CA correlate with one another; when we compare a number index.php?curid=85075306 of countries, those with higher growth rates usually have higher total fertility rates. The replacement fertility rate is the number of children each woman must have on average to replace the current population. Replacement level fertility is usually 2.1: a total of 2.1 children, on average, are needed to replace two parents because some children never reproduce. Therefore, the United States is below replacement level fertility. Based on that statistic alone, we would expect the population in the United States to decrease over time. However, we must also consider immigration (remember the equation at the beginning of this section), which is projected to add almost one million people per year to the population of the United States as well as the individuals in the population that are not yet reproductively mature who will soon begin to contribute to the birth rate. Life Expectancy and Infant Mortality Life expectancy is the average number of years that an infant born in a given year can be expected to live, given the current average lifespan and the death rate. Life expectancy is often reported for the overall population of a country and for males and females within the population. In almost every situation, the life expectancy for men is shorter than that for women, reflecting greater hardships and dangers generally experienced by men in the workplace and different lifestyle choices. The gap between life expectancy for men and women is decreasing as more and more women enter the workforce. Infant mortality is the number of deaths of infants (children under age one) per one thousand live births. Life expectancy and infant mortality together usually provide an accurate representation of the level of health care in a given country. If life expectancy is fairly high and infant mortality is fairly low, it is likely that the country has a relatively high level of health care. Note that crude death rate is not a good indicator of health care. Even with a high life expectancy and a low infant mortality, a country could have a high crude death rate because it has a large number of older individuals. For example, the United States has a higher crude death rate (9) than Mexico (5), which is a reflection of an older population in the U.S. than in Mexico. Over a dozen developed countries have lower infant mortality rates than the United States, including Canada, Finland, Iceland, Ireland, Japan, Sweden, and France. What accounts for a U.S. infant mortality rate that is one to two deaths per thousand greater than other comparable countries, many of which spend less per capita on health care? Universal health care and more generous allowances for time off during the later stages of pregnancy are two reasons. The large disparity in the level of health care provided to Black Americans, Hispanics, Native Americans. and other minorities in the United States relative to whites is also a factor. The infant mortality rate for the entire 2024–2025 Science Resource Guide 97 U.S. population is 5.4, but for Black Americans in the U.S., it is 10.4 and for Native Americans, 8.2.19 In addition to having less access to health care, less prenatal care, and poorer nutrition, minorities and lower socioeconomic groups are also disproportionately exposed to pollutants, which contribute to higher infant mortality and poor health. Age Structure One method for assessing the age distribution of a population is to look at the percentage of the population under the age of fifteen and the percentage over sixty- Japan is one of a number of countries with negative population growth, and so its elderly population is larger than five. Commonly reported as %65, this value younger age groups. shows us the relative age distribution in a country. For Photo by Issei Kato example, the %65 for Mexico is 24/8 while the value for the U.S. is 18/18.20 This tells you that 24 percent of the population in Mexico is under age fifteen while in the U.S. 18 percent is under age fifteen. Granada Hills Charter High School - Granada Hills, CA Eighteen percent of the population in the U.S. is over sixty-five; only 8 percent of the population in Mexico is over sixty-five. However, compared with other countries, Mexico’s age structure is actually relatively close to that of the U.S. In Nigeria, part of the sub-Saharan region that is experiencing the highest population growth rates, 41 percent of the population is under fifteen years of age, while only 3.3 percent is over sixty-five! In order to understand the potential environmental impact of a country, it is important to know how many young people there are and will be in the population. How many potential consumers of soft drinks or “fast fashion” will there be? How many potential drivers of automobiles or bicycles? How many future parents of more consumers? The % 65 figure can give us some idea of the distribution of ages, but we don’t know how many people are just about to turn sixty-five, or how many people are in their child-bearing years, having just moved out of the