BioChapter7.docx

Can Cambodia heed a warning from history? Phenomenon Silently, a fishing canoe leaves a floating house on the Cambodian lake called Tonie Sap In southeast Asia. Its target? The same fishes, from the same lake that fed the ancient Khmer Empire and its capital Angkor a thousand years ago. But that f...

Can Cambodia heed a warning from history? Phenomenon Silently, a fishing canoe leaves a floating house on the Cambodian lake called Tonie Sap In southeast Asia. Its target? The same fishes, from the same lake that fed the ancient Khmer Empire and its capital Angkor a thousand years ago. But that fishery, which was productive for hundreds of years, is in danger of collapse today ... for some of the same reasons that led to the fall of Angkor and the Khmer empire, centuries ago. What kind of trouble is the fishery in? That floating house isn't in trouble. It always floats during the rainy season, when Tonie Sap is in flood stage. Local residents welcome the annual rains, which cause the lake to expand to five times its dry-season size, flooding sur­ rounding wetlands and forest. Nutrients in the floodwaters power the aquatic food chain and enrich wetlands and forests. This complex ecosystem is home to an incredible diversity of fishes-lots of them! More than 350,000,000 kilograms of fish are harvested each year. This incredibly productive inland fishery, has been feeding millions of people globally. But Tonie Sap is in trouble. Fish catches are dropping. While some people move to the area to fish or farm, others move to cities for jobs as fish disappear. Land around the lake is being converted from forest to rice paddies. Many fishes feed and breed in the seasonally flooded forest, so cutting them removes vital habitat. Hydroelectric dams are planned for rivers that flow into Tonie Sap, because most people in the region have no electricity. But in addition to interfering with water and sediment flow, dams would block migrating fishes. Climate change adds to these stresses, creating what investigator Les Kaufman and his colleagues know that history offers reason to worry that all these changes could cause an ecological disaster. Not far from Tonie Sap lie the ruins of Angkor. Once housing more than a million people, Angkor was the largest city in the preindus­ trial world. Today the city lies in ruins, except for its famous temples. Some temples are decorated with carvings of fishes, offering evidence that Angkor depended on Tonie Sap for food. Then, about 600 years ago, Angkor was abandoned. What happened to Angkor back then? Could it happen again now? Tonie Sap is an example of the challenge of providing three basic human needs: water, food, and energy. Kaufman and his colleagues are gathering data and creating sophisticated models that combine ecological and socioeconomic data. The models predict possible futures for the ecosystem under different regional develop­ ment plans. Some of these projections show possibilities of ecosystem collapse. How might planners avoid those outcomes? What would the warning signs be? How could a model guide planning? How do ecological footprints of typical Americans compare to the global average? What is the Anthropocene? How do human and nonhuman causes of change affect Earth's systems? An astronaut's view of Earth as an island of life in empty space fit well with the term "spaceship Earth." Until recently, we could think of ourselves simply as passengers on our planetary spaceship. Why? Because we thought global systems worked like a spaceship's life­ support systems. We knew that human activity had affected local ecosystems. But we thought global systems were too big for us to change and would function regardless of we did. We were wrong. Humanity's Global Impact Why were we wrong? How can we wrap our heads around the fact that human activity is causing significant changes in several global systems? The Understanding Global Change model we've been building can help. But first we need to understand how, and why, each of us impacts the environment, and how the size of our global population and technology amplify that impact. Ecological Footprints Let's start with what ecologists call your ecological footprint. Your ecological footprint is the total area of healthy­ land and water ecosystems needed to provide the resources you use, and to absorb wastes you produce. As Figure 7-1 shows, your footprint includes all the resources that enable you to live as you do. Energy is used for transportation, as well as to heat our homes. Growing food requires land and fresh water. Everything you buy-from clothes to cell phones-is produced using energy and materials that come from somewhere. You also produce wastes including sewage, trash, and greenhouse gases Your ecological footprint includes both land and water areas affected by all the resources you use and the waste that you create. National and Global Ecological Footprints There is no universally accepted formula for calculating ecological footprints. Still, we can make useful comparisons among footprints of people in different countries, as shown in Figure 7-2. To determine a country's ecological footprint, researchers calculate the footprint of a typical citizen and .multiply that by the size of the population. According to some calculations, the average American has an ecological footprint roughly three times larger than the global average. An average American uses almost twice the resources of an average person in England, more than twice the resources used by an aver­ age person in Japan, and almost six times the resources used by an average person in China. Now think, not just about your foot­ print, but about the footprints of nearly 9 billion people together. That incredible amount of human activity is what drives changes in global systems. Describe What is one way to calculate the ecological footprint of a country? Calculating Ecological Footprint Problem How can you calculate your use of natural resources? In this lab, you will determine what your ecological footprint is regarding three types of natural resources: water, land, and fossil fuels. Then, you will explore ways to effectively reduce your eco­ logical footprint in one of these areas. You can find this lab in your digital course. The Age of Humans Humans have affected local environments for a long time. Ancient civilizations in China, Southeast Asia, Central America and South America cut down vast forests to build cities and farms. Even the most remote parts of the Amazon basin were changed by human activity long ago. But that was all "local stuff." Our effects on global systems started growing more rapidly during Europe's Industrial Revolution in the 1800s. That's when a series of brilliant inventions· harnessed fossil fuels to power machinery. Railroads and other forms of transportation connected cities around the globe. Mass production began and spread. And that was just the beginning of the change. The Great Acceleration The greatest change in humanity's relationship with Earth began during "The Great Acceleration" in the 1950s. What was accelerating? Just about everything related to humanity and our impact on the environment, as shown in Figure 7-3. Humans burned more fossil fuels. We farmed more land enriched with more fertilizers and we caught more fish, so we could feed more people. Medical discoveries saved millions of lives. Within a single lifetime, the well-being of millions of people improved dramatically. Death rates fell worldwide. Birth rates stayed high, so global population grew rapidly. Advancing technol­ ogy was used by more people, multiplying our impact on local and global systems. The Great Acceleration Starting around the 1950s, the pace at which human activity affected Earth's resources skyrocketed. The Anthropocene Global systems are driven by geological, chemical, and physical processes, along with biological processes such as photosynthesis and respiration. At first, human activity was a small part of those biological processes. Today, human activities drive measurable changes in several global systems. We have altered roughly three quarters of all land outside polar regions and mountain ranges, as shown in Figure 7-4. We move more sediment and rock every year than is moved by erosion and all the world's rivers. We've dramatically altered the global nitrogen cycle by fixing and distribut­ ing vast quantities of nitrogen for fertilizer. By burning fossil fuels, and through other activities, we've increased greenhouse gases to concentrations higher than Earth has seen for more than a million years. Given the scale of those activities, and given how quickly they've accelerated, how could anyone imagine that we're not affect­ ing global systems? As we discuss global effects of human activity, remember that human causes of global change occupy a larger part of our model's outer ring than non-human causes. Given our new role as a the most powerful source of global change, many scientists call the time period we're living in the Anthropocene. The Anthropocene, or "age of humans," is the period during which human activity has become the major cause of global change. How do the east and west coast anthromes differ from those anthromes found in the central part of the United States Understanding and Modeling Global Change The Great Acceleration "promoted" us from passengers on space­ ship Earth to ,,crew." There's just one problem. We've grabbed the controls-but don't know how they work! We need to write an operating.manual ourselves now ... and quickly! How do we begin? To plan for humanity's future, we need to understand the best available scientific data on how Earth systems work, and to build a model'that shows how both human and nonhuman causes of change are affecting those systems. The full Understanding Global Change model (UGC), is shown in Figure 7-5. Imagine that this graphic represents spaceship Earth's "control panel." Pushing "buttons" in the outer ring is like hitting an accelerator, stepping on a brake, or turning a steering wheel. Each action affects earth systems in the middle ring and causes measurable changes in the inner circle. Thinking about the model this way will help you make cause-and-effect connections among phenomena, and better understand the impacts of human activities on natural systems. Global system processes and phenomena occur in the hydro­ sphere, atmosphere, geosphere, biosphere, and across two or more of those "spheres." This model includes most of what some scien­ tists call the cryosphere ("frozen" sphere) within the hydrosphere. Biogeochemical cycles and other global system processes occupy the model's middle ring. Plant and animal populations, communities, ecosystems, and their interactions with global systems are also in that middle ring, mainly in the biosphere. Causes of global change that affect those systems are in the outer ring, with nonhuman causes in the lower portion, and human causes in the upper portion. Measurable changes in Earth systems that are produced when causes of change affect those systems are in Earth systems that are produced when causes of change affect those systems in the model's inner circle. What kinds of resources make up your ecological footprint? Why are some scientists using the name Anthropocene to describe the current time period? Give one example of a human and nonhuman change that affects Earth's systems. CRITICAL THINKING SEP Cite Evidence What evidence supports the argument that human activities are causing major changes to global systems? Use an Analogy Buckminster Fuller compared Earth to a spaceship. During the period called the Great Acceleration, what changes affected the spaceship analogy? SEP Design a Solution Which part of your eco­ logical footprint could be reduced most signifi­ cantly? Describe a method for reducing it. 7.2 Anthropogenic Global Change and its effects How do human activities change the atmosphere and climate? How do changes in the atmosphere drive climate change and other changes in global systems? How do the ways we use land drive change in global systems? How do humans directly effect populations? What kinds of pollutants are drivers of global change? Global change can be driven by both human and non-human processes. Most non-human causes of change operate very slowly, on timescales of thousands to millions of years. Today, human causes of change affect global systems more rapidly, producing measurable changes on time scales as short as years or decades. Some human causes of change are now more powerful than non-human causes of change. Human Causes of Global Change Humanity's total ecological footprint includes activities that affect global systems and drive measurable changes in those systems. Human activities affect global systems by changing the com­ position of the atmosphere in ways that change climate and ocean chemistry, by changing the way we use land, by over­ harvesting some species, by introducing species to new envi­ ronments, and by producing pollutants and wastes that include plastics. These actions create stress on organisms and ecosystems that threatens biodiversity and ecosystem services. Stress caused by all human activities together is much more powerful than the stress caused by any singTe activity. In addition, a single activity, such as converting biomes to anthromes or burning fossil fuels, can affect several global systems. As we discuss each of these activities, keep referring back to Fig re 7-5 to see how it fits into the UGC model. Changing the Atmosphere Human activity is changing Earth's atmosphere faster than it has changed over the entire history of life. Some activities raise con­ centrations of greenhouse gases, driving climate change. Other activities release different gases, causing other effects on global systems. Burning Fossil Fuels Quantitative data confirm two scientific facts. These are that atmospheric carbon dioxide concentrations have been increasing since the Industrial Revolution, and that cur­ rent concentrations are higher than they have been for more than a million years. Other data confirm that most of that "extra" carbon dioxide is released by-burning fossil fuels. Burning fossil fuels also releases several forms of nitrogen that can travel over long distances through the air in dry form as tiny particles or dissolved in water droplets. Because nitrogen is a limiting nutrient for primary produc­ ers in some environments, nitrogen enrichment from burning fossil fuels can affect growth of land plants or cause algal blooms Climate Change Climate change is defined as measurable long­ term changes in averages of temperature, clouds, winds, precipita­ tion, and frequency of extreme weather events such as droughts, floods, major storms, and heat waves. Recall from Chapter 3 that the climate system is powered by the total amount of heat retained within the atmosphere and is shaped by the distribution of heat between the equator and the poles. Higher concentrations of green­ house gases, such as carbon dioxide and methane, trap more heat in the biosphere and cause global warming, which drives climate change. Global warming is the increase in average global tempera­ tures. Changes in the glob I distribution of heat affect winds, ocean currents, and other parts of the global climate system in ways that change patterns of precipitation and other environmental factors. Now recall that organisms have tolerance ranges for environ­ mental conditions. If climate change alters environmental conditions beyond organisms' tolerance ranges, they must adapt, move to more suitable areas, or face extinction. For similar reasons, climate change has major impacts on agriculture. Crop plants have tolerance ranges too. So, if an area gets warmer and drier, crops that grow well in a particular place now may not grow well there in the future. Increasing temperatures also affect marine life. You will learn more about cli­ mate change and its effects in the next lesson How Does Acid Affect Shells? Vinegar is a solution of acetic acid. Mix vinegar and water in 5 beakers. Put only water in one beaker, only vinegar in another beaker, and mixtures of varying concentrations iR the other beakers. Label each beaker with its contents and the concentration of vinegar {if appropriate). Place 6 tb 10 crushed pieces of egg shells in each beaker. Wait one day. Then pour out the liquid from each beaker, and place the egg shell pieces on a paper towel. Examine the egg shell pieces. Observe How did vinegar - affect the egg shell pieces? Make a chart to record your observations. Draw Conclusions Egg shells are made of cal­ cium carbonate. How could ocean acidification affect corals, lobsters, snails, and other marine organisms that also have skeletons or shells made of calcium carbonate? Construct an Argument How could ocean acidi­ fication become a severe problem? Use evidence and logical reasoning to support your answer. Acid Rain Burning fossil fuels also releases sulfur dioxide (S20) and nitrous oxides (N20) that dissolve in fog or raindrops to form sulfuric acid and nitric acid. This creates acid rain, fog, and snow. Combined with other airborne pollutants, acid rain damages plant leaves and harms roots by releasing aluminum and other metals from some soils. Soil acidification can also interfere with bacterial qecay, altering nutrient cycling. Acid rain can also cause acidification of fresh water that kills aquatic organisms from algae to fishes Ocean Acidification Researchers have compared the amount of carbon dioxide accumulating in the atmosphere to the amount released by burning fossil fuels. They found that atmospheric car­ bon dioxide was not increasing as much as expected, given the, amount of emissions. Where was the "missing" carbon dioxide? In the oceans! As carbon dioxide concentration in the atmosphere increases, more and more of it dissolves in seawater. There, the extra dissolved carbon dioxide drives a chemical reaction that produces an acid, as shown in Figure 7-6. Ocean acidification poses serious prob­ lems for marine life. Many marine organisms, from plankton to corals and shellfish, remove calcium carbonate from seawater to build their skeletons. As seawater becomes more acidic, these organisms expend more energy to build those skeletons, stressing many marine organisms and ecosystems. How does excess carbon dioxide affect marine organisms? Ocean Acidification Many marine organisms-such as plankton, cora!, marine snails and slugs, and shellfish-build skeletons from calcium carbon­ ate. Carbon dioxide dissolves in seawater to form carbonic acid. Both the decrease in pH and the consumption of carbonate ions harm marine life. Agriculture and the Atmosphere Agriculture is one of the most important and widespread human activities, so it isn't surprising that it affects the atmosphere. Cattle farming and cultivation of rice in flooded paddies release methane, a more·powerful greenhouse gas than carbon dioxicrle. Methane (CHJ contributes to global warm­ ing and climate change. Changes in Land Use It takes a lot of land to provide housing, food, and energy for nearly nine billion people! Human activity has transformed roughly three-quarters of Earth's land surface in several ways and for several reasons. These include agriculture, monoculture, deforestation, and development. Agriculture The dependable food supply provided by agriculture was a key element in fueling the growth of civilization. During the Great Acceleration, agriculture went through changes in technology and farming techniques called the "Green Revolution." The Green Revolution enabled farmers to dramatically increase crop yields to feed the world's growing population. Today, agricultural activities cover more of Earth's land surface than any other human activity. Another key part of the Green Revolution was the use of chemical fertilizers containing nitrogen and other nutrients. High-nitrogen fertil­ izers are produced by industrial processes that fix atmospheric nitro­ gen. This added nitrogen fueled the Green Revolution and helped increase food production. Today, fertilizer manufacture and applica­ tion has more than doubled the amount of biologically active nitro­ gen cycling through the biosphere, dramatically changing the natural nitrogen cycle. Lots of nitrogen "leaks" out of agriculture in soil water runoff. Excess nitrogen in streams and rivers can upset the balance in freshwater and ,marine ecosystems, as shown in Figure 7-7. Monoculture One key part of the Green Revolution was a strategy called monoculture, which involves planting large areas with a single highly productive crop year after year. Monoculture enables efficient sowing, tending, and harvesting using machines. These techniques dramatically increa ed crop yields. But large-scale monoculture requires lots of artificial fertilizers and pesticides. When large areas are used for grazing, or to grow monocultures for long periods, fertilizers and pesticides can change soil structure and microbiomes in ways that degrade soil and prevent secondary succession. Deforestation/Reforestation Healthy forests hold soil in place, protecting the quality of freshwater supplies, absorbing carbon dioxide, and moderating local climate. When forests are lost, those ecosystem services disappear. Deforestation It's hard to appreciate how much deforestation, or cutting of forests, has altered natural environments. Most of us live in anthromes that haven't been in a natural state for a long time, as Figure 7-8 shows. Between 1620 and 1920, roughly 90 percent of the forests that covered the continental United States were cut for lumber, farming, or both. Deforestation can affect water quality in streams and rivers by altering clarity, taste, and odor. In moun­ tainous areas, deforestation increases soil erosion, which can cause landslides. Deforestation often divides natural ecosystems into frag­ ments, which can cause loss of biodiversity. Natural Regrowth Through Succession Almost anywhere in the United States, east of the Mississippi River, today's forests are secondary forests that grew back after primary forests were cut. This regrowth is possible in the southeast because logged areas can undergo secondary succession. In tropical rain forests, topsoil is thin, and organic matter decomposes rapidly. If small areas are cleared and left alone, secondary succession can occur and restore biodiversity. If large areas are cleared and used for agriculture for more than a short time, regrowth may not be possible. Reforestation Scientifically guided reforestation, or replanting of forests, can replace trees that have been cut. Reforestation efforts by local communities around the world are bringing back forests and restoring ecosystem services. Figure 7-9 shows reforestation work by a local Mayan community in Totonicapan, Guatemala, where deforestation had caused local streams and springs to dry up. Those water sources are now returning and supplying clean drinking water. Development/Urbanization As modern societies develop, many people move to cities and to suburbs. Roughly two-thirds of Americans live in urban areas today, and migration to cities is increasing in devel­ oping countries around the world. These dense human communities produce large amounts of wastes. If these wastes are not disposed of properly, they affect air, water, and soil resources. Development also consumes farmland and divides natural habitats into fragments. One result of urbanization has been an increase in production of sewage, which includes everything you flush down the toilet or the drain. In some cities, sewage includes runoff from roofs, sidewalks, and streets. Sewage isn't always poisonous, but it does contain lots of nitrogen and phosphorus, as well as drugs and hormones that can affect aquatic organisms. Reasonable amounts of these nutrients can be processed and absorbed by healthy ecosystems. But large amounts of sewage can disrupt nutrient cycles and stimulate the growth of toxic or ecologically damaging blooms of bacteria and algae. Raw sewage also contains microorganisms that can spread disease. Habitat Loss, Fragmentation, and Restoration Human­ caused changes in natural habitats can occur in a number of ways and for several reasons. As discussed in Chapter 6, these include habitat loss, habitat fragmentation, and habitat restoration,. The noun fragment means "a small broken-off piece." The verb fragment means "to break or cause to break into fragments." The noun frag­ mentation refers to the action of breaking up or being broken up. What is the relationship between habitat size and the number of species that can live there? Direct Human Effects on Populations In addition to activities that indirectly affect plant and animal .popu­ lations, humans have directly interacted with wild species for many centuries. Humans have hunted some terrestrial animals extinction, have overfished both fresh and saltwater species, and have introduced invasive species into new habitats. Hunting and Fishing Hunting animals for food has been an important part of human culture for thousands of years. When human populations were small, and when hunting served mainly to pro- vide food, our ancestors' actions had relatively limited effects. But as our population has grown, and as technologies used in hu t- ing and fishing have become more sophisticated, these activities have threatened many species with extinction. In addition, many animals are killed in large numbers for sport, for hides, feathers, ivory, or body parts believed to have medicinal properties. Illegal trophy hunting threatens many species, including rhinos, gorillas and elephants. Overfishing is causing dramatic declines in fish popula­ tions worldwide. In the United States, endangered species on land, and in both freshwater and saltwater habitats, are protected from hunting and fishing. The Convention on International Trade in Endangered Species {CITES) bans international trade in products from endan­ gered species, but it's difficult to enforce laws in remote areas. Invasive Species Recall that organisms introduced to new habitats where they lack predators and parasites can experience exponential population growth and become invasive species. An invasive species is any nonnative species whose introduction causes, or is likely to cause, economic harm, environmental harm, or harm to human health. Some invasive animal species eat animals, while oth­ ers become parasites on native plants or crops. Invasive species of both plants and animals may compete with native species for limited resources, including water, space, food or nutrients, and sunlight. Any of these interactions can drive native species to extinction, and disrupt ecosystem services. Most invasive species are carried to new habitats by human trade and travel. Sometimes, invasives are introduced by accident, as "stowaways" in fruits, vegetables, or plants. Other times,,they have been introduced intentionally, without understanding the problems they can cause. Ecological problems caused by invasive species around the world have grown to the point where they are included as drivers of global change. There are roughly 3000 invasive species in the United States, with over 200 in the San Francisco area alone. Figure 7-10 show some examples of invasive species in California. How do invasive species threaten biodiversity? Invasive Species Three invasive species that are common in California include the northern water snake; ailanthus trees, and the brown marmorated stink bug. Pollution A pollutant is any harmful material created by human activity and released into the environment. Many pollutants threaten biodiversity. Certain kinds of pollution that were once considered "local prob­ lems" are now known to have global effects. Air pollution is a serious problem in California, which has been ranked as the state with the worst air quality in the country. This situation has led the California to create one of the most aggressive anti-pollution efforts in the nation. Common forms of air pollution include smog, greenhouse gases, heavy metals, and aerosols. Primary sources of water pol­ lution are industrial and agricultural chemicals, residential sew­ age, and nonpoint sources. Roughly one million Californians around the state lack access to safe drinking water. Notice how pollutants fit into the Understanding Global Change model. CFCs and Stratospheric Ozone, Chlorofluorocarbons (CFCs) are industrially produced gases. CFCs belong to a group of chemicals containing chlorine or fluorine and are known as halogens. CFCs once were widely used as propellants in aerosol cans and fire extinguishers, as coolants in refrigerators and air conditioners, and in the produc­ tion of plastic foams. A few decades ago, the use of CFCs was tied to the destruction of ozone in a section of the upper atmosphere called the stratosphere. This high-level ozone, called the ozone layer, absorbs ultraviolet light, acting like a global sunscreen. Beginning in the 1970s, satellite data revealed that the ozone concentration over Antarctica was decreasing, as shown in Figure 7-11. The area of lower ozone concentration was called an "ozone hole." For several years after the hole was discovered, ozone concentrations continued to drop, and the hole grew larger and lasted longer every year Ozone Hole In these satellite images, the size and intensity of the blue region increased from 1981 to 1999, indicating a thinning of the ozone layer over Antarctica. The graph shows how the levels of atmospheric halogens have decreased since legisla­ tion was passed to ban CFCs No one could explain this phenomenon until three research- ers made a breakthrough that earned them a Nobel Prize. In 1974, researchers demonstrated that CFCs act as catalysts to destroy ozone molecules under conditions in the upper atmosphere. This research led to hypotheses that were tested in several ways. Research flights over the poles gathered data demonstrating that CFCs combine with ice crystals in frigid air in a way that allows ' sunlight to destroy ozone. Once this research was published and accepted by the scientific community, the rest was up to policymak­ ers and industry-as you will learn later in this chapter. Ground-Level Ozone Ozone in the upper atmosphere is a good thing for us, but not at ground level. If you live in a large city in California, you've undoubtedly seen smog, a gray-brown haze formed by chemical reactions among pollutants released by industrial processes and automobile exhaust.' Smog in Los Angeles is shown in Figure 7-12. Ozone is one product of these reactions. Ozone and other pollutants at ground level threaten human health, especially for people with respiratory conditions. In 2017, Los Angeles, Long Beach, Bakersfield, and Fresno-Madera had the worst smog levels in the country. In response, California has become a national leader in improving automobile emission standards and clean-air regulations. Air quality has improved, but still has a long way to go. Industrial and Agricultural Pollution Industry, science, and technology provide us with the conveniences of modern life. Lots of energy is used to produce and power these conveniences. We pro­ duce most of this energy by burning fossil fuels that release green­ house gases and other pollutants. Since the Industrial Revolution, many industries have discarded wastes from manufacturing and energy production into air, water, and soil. Largescale monoculture increased the use of pesticides and insecticides. These chemicals can enter the water supply in the form of runoff after heavy rains, or they can seep directly into groundwater. This type of pollution is called nonpoint source pollution. Air quality problems in the Bakersfield <!rea are produced by a combination of industrial activity and agricultural production Biological Magnification In the process of biological magnification, the concentration of a pollutant like DDT-represented by the orange dots-is multiplied as it passes up the food chain from producers to consumers. Biological Magnification Living systems can absorb and concentrate these chemicals and pollcitants in a process called biological magnification. Biological magnification occurs when certain pollut­ ants are picked up by organisms and are not broken down or eliminated. Instead, they collect in body tissues. Primary producers can absorb pollutants, even if those pollut­ ants are present in very low concentrations. Herbivores that eat those producers store the pollutant and concentrate it. When carnivores eat herbivores, pollutants are further concentrated. In the highest trophic levels, pollutant concentrations may reach 10 million times their original concentration in the environment, as shown in Figure 7-13. These high concentrations can cause serious problems for wildlife and humans DDT One of the first widely-used pes­ ticides, DDT, is cheap, long-lasting, and effective at controlling agricultural pests and disease-carrying mosquitoes. When DDT gets into a water supply, the DDT is concentrated by biological magnification and can have disastrous effects. Widespread DDT use in the 1950s threatened fish-eating birds like pelicans, osprey, falcons, and bald eagles. DDT acts like a hormone mimick- ing estrogen which caused birds to lay eggs with thin, fragile shells, reducing hatching rates and causing a decrease in bird popula­ tions. Since DDT was banned in the 1970s, bird populations have been recovering. PCBs One industrial water pollutant is a class of toxic organic chemicals called PCBs (polychlorinated biphenyls}, which were widely used in industry until the 1970s. PCBs, are odorless and tasteless, but they persist in the environment and accumulate in food webs through biological magnification. PCBs have been banned, but they can enter mud and sand, whic;h makes them difficult, if not impossible to eliminate. According to California's Office of Environmental Health Hazard Assessment, high levels of PCBs have been found in some species of fish from San Francisco to San Diego. Fish advisories for affected fishing spots are available online and in places that sell fishing licenses. Heavy Metals Other harmful industrial pollutants include heavy metals like arsenic, cadmium, lead, mercury, and zinc. Heavy met­ als also accumulate in food webs and pose health threats. Mercury, for example, accumulates in certain marine fishes such as tuna and swordfish. Even at low concentrations, mercury and lead can cause neurological problems in young children and adults. In parts of California, arsenic occurs naturally in soils and groundwater. Arsenic has been reported in drinking water in numerous places, particularly in and around the San Joaquin Valley. Several California state agen­ cies provide information on arsenic in drinking water. Although lead levels around the country could still be improved, the current situation demonstrates the positive effects of scientifi­ cally informed environmental legislation. At one time, all gasoline was enriched with lead. But as leaded gasoline burned, lead was released in exhaust fumes and washed onto land and into rivers and streams. U.S. efforts to phase out leaded gasoline started in 19 3 and were completed in 1996, when the sale of leaded gasoline was banned. Now that unleaded gasoline is used widely, lead levels in soils, rivers, and streams have dropped significantly, as shown in Figure 7-14. Paint also used to contain lead. In 1978, the use of lead­ based paint in homes was banned, but this is still a problem in some older homes. Why do human causes of global change occupy a larger portion of the global change model than nonhuman causes? What is the relationship between global warming and global climate change? Explain one way that land use by humans affects nutrient cycles. How does the introduction of invasive species impact populations? What kinds of harmful changes can pollution cause? SEP Use Models How does the Understanding Global Change model illustrate relationships between human activities and changes in Earth systems? SEP Design a Solution What is a possible solu­ tion for preventing the loss of biodiversity by habitat fragmentation? How is ocean water becoming more acidic? 7.3 Measuring and Responding to Climate Change What evidence supports the claims that the climate is changing? What do models show about climate change? What are some impacts of climate change? Mummified human bodies are peeking out of melting glaciers. One fellow, nicknamed Otzi, died about 5300 years ago in the Alps, and stayed frozen until rising temperatures melted ice above him. As Worldwatch Institute put it "Our ancestors are emerging from the ice with a message for us: Earth is getting warmer.".Dramatic announce­ ments get public attention. But scientists need data Climate Change: Data The most reliable climate data come from the Intergovernmental Panel on Climate Change (IPCC}, from the National Oceanic and Atmospheric Administration, (NOAA) and the National Aeronautics and Space Administration (NASA). IPCC data, analyses, models, and scientific consensus reports have been gathered, checked, and accepted by mq_re than 2500 climate scientists and all participating governments. Data from the IPCC, NASA, NOAA, and other sources, all confirm that "Human influence on the climate system is cleqr, and recent anthropogenic emissions of greenhouse gases are the highest in history." All these data show that the atmosphere and oceans are warming; that sea levels are rising; and that Arctic sea ice, glaciers, and snow cover are decreasing. Data also show that cur­ rent warming is greater, and occurring faster, than at any other time over the last 16,000-22,000 years. Warming is most intense in and near the Arctic Circle. Average temperatures in Alaska, for example, increased 2.4 deg°rees Celsius over the last 50 years. Some of these data, all of which fall into the "measurable changes" part of the UGC Model, are shown in Figure 7-15. It is important to remember that these numbers are not hypotheses. They are data, measured as with the best scientific equipment available. Climate Change: Models Computer models, based on accurate data, are vital in climate science. Researchers often compare or combine results of several models that are based on different kind of data, or that model the predictions of different assumptions about interactions among dif­ ferent possible causes of climate change. Modelers then compare the predictions of various models, and also compare the predictions of those models against existing records of temperature and other measurable changes. One way to test and compare climate models is to run them "backwards" into the past. This technique is known as hindcasting. The results of hindcasting using the best models match the historical record. Those models are then run "forwards" to pre­ dict future climate trends. Using models to predict the future is more familiar to you ... we call it forecasting. When the models whose hindcasts best match existing data are used to forecast future climate, they predict an increase in average global temperatures of between 0.3 and 1.7 degrees Celsius from 2000 to the end of the twenty- first century if all nations agree on very strong measures to curb greenhouse gas emissions. If emissions continue to increase as they have recently, those models predict that global temperatures could increase by as much as 2.6 and 4.8 degrees Celsius by the year 2100. Remember that non-human causes of climate change have oper­ ated throughout Earth's history. Can information from models be used to support or refute the hypothesis that human activity drives climate change today? Yes-by using the models in the way we have just described. In one test, researchers ran hindcasts of the most.widely accepted models two ways. One way included both human and non­ human causes of change, and the other way only non-hum n causes of change. As shown in Figure 7-16, models that include only non-human causes of change predict that Earth should be getting cooler, rather than warmer. Models with effects of human activity included predict the rising temperatures documented so far impacts on natural and human systems on all continents and across oceans.11 As you've learned, climate change includes more than just higher temperatures. Total precipitation and seasonal distribution of precipitation are changing. The frequency of extreme weather events, such as heat waves, droughts, and powerful storms, is expected to increase Increasing Temperatures Higher-than-normal tempera­ tures are shown in yellow and red. The highest above-normal temperatures (red) are concen­ trated in the Arctic region. The Jet Stream and Extreme Events Temperatures are increasing faster in the Arctic than in the temperate zone and trop­ ics, as shown in Figure 7-17. Recall that the global climate system is powered and shaped both by the total amount of heat retained by the atmosphere and by differences in temperatures between polar regions and warmer areas. As the North Pole warms more than the northern temperate zone, the difference in temperature between those air masses decreases. This temperature change affects both the speed and the behavior of the jet stream. These days, the jet stream often slows down, and loops southward much further than it used to as you can see in Figure 7-18. The frigid air that the jet stream normally "walls in" over the arctic extends much further south. This change can bring record cold temperatures to Florida, and can create conditions that worsen heat waves, droughts and floods in California Jet Stream The image on the left shows the normal jet stream pattern. The image on the right shows an extreme loop in the_jet stream that brings cooler polar air to the eastern seaboard of the United States. The extreme loop in the right image is occurring more frequently due to climate change, but is not permanent Ecological Impacts Remember that each organism's geographic range is determined by its tolerance to ranges in temperature, humidity, and rainfall. If conditions change beyond an organism's tol­ erance, the organism must adapt, move to a more suitable location, or face extinction. For example, if temperatures rise, organisms move away from the equator toward cooler places. They also move (if they can) from warm lowlands to cooler, higher altitudes. Some animals, like Pikas, may soon have no place to go, and may become extinct. Life cycles of many organisms are cued by seasonal changes in both daytime and nighttir:!)e temperatures. These clues include plant flowering, animal breeding, and migration. As warming occurs, organisms respond as though spring begins earlier. Studies of more than 1700 plant and animal species confirm that plants are flower­ ing earlier, and animals are breeding earlier ... which makes sense if they are sensing rising temperatures. Unfortunately, climate change by itself threatens many species with extinction, locally and globally. Adding climate change to other human-caused changes in ecosys­ tems and global systems, puts many more organisms, and some entire ecosystems, at risk. Agricultural Impacts Changes in temperature are already negatively affecting yields of corn and wheat in some places. Water availability is also changing in many areas. F r example, average winter snowpack in the Cascades and Sierra Nevada is decreasing. Snow is melting earlier in the spring. Many farmers in California depend on water stored in this snowpack and the timing of sum­ mer melt. Less water available during summer spells trouble for farmers ... and others. Sea Level Rise Climate change is causing sea level to rise at an average rate of 1.8 millimeters a year since 1961. This increase has two causes. Melting ice from gla­ ciers and polar ice caps add water to the oceans. In addition a lot of the extra heat retained by the atmosphere is absorbed by the oceans. As ocean water warms, it expands slightly. This expansion might not seem to matter much. But when you recall that some ocean basins have a depth of a mile or more, even a small amount of expansion in that amount of water affects sea level. Figure 7-19 shows how low-lying areas in the San Francisco Bay area would be affected by a 1-meter rise in sea level. Climate Change Challenge Of all ecological challenges humanity has faced, climate change is the most complicated and difficult to fix. The world depends heavily on fossil fuels and agriculture that produces methane. It will be tough to find solutions that work. Hopefully, governments will let science inform decisions on this global issue. KEY QUESTIONS How does the climate change that scientists are observing now compare with climate change in the past? How has climate change affected plant and animal species on Earth? What actions have scientists already taken to help society address global climate change? What actions should be taken next? CRITICAL THINKING SEP Use Models According to the climate mod­ els that scientists have developed, what variable will most affect the average increase in global temperature this century? Construct an Explanation How can increasing temperatures in polar regions affect climate all across Earth? 7.4 Modeling Sustainability, Resilience, and Adaption What criteria can be used to evaluate whether development is sustainable? What are complex ecosystems? Ecology can model ecosystems and their responses to disturbances. Innovation can help minimize negative impacts. But just thinking "we'll figure it out" isn't enough. Banks, corporations, and govern­ ments have often ignored ecology when making investments. Those institutions have ignored ecosystem services when calculating how economies function. But recent studies note that global ecosys- tem services are worth more than four times the total value of all the world's economies! So the value of "natural capital" must be included in development plans. Cutting down forests might increase short-term cash flow. But what if removing forests damages water supplies? Sooner or later, "ecological debt" comes due. Sustainable Development I What happens if the stress and damage to ecosystems that we call ecological debt becomes too large? Damaged ecosystems can change their structure and function in ways that cause a loss of. essential ecosystem services. If that happens, local human popula­ tions can be in serious trouble. They may run out of clean drinking water, or soil on their farms may no long_er grow crops. One strategy for avoiding loss of ecosystem services is called sustainable develop­ ment. Sustainable development should provide for human needs while preserving ecosystem services. Sustainable development should cause no long-term harm to soil, water, and climate. This development should consume as little nonrenewable energy and resources as possible. Finally, sustainable development must take into account human needs and economic systems. Working towards those goals, ecologists envision sustainable development as three nested spheres: Global life-support, society, and the economy. Renewable Resources Renewable resources can be produced or replaced by healthy ecosystems. Drinking water can be a renew­ able resource, filtered by ecosystems as part of the water cycle. But if forests and soils are degraded, cities and towns must pay for treatment to provide safe drinking water. Electricity from solar power or wind farms, shown in Figure 7-21, are also forms of renewable energy resources. Nonrenewable Resources Resources that natural processes can't replenish are called nonrenewable resources. Fossil fuels such as coal, oil, and natural gas are nonrenewable resources. Some resources, such as fisheries or forests, can be renewable if managed properly, but can be nonrenewable if mismanaged. Innovation Innovations can offer new ways to provide sustainable service at reasonable cost. Solar electricity generation was technically possible decades ago, but was very expensive. Since then, engineer­ ing and manufacturing innovations dramatically lowered the price of solar panels, which are now installed on many homes and com­ mercial buildings. But innovation won't solve long-term ecological problems, unless it is guided by sustainable goals. How should those goals be developed? Economy and Human Needs To be truly sustainable, development must do more than just enable people to survive. Participants in sustainable development need opportunities to use both innovation and changes in local economies that imprqve their standard of living. As an example, how many household members in Tonie Sap need to fish in order to support a family? Would that number change if they catch different kinds of fish? Renewable Energy The electricity produced by these wind turbines is consid­ ered a renewable resource. The wind energy that turns the turbines cannot be used up Uncertainty, Models, and Resilience Life in the Anthropocene involves unpredictable changes in the natural world. That unpredictability will increase because of human­ caused changes in global systems. Even more unpredictability will come from changes in ecosystem structure and function. Complicated Systems and Complexity You've seen that communities and ecosystems are complicated. To ecologists, complicated means that an ecosystem has lots of moving parts­ producers, herbivores, predators, parasites, and so on. Some complicated ecosystems are also comp/ex. What's the difference between complicated and complex? Complexity means that an ecosystem can change unexpectedly into a very different-looking system. A change from one condition to a very different condition can dramatically affect ecosystem services. Take Isle Royale in Lake Superior, as an example. Predator-prey oscillations, interactions of moose with plants, and responses of wolves to disease are complicated. But the system as we described it usually stays more or less the same. In contrast, removing otters along the Pacific coast caused a major trophic cascade. Many kelp forests disappeared, along with their inhabitants. That was an unex­ pected, complex change that totally transformed an ecosystem. The Tonie Sap Food Web Tonie Sap is a complex system. A very simplified version of its food web is shown in Figure 7-22. Note that boxes in this figure with labels like "bottom-dwelling organisms" represent entire groups of organisms, not just a single species. In addition, this is just the food web of Tonie Sap lake. This food web is connected with other food webs that stretch out through surrounding wetlands, rivers and forests! All those habitats experience major seasonal changes between rainy and dry season. And even that complexity doesn't yet factor in a major environmental force: humans. Tonie Sap Food Web This very simple model of the Tonie sap food web is just the starting point for the mathematical model of this ecosystem that researchers are building. In the full ver­ sion, each line between boxes is assigned a numerical value based on data collected. These data indicate the nature and strength of interactions between organisms. Equations based on these numbers and relationships are then used to build computer models that try to predict how changes in one part of the food web will affect the rest of the web. Adding Humans Taking into account all the ways that humans interact with this complex system piles on still more complexity! What are the outside social and economic fo·rces that cause people to move into the Tonie Sap area? What would happen if th'e pop ula­ tion of a major food fish declines? Would people fish longer hours? Would they try to catch other kinds of fishes? Or would some . people leave to seek work in cities? How might the health of Ice.al people change if certain fishes are no longer part of their diet? And how does the Tonie Sap ecosystem respond to changes in the w y people interact with it? These interactions show Tonie Sap is an example of what ecolo­ gists call Coupled Human And Natural Systems, or CHANS for short. In fact, in the Anthropocene, the entire world is composed of CHANS that are linked through global systems. To guide sustainable development, researchers are trying to model this extraordinary complexity using a type of mathematical model called MIMES: Multiscale Integrated Model of Ecosystem Services. A MIMES model is different from the conceptual UGC model we've been building. MIMES models are based on numerical data and complex calculations. They try to predict possible future outcomes of interactions between human and natural systems. A VERY simplified view of a MIMES model is shown in Figure 7-23. Every box in this model contains at least one system that is at least as complex as the Tonie Sap food web! And, like the model of the ecosystem alone, researchers try to gather numerical data indicating the nature and strength of all the interactions shown here by arrows. I This model is not complete. But it has shown that that certain c ndi- tions could cause unexpected problems for Tonie Sap and for people who depend on its ecosystem services. MIMES Model This simplified representation of a MIMES model is designed to give a "big picture" over-. view of all the different parts of Coupled Human and Natural Systems. Note that in addition to the four spheres we've been discussing in our UGC model of global systems, this model includes a set of systems called the Anthroposphere, which includes the interactions among humans and human systems such as societies and economies. Resilience Awareness of these sorts of possible changes helps guide sustainable development towards resilience-the ability of a system to deal with change. Sustainable development must be resil­ ient enough to survive enviro-nmental stresses like droughts, floods, storms, heat waves, cold snaps, and unexpected changes in the structure and function of local ecosystems. Designing Solutions The goal of science is to understand the natural world and to apply that knowledge to improve the human condition. Data about measurable changes in global systems, prop­ erly collected, analyzed, and applied, can inform a rational approach based on our best understanding of those global systems. Research can help us respond to global ecological challenges by (1) recogniz­ ing an environmental problem created by human or other causes, (2) gathering data. to document and analyze that problem and iden­ tify its cause, and then (3) using a scientifically informed approach to guide economists, politicians, and stakeholders in crafting sustain­ able and resilient environmental policy. Environmental Successes Research has often guided us towards informed environmental management. Years ago, for e ample, ecologists discovered lead in North American streams, and conducted research that identified car exhaust as the source of that lead. Industry then designed engineering solutions that now enable cars to run efficiently on unleaded fuel. Leaded gasoline was phased out, and lead concentrations in environments across the country dropped. Global response to loss of ozone in the stratosphere is another example. Once research linking CFCs with ozone depletion was published, replicated, and accepted by the scientific community, the rest was up to policymakers and industry. Following scientific recommendations, 191 countries signed the Montreal Protocol, an agreement banning most uses of CFCs. Ronald Reagan, then presi­ dent of the United States, signed the Montreal Prot_ocol on behalf of the United States. Then, manufacturers developed alternatives to CFCs that work in most applications. Stratospheric ozone is now recovering! Addressing climate change is our next global scientific challenge. Mario Molina won the Nobel Prize in 1995 for his research on the factors that can destroy the ozone. KEY QUESTIONS How are resources used in sustainable development? Why is resilience important for sustainable development? Identify Variables City planners are deciding where to build a new stadium. Choices include the city center, an old farm just outside the city, and wetlands by a river. To make a decision that promotes sustainable development, what vari­ ables should the planners identify? Understanding Tonie Sap's complex ecosystems and equally complex effects of human activity on those systems, show how researchers use interdisciplinary mQdeling to plan sustainable development. Meuae Phenomenon Planning for sustainable develop­ ment anywhere requires understanding interac­ tions between human and natural systems. Human use of ecosystem services can profoundly change the ecosystems that provide those services. To predict how an ecosystem will respond to chang­ ing demands and changing climate, researchers gather data from past and present, and build models based on those data. Fish Farmer Government officials and organizations are training people in fish farming, or aquaculture. Fish farming involves raising aquatic animals for consumption or release. A fish farmer must be knowledgeable about the life cycle and biology of the organisms that they raise. They also must conform to all state and local regulations. To be a fish farmer, you need a bachelor's degree in either aquaculture or biology. You also need to be able to know how to treat diseases and main­ tain the proper environment for the organisms that you are raising. Where Floods Are Helpful Flood! To many, that word signals danger. But in places like Tonie Sap, annual floods support eco­ system services. Where people understand the value of floods and know how to deal with them, human systems can benefit too. In Tonie Sap, many people live in houses that sit on the lake floor during dry season, and later • float on floodwaters! Locals know that flooded forest areas are great fishing spots. Floodwaters enable fishes to leave rivers and lakes to wander through the forests. Many fishes feed on leaves, seeds, or fruits, and some species breed there. A single hectare of flooded forest can support up to 240 kilograms of fish! But, poor people migrating into the area often cut down forests to plart rice or other crops. With trees gone, fish production drops dramatically-to about 30 kilograms per hectare. That's why understanding ecology is just the first step in sustainable development. MIMES models must include social and economic behaviors of local people. What happens when one or two family members leave to work in factories? Can those left behind fish and pay their debts? How much fish feeds a family? Lessons learned here can often be useful elsewhere. Many people­ from the Amazon to the Mississippi delta-live where floods are, or once were, vital parts of ecosystem function. Humanity, Global Systems, and Change Humanity's ecological footprint-which includes the use of resources such as energy, food, water, and shelter, and the production of wastes such as sewage and greenhouse gases-is measurable. By some calculations, the average American has an ecological footprint roughly three times larger than the global average. The Age of Humans, or the Anthropocene, is the period during which human activity has become the major cause of global change. To plan for humanity's future, we need to under­ stand the best available scientific data on how Earth systems work, and to build a model that shows how both human and nonhuman causes of change are affecting those systems. ecological footprint Anthropogenic Global Change and its Effects Human activities affect global systems by changing the composition of the atmosphere in way5-:that change climate and ocean chemistry, by chang­ ing the way we use land, by over-harvesting some species, by introducing species to new environ­ ments, and by producing pollutants and wastes that include plastics. Some activities raise concentrations of greenhouse gases, driving climate change. Other acti