Encyclopedia of Global Resources part 38 docx

31 million square kilometers, which is nearly 21 per - cent of the entire world landmass. Deserts, semi- deserts, thorn savanna, and thorn steppe liewithinit. The tropics with summer rain zone constitutes, ap- proximately, bands of moist and dry savannas north and south of the equator, 25 million square kilometers, in northern and eastern South America, central and southern Africa, India, SoutheastAsia,andnorth- ern Australia and nearby islands. Areas of it lie in Cen- tral America as well. The last zone, tropics with year-round rain, is pri- marily equatorial: northern South America, central Africa, Indonesia, and Malaysia. This zone comprises tropical rain forests in its 12.5 million square kilometers and has highest values in all categories of ecozone messurement—for example, the highest average temperature, precipitation, length of growing season, and biomass. Human Impact In comparison with Earth’s landmass, the planet’s oceans are not yet thoroughly studied for classifica- tion into biological regions. The difficulty of explora- tion and the flowing, changing nature of oceans make it difficult to distinguish boundaries underwater. However, in order to identify and protect at-risk ecosystems and to estimate exploitable resources, scientists have proposed various marine ecozones for coastal areas, which are the best understood. They also have the greatest human presence and use, including fishing, waste disposal, recreation, and trans- portation. These zones include beaches, coral reefs, kelp forests, human-made structures such as docks and pilings, mangrove swamps, mudflats, rocky shores, and salt marshes. (Deep-sea ecosystems may eventually be construed to compose ecozones, such as the ecosystems around underwater volcanic vents.) On land, logging, farming, grazing domestic animals, and construction of cities account for the greatest modifications to ecozones. Because of these, the original vegetationcoverinmanytemperateand tropical zones has been removed, wholly or partly. Schultz contends that agriculture and grazing represent the optimal expression of biological production within the physical environment of an ecozone. Roger Smith Further Reading Dickinson, Gordon, and Kevin Murphy. Ecosystems.2d ed. New York: Routledge, 2007. MacDonald, Glen Michael. Biogeography: Space, Time, and Life. New York: John Wiley & Sons, 2003. Moles, Manuel C., Jr. Ecology: Concepts and Applications. 5th ed. Boston: McGraw Hill Higher Education, 2010. Pickett, Steward T. A., Jurek Kolasa, and Clive G. Jones. Ecological Understanding: The Nature of Theory and the Theory of Nature. 2d ed. Boston: Academic Press, 2007. Schultz, Jürgen. The Ecozones of the World: The Ecological Divisions of the Geosphere. 2d ed. New York: Springer, 2005. Web Sites Ecological Society of America http://www.esa.org Environmental Information Coalition The Encyclopedia of Earth http://www.eoearth.org See also: Deep ecology; Deserts; Ecology; Ecosystem services; Ecosystems; Forests; Grasslands; Rangeland; Wetlands. Edison, Thomas Category: People Born: February 11, 1847; Milan, Ohio Died: October 18, 1931; West Orange, New Jersey Edison, whose inventions include the modern form of incandescent light, typified the age of technology-driven innovation, which demanded the widespread avail- ability of electrical power. Biographical Background Thomas Edison spent his early years selling news- papers on a railroad and working as a telegraph operator in Boston. Familiarity with electrical equipment led him to a number of early inventions, one of which, an improved stock ticker, he was able to sell for $40,000, a sum he spent in setting up his own work- shop at the age of twenty-three. Impact on Resource Use In 1876, he established a research laboratory in Menlo Park, New Jersey, and he turned his attention 340 • Edison, Thomas Global Resources to developingasystemof electric lighting in 1878.Elec - trical arc lighting had been demonstrated in 1808 by British scientist Sir Humphry Davy, but it required high currents and was very dangerous. In the search for a more practical electric light, Edison joined a field of other eager inventors. Joseph W. Swan, an En- glish chemist, had limited success before abandoning the idea in 1860. Edison’s approach was to seek a low- power lightbulb sothatseveralcouldbe used together to illuminate a room. After an exhaustive search for a filament material that would provide moderate illu- mination for many hours without burning out, he set- tled on a carbonized thread. Edison also tackled the problem of electric power distribution, opening the first distribution station, the Pearl Street Station, in New York in 1882. Donald R. Franceschetti See also: Electrical power; Hydroenergy. Edison Electric Institute Category: Organizations, agencies, and programs Date: Established 1933 The Edison Electric Institute is an association ofinves- tor-owned electric utility companies operating all over the world. Member companies generate 79 percent of the power produced in the United States and service 70 percent of the nation’s electricity consumers. Background The Edison Electric Institute was formed when public investors realized that their companies needed a col- lective regulatory policy regarding assignment of service territories (franchises) so as to eliminate the du- plication of service and equipment and become more economically efficient. The Edison Electric Institute assumed the promotional responsibilities of the Na- tional Electric Light Association, the forerunner to the Edison Electric Institute. The institute continued to grow by absorbing the Electric Energy Association in 1975 and the National Association of Electric Com- panies in 1978. Impact on Resource Use The Edison Electric Institute represents the interests of the shareholder-owned electric power industry. Millions of small investors collectively own most electric utilities, either by the direct purchase of stock or indirectly through life insurance policies, retire- ment funds, and mutual funds. Electric utilities that are Edison Electric Institute members market some of their electricity at wholesale rates to other electricity- producing entities. These other entities include more than two thousand municipality-owned systems, some federally owned hydroelectric projects, and many of the one thousand rural electric cooperatives. The Edison Electric Institute also functions as an information center by educating the general public, communicating with government agencies on topics of public interest, and serving as a forum for the inter- change of ideas and information with its member companies and their personnel. The Edison Electric Institute conducts numerous surveys and studies that provide information to its members on utility operations, regulations, sales, revenues, environmental practices, and marketing opportunities. Dion C. Stewart Global Resources Edison Electric Institute • 341 Thomas Edison’s numerous inventions, which included the electric lightbulb, helpedpropel humanityinto the modern age.(Libraryof Congress) Web Site Edison Electric Institute http://www.eei.org/Pages/default.aspx See also: Edison, Thomas; Electrical power; Energy politics; Tennessee Valley Authority. El Niño and La Niña Category: Geological processes and formations The replacement of normal near-surface Pacific Ocean temperatures by either warmer waters off the Peruvian coast (El Niño) or colder waters in the eastern Pacific (La Niña) causes significant changes in climate that lead to agricultural losses or surpluses, outbreaks of disease, unexpected losses or increases in wildlife, and floods or droughts. El Niño also has affected the rate of the Earth’s rotation. Definition El Niñoissignaledby a warm current of water off the Peruvian coast in contrast to the normally cold waters that rise to the surface. This change alters the circulation pattern of the Pacific Ocean, which in turn causes changes in climate. La Niña creates an opposite effect by extending and deepening the impact of the normal circulation pattern in the Pacific because of colder water than normal in the eastern Pacific. Overview Peruvian and Ecuadorian fishermen have long noted that for a few weeks in December the waters off their coasts grow warmer, an effect they called El Niño (“the boy child”) because of the event’s proximity to Christmas. In some years this warming is more significant in both its temperature and its duration and can have worldwide impact. Sir Gilbert Walker, in his study of Asian monsoons, was the first to doc - ument the normal pattern of Pacific Ocean circulation. Walker realized there was a yearly cyclical variation in the atmosphere over the southwest Pacific Ocean, which he termed the “Southern Oscillation.” The Pacific Ocean is normally character- ized by strong equatorial currents and trade winds driven by rising cool water off the coast of Peru that moves toward the equator and heads westward, setting up a circulationcelleffect. This Southern Oscilla- tion circulation results in warm water and an area of low pressure producing wet conditions in the South Pacific and correspondingly relatively dry conditions on the west coasts of the Americas. The rising cool water off Peru also brings nutrients to the surface that attract plankton, which in turn sustain an anchovy population that proves a stable food source for many marine creatures, birds, and humans. The birds fur- nish a steady supply of guano, a source for fertilizer. El Niño entirely reverses this circulation model within the Pacific Ocean with dramatic consequences during years of its occurrence. With El Niño there are 342 • El Niño and La Niña Global Resources El Niño, shownin this 2006 satellite imageas it passes across thePacific Ocean, is a con - dition occurring every three to eight years that causes numerous worldwide atmospheric changes. (NASA) dryconditionsinthe South Pacific andwetconditions on the western coasts of North and South America. Fishing off the coasts of Peru and Ecuador becomes a futile endeavor, stormy weather is common, and the fertilizer industry collapses. Droughts are triggeredin various parts of the globe, including Australia, New Zealand, Southeast Asia, India, the Philippines, Mex- ico, and southeast Africa. Excessive beach erosion oc- curs in California. Huge floods strike Cuba, Louisi- ana, and Mississippi. Coral reefs in the Pacific Ocean experience massive death. La Niña (“the girl child”) is an oceanic and atmospheric phenomenon that is the opposite of El Niño, as surface waters in the eastern Pacific become much colder than normal. A La Niña winter produces colder than normal air over the Pacific Northwest and the northern Great Plains and warms much of the rest of the United States. It results in increased precipitation in the Pacific Northwest and also increases hurri- cane activity in the Caribbean and Gulf of Mexico, perhaps twenty times higher than during El Niño years. Dennis W. Cheek See also: Erosion and erosion control; Floods and flood control; Geothermal and hydrothermal energy; Guano; Monsoons; Ocean thermal energy conversion; Ocean wave energy; Oceanography; Oceans; Weather and resources. Electrical power Categories: Obtaining and using resources; energy resources Electrical power is so convenient that $350 billion worth of it was sold by utility companies in the United States alone in 2008. However, a need for greater efficiency and environmental care will probably slow growth in sales, and it is possible that in the future power distribution methods and the mix of power sources will change radically. Background People have always feared the power of lightning. An- cient peoples undoubtedly knew of static electricity (as in making sparks by walking across wool rugs). Some archaeologists believe that certain ancient Mes - opotamian and Egyptian pots might have been batter - ies, perhaps for creating metal plating on jewelry or weapons. However, nothing lasting was developed until electricity had a scientific basis. Benjamin Frank- lin’sfamousexperiment—flyingakite in the thunder- storm—proved that lightning is essentially the same phenomenon as static electricity. Besides leading to lightning rods to protect from lightning, the discov- ery encouraged other researchers to seek the power of lightning. Development of Electrical Power In 1800, Alessandro Volta demonstrated that two different metals, connected by a wire and placed in an acid solution, could generate electricity—just as millions of lead-acidcarbatterieshavedone in the twentieth century. In 1801, Sir Humphry Davy demonstrated an arc lamp, which gotsomeuse.In1832,both Michael Faraday and Joseph Henry demonstrated generators, although these were only laboratory-scale machines. Batteries were still the major power source in 1837, when the first electrical appliance arrived: the telegraph. This device revolutionized communications. A telegraph operator could instantly send a coded mes- sage through a wire by using a “key” to connect and disconnect electrical power. Hundreds or thousands of kilometersaway,themessage was received whenthe bursts of transmitted electricity moved a tiny electro- magnet in a pattern that could be decoded by the operator at that end. Then Thomas Edison, the towering figure in electrical power, invented the incandescent lightbulb in 1870 (the same year that Joseph Wilson Swan also developed one in England). When Edison tried to sell lights, there were few buyers because batteries were too expensive. In a desperate race with creditors, Edi- son’s company built improved industrial-sized generators, strung wires, and discovered vital refinements, including fuses and switches. Edison invented the electric utility, which allowed thousands of electrical inventions to follow. Edison’s direct current, however, could not be increased in voltage to go more than a few kilometers. Nikola Tesla’s invention of the alternating current (AC) motor allowed electricity to increase in voltage to press through resistance in the wires and then decrease in voltage at the using site. AC electrical grids began to serve customers tens, hundreds, then thou - sands of kilometers away. Mass production and im - Global Resources Electrical power • 343 provements in technology allowed the price per kilowatt ofelectricityto drop fromdollarsto mere cents. Power from Coal Anything with chemical energy, motion, or a difference in temperature has the potential to generate electrical power. Combustion of fossil fuels has been the greatest energy source, and coal is the most heavily used fossil fuel. Its abundance (particularly in the United States and China) makes it cheap, and some estimate that coal could provide most of the world’stotalenergy by itself formore thanacentury. Most coal-fired generators boil water to steam, which flows through turbine blades similar to those of jet engines. Such plants cause complaints because they also release soot and sulfur dioxide (from sulfur impurities in the coal) through their smokestacks. Also, they only transform one-third of the coal energy into electricity,thebalancebeing lost as“wasteheat.” For older plants in rich countries, low-sulfur coal is burned or various scrubbing technologies are used to clean the exhaust gas. Filters or electrostatic plates may be used to catch exhaust dust. Calcium carbonate (CaCO 3 ) dust in the combustion chamber turns the sulfur dioxide into sodium sulfate, which can be caught as dust. Coal can also be cleaned of sulfur and metals before being burned. However, poorer countries that cannot afford to implement such technologies often simply must suffer with dirty, unhealthful air. More advanced coal-fired plants avoid generating pollutants that must be cleaned from the exhaust gases. Combined-cycle plants heat a water-coal mixture, so hydrogen and oxygen in the water (H 2 O) generate hydrogen sulfide (H 2 S, which can be easily stripped out), methane (CH 4 ), and carbon monoxide (CO). Burning the latter two gases shoots hot gases through a turbine. Gases leaving the turbine “topping cycle” make steam in a boiler, just as in the old plants. Combining the two cycles yields efficiencies greater than 50 percent. Another advanced method, fluidized-bed combus - tion, uses a hot bed of sand with coal, air, and calcium carbonate flowing up through the sand. Slag at the 344 • Electrical power Global Resources PEAK PART-TIME BASE LOAD 300 250 200 150 100 50 Megawatts Time of Day 12 MIDNIGHT 3 A.M. 6 A.M. 9 A.M. 12 NOON 3 P. M. 6 P. M. 9 P. M. 12 MIDNIGHT Typical Daily Demand Cycle for a U.S. Power Plant top contains calcium sulfate, so air cleaning is easier. Fluidized-bed systems often increase efficiency with a liquid-metal topping cycle. Molten metals, such as sodium or potassium, can stand hotter temperatures than steam, so one of these metals is circulated through pipes in the fluidized bed and out to a turbine. Waste heat from that topping cycle then powers a steam boiler. Coal-fired plants can be clean andefficient, but the required equipment generally involves large, expensive plants, with the equipment cost being a major part of the electricity cost. Hence, coal-fired plants must run nearly continuously to pay for themselves. As such, they are “base-load” plants. Power from Oil, Hydroenergy, and Fuel Cells Plants burning oil or natural gas (CH 4 ) use the same gas and steam turbines as coal-fired plants. They can be built much more cheaply because the fuel can be easily cleaned of sulfur, they have more concentrated energy, and pumping fluids is easier than moving sol- ids. However, these fuels are more expensive. Thus, oil- and gas-fired electricity is more expensive than coal-fired, and it is cheaper for the owners not to run them all the time. Consequently, oil- and gas-fired plants are often “peaking plants,” switched on when electrical demand is highest and off when demand drops. Hydroelectric power (hydroenergy) is the modern version of ancient waterwheels. Water from a dammed river flows down through a turbine. Hydro- energy is cheap and is available on a few minutes’ no- tice. The limitation is thatmostgoodsitesinthe developed countries already have dams. Likewise, tidal power, as in the Bay of Fundy and the Rance River delta, has limited sites. Fuel cells are also more efficient and less polluting. They operate as batteries do, except that fossil fuels become carbon dioxide and water at the electrodes. Fuel cells yield efficiencies as high as 70 percent; if the catalysts can be made cheaply enough, fuel cells may eventually dominate the market. Some researchers have even suggested the development of sugar- powered fuel cells, based on the principle that all life is powered by biological sugar fuel cells. Power from Nuclear Reactors Nuclear fission (splitting atoms) is another way to get heat to spin turbines. Heavy metals (uranium and heavier elements) are less stable than other elements. Certain isotopes (versions of an element with more or less neutrons) are radioactive because they natu- rally fission into lighter elements, emitting heat and radiation in the process. When a critical mass of fis- sionable material is brought together, neutrons re- leased from radioactive decay trigger fissions of enough other atoms to cause a self-sustaining nuclear chain reaction. A secret Allied World War II project culminated in two fission bombs being dropped on Japan in 1945, ending the war. It was predicted that this awesome technology would supplant other energy sources and produce “electricity too cheap to meter.” Breeder reactors were designed both to produce power and to bombard slightly radioactive material to transmute it into fuel. Fission energy has not achieved prices lower than coal-fired electricity, and there are long-term costs of protecting spent (but still radioactive) fuel from acci- dental release or diversion into bombs. The most important immediate cost factor is that a power plant, as opposed to a bomb, must operate for years without killing people or damaging the equipment. This protection involves great expense, because a fission reactor produces intense radiation. Personnel must be shielded by massive amounts of lead and concrete, and much of the structure of a reactor can be weak- ened by neutron embrittlement during years of oper- ation. Worse, an out-of-control fission reactor can overheat, explode (although not as powerfully as a bomb), and release highly poisonous radioactive ma- terials. Consequently, fission reactors must have complex redundant safety features and containment domes to protect against radioactive leaks. Breeder reactors, with their massive neutron fluxes, are the most likely reactors to have serious accidents. High-temperature gas reactors could operate at higher temperatures, could have greater safety mar- gins, and could have continuously replaced spherical fuel elements. However, the 1986 Chernobyl reactor disaster (in what was then the Soviet Union) and the earlier accident at Three Mile Island, Pennsylvania, in 1979, have caused thepublictohavea negative view of fission, so research into gas reactors has not received sufficient funding. Nuclear fusion (combining lighter atoms into heavier ones) is being researched, but it is an unlikely competitor. In the Sun, four hydrogen atoms are fused into one helium atom. A reactor on Earth making a similar reaction could not achieve the pressure of the Global Resources Electrical power • 345 Sun, so it would have to compensate with higher tem - perature (held in by a magnetic field) and heavier isotopes of hydrogen (deuterium and tritium). Advan- tages to fusion would be that hydrogen isotope fuels are essentially inexhaustible and that a fusion reactor with mechanical problems would simply stop rather than going out of control. The problems would be that fusion, with its heavier hydrogen isotopes, gener- ates neutron fluxes comparable to those of a fission breeder, which would soon damage the complex magnetic containment system. Worse, fusion reactor heat flux per unit volume is less than that of fission reactors, so costs per kilowatt would be high. Power from Wind, Photovoltaic Cells, and Geothermal Sources Wind power was reborn in the energy crisis of the 1970’s. Tax incentives given during the energy crisis allowed “wind farms” in high-wind areas to approach profitability. Eventually, these machines evolved into more cost-effective systems. Then gears were developed to accommodate a range of wind speeds. Today, wind systems produce power at prices comparable to coal-fired plants, and wind systems can operate profit- ably in areas with less than maximum wind. However, wind power is variable. An electrical grid cannot count on receiving more than 20 percent of its power from wind lest a calm day cause a power failure. Photovoltaic (solar) cells are large transistors that produce electricity when struck by sunlight. Prices of photovoltaic power dropped from hundreds of times that of grid power in the 1960’s to three times that of coal-fired power in the mid-1990’s. Further price drops from lower production cost, higher cell efficiencies, and the integration of cells into building construction could allow photovoltaics to produce many times the electricity presently used. (Produc- tion peaks during afternoon peak demand, but production stops after dark.) Even if prices do not decline, photovoltaics are competitive for small and distant sites (such as roadsidephonesandrailroad sig- nals) because they do not require large installations and they have no moving parts. Geothermal energy taps hot steam underground to run turbines. Advanced systems can use hot water, and future systems may pump fluids (such as water or helium) into areas of hot rock so the fluids can carry heat back up to a power plant. If drilling costs could be reduced sufficiently, geothermal energy could grow into a major source of electricity. Ocean Energies, Efficiency, and Cogeneration If the foregoing systems do not provide enough power, more exotic methods may conceivably be used in the future. Ocean waves and currents could supply a major fraction of energy used. The difference be- tween hot tropical ocean waters and the near-freezing deep water has powered experimental power plants, and this ocean thermal energy conversion (OTEC) could theoretically supply many times the world’s electrical use. However, many practical problems re- main to be solved. Finally, increased efficiency of electrical use would have the same effect as more generators, perhaps as much as 75 percent more, and at costs cheaper than building new power plants. There are hundreds of ways to increasetheefficiency of electrical use,including more efficient electric motors, compact fluores- cent lights, greater use of light-emitting diodes (LEDs), more insulation, smart windows, and solid state displays instead of picture tubes in televisions and computer monitors. (The last item alone could retiretheequivalent of several nuclearpowerplants.) A similar increase in efficiency comes from cogeneration, the use of “waste heat” from power plants for other uses, such as district heating or chemical pro- cessing. Becausemostpowerplants are far lessthan50 percent efficient, full cogeneration would effectively double energy from electric utilities. Many industrial plants are adding cogeneration to existing heating operations. Ultimately, fuel cells might be made small enough to combine water heating and space heating with electrical generation, making houses tiny power plants. Issues for Electric Utilities The electric power industry is one of the largest in the world, generating power and maintaining cables link- ing generators and power uses. Such networks entail technology and management issues affecting trillions of dollars. First, the power sources must be chosen. Second, storing electricity is expensive, so generated power must be used when generated. Conse- quently, generating capacity must be enough to cover the highest use “peaks” in early afternoon (notably air-conditioning), morning, and early evening. Gen- erators are not fully used at other times. Conse- quently, utilities increasingly charge extra for peak times, charge less for off-peak hours, and offer bo - nuses for appliances that switch off on command. Likewise, some areas have seasonal variations in 346 • Electrical power Global Resources supply and demand. Pacific Northwest power dams have maximum water flow during spring and summer, when the Southwest has the greatest air-conditioning load. In the winter, water flow is low, but the Southwest has less demand then. High voltage lines allow the two regions to ex- change power. A world grid has been suggested for much greater savings. Batteries for vehicles and portable appliances are a growing part of electricity use. Dry cells cost the equivalent of dollars per kilowatt hour. Liq- uid-cell batteries, such as the lead-sulfuric acid batteries for cars, are cheaper, but they are still expensive and heavy. Furthermore, as much as one- third of energy is lost. Increasing battery perfor- mance and lowering costs are key to practical electric-driven cars. Such cars would decrease pollution (one big plant cleans emissions better than thousands of car engines), and energy efficiency would increase (gasoline engines have low efficiency). They would vastly increase power plant construction, and nightly charging would help balance the day peak. Finally, electrical utilities are large enough to be a major factor in possible greenhouse warming caused by increased carbon dioxide in the atmosphere. If greenhouse warming continues at its present rate, there will be a greater push toward efficiency and away from fossil fuels. Roger V. Carlson Further Reading Bodanis, David. Electric Universe: How Electricity Switched on the Modern World. London: Little, Brown, 2005. Breeze, Paul. Power Generation Technologies. Burling- ton, Mass.: Elsevier/Newnes, 2005. Casazza, J. A., and Frank Delea. Understanding Electric Power Systems. New York: Wiley, 2003. Flavin, Christopher, and Nicholas Lenssen. Powering the Future: Blueprint for a Sustainable Electricity Indus- try. Washington, D.C.: Worldwatch Institute,1994. Gabriel, Mark A. Visions for a Sustainable Energy Future. Lilburn, Ga.: Fairmont Press, 2008. Grigsby, Leonard Lee, ed. Electric Power Generation, Transmission, and Distribution. Boca Raton, Fla.: CRC Press, 2007. Grubb, Michael, Tooraj Jamasb, and Michael G. Pollitt. Delivering aLow-CarbonElectricity System: Tech - nologies, Economics,andPolicy.NewYork: Cambridge University Press, 2008. Kutz, Myer, ed. Environmentally Conscious Alternative Energy Production. Hoboken,N.J.:John Wiley, 2007. Shively, Bob, and John Ferrare. Understanding Today’s Electricity Business. San Francisco: Enerdynamics, 2007. Warkentin-Glenn, Denise. Electric Power Industry in Nontechnical Language. 2d ed. Tulsa, Okla.: Penn- Well Books, 2006. Web Site U.S. Environmental Protection Agency Electric Power http://www.energy.gov/energysources/ electricpower.htm See also: Biofuels; Coal; Cogeneration; Department of Energy, U.S.; Energy economics; Energy Policy Act; Energy storage; Fuel cells; Geothermal and hydro - Global Resources Electrical power • 347 Electrical power lines demarcate much of the American landscape. (©Alexfiodorov/Dreamstime.com) thermal energy; Greenhouse gases and global climate change; Hydroenergy; International Atomic Energy Agency; Nuclear energy; Ocean current energy; Ocean thermal energy conversion; Ocean wave energy; Photovoltaic cells; Solar energy; Wind energy. Emery. See Corundum and emery Eminent domain. See Takings law and eminent domain Endangered species Category: Plant and animal resources Because endangered plants and animals constitute a large and growing proportion of all organisms on Earth, their loss would mean a devastating decline of proven and potential resources for agriculture, medi- cine, and the global economy. Their vanishing would also result in the deprivation of less tangible but also important ecological and aesthetic benefits. Background Although countless species have passed from an endangered condition to extinction throughout the history of life on Earth, the concept of “endangered species” is a human creation. After humans emigrated from their birthplace in Africa and populated large areas of Europe and Asia, they began imperiling the habitats and lives of their fellow earthlings, often to the point of extinction. With the growth of advanced industrialized societies, this rate of extinction increased. For example, during this period such creatures as the dodo, great auk, and passenger pigeon ceased to exist. Some people, such as George Perkins Marsh in his Man and Nature (1864), protested against humanity’s mindless assault on wild flora and fauna, but other scientists became enthusiastically involved in locating and exploiting the Earth’s natural resources. Conservation efforts did begin in Africa, In - dia, and North America in the late nineteenth and early twentieth centuries, but not until the develop - ment of the modern environmental movement in the second half of the twentieth century did large numbers of people, scientists as well as laypersons, recog- nize the dire status of endangered species and begin to become actively engaged in their preservation. Nature, Quantity, and Variety of Endangered Species Resources Lawyers, landowners, businesspeople, and environ- mentalists have understood the term “endangered species” from their distinctive viewpoints, but scientists, striving for objectivity, have defined endangered species as undomesticated plants and animals with so few interbreeding individuals that the species faces imminent extinction in all or most of its habitat. The numbers can range from single individuals—such as “Lonesome George,” the last member of a species of Galápagos tortoise—to fewer than twenty whooping cranes in the late 1940’s, to thousands of such whale species as the blue, bowhead, humpback, and gray. When wild species have abundant but declining numbers in their ecological niches, they are often de- scribed as “threatened.” Some scientists classify species as safe, vulnerable, endangered, or critical in quantitative terms, depending on the probability of a species’ declining by a certain percentage over the subsequent fifty years. With the growth of legislation to protect threatened and endangered species, such as the Endangered Species Act (1973) in the United States, lawmakers discovered that, to save these species, they also had to protect their habitats, because they needed not only food, water, air, and light but also sites for breeding, reproduction, and rearing off- spring. Uncertainty exists about how many different life- forms now exist on Earth. Estimates range from 1.5 million to as high as 30 or even 100 million. Further uncertainty exists about the precise numbers of endangered species. Based on samples of species numbers that scientists of the International Union for Conservation of Nature (IUCN) had evaluated through 2006, the percentage of endangered species might be as high as 40 percent of all life-forms, which would mean 600,000 to 12 million endangered species, depending on whether one accepts low or high evaluations for total species numbers. When scientifi- cally counted rather than estimated numbers are proffered, as they are in IUCN’s Red List of Endan - gered Species, the figures are considerably smaller: In 2007, the list stated that more than 40,000 species 348 • Endangered species Global Resources were at “heightened risk,” with 16,306 at an “extreme risk” ofextinction.InMay, 2007, the numbersgivenby the U.S.Environmental ProtectionAgencywere 1,351 endangered American invertebrates, plants, and animals. Because of the continuing discoveries of both safe and endangered species, these numbers must be viewed as tentative. Agriculture and Endangered Species Resources Some scientists estimate that more than 80,000 plant species are edible, but, throughout history, humans have utilized only about 10 percent of these for food. In advanced industrialized societies, the number of species employed in commercialized agriculture was considerably smaller, about 150, and by the twenty- first century, an even smaller number, fewer then 20, had become the source of 95 percent of the world’s food. Nonedible plants also serve humankind, by pu- rifying water, enhancing soil fertility, and moderating climate changes. Other species—such as bees, birds, and bats—have had a pivotal influence in pollinating the world’s crops. However, declines among various species of these pollinators have led scientists to search for causes and induced governments to protect the most seriously threatened. The extinctions of some species of pollinators have already caused reduced harvests of certain fruits and vegetables. Be- cause of the mixture of wild and domesticated pollinators, placing a monetary value on these resources is difficult, though some have ventured an estimate as high as $200 million. Doubt also exists about precisely how many of the more than 100,000 pollinators are endangered, but even domesticated bee species have undergone an alarming drop in numbers that has created concern among agriculturalists. These pollinators are sometimes called keystone species because they serve an ecological role much greater than their numbers by directly and indirectly influencing the kinds and quantities of many other species. Just as in architecture the removal of a keystone leads to the collapse of an arch, the extinction of these species will result in the extinctions of many other species and the collapse of entire communities of life-forms. Another role for endangered plants in agriculture is in breeding programs. When an endangered plant becomes extinct, an irreplaceable store of genetic information is lost for humanity. Some of these genes may contain information on how to resist disease, counteract insects, or survive droughts. Plant geneti- cists have pointed out that massive monocultures, which rely on a restricted variety of plants, pose great dangers, because disease, drought, and insect infes- tations can quickly destroy millions of hectares. By using species of wild plants, botanists have been able to create crops that are pest-, disease-, and drought- resistant. Becausemanyof these plants arethreatened or endangered, various countries are collecting, or- ganizing, stockpiling, and preserving seeds of these species in “seed banks,” to be drawn on for breeding Global Resources Endangered species • 349 Endangered and Threatened and Species, 2008 Mam- mals Birds Rep- tiles Amphib- ians Fishes Snails Clams Crusta- ceans Insects Arach- nids Plants Total listings 357 275 119 32 151 76 72 22 61 12 747 Endangered species 325 254 79 21 85 65 64 19 51 12 599 United States 69 75 13 13 74 64 62 19 47 12 598 Other countries 256 179 66 8 11 1 2 — 4 — 1 Threatened species 32 21 40 11 66 11 8 3 10 — 148 United States 12 15 24 10 65 11 8 3 10 — 146 Other countries 20 6 16 1 1 — ————2 Source: Data from U.S. Department of Commerce, Statistical Abstract of the United States, 2009, 2009. Note: Numbers reflect species listed by U.S. government as “threatened” or “endangered”; actual worldwide totals of species that could be considered threatened or endangered are unknown but are believed to be higher. . of sand with coal, air, and calcium carbonate flowing up through the sand. Slag at the 344 • Electrical power Global Resources PEAK PART- TIME BASE LOAD 300 250 200 150 100 50 Megawatts Time of. be shielded by massive amounts of lead and concrete, and much of the structure of a reactor can be weak- ened by neutron embrittlement during years of oper- ation. Worse, an out -of- control fission reactor. charge less for off-peak hours, and offer bo - nuses for appliances that switch off on command. Likewise, some areas have seasonal variations in 346 • Electrical power Global Resources supply