Science Section 3 & 4 PDF - Human Population & Resources

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 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 Seven Lakes High School - Katy, TX 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 Revised Page July 16, 2024 93  FIGURE 52 Seven Lakes High School - Katy, TX 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 Revised Page July 16, 2024 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 Seven Lakes High School - Katy, TX 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 Revised Page July 16, 2024 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. 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 Seven Lakes High School - Katy, TX 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 Revised Page July 16, 2024 96 Fertility We can consider the human population as a system comprising a pool of 8 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/ 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. Seven Lakes High School - Katy, TX 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 Revised Page July 16, 2024 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. 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 Seven Lakes High School - Katy, TX 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 400 ppm) are the highest they have been for millions of years. Global change incorporates all the previous topics that we have dealt with—the interconnectedness of Earth’s systems, the current and future status of Earth and the environmental indicators that enable us to evaluate it, and the interaction of environmental science and policy. The terms global change, climate change, and global warming are often used synonymously, particularly in the popular press, but they should not be. Climate change is variation in the average weather—temperature, precipitation, storm frequency and strength, etc.—over years and decades. Global warming deals with the fact that the Earth’s global surface temperature has been increasing relative to pre-industrial temperatures. Global change includes those issues, as well as the other environmental changes that have been largely caused by human activity. This includes large-scale deforestation and other land conversions and the correlated loss of biodiversity, non-greenhouse gas pollution and its impact on human health, and other large-scale changes. Seven Lakes High School - Katy, TX The Sun–Earth Heating System The physical and biogeochemical systems that regulate temperature at the surface of the Earth are essential to life on our planet. These systems derive ultimately from what we can think of as the Sun–Earth system, which— like other systems—can be treated as a series of inputs and outputs, and which involves the interaction between multiple environmental systems. If you have entered an automobile that has been parked in the sun with its windows closed on a relatively cool day, you have experienced the greenhouse effect. Though the outside temperature may be 10ºC (50ºF), the inside of the car might be 30ºC (86ºF). On a day when the outside temperature is 30ºC, the inside of the car might be 38ºC (100ºF) or even higher. These striking temperature differentials can be explained by the greenhouse effect, a natural process that leads to the warming of an area that is underneath something that traps heat—in the case of a greenhouse or the car, the glass of the windows. Most incoming solar energy passes through the windows without being absorbed by the glass, which is transparent to solar radiation in the visible range. The solar energy is absorbed by the upholstery, the dashboard, and the steering wheel, which experience an increase in temperature and then begin to radiate energy outward. Though the windows of the car allowed solar radiation to pass through, they do not allow passage of very much of the outgoing “car” radiation, which is in the infrared range. This energy is absorbed and reradiated back into the car. The inflow of energy into the car is greater than the outflow of energy, so there is a positive net flux of energy into the car, causing the car to become increasingly warmer, even on a relatively cool day. A very similar process takes place at the surface of Earth. As energy from the Sun travels toward Earth, it is absorbed by the atmosphere or is reflected and scattered back into space. Almost half of this solar energy passes through Earth’s atmosphere, much like the solar energy passed through the car windows, and is absorbed by objects at the surface of Earth, such as water, land, vegetation, rocks, and human-made structures, and radiated back out. Since objects at the surface of Earth are roughly the temperature of Earth (15ºC), they radiate in the infrared. Like the car windows, heat-trapping gases make the atmosphere almost opaque to outgoing infrared radiation. In the Sun–Earth heating system, there is one major energy input—solar radiation—and two major outputs— reflection of solar energy from the atmosphere or from the surface of the Earth and infrared radiation of Earth energy. Over the long term, the net flux of heat is zero; inputs of heat to Earth equal outputs from Earth, and the 2024–2025 Science Resource Guide Revised Page July 16, 2024 184  FIGURE 108 Seven Lakes High School - Katy, TX The Sun–Earth heating system. Source: NASA system is in a steady state. However, the input can be greater than the outputs because of an increase in incoming solar radiation (from sunspots, for example) or because of a decrease in outgoing reflected solar radiation either from a change in materials covering the surface of the Earth or from an increase in heat-trapping greenhouse gases. If solar radiation is greater than the sum of reflected solar energy and radiating infrared Earth energy, Earth becomes warmer in response to the input of additional heat energy. If solar radiation is less than the other two fluxes, Earth becomes cooler. This is where the greenhouse effect becomes important. Greenhouse Gases The relatively hospitable temperatures on Earth are largely a function of the heat-trapping gases that are present in the atmosphere, commonly called greenhouse gases (GHGs). We discussed the generation of GHGs when discussing pollution and energy production. Nevertheless, you may be surprised to learn that the most common GHG is water: water vapor (H2O gas) absorbs infrared energy radiating from the Earth. The major, but not the only, heat-trapping gases added to the atmosphere by human activities, such as the combustion of fossil fuels and clearing of land, are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and chlorofluorocarbons (CFCs). In the absence of GHGs, the temperature on Earth would be approximately negative 18ºC (0ºF). Thus, although we commonly think of GHGs—and the global greenhouse effect—as a negative, it is actually necessary for 2024–2025 Science Resource Guide Revised Page July 16, 2024 185 human life on Earth. The problem arises when the natural greenhouse effect is increased by the human addition of GHGs, making for a hotter greenhouse. While the temperature of Earth has fluctuated over geologic time, most of the temperature changes have been very slow, and in any given decade, century, and sometimes millennium, the Earth’s temperature has been relatively constant. Our system analysis makes clear that in order for Earth to stay at a constant temperature, the energy inputs must equal the energy outputs. However, a variety of natural processes and human activities may increase or decrease the concentration of GHGs, and the extent of absorption and radiation of energy will increase or decrease accordingly, resulting in variations in the greenhouse effect. The re-radiation and reabsorption of energy by greenhouse gases is called radiative forcing because the gases that are present return energy to Earth, forcing a change in Earth’s energy balance. When assessing the impact of each GHG, we need to consider three environmental parameters: the concentration of the gas in the atmosphere, its global warming potential, and how long the gas molecules will persist in the atmosphere. The global warming potential of a gas is an estimate of how much a molecule of that gas can warm the atmosphere over a hundred years, relative to a molecule of CO2. Methane, nitrous oxide, and CFCs all have greater warming potential than CO2. However, it is the much greater concentration of CO2 in the atmosphere— along with its much longer duration in the atmosphere—that makes it the most important greenhouse gas. FIGURE 109 Seven Lakes High School - Katy, TX Concentration in 2022 Global warming Duration in the Greenhouse gas (ppm = parts per potential (based on atmosphere million) Carbon Dioxide = 1) Water vapor Variable with temperature 500 years Major greenhouse gases and their impacts on warming. The major greenhouse gases differ in their atmospheric concentrations, their ability their global warming potential, and the duration that molecules of the gas will remain in the atmosphere. Source: NOAA At the beginning of our discussion of global change, you saw the current estimates—from the IPCC’s 6th Assessment Report—for several climate change indicators, including the increase in global surface temperatures. We will now explore some of the ways that these indictors have been measured. Evidence of Temperature Change over Time Global warming refers to the increased warming of Earth’s atmosphere and surface due to an increase in gases that trap heat and, in particular, warming caused by human activity. As previously mentioned, global warming is one component of the broader phenomenon of global change. One of the greatest difficulties in determining if global warming is occurring is the difficulty of establishing what, if any, temperature change has occurred in recent decades. Though indirect measurements have made it clear that global temperatures have fluctuated over 2024–2025 Science Resource Guide Revised Page July 16, 2024 186 geologic time, what is needed is precise, widespread measures of temperature from locations around the globe for hundreds and thousands of years. Earth surface and ocean temperatures have been measured directly only since about 1880, with varying, though increasing, degrees of confidence. There is a high degree of confidence in at least one global temperature data set maintained by James Hansen at the NASA Institute for Space Studies in New York City. Hansen and his colleagues have generated a graph of global temperature change that is updated monthly and posted on NASA’s website (Figure 110). This graph, which is comprised of thousands of measurements from around the world, clearly shows a steady increase in global temperatures from 1880 through 2020 (although there are yearly variations). Measurements for 2023 are not yet complete; however, we can note that June, July, August, and September of 2023 were the hottest for those months on record. Historical evidence and scientific models suggest that Earth is becoming warmer. FIGURE 110 Seven Lakes High School - Katy, TX Global surface temperature measurements. Lowess smoothing is a method of fitting a smooth curve (the black line in the figure) to data points, such as the yearly temperature variation in the figure. Source: NASA Indicators of Climate Change Indirect measurements that can be obtained through biological and physical parameters suggest that current global temperatures are higher than at any time in at least the last 150,000 years. One such indicator is the sampling of ice cores that we discussed in the first part of Section I. Trees can provide indirect records of temperatures for decades and centuries and on rare occasions for more than a thousand years. Each year, most trees add layers of wood from millimeters to centimeters thick. In middle and high latitudes, these annual rings are quite distinct and allow careful measurement of tree growth and a subsequent estimate of temperature. Wider rings correspond with better temperatures for growth (if there is also enough moisture), which usually means warmer and/or wetter conditions in the year when—or the year before—the rings were added to the tree. Corals are another surrogate indicator. In 2024–2025 Science Resource Guide Revised Page July 16, 2024 187 relatively clean ocean waters in and near the tropics, marine corals add annual bands of calcium carbonate. A number of geochemical signals in the calcium carbonate allow researchers to reconstruct the approximate temperature of the water in which the corals have been growing. Corals can record temperatures for tens and sometimes hundreds of years. Models We’ve previously discussed the use of models to predict the environmental effects of various factors such as energy use or pollution. Because direct measurements are scarce, models are particularly important in calculating changes in temperature and other aspects Corals can serve as an indicator of climate change, as they of climate. Environmental scientists use recorded can record temperatures for tens and sometimes temperatures to construct models that correlate many hundreds of years. By Holobionics - Own work, CC BY-SA 4.0, https://commons.wikimedia. parameters, including past concentrations of GHGs, org/w/index.php?curid=49070224 with past temperatures. The models are then used to predict future concentrations of greenhouse gases and estimate future temperatures based on the predicted gas concentrations. Based on the projected temperatures, estimates are then made of how another parameter, such as sea level or precipitation patterns, will be affected by the change in temperature. Seven Lakes High School - Katy, TX For example, when Earth becomes one degree warmer, eventually the oceans will become one degree warmer as well. Because of thermal expansion, each degree Centigrade increase in ocean temperature results in approximately a six centimeter rise in the height of the ocean. Sea level change is difficult to measure precisely—although current satellite data is becoming more reliable for recent measurements—but it appears that over the past century, as ocean temperature has risen approximately 1ºC, sea level has risen by approximately 10 cm. Based on these correlations, predictions for the next hundred years suggest that sea level might rise another 10 cm or more. Other models can be used to predict, for instance, a particular change in ocean or atmospheric circulation patterns resulting from certain air or water temperature changes. The changes in circulation might lead to warmer or cooler temperatures in one region of Earth, in turn influencing the precipitation patterns that occur in this region. Finally, the combined effects of changes in temperature and precipitation may influence a particular species of tree, which may expand or constrict its geographic range. The effect might also include the length of the growing season in a particular area, or increased temperature of water in freshwater lakes, which could lead to a decrease in biodiversity in those lakes. A variety of models, known collectively as atmosphere/ocean/sea-ice general circulation models (AOGCMs), are used to predict the effects of global climate change. Researchers first characterize past climate based on existing data for air and ocean temperatures, CO2 concentrations, size of different biological populations, extent of sea ice coverage at the poles, and many other parameters. Characterizing past climate conditions, which can be assessed against the actual climate conditions that were measured by meteorological instruments, is a test of how well the model works and thus how well it will predict future conditions. The model is calibrated and refined to better “predict” what has already happened. Then future parameters, such as the estimated atmospheric CO2 concentration in 2050, are inserted into the model to predict what the temperature might be at a given location on Earth at a certain time in the future, such as 2050 or 2100. Feedback in the Global Greenhouse System The global greenhouse system is similar to the Mono Lake system we examined in Section I in that it is made up of several interconnected systems. However, both the number of subsystems and the number of different components within each system make the global greenhouse system much more complex. Several important 2024–2025 Science Resource Guide Revised Page July 16, 2024 188 feedback loops contribute both to increased atmospheric concentration of GHGs and to increased global temperatures. Global warming affects all environmental and human systems. The Temperature–CO2 Feedback Loop As you learned in Section II, soils of different kinds cover much of the land surface on Earth, and in many locations the soils contain a significant amount of organic matter. When oxygen is present, the organic matter is broken down by microorganisms, which give off CO2 as a by-product of this aerobic (oxygen-rich) decomposition, much as human beings give off CO2 as a by-product of respiration. In general, organic matter in soils is at steady state: it is decomposed at roughly the same rate at which new organic matter is contributed. However, certain changes can disrupt this steady state. Decomposition generally occurs more rapidly in warmer environments than in cooler environments. If an increase in CO2 emissions leads to warmer temperatures, decomposition will increase, giving rise to more CO2 production. The increase in CO2 production will increase atmospheric CO2 concentrations further and enhance the greenhouse effect. This in turn will promote more decomposition, which will lead to more atmospheric CO2, and so on, in a positive feedback cycle that will continue to move CO2 toward an exceedingly high concentration. In the real world, something would eventually limit the positive feedback, such as the availability of dead organic matter, but in the meantime the net concentration of CO2 in the atmosphere would have increased. FIGURE 111 Seven Lakes High School - Katy, TX Temperature–CO2 feedback loop. The Temperature−Permafrost Feedback Cycle In the northern latitudes, a large amount of dead organic matter is bound within the arctic tundra, which is frozen much of the year. When the tundra thaws, it is very wet. Extremely wet organic matter contains little oxygen and therefore does not undergo aerobic decomposition. However, the tundra contains organisms that can decompose organic matter anaerobically, which produces methane as well as CO2. Even a slight warming of temperatures in northern latitudes would increase the number of days each year that the tundra is not frozen, thereby increasing the number of days during which anaerobic decomposition, and hence methane production, would occur. Since the greenhouse gas efficiency of methane is twenty-five times that of CO2, a positive feedback cycle could easily result. An increase in methane in the atmosphere would lead to more radiative forcing, which would lead 2024–2025 Science Resource Guide Revised Page July 16, 2024 189 to slightly warmer temperatures, which would lead to more days with unfrozen tundra and increased anaerobic decomposition. Like the temperature–CO2 feedback cycle, the temperature–permafrost feedback cycle will create a net increase of greenhouse gas in the atmosphere, which will have an impact everywhere in the world, not simply in the arctic. FIGURE 112 Seven Lakes High School - Katy, TX Temperature–permafrost feedback loop. Source: Professor Ross Virginia, Environmental Studies Department, Dartmouth College. The Ice−Albedo Feedback Loop One last feedback loop to consider is of particular importance in ice- and snow-covered areas: the ice−albedo feedback loop. Sea ice and snow-covered ground are solar reflectors, sending solar energy from the Earth’s surface back to the atmosphere, with some escaping back into space. The overall effect is to cool global surface temperatures. However, as global warming decreases the amount of sea ice and snowpack, the albedo decreases since the ocean and uncovered ground have lower albedo and absorb more A young male polar bear found a remaining iceberg, clawed of the solar energy. out a bed, and drifted off to sleep in Norway’s Svalbard archipelago. The impacts of climate change are significant, Effects of Global Warming and environmental scientists foresee still more extensive Global warming is already contributing to overall changes throughout all of Earth’s systems in the future. global change. Atmospheric CO2 has increased 50 Photo by Nima Sarikhani/Wildlife Photographer of the Year percent since 175041, and global average temperature has increased by about 2ºF since 1880. Although a temperature increase of 2 degrees may seem small, it is enough to affect global processes significantly, as suggested by many environmental indicators, including the amount of arctic ice. Snow cover has decreased by at least 10 percent since observations were first conducted in the 1960s. Permafrost has thawed, warmed, and degraded in polar, sub-polar, and some mountainous regions. The growing season has lengthened by one to four days per decade since the 1960s in the Northern Hemisphere. 2024–2025 Science Resource Guide Revised Page July 16, 2024 190  FIGURE 113 Melting Lower albedo Seven Lakes High School - Katy, TX The ice–albedo feedback loop. Source: Professor Ross Virginia, Environmental Studies Department, Dartmouth College. The geographic range for many plants, insects, and birds has shifted northward in the Northern Hemisphere and on some occasions has moved up in altitude on mountains. In some cases, species that have increased the northern extent of their range in the Northern Hemisphere have constricted their southern range because conditions are less favorable for them further south. Flowering plants have been blooming earlier, birds arrive earlier at their spring nesting grounds, and insects are emerging earlier in the Northern Hemisphere. “The tip of the iceberg” is an almost literal description of the changes that have already occurred. Environmental scientists foresee extensive changes throughout all of Earth’s systems in the future. Predicted Future Effects of Global Warming A number of global changes have been predicted to occur by the end of the twenty-first century as a result of global warming, a few of which we have already mentioned. Here we outline some other projections based on available data and the models we described earlier. Though these occurrences represent moderate to worst-case scenarios, many of them are nevertheless considered likely. 6 Continental glaciers and the Greenland ice sheet are expected to continue to retreat. Global mean sea level, in part as a result of the melting of glaciers, is expected to rise by 0.1 to 0.9 m by 2100. 2024–2025 Science Resource Guide Revised Page July 16, 2024 191  6 Maximum temperatures will be higher, and more heat waves will occur across virtually all land areas. There will be a potential for heat and drought damage to crops or greater irrigation requirements for crops. Demand for energy for cooling of living spaces and food will increase. 6 Minimum temperatures will increase over most land areas, with fewer extremely cold days and fewer days below freezing in certain locations. Such conditions will result in fewer cold-temperature deaths among humans and a decrease in the risk of crop damage. A decrease in killing frosts that limit the geographic extent U.S. Secretary of State John Kerry, with his two-year-old of pest species will lead to an increase in the granddaughter Isabelle Dobbs-Higginson on his lap and range of pest and disease vectors. Demand for United Nations Secretary-General Ban ki-Moon looking on, heating of living spaces should decrease, which signs the COP21 Climate Change Agreement on behalf of the will decrease the demand for energy. United States during a ceremony on Earth Day, April 22, 2016, at the U.N. General Assembly Hall in New York. 6 Precipitation patterns will change. Higher rainfall amounts over certain land areas are projected, although models differ on which areas of the globe will receive the greatest rainfall. Increased Seven Lakes High School - Katy, TX precipitation is expected to result in increased flooding, landslides, and mudslides, as well as increased soil erosion. Benefits may include increased recharge to aquifers and in some cases increased crop yields. At the same time, changes in regional climates may either increase or decrease precipitation and storm frequency; how regional climates will change is not well understood. 6 Global ocean currents may shift, which would dramatically disrupt the distribution of heat on the planet (remember that the unequal distribution of heat is the basis for the circulation currents present on Earth). 6 The natural processes of ecosystems, especially those that have already been fragmented by human development, will change. Anticipated changes in ecosystems in the northeastern and north-central U.S., for instance, suggest that spruce-fir, aspen-birch, and maple-beech-birch stands of forest will move significantly northward, greatly decreasing their abundance in existing locations. This change in the makeup of vegetation will have profound impacts on the wildlife that depends on these particular types of trees. Many other species may be threatened by extinction, as rapid temperature change does not allow every population of organisms time to adapt. As the productivity of an ecosystem and the ecological services it provides are generally a result of the variety of species that are present in the ecosystem, a reduction in species may mean that overall ecosystem function and productivity will be reduced. 6 Global warming and the resulting changes will dramatically affect human populations. As sea levels rise, coastal communities and certain open ocean islands will be threatened by inundation and, even before that, contamination of their drinking water and erosion of their coastal areas. In the South Pacific, a number of islands and island nations have already been threatened with flooding from rising sea levels. High tides and rough seas have led to short-term inundation of areas in the Marshall Islands, Cook Island, Tuvalu, and lower lying areas of Papua New Guinea. 6 A general decrease in water availability in landlocked regions is also predicted. As the planet warms, disease vectors, such as the mosquitoes carrying West Nile virus and malaria, will extend over greater areas, bringing disease to areas that were once relatively untouched. Heat waves will cause more deaths among the very young, the very old, and those without access to air conditioning. Infectious diseases and bacterial and fungal illnesses will extend over a wider range than at present. Climate change is already having economic and environmental justice consequences. In northern locations, 2024–2025 Science Resource Guide Revised Page July 16, 2024 192 warmer average temperatures and shorter winters may sound appealing at first but would drastically alter the character of northern communities that depend on snow for the tourism industry. The damage to marine corals will have an impact on eco-tourism. Poorer communities close to or along coastlines will not have the resources to rebuild on higher ground. In general, the poor will bear the greatest costs of global change because they have the fewest resources to deal with the changes. While environmental science, in general, and climate change science in particular, can provide important data on the current and potential future states of our Earth, the issues summarized above cannot be solved by science. Reducing GHG levels in the atmosphere—as well as funding and building the necessary infrastructures required to deal with the climate change impacts that we are facing—require global policy agreements, such as the 2015 Paris Agreement that provides a framework for every country to do what it can to reduce GHG emissions and provide the help necessary to those countries that are on the frontlines of climate change. SECTION IV SUMMARY Atmospheric Science and Air Pollution 6 Air pollution includes the compounds present in the troposphere at levels high enough to cause damage to human beings, animals, plants, and structures or to alter ecosystems. The six U.S. criteria air pollutants are sulfur dioxide, nitrogen oxides, carbon monoxide, lead, particulate matter, and ozone. Primary pollutants—compounds that are pollutants in the form that comes directly out of a smokestack, exhaust pipe, or natural emission source—include CO, CO2, SO2, NOX, most suspended Seven Lakes High School - Katy, TX particulate matter, and many VOCs. In the atmosphere, primary pollutants are transformed through complex chemical reactions into secondary pollutants. Ozone and components of acidic deposition are some of the secondary pollutants of greatest concern. 6 A large percentage of air pollution comes from natural sources such as volcanoes, fires, and plants. Anthropogenic sources are transportation, industrial processes, and other fuel combustion, primarily electricity generation. Transportation is responsible for more than half of outdoor air pollution. 6 Through a series of reactions, SO2 and NOx form into the secondary pollutants nitric acid and sulfuric acid, which produce acid rain. 6 Photochemical smog forms when oxides such as NOX combine with oxygen and VOCs in the presence of sunlight to produce photochemical air pollutants, particularly ozone. Human activity is an important contributor to smog because it supplies the VOCs without which ozone would be destroyed. Smog is common in urban areas, particularly if a thermal inversion traps pollutants at ground level, but it also occurs in nonurban settings. Photochemical smog is detrimental to both human health and ecosystems. 6 Particulates can be removed from industrial emissions by a number of technological devices. Primary pollutants are harder to control, and photochemical smog is particularly difficult because of the complex of primary pollutants involved. Predictive models help environmental scientists and governments determine where and when pollution might be a problem. Nonrenewable Energy Sources 6 Energy use has changed over time with the appearance of different technologies. The United States and the rest of the developed world have moved from a heavy reliance on wood and coal to mostly fossil fuels and nuclear power, whereas the developing world still relies largely on biomass. Different sources of energy are suited for different activities. 6 Energy efficiency, the amount of usable work that can be obtained from a given input of energy, can be broken down into three different types. To determine how efficient a particular device is, we must compare its thermal, machine, and system efficiencies. In general, the energy source that entails the fewest conversions from its original form to the end use will likely be the most efficient. Though multi- 2024–2025 Science Resource Guide Revised Page July 16, 2024 193  passenger transportation is the most energy-efficient way to travel, in the United States the single- passenger vehicle is most popular. 6 Electricity-generating power plants convert the chemical potential energy of fuel into electrical potential energy (electricity). Coal, oil, natural gas, and nuclear power are the most common energy sources for generating electricity. The power grid ties electricity-generating plants together over defined regions. 6 Coal is a very dense fossil fuel that is a good source for efficient electricity generation. Deep-shaft coal mining has serious health and safety consequences and leaves toxic slag piles in the environment. Surface mining can remove whole mountain tops and contaminate nearby waterways. Coal combustion is a major source of air pollution. 6 Petroleum includes both crude oil and natural gas. Oil is currently the greatest energy source in the United States, used primarily for transportation. It produces significant air pollution as well as greenhouse gas, and oil spills are a major hazard to organisms and habitats. Oil extraction in various parts of the world has led to environmental justice issues. Natural gas (methane), the fuel of choice for cooking and heating, does not produce particulate air pollution, but it is a major GHG. 6 Nuclear power is a relatively clean means of electricity generation, though fossil fuels are used in constructing nuclear power plants and mining uranium. The major environmental hazards of nuclear power are accidents and radioactive waste. The fuel used in a nuclear plant will remain radioactive for as long as 100,000 years; disposing of it is currently a political as well as environmental issue. 6 Total energy consumption in the United States is projected to increase in the future, while the country’s Seven Lakes High School - Katy, TX fossil fuel reserves are shrinking, indicating that the existing energy program in the U.S. is not sustainable. Renewable Energy Sources 6 Sustainable energy is energy consumed at a level that will allow an adequate supply to remain for future generations and at the same time does as little direct damage to the environment as possible. Renewable energy is created continuously from perpetual sources such as the Sun and wind and will always be available. 6 The Sun is the ultimate source of most energy on Earth. Direct solar energy is the energy from the Sun’s rays striking the Earth directly, or the solar constant. The Sun is also responsible for causing winds and promoting the hydrologic cycle, which are thus indirect forms of solar energy. Passive solar refers to the collection of solar energy without an intermediate technology such as a pump or blower, as in a solar cooker. Active solar utilizes mechanical devices, such as photovoltaic cells, to harness or transfer the energy to useable forms of heat or electricity. 6 The kinetic energy of wind is converted to potential energy in electricity. Wind power is the fastest growing source of electricity in the world. Large wind turbines are frequently grouped in wind farms or offshore wind parks. Wind is a very clean form of energy, though some people object to wind turbines largely on aesthetic grounds. 6 Biomass energy, the potential energy contained in organic matter, is one of the major forms of energy in the developing world but is also used in developed countries. The carbon produced by the burning of biomass does not add appreciably to atmospheric CO2 levels because it is modern, rather than fossil, carbon. Wood and wood byproducts, dung, municipal solid waste, ethanol, and biodiesel are all biomass energy sources. Wood is potentially renewable because if managed correctly, it can be a continuous source of biomass energy. 6 The kinetic energy of water can be harnessed to generate electricity. Run-of-the-river hydroelectric power uses little or no water impoundment. More common are larger dammed hydro systems. 6 Heat from deep in the Earth produces geothermal energy. This energy is used to generate electricity. Hydropower is one of the cleanest forms of energy, as fossil fuels are used only in construction and 2024–2025 Science Resource Guide Revised Page July 16, 2024 194  maintenance of the facilities; but hydropower facilities impact the environment by flooding or otherwise disrupting ecosystems. Tidal energy is derived from the twice-daily movement of water along coastlines. 6 Though many scenarios have been predicted for the world’s energy future, conservation—the reduction in energy demand—and increasing energy efficiency—the use of less energy to do the same amount of work—as well as new technologies will be necessary for energy sustainability. Global Climate Change 6 Changes to Earth’s biogeochemical, climatic, and biological systems are interconnected. Global warming and climate change are subsets of overall global change. 6 Radiant solar energy of differing wavelengths reaches Earth, where energy is absorbed and radiated back. In the Sun–Earth heating system, if the solar radiation reaching Earth is greater than the sum of the solar energy reflected back and the energy radiated by Earth, Earth becomes warmer. The greenhouse effect is a natural process that leads to the warming of an area underneath something that traps heat. On Earth, heat can be trapped by a number of greenhouse gases, the most common of which is water vapor. Radiative forcing—the radiation and absorption of energy by greenhouse gases—forces a change in Earth’s energy balance. The impact of each GHG is measured by its relative GHG efficiency, which depends in part on the concentration of other GHGs in the atmosphere. CO2 is the greatest contributor to total anthropogenic radiative forcing because of its high concentration in the atmosphere. 6 Global warming is the increased warming of Earth’s atmosphere due to an increase in gases that trap heat—in particular, warming caused by human activity. Because of the scarcity of direct temperature Seven Lakes High School - Katy, TX measurements over historical time (more than 140 years), evidence of the warming of Earth is based largely on surrogate indicators. Models are used to predict future warming on the basis of past trends. 6 Natural causes of global warming include volcanoes, denitrification, and evaporation from all sources of water on Earth. Currently, anthropogenic causes of global warming are of more concern than natural causes because they are increasing over a much shorter time scale and are of a greater magnitude. 6 Burning of fossil fuels is the greatest anthropogenic source of global warming, adding new carbon to the carbon cycle and thus increasing the amount of CO2 in the atmosphere. Other anthropogenic causes include deforestation that is not balanced by replanting and, to a lesser extent, certain agricultural practices and biomass burning. Developed countries are by far the largest contributors to global warming. 6 Global warming affects all environmental and human systems through three interconnected feedback cycles. Global average temperature has increased over the past hundred years to a level which is enough to affect natural processes significantly. Predicted future effects include weather and climate changes; disruption of natural ecosystem processes; loss of biodiversity; and health, social, and economic problems for humans. 2024–2025 Science Resource Guide Revised Page July 16, 2024 195