Mercury: Man's Helper and Poisoner

All of us—including farmers, industrialists, and sewage-plant superintendents—want a clean and healthful world. Then why is our environment being polluted? It comes down to this: Engrossed in our own activities, we have little awareness of side effects that those activities may be having on the world outside. Let me illustrate by following one pollutant—mercury—in its course from helper to poisoner of man.

The first mercury seed dressing was developed half a century ago, and became popular because it inhibited seed mold. Other industries were attracted by those fungicidal abilities. Mercury became common in such businesses as papermaking and diaper laundering; mercury is an important catalyst in the manufacture of a basic plastic, polyvinyl chloride.

But Dr. Barry Commoner's "no-free-lunch" rule comes into play at this point. Sweden's pheasant population was drastically reduced because the birds ate seeds treated with mercury. Canadians found mercury in partridges and fish. Almost 100 Japanese died from eating fish caught in Minamata Bay—a polyvinyl chloride plant dumped its waste there.

Americans became mercury conscious last July, when fish from 20 states and Canada were found to contain concentrations of the poison. The Department of Justice filed suits against eight U. S. chemical and paper companies, insisting on an immediate halt to water pollution by mercury.…

Sweden Teaches Its Citizens Ecology

Among European countries, one of the leaders in the fight against pollution is Sweden. In Stockholm, I lunched with Tage Erlander, Sweden's recently retired Prime Minister, who heads the planning committee for the International Pollution Control Conference to be held in the Swedish capital in 1972.

"When Rachel Carson's book Silent Spring was published here," he said, "it made quite an impact. About that time, too, we looked around to discover that our environment was deteriorating. But you don't just make a law saying there shall be no pollution. To get it under control, we needed public support."…

Education was the key. A Swedish student starts learning ecology in primary grades, and he'll be exposed to the subject all the way through high school. In college he can cross normal academic lines—for instance, he can major in biology and also in the legal aspects of pollution control. In 1968 adult courses were set up all over Sweden, financed by folksam, a large insurance cooperative. More than 150,000 adults took the courses in that first year—in a country of eight million.

Hans Palmstierna, secretary of the government's advisory committee on environment, explained the ultimate goal. "Our targets are the people at local government levels," he said. "Before a community agrees to let a new factory come to town, we want its people to consider more than just the short-range economic gains. Will the new factory create environmental hazards? In our public-education courses, we teach adults to ask just such unpleasant question."…

"Recycling is one good answer to the pollution problem," Mr. Palmstierna told me. "Our natural resources, like everyone else's, are limited. It doesn't make sense to dig them up, use them once, and then throw them into the environment as pollutants. We want to use them over and over."

Remember one of Aesop's Fables—the story of the feckless grasshopper who frittered his summer away with no thought of barren months ahead? This has been a planet of grasshoppers.

But no longer. Anxious to mend our ways, we laymen are listening earnestly to a range of experts. The result, too often, is confusion. We're unsure of the priorities—is cleaner air more vital than cleaner water? What can an individual do to help? Must he give up his air conditioner and his car?

I make no claim of expertise—but I have had the rare opportunity of interviewing experts in many countries. Here is the gist of what I have learned:

Virtually every scientist I listened to—and they numbered in the dozens—emphasized that mankind must control population growth. They forecast widespread famine if population soars unchecked. Plagues, too—for in the megalopolitan sprawl of the future there will no longer be sparsely settled buffer zones around cities to curb epidemics.…

What are the priorities? Most ecologists answered something like this: Clean up the most threatened areas first. Work to unsnarl the fragmented, overlapping responsibility on national, state, and local levels. Focus research on finding environmental answers—there is so much yet to be learned.

Be realistic about immediate goals. At least for now, settle for making a river clean enough to serve its particular purpose. Later, it can be made clean enough to drink.

Get practical, enforceable pollution laws passed—standardized ones that will apply to both sides of a river, for instance, when it flows between two states.

Before using a new chemical, explore for side effects. And when a new product is developed, plan for its ultimate disposal. Work toward recycling; one factory's industrial waste can be another plant's raw material.

And make each individual aware of the problems—and his role in solving them.…

Source: Young, Gordon. “Pollution, Threat to Man’s Only Home.” National Geographic, December 1970.

Microsoft ® Encarta ® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved.

Pollution

I

INTRODUCTION

Pollution, contamination of Earth’s environment with materials that interfere with human health, the quality of life, or the natural functioning of ecosystems (living organisms and their physical surroundings). Although some environmental pollution is a result of natural causes such as volcanic eruptions, most is caused by human activities.

There are two main categories of polluting materials, or pollutants. Biodegradable pollutants are materials, such as sewage, that rapidly decompose by natural processes. These pollutants become a problem when added to the environment faster than they can decompose (see Sewage Disposal). Nondegradable pollutants are materials that either do not decompose or decompose slowly in the natural environment. Once contamination occurs, it is difficult or impossible to remove these pollutants from the environment.

Nondegradable compounds such as dichlorodiphenyltrichloroethane (DDT), dioxins, polychlorinated biphenyls (PCBs), and radioactive materials can reach dangerous levels of accumulation as they are passed up the food chain into the bodies of progressively larger animals. For example, molecules of toxic compounds may collect on the surface of aquatic plants without doing much damage to the plants. A small fish that grazes on these plants accumulates a high concentration of the toxin. Larger fish or other carnivores that eat the small fish will accumulate even greater, and possibly life-threatening, concentrations of the compound. This process is known as bioaccumulation.

II

IMPACTS OF POLLUTION

Because humans are at the top of the food chain, they are particularly vulnerable to the effects of nondegradable pollutants. This was clearly illustrated in the 1950s and 1960s when residents living near Minamata Bay, Japan, developed nervous disorders, tremors, and paralysis in a mysterious epidemic. More than 400 people died before authorities discovered that a local industry had released mercury into Minamata Bay. This highly toxic element accumulated in the bodies of local fish and eventually in the bodies of people who consumed the fish. More recently research has revealed that many chemical pollutants, such as DDT and PCBs, mimic sex hormones and interfere with the human body’s reproductive and developmental functions. These substances are known as endocrine disrupters. See Occupational and Environmental Diseases.

Pollution also has a dramatic effect on natural resources. Ecosystems such as forests, wetlands, coral reefs, and rivers perform many important services for Earth’s environment. They enhance water and air quality, provide habitat for plants and animals, and provide food and medicines. Any or all of these ecosystem functions may be impaired or destroyed by pollution. Moreover, because of the complex relationships among the many types of organisms and ecosystems, environmental contamination may have far-reaching consequences that are not immediately obvious or that are difficult to predict. For instance, scientists can only speculate on some of the potential impacts of the depletion of the ozone layer, the protective layer in the atmosphere that shields Earth from the Sun’s harmful ultraviolet rays.

Another major effect of pollution is the tremendous cost of pollution cleanup and prevention. The global effort to control emissions of carbon dioxide, a gas produced from the combustion of fossil fuels such as coal or oil, or of other organic materials like wood, is one such example. The cost of maintaining annual national carbon dioxide emissions at 1990 levels is estimated to be 2 percent of the gross domestic product for developed countries. Expenditures to reduce pollution in the United States in 1993 totaled $109 billion: $105.4 billion on reduction, $1.9 billion on regulation, and $1.7 billion on research and development. Twenty-nine percent of the total cost went toward air pollution, 36 percent to water pollution, and 36 percent to solid waste management.

In addition to its effects on the economy, health, and natural resources, pollution has social implications. Research has shown that low-income populations and minorities do not receive the same protection from environmental contamination as do higher-income communities. Toxic waste incinerators, chemical plants, and solid waste dumps are often located in low-income communities because of a lack of organized, informed community involvement in municipal decision-making processes.

III

TYPES OF POLLUTION

Pollution exists in many forms and affects many different aspects of Earth’s environment. Point-source pollution comes from specific, localized, and identifiable sources, such as sewage pipelines or industrial smokestacks. Nonpoint-source pollution comes from dispersed or uncontained sources, such as contaminated water runoff from urban areas or automobile emissions.

The effects of these pollutants may be immediate or delayed. Primary effects of pollution occur immediately after contamination occurs, such as the death of marine plants and wildlife after an oil spill at sea. Secondary effects may be delayed or may persist in the environment into the future, perhaps going unnoticed for many years. DDT, a nondegradable compound, seldom poisons birds immediately, but gradually accumulates in their bodies. Birds with high concentrations of this pesticide lay thin-shelled eggs that fail to hatch or produce deformed offspring. These secondary effects, publicized by Rachel Carson in her 1962 book, Silent Spring, threatened the survival of species such as the bald eagle and peregrine falcon, and aroused public concern over the hidden effects of nondegradable chemical compounds.

A

Air Pollution

Human contamination of Earth’s atmosphere can take many forms and has existed since humans first began to use fire for agriculture, heating, and cooking. During the Industrial Revolution of the 18th and 19th centuries, however, air pollution became a major problem. As early as 1661 British author and founding member of the British Royal Society John Evelyn reported of London in his treatise Fumifugium, “… the weary Traveller, at many Miles distance, sooner smells, than sees the City to which he repairs. This is that pernicious Smoake which fullyes all her Glory, superinducing a sooty Crust or Furr upon all that it lights.…”

Urban air pollution is commonly known as smog. The dark London smog that Evelyn wrote of is generally a smoky mixture of carbon monoxide and organic compounds from incomplete combustion (burning) of fossil fuels such as coal, and sulfur dioxide from impurities in the fuels. As the smog ages and reacts with oxygen, organic and sulfuric acids condense as droplets, increasing the haze. Smog developed into a major health hazard by the 20th century. In 1948, 19 people died and thousands were sickened by smog in the small U.S. steel-mill town of Donora, Pennsylvania. In 1952, about 4,000 Londoners died of its effects.

A second type of smog, photochemical smog, began reducing air quality over large cities like Los Angeles in the 1930s. This smog is caused by combustion in car, truck, and airplane engines, which produce nitrogen oxides and release hydrocarbons from unburned fuels. Sunlight causes the nitrogen oxides and hydrocarbons to combine and turn oxygen into ozone, a chemical agent that attacks rubber, injures plants, and irritates lungs. The hydrocarbons are oxidized into materials that condense and form a visible, pungent haze.

Eventually most pollutants are washed out of the air by rain, snow, fog, or mist, but only after traveling large distances, sometimes across continents. As pollutants build up in the atmosphere, sulfur and nitrogen oxides are converted into acids that mix with rain. This acid rain falls in lakes and on forests, where it can lead to the death of fish and plants, and damage entire ecosystems. Eventually the contaminated lakes and forests may become lifeless. Regions that are downwind of heavily industrialized areas, such as Europe and the eastern United States and Canada, are the hardest hit by acid rain. Acid rain can also affect human health and man-made objects; it is slowly dissolving historic stone statues and building facades in London, Athens, and Rome.

One of the greatest challenges caused by air pollution is global warming, an increase in Earth’s temperature due to the buildup of certain atmospheric gases such as carbon dioxide. With the heavy use of fossil fuels in the 20th century, atmospheric concentrations of carbon dioxide have risen dramatically. Carbon dioxide and other gases, known as greenhouse gases, reduce the escape of heat from the planet without blocking radiation coming from the Sun. Because of this greenhouse effect, average global temperatures are expected to rise 1.4 to 5.8 Celsius degrees (2.5 to 10.4 Fahrenheit degrees) by the year 2100. Although this trend appears to be a small change, the increase would make the Earth warmer than it has been in the last 125,000 years, possibly changing climate patterns, affecting crop production, disrupting wildlife distributions, and raising the sea level.

Air pollution can also damage the upper atmospheric region known as the stratosphere. Excessive production of chlorine-containing compounds such as chlorofluorocarbons (CFCs) (compounds formerly used in refrigerators, air conditioners, and in the manufacture of polystyrene products) has depleted the stratospheric ozone layer, creating a hole above Antarctica that lasts for several weeks each year. As a result, exposure to the Sun’s harmful rays has damaged aquatic and terrestrial wildlife and threatens human health in high-latitude regions of the northern and southern hemispheres.

B

Water Pollution

The demand for fresh water rises continuously as the world’s population grows. From 1940 to 1990 withdrawals of fresh water from rivers, lakes, reservoirs, and other sources increased fourfold. Of the water consumed in the United States in 1995, 39 percent was used for irrigation, 39 percent was used for electric power generation, and 12 percent was used for other utilities; industry and mining used 7 percent, and the rest was used for agricultural livestock and commercial purposes.

Sewage, industrial wastes, and agricultural chemicals such as fertilizers and pesticides are the main causes of water pollution. The U.S. Environmental Protection Agency (EPA) reports that about 37 percent of the country’s lakes and estuaries, and 36 percent of its rivers, are too polluted for basic uses such as fishing or swimming during all or part of the year. In developing nations, more than 95 percent of urban sewage is discharged untreated into rivers and bays, creating a major human health hazard.

Water runoff, a nonpoint source of pollution, carries fertilizing chemicals such as phosphates and nitrates from agricultural fields and yards into lakes, streams, and rivers. These combine with the phosphates and nitrates from sewage to speed the growth of algae, a type of plantlike organism. The water body may then become choked with decaying algae, which severely depletes the oxygen supply. This process, called eutrophication, can cause the death of fish and other aquatic life. Agricultural runoff may be to blame for the growth of a toxic form of algae called Pfiesteria piscicida, which was responsible for killing large amounts of fish in bodies of water from the Delaware Bay to the Gulf of Mexico in the late 1990s. Runoff also carries toxic pesticides and urban and industrial wastes into lakes and streams.

Erosion, the wearing away of topsoil by wind and rain, also contributes to water pollution. Soil and silt (a fine sediment) washed from logged hillsides, plowed fields, or construction sites, can clog waterways and kill aquatic vegetation. Even small amounts of silt can eliminate desirable fish species. For example, when logging removes the protective plant cover from hillsides, rain may wash soil and silt into streams, covering the gravel beds that trout or salmon use for spawning.

The marine fisheries supported by ocean ecosystems are an essential source of protein, particularly for people in developing countries. Yet pollution in coastal bays, estuaries, and wetlands threatens fish stocks already depleted by overfishing. In 1989, 260,000 barrels of oil was spilled from the oil tanker Exxon Valdez into Alaska’s Prince William Sound, a pristine and rich fishing ground. In 1999 there were 8,539 reported spills in and around U.S. waters, involving 4.4 billion liters (1.2 billion gallons) of oil.

C

Soil Pollution

Soil is a mixture of mineral, plant, and animal materials that forms during a long process that may take thousands of years. It is necessary for most plant growth and is essential for all agricultural production. Soil pollution is a buildup of toxic chemical compounds, salts, pathogens (disease-causing organisms), or radioactive materials that can affect plant and animal life.

Unhealthy soil management methods have seriously degraded soil quality, caused soil pollution, and enhanced erosion. Treating the soil with chemical fertilizers, pesticides, and fungicides interferes with the natural processes occurring within the soil and destroys useful organisms such as bacteria, fungi, and other microorganisms. For instance, strawberry farmers in California fumigate the soil with methyl bromide to destroy organisms that may harm young strawberry plants. This process indiscriminately kills even beneficial microorganisms and leaves the soil sterile and dependent upon fertilizer to support plant growth. This results in heavy fertilizer use and increases polluted runoff into lakes and streams.

Improper irrigation practices in areas with poorly drained soil may result in salt deposits that inhibit plant growth and may lead to crop failure. In 2000 bc, the ancient Sumerian cities of the southern Tigris-Euphrates Valley in Mesopotamia depended on thriving agriculture. By 1500 bc, these cities had collapsed largely because of crop failure due to high soil salinity. The same soil pollution problem exists today in the Indus Valley in Pakistan, the Nile Valley in Egypt, and the Imperial Valley in California.

D

Solid Waste

Solid wastes are unwanted solid materials such as garbage, paper, plastics and other synthetic materials, metals, and wood. Billions of tons of solid waste are thrown out annually. The United States alone produces about 200 million metric tons of municipal solid waste each year (see Solid Waste Disposal). A typical American generates an average of 2 kg (4 lb) of solid waste each day. Cities in economically developed countries produce far more solid waste per capita than those in developing countries. Moreover, waste from developed countries typically contains a high percentage of synthetic materials that take longer to decompose than the primarily biodegradable waste materials of developing countries.

Areas where wastes are buried, called landfills, are the cheapest and most common disposal method for solid wastes worldwide. But landfills quickly become overfilled and may contaminate air, soil, and water. Incineration, or burning, of waste reduces the volume of solid waste but produces dense ashen wastes (some of which become airborne) that often contain dangerous concentrations of hazardous materials such as heavy metals and toxic compounds. Composting, using natural biological processes to speed the decomposition of organic wastes, is an effective strategy for dealing with organic garbage and produces a material that can be used as a natural fertilizer. Recycling, extracting and reusing certain waste materials, has become an important part of municipal solid waste strategies in developed countries. According to the EPA, more than one-fourth of the municipal solid waste produced in the United States is now recycled or composted. Recycling also plays a significant, informal role in solid waste management for many Asian countries, such as India, where organized waste-pickers comb streets and dumps for items such as plastics, which they use or resell.

Expanding recycling programs worldwide can help reduce solid waste pollution, but the key to solving severe solid waste problems lies in reducing the amount of waste generated. Waste prevention, or source reduction, such as altering the way products are designed or manufactured to make them easier to reuse, reduces the high costs associated with environmental pollution.

E

Hazardous Waste

Hazardous wastes are solid, liquid, or gas wastes that may be deadly or harmful to people or the environment and tend to be persistent or nondegradable in nature. Such wastes include toxic chemicals and flammable or radioactive substances, including industrial wastes from chemical plants or nuclear reactors, agricultural wastes such as pesticides and fertilizers, medical wastes, and household hazardous wastes such as toxic paints and solvents.

About 400 million metric tons of hazardous wastes are generated each year. The United States alone produces about 250 million metric tons—70 percent from the chemical industry. The use, storage, transportation, and disposal of these substances pose serious environmental and health risks. Even brief exposure to some of these materials can cause cancer, birth defects, nervous system disorders, and death. Large-scale releases of hazardous materials may cause thousands of deaths and contaminate air, water, and soil for many years. The world’s worst nuclear reactor accident took place near Chernobyl’, Ukraine, in 1986 (see Chernobyl’ Accident). The accident killed at least 31 people, forced the evacuation and relocation of more than 200,000 more, and sent a plume of radioactive material into the atmosphere that contaminated areas as far away as Norway and the United Kingdom.

Until the Minamata Bay contamination was discovered in Japan in the 1960s and 1970s, most hazardous wastes were legally dumped in solid waste landfills, buried, or dumped into lakes, rivers, and oceans. Legal regulations now restrict how such materials may be used or disposed, but such laws are difficult to enforce and often contested by industry. It is not uncommon for industrial firms in developed countries to pay poorer countries to accept shipments of solid and hazardous wastes, a practice that has become known as the waste trade. Moreover, cleaning up the careless dumping of the mid-20th century is costing billions of dollars and progressing very slowly, if at all. The United States has an estimated 217,000 hazardous waste dumps that need immediate action. Cleaning them up could take more than 30 years and cost $187 billion.

Hazardous wastes of particular concern are the radioactive wastes from the nuclear power and weapons industries. To date there is no safe method for permanent disposal of old fuel elements from nuclear reactors. Most are kept in storage facilities at the original reactor sites where they were generated. With the end of the Cold War, nuclear warheads that are decommissioned, or no longer in use, also pose storage and disposal problems.

F

Noise Pollution

Unwanted sound, or noise, such as that produced by airplanes, traffic, or industrial machinery, is considered a form of pollution. Noise pollution is at its worst in densely populated areas. It can cause hearing loss, stress, high blood pressure, sleep loss, distraction, and lost productivity.

Sounds are produced by objects that vibrate at a rate that the ear can detect. This rate is called frequency and is measured in hertz, or vibrations per second. Most humans can hear sounds between 20 and 20,000 hertz, while dogs can hear high-pitched sounds up to 50,000 hertz. While high-frequency sounds tend to be more hazardous and more annoying to hearing than low-frequency sounds, most noise pollution damage is related to the intensity of the sound, or the amount of energy it has. Measured in decibels, noise intensity can range from zero, the quietest sound the human ear can detect, to over 160 decibels. Conversation takes place at around 40 decibels, a subway train is about 80 decibels, and a rock concert is from 80 to 100 decibels. The intensity of a nearby jet taking off is about 110 decibels. The threshold for pain, tissue damage, and potential hearing loss in humans is 120 decibels. Long-lasting, high-intensity sounds are the most damaging to hearing and produce the most stress in humans.

Solutions to noise pollution include adding insulation and sound-proofing to doors, walls, and ceilings; using ear protection, particularly in industrial working areas; planting vegetation to absorb and screen out noise pollution; and zoning urban areas to maintain a separation between residential areas and zones of excessive noise.

IV

HISTORY

Much of what we know of ancient civilizations comes from the wastes they left behind. Refuse such as animal skeletons and implements from stone age cave dwellings in Europe, China, and the Middle East helps reveal hunting techniques, diet, clothing, tool usage, and the use of fire for cooking. Prehistoric refuse heaps, or middens, discovered by archaeologists in coastal areas of North America reveal information about the shellfish diet and eating habits of Native Americans who lived more than 10,000 years ago.

As humans developed new technologies, the magnitude and severity of pollution increased. Many historians speculate that the extensive use of lead plumbing for drinking water in Rome caused chronic lead poisoning in those who could afford such plumbing. The mining and smelting of ores that accompanied the transition from the Stone Age to the Metal Age resulted in piles of mining wastes that spread potentially toxic elements such as mercury, copper, lead, and nickel throughout the environment.

Evidence of pollution during the early Industrial Revolution is widespread. Samples of hair from historical figures such as Newton and Napoleon show the presence of toxic elements such as antimony and mercury. By the 1800s, certain trades were associated with characteristic occupational diseases: Chimney sweeps contracted cancer of the scrotum (the external sac of skin enclosing the testes, or reproductive glands) from hydrocarbons in chimney soot; hatters became disoriented, or “mad,” from nerve-destroying mercury salts used to treat felt fabric; and bootblacks suffered liver damage from boot polish solvents.

During the 20th century, pollution evolved from a mainly localized problem to one of global consequences in which pollutants not only persisted in the environment, but changed atmospheric and climatic conditions. The Minamata Bay disaster was the first major indication that humans would need to pay more attention to their waste products and waste disposal practices, in particular, hazardous waste disposal. In the years that followed, many more instances of neglect or carelessness resulted in dangerous levels of contamination. In 1976 an explosion at a chemical factory in Seveso, Italy, released clouds of toxic dioxin into the area, exposing hundreds of residents and killing thousands of animals that ate exposed food. In 1978 it was discovered that the Love Canal housing development in New York State was built on a former chemical waste dump. The development was declared uninhabitable. The world’s worst industrial accident occurred in Bhopal, India, in 1984. A deadly gas leaked from an American chemical plant, killing more than 3,800 people and injuring more than 200,000.

The 1986 Chernobyl’ nuclear reactor accident demonstrated the dangerous contamination effects of large, uncontained disasters. In an unprecedented action, pollution was used as a military tactic in 1991 during the conflict in the Persian Gulf. The Iraqi military intentionally released as much as 1 billion liters (336 million gallons) of crude oil into the Persian Gulf and set fire to more than 700 oil wells, sending thick, black smoke into the atmosphere over the Middle East.

V

CONTROLLING POLLUTION

Because of the many environmental tragedies of the mid-20th century, many nations instituted comprehensive regulations designed to repair the past damage of uncontrolled pollution and prevent future environmental contamination. In the United States, the Clean Air Act (1970) and its amendments significantly reduced certain types of air pollution, such as sulfur dioxide emissions. The Clean Water Act (1977) and Safe Drinking Water Act (1974) regulated pollution discharges and set water quality standards. The Toxic Substances Control Act (1976) and the Resource Conservation and Recovery Act (1976) provided for the testing and control of toxic and hazardous wastes. In 1980 Congress passed the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), also known as Superfund, to provide funds to clean up the most severely contaminated hazardous waste sites. These and several other federal and state laws helped limit uncontrolled pollution, but progress has been slow and many severe contamination problems remain due to lack of funds for cleanup and enforcement.

International agreements have also played a role in reducing global pollution. The Montréal Protocol on Substances that Deplete the Ozone Layer (1987) set international target dates for reducing the manufacture and emissions of the chemicals, such as CFCs, known to deplete the ozone layer. The Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal (1989) serves as a framework for the international regulation of hazardous waste transport and disposal.

Since 1992 representatives from more than 160 nations have met regularly to discuss methods to reduce greenhouse gas emissions. In 1997 the Kyōto Protocol was devised, calling for industrialized countries to reduce their gas emissions by 2012 to an average 5 percent below 1990 levels. At the end of 2000 the Kyōto Protocol had not yet been ratified; negotiators were still working to find consensus on the rules, methods, and penalties that should be used to enforce the treaty.

Regulations and legislation have led to considerable progress in cleaning up air and water pollution in developed countries. Vehicles in the 1990s emit fewer nitrogen oxides than those in the 1970s did; power plants now burn low-sulfur fuels; industrial stacks have scrubbers to reduce emissions; and lead has been removed from gasoline. Developing countries, however, continue to struggle with pollution control because they lack clean technologies and desperately need to improve economic strength, often at the cost of environmental quality. The problem is compounded by developing countries attracting foreign investment and industry by offering cheaper labor, cheaper raw materials, and fewer environmental restrictions. The maquiladoras, assembly plants along the Mexican side of the Mexico-U.S. border, provide jobs and industry for Mexico but are generally owned by non-Mexican corporations attracted to the cheap labor and lack of pollution regulation. As a result, this border region, including the Río Grande, is one of the most heavily polluted zones in North America. To avoid ecological disaster and increased poverty, developing countries will require aid and technology from outside nations and corporations, community participation in development initiatives, and strong environmental regulations.

Nongovernmental citizen groups have formed at the local, national, and international level to combat pollution problems worldwide. Many of these organizations provide information and support for people or organizations traditionally not involved in the decision-making process. The Pesticide Action Network provides technical information about the effects of pesticides on farmworkers. The Citizen’s Clearinghouse for Hazardous Waste, established by veterans of the Love Canal controversy, provides support for communities targeted for hazardous waste installations. A well-organized, grassroots, environmental justice movement has arisen to advocate equitable environmental protections. Greenpeace is an activist organization that focuses international attention on industries and governments known to contaminate land, sea, or atmosphere with toxic or solid wastes. Friends of the Earth International is a federation of international organizations that fight environmental pollution around the world.

Contributed By: Paul Engelking

Microsoft ® Encarta ® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved.

Thermal Pollution

I

INTRODUCTION

Thermal Pollution, harmful increase in water temperature in streams, rivers, lakes, or occasionally, coastal ocean waters. Thermal pollution is caused by either dumping hot water from factories and power plants or removing trees and vegetation that shade streams, permitting sunlight to raise the temperature of these waters. Like other forms of water pollution, thermal pollution is widespread, affecting many lakes and vast numbers of streams and rivers in the United States and other parts of the world. A temperature increase as small as 1 or 2 Celsius degrees (about 2 to 4 Fahrenheit degrees) can kill native fish, shellfish, and plants, or drive them out in favor of other species, often with undesirable effects.

II

MAJOR SOURCES

The major sources of thermal pollution are electric power plants and industrial factories. In most electric power plants, heat is produced when coal, oil, or natural gas is burned or nuclear fuels undergo fission to release huge amounts of energy. This heat turns water to steam, which in turn spins turbines to produce electricity. After doing its work, the spent steam must be cooled and condensed back into water. To condense the steam, cool water is brought into the plant and circulated next to the hot steam. In this process, the water used for cooling warms 5 to 10 Celsius degrees (9 to 18 Fahrenheit degrees), after which it may be dumped back into the lake, river, or ocean from which it came. Similarly, factories contribute to thermal pollution when they dump water used to cool their machinery.

The second type of thermal pollution is much more widespread. Streams and small lakes are naturally kept cool by trees and other tall plants that block sunlight. People often remove this shading vegetation in order to harvest the wood in the trees, to make room for crops, or to construct buildings, roads, and other structures. Left unshaded, the water warms by as much as 10 Celsius degrees (18 Fahrenheit degrees). In a similar manner, grazing sheep and cattle can strip streamsides of low vegetation, including young trees. Even the removal of vegetation far away from a stream or lake can contribute to thermal pollution by speeding up the erosion of soil into the water, making it muddy. Muddy water absorbs more energy from the sun than clear water does, resulting in further heating. Finally, water running off of artificial surfaces, such as streets, parking lots, and roofs, is warmer than water running off vegetated land and, thus, contributes to thermal pollution.

III

IMPACTS

All plant and animal species that live in water are adapted to temperatures within a certain range. When water in an area warms more than they can tolerate, species that cannot move, such as rooted plants and shellfish, will die. Species that can move, such as fish, will leave the area in search of cooler conditions, and they will die if they can not find them. Typically, other species, often less desirable, will move into the area to fill the vacancy.

In general, cold waters are better habitat for plants and animals than warm ones because cold waters contain more dissolved oxygen. Many freshwater fish species that are valued for sport and food, especially trout and salmon, do poorly in warm water. Some organisms do thrive in warm water, often with undesirable effects. Algae and other plants grow more rapidly in warm water than in cold, but they also die more rapidly; the bacteria that decompose their dead tissue use up oxygen, further reducing the amount available for animals. The dead and decaying algae make the water look, taste, and smell unpleasant (see Eutrophication).

IV

CONTROLS

Thermal pollution from power plants and factories is relatively easy to control. Instead of discharging heated water into lakes and streams, power plants and factories can pass the heated water through cooling towers or cooling ponds, where evaporation cools the water before it is discharged. Alternatively, power plants can be designed or refitted to be more efficient and to produce less waste heat in the first place. In a process called cogeneration, the excess heat energy from generating electricity can be used in another manufacturing process that needs such energy. Where homes or other buildings are located near industrial plants, waste hot water can be used for heating—an arrangement often found in Scandinavian towns and cities, and proposed for use in China.

In the United States, the problem of industrial thermal pollution was first addressed in 1970, when Congress gave the Atomic Energy Commission authority to regulate thermal pollution from nuclear power plants. In 1972, the comprehensive Clean Water Act instructed the Environmental Protection Agency to issue regulations to clean up all hot water discharges from all power plants, nuclear or conventional. Since then, thermal pollution from power plants has not been a major issue in the United States.

To prevent thermal pollution due to devegetation, the prescription is simple: do not devegetate. Landowners can leave strips of trees and vegetation along streams and shorelines. Grazing livestock can be kept away from streamsides by fencing. All efforts to control erosion also have the effect of keeping water clearer and, thus, cooler.

As a practical matter, however, thermal pollution from devegetation is quite hard to control because it is caused by the cumulative effect of many peoples’ actions, most of which are individually minor. Regulations focus on a few of the most important threats. Grazing management plans, for instance, are intended to counter thermal pollution and other problems on lands owned by the federal government. In the United States, regulations governing logging on both public and private lands supposedly protect streamsides, though enforcement is often lax. Elsewhere, streamside protection is largely up to private landowners, encouraged and aided by such advisory organizations as the federal Natural Resources Conservation Service and cooperative Resource Conservation Districts.

Contributed By: John Hart

Microsoft ® Encarta ® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved.

Noise Pollution

I

INTRODUCTION

Noise Pollution or Sound Pollution, exposure of people or animals to levels of sound that are annoying, stressful, or damaging to the ears. Although loud and frightening sounds are part of nature, only in recent centuries has much of the world become urban, industrial, and chronically noisy.

Sound intensity is measured in units called decibels. The decibel scale is logarithmic and climbs steeply: An increase of about three decibels is a doubling of sound volume. In the wilderness, a typical sound level would be 35 decibels. Speech runs 65 to 70 decibels; heavy traffic generates 90 decibels. By 140 decibels, sound becomes painful to the human ear, but ill effects, including hearing loss, set in at much lower levels.

Most noise pollution comes from machines, especially automobiles, trucks, and aircraft. Construction equipment, farm machines, and the din of machinery inside factories can be dangerously loud. Some home appliances, shop tools, lawnmowers, and leaf blowers can also be noisy, as are guns, firecrackers, and some toys. Even music, when played at very high volume, particularly through personal headphones, is as damaging to the ears as a roaring chain saw.

Even the oceans are increasingly noisy. The engines of ships, especially large vessels and supertankers, produce a lot of sound, and traffic is increasing. Offshore oil exploration and drilling are also noisy. And more recently, very loud, low-frequency sonar signals are being sent through the seas to detect submarines and to gain information about water temperatures and global warming.

II

IMPACTS

The most significant health problem caused by noise pollution is hearing loss (see Deafness). Any noise appreciably louder than talking can damage the delicate hair cells in the cochlea, the structure in the inner ear that converts sound waves into auditory nerve signals. The initial damage to the cochlea may be temporary, but with repeated exposure, the damage becomes permanent. Loud noise deafens quickly—extremely loud sounds, such as gunshots at close range, can cause immediate hearing loss. But even sound levels of only 85 decibels will cause some hearing loss after prolonged exposure. Ten million Americans have some hearing loss due partly or wholly to exposure to loud sounds, and 20 million are at risk. In addition to deafness, many people with damaged ears are afflicted with tinnitus, or ringing in the ears.

Most hearing loss occurs in workplaces, where workers may be unable to avoid unhealthy noise, and where exposure may continue for years. Factory workers, construction workers, farmers, military personnel, police officers, firefighters, and musicians all have reason to be concerned about their occupational exposure to noise.

Even at levels below those that cause hearing loss, noise pollution produces problems. Noise makes conversation difficult, interferes with some kinds of work, and disturbs sleep. As a source of stress, it can promote high blood pressure and other cardiovascular problems, as well as nervous disorders. According to the National Institutes of Health, 65 million Americans are exposed to noise levels that can hamper their work or disrupt their sleep, and 25 million risk health problems due to noise.

Noise also puts stress on domestic animals and wildlife. In remote areas, helicopters and military aircraft often frighten animals. Aircraft noise in Alaska, for example, has been shown to reduce the survival rate of caribou calves. There is concern that increasing noise levels in the oceans may confuse the natural sonar that whales use to navigate, communicate, and locate food.

III

CONTROLS

Noise pollution is not a necessary price to pay for living in an industrial society. Much can be done to reduce the severity of the problem. For example, vehicles and other machines can be built to produce less noise. Four-cycle engines can replace much noisier two-cycle engines in such products as lawnmowers, motorboats, and jet skis. Labels that indicate the noise levels of appliances and tools can help consumers avoid noisy products and choose quieter alternatives.

Even after noise is generated, steps can be taken to reduce human exposure to it. At homes or in offices, insulation of walls and double-glazing of windows can muffle sound from traffic, neighbors, and other sources from the outside world. Sound walls along highways can shield nearby neighborhoods from traffic noise. Individuals should protect themselves with earplugs or mufflike ear protectors, particularly when noise levels exceed 85 decibels.

In the industrialized nations, governments have laws and policies to counter noise pollution. In the United States, at least six federal agencies are involved in controlling noise pollution. Since 1969 the Federal Aviation Administration (FAA) has monitored and controlled noise from airplanes. The agency requires that new aircraft meet specified noise standards and that old ones be retrofitted or retired. Local airport authorities, with FAA approval, reduce the impacts of noise pollution by routing flights over water or unpopulated areas on takeoff and landing, and by limiting traffic at night. The FAA also encourages airports and local governments to take steps on the ground, such as constructing sound barriers, insulating buildings, and restricting residential development in noisy areas. In extreme cases, airports have relocated people living under flight paths.

The Occupational Safety and Health Administration (OSHA) is charged with reducing noise in workplaces. Under OSHA regulations, no exposure above 115 decibels is permitted, exposure up to 115 decibels is limited to 15 minutes for an 8-hour shift, and average noise levels above 85 decibels are regulated. OSHA requires employers to measure noise levels, to muffle extremely noisy equipment, to provide ear-protection gear if necessary, and to offer regular hearing tests to workers who are regularly exposed to high sound levels. The Bureau of Mine Safety has comparable rules to protect miners. The Department of Housing and Urban Development and the Veterans Administration require noise-proofing in dwellings whose mortgages they finance. The Department of Defense even has noise standards for certain military situations.

In 1972 Congress passed a Noise Control Act establishing an Office of Noise Abatement and Control in the Environmental Protection Agency. The office conducted research, coordinated the work of other agencies, and directly set noise standards for trucks, motorcycles, air compressors, truck-mounted garbage compactors, and railroads. More standards would have followed, but in 1981 Congress cut off funding for this effort.

Some state and many local governments work to reduce noise pollution. State and local building codes include noise insulation requirements, and land-use planning is used to keep noise sources away from housing and offices. Local ordinances can ban the use of some equipment, such as leaf blowers, or limit use to certain times of day.

In the last 30 years, the United States and other countries have expended considerable efforts to control noise pollution. Most vehicles and many other noise producers are quieter than they used to be. On the other hand, there are more noise-making machines than ever, operating more of the time. In the United States, most of the rules governing noise pollution were established at least two decades ago, and critics are calling for new, stronger measures, as well as for better enforcement of the old ones. What is true of most other kinds of pollution is also true of noise: Our best efforts against it tend merely to keep matters from getting dramatically worse.

Contributed By: John Hart

Microsoft ® Encarta ® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved.

Environment

I

INTRODUCTION

Environment, all of the external factors affecting an organism. These factors may be other living organisms (biotic factors) or nonliving variables (abiotic factors), such as water, soil, climate, light, and oxygen. All interacting biotic and abiotic factors together make up an ecosystem.

Organisms and their environment constantly interact, and both are changed by this interaction. Additionally, environmental factors, singly or in combination, ultimately limit the size that any population may attain. This limit, a population’s carrying capacity, is usually reached because needed resources are in short supply. Occasionally, carrying capacity may be dictated by the direct actions of other species, as when predators limit the number of their prey in a specific area.

Like all other living beings, humans have clearly changed their environment, but they have done so generally on a grander scale than have other species. Some of these changes—such as the destruction of the world’s tropical rain forests to create grazing land for cattle or the drying up of almost three-quarters of the Aral Sea, once the world’s fourth-largest freshwater lake, for irrigation purposes—have led to altered climate patterns, which in turn have changed the distribution of species of animals and plants.

Scientists are working to understand the long-term consequences that human actions have on ecosystems, while environmentalists—professionals in various fields, as well as concerned citizens in the United States and other countries—are struggling to lessen the impact of human activity on the natural world.

II

UNDERSTANDING THE ENVIRONMENT

The science of ecology is the study of the interactions that determine the abundance and distribution of organisms. In other words, ecology attempts to explain why individuals live where they do and why their populations are the sizes they are.

No population, human or otherwise, can grow indefinitely; eventually, some biotic or abiotic variable will begin to limit population growth. This basic ecological principle was first established in 1840 by German chemist Justus von Liebig and has been called the Law of the Minimum. From a human standpoint, this means that all of the world’s physical resources are in finite supply.

Ecologists also have discovered that all species in an ecosystem interact with one another, either directly or indirectly. A classic ecological experiment illustrates this point very well. American ecologist Robert Paine, working in the rocky intertidal region of the Pacific coast, found stable invertebrate communities dominated by 15 species of animals, including starfish, mussels, limpets, barnacles, and chitons. When Paine removed all of the starfish from the area, the community collapsed, and eventually only 8 invertebrate species were common. Although it was not obvious in the undisturbed regions, the starfish were preying heavily on one of the mussel species and keeping its numbers down. With the starfish removed, the population of this mussel increased, and the mussel was able to outcompete many other species of invertebrates. Thus, the loss of one species, the starfish, indirectly led to the loss of an additional six species and a transformation of the community.

Typically, because the species that coexist in natural communities have evolved together for many generations, they have established a balance, and their populations remain relatively stable. Occasionally, when humans introduce a non-native species to an ecosystem, dramatic disruptions occur, often because the natural predators of the introduced species are not present. For example, early sailors routinely introduced goats to isolated oceanic islands, intending for the goats to roam freely and serve as a source of meat when the sailors later came ashore. Free from all natural predators, the goats thrived and, in the process, overgrazed many of the islands. With a change in plant composition, many of the native animal species were driven to extinction. A simple action, the introduction of goats to an island, yielded many changes in the island ecosystem, demonstrating that all members of a community are closely interconnected.

In the 1970s the British scientist James Lovelock formulated the Gaia hypothesis, which has attracted many followers. According to this theory, named after the Greek goddess of the earth, the planet behaves like a single living organism. Lovelock postulated that the earth, like many organisms, can regulate its temperature, dispose of its wastes, and fight off disease. Although the Gaia hypothesis serves as a convenient metaphor for the interconnections among living beings, it does not have any particular scientific merit.

From a scientific viewpoint, the earth is not a single living organism, but it can be viewed as a single integrated system. The National Aeronautics and Space Administration (NASA), using its expertise in planetary and space sciences, is collaborating with other U.S. governmental agencies in the use of artificial satellites to study global change. NASA’s undertaking, begun in 1991, is called Mission to Planet Earth. This project is part of an international effort linking numerous satellites into a single Earth Observing System (EOS). EOS is designed to increase knowledge of the interactions taking place among the atmosphere, land, and oceans; to assess the impact of natural and human events on the planet; and to provide the data that permit sound environmental policy decisions to be made.

III

HISTORY OF ENVIRONMENTALISM

The modern American environmental movement is rooted in a 19th-century New England philosophical movement called transcendentalism, of which the poet and essayist Ralph Waldo Emerson and the naturalist and author Henry David Thoreau were leaders. In their writings, both expressed a reverence for the natural world, believing that humans and nature shared a divine spirit. Emerson asserted that nature was eternal and, much like the Gaia followers of the present day, contended that it was capable of recovering from mistreatment at the hands of humans. Thoreau, more protective and pessimistic, has been quoted as saying, “Thank God, men cannot yet fly and lay waste the sky as well as the earth.”

Although Emerson and Thoreau wrote eloquently about the value of nature and its spiritual importance to humans, neither of them undertook a systematic analysis of the effects that humans could have on their environment. That task was left for George Perkins Marsh, who published Man and Nature; or, Physical Geography as Modified by Human Action in 1864. This important book was the first to demonstrate that human activity could cause dramatic and irreversible damage to the earth. Marsh explained how agricultural practices had led to deforestation, loss of wetlands, desertification (the process of land becoming desert), species extinction, and changes in weather patterns.

Protection of federal lands defined the tenure of U.S. President Theodore Roosevelt, and during his years in office, from 1901 to 1909, he greatly expanded both the national forest and national park systems and created a system of national wildlife refuges. Roosevelt appointed forester Gifford Pinchot as head of the U.S. Forest Service, and together they molded American conservation on two major premises. They recognized that even the vast natural resources of the United States were not limitless and thus had to be managed carefully, and they believed that those resources should be used for the betterment of the American people. Roosevelt, thinking broadly about resources, claimed that one of the most valuable natural assets was the American people themselves, and he argued that the protection of human health was a central and valid focus for the conservation movement.

Roosevelt also was a friend of Scottish-American naturalist and essayist John Muir, founder of the Sierra Club. Muir’s philosophical approach to the environment was very different from Pinchot’s: Muir valued nature for its own sake and argued forcefully to protect species and preserve wilderness, whereas Pinchot was much more concerned with the use of natural resources to serve human needs. Their perspectives fully diverged in the debate over California’s Hetch Hetchy Valley, often considered a twin to the Yosemite Valley, also in California. Pinchot wanted to dam the Tuolumne River and flood the valley to provide water and electricity to San Francisco, while Muir thought the destruction of such a natural wonder an abomination. Roosevelt sided with Pinchot and the dam was authorized in 1913.

When Franklin D. Roosevelt assumed the U.S. presidency in 1933, he continued and expanded on the conservation efforts begun earlier in the century during the administration of his second cousin. Not only did he expand national parks and national forests, but, in response to the twin challenges of massive unemployment in the Great Depression and environmental havoc wreaked by the Dust Bowl conditions in the Midwest, he created the Civilian Conservation Corps to replant forests and improve recreational opportunities on public land and the Soil Conservation Service to protect valuable topsoil.

In 1962 in her book Silent Spring, American biologist Rachel Carson warned of the grave dangers posed by the indiscriminate use of dichlorodiphenyltrichloroethane (DDT) and related pesticides. The title suggested a time when birds, their populations greatly reduced by pesticides, could no longer be heard singing in the spring. Carson, by arguing that humans as well as wildlife were at risk, issued a call to action. A combination of solid science, a reverence for nature as strong as that of the transcendentalists, and a wonderfully poetic style moved people to a new level of environmental awareness and activism.

On April 22, 1970, the first Earth Day, approximately 20 million Americans gathered at various sites across the country to protest corporate and governmental abuse of the environment. Earth Day, the events leading up to it, and its aftermath transformed American culture. Environmental awareness became much more commonplace, and numerous grassroots environmental organizations were established to work for political change, including the Environmental Defense Fund in 1967, Friends of the Earth in 1968, Greenpeace in 1970, the Natural Resources Defense Council in 1970, and the Sierra Club Legal Defense Fund in 1971.

IV

LEGISLATION AND LITIGATION

The strong environmental sentiments that led to Earth Day yielded dramatic changes in American legislation and reflected an expanded set of priorities. In 1964 the Congress of the United States passed the Wilderness Act in an attempt to set aside, in the words of the act, “an area where earth and its community of life are untrammeled by man”; the lands designated as wilderness areas were to be “affected primarily by nature.” In 1968 Congress adopted the Wild and Scenic Rivers Act to ensure that at least some of the scenic and recreational value of the country’s rivers was preserved in the face of a growing number of dams and riverside development.

In 1970 the Environmental Protection Agency (EPA) was established, and attention began to shift toward pollution control and the establishment of national environmental quality standards. The EPA was responsible for the environmental well-being of the country as defined through numerous specific pieces of legislation. One of these, the Clean Air Act of 1970, became the model for future measures. The act established national air-quality standards, gave states the responsibility for developing and enforcing plans to use these standards, and set up compliance schedules. Additionally, the act made federal funding available to states to assist in their efforts. The National Environmental Protection Act (NEPA), also enacted in 1970, required an environmental assessment of all federally funded projects.

The Occupational Safety and Health Administration (OSHA) was formed in 1970 as well, although it was placed under the control of the Department of Labor rather than the EPA. Reflecting Theodore Roosevelt’s belief that human health was a natural resource worthy of protection, OSHA’s mission was “to assure so far as possible every working man and woman in the Nation safe and healthful working conditions.”

In 1972 Congress passed the Clean Water Act, designed to do for the nation’s water supply what the Clean Air Act accomplished for the atmosphere. The Endangered Species Act was passed the following year and has been described by the Supreme Court of the United States as “the most comprehensive legislation for the preservation of endangered species ever enacted by any nation.” The most important aspect of the legislation is its reliance on scientific rather than economic data.

The Resource Conservation and Recovery Act (RCRA) was adopted in 1976 with the twin goals of protecting human health and the environment and conserving valuable natural resources. Through this act, the federal government took a more active role in controlling solid and hazardous waste, as well as in promoting recycling. Despite the good intentions of RCRA, numerous hazardous waste sites were created throughout the country. To combat the dangers posed by these sites, Congress passed the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980. Known as Superfund, the act created a $15 billion fund of public money, to be increased by taxes on polluting industries. As huge as this fund is, it is inadequate to deal with the thousands of hazardous sites in need of cleanup. The vast majority of these sites occur on federal military reservations. Of the 35,000 sites screened since the passage of CERCLA in 1980, the EPA has chosen or is considering 1295 sites for its National Priorities List and estimates that 3000 sites eventually could be given this status.

The body of federal environmental legislation has been under increasing attack since the election of Ronald Reagan as president in 1980. Conservatives have argued that too much public money is being spent on the environment and that the federal government should play a much-reduced role in environmental regulation. In addition, some people believe that most restrictions on the use of private property are forbidden by the Fifth Amendment to the Constitution of the United States, which prohibits the taking of property “without just compensation.” When environmental laws limit use, the argument goes, property values decline and the government has “taken” or reduced the worth of private holdings. The U.S. Supreme Court has agreed with this reasoning and ruled that some environmental protection laws have placed unfair burdens on property owners. As each piece of environmental legislation is modified or comes before Congress for reauthorization, battles are fought between those who believe industry and development are being unnecessarily stifled and those who contend that the environment is being irreparably damaged.

Environmental advocacy groups have regularly taken to the courts in defense of the environment. Suits have been filed against the federal government in the hope of compelling its various agencies to enforce congressionally mandated acts. Additionally, advocacy groups have sued corporations directly for failing to follow various environmental laws.

V

A GLOBAL APPROACH

The environmental concerns growing in the United States during the late 1960s and early 1970s increased internationally as well. Perhaps the biggest impetus for developing a worldwide effort to monitor and restrict global pollution is the fact that most forms of pollution do not respect national boundaries. The first major international conference on environmental issues was held in Stockholm, Sweden, in 1972 and was sponsored by the United Nations (UN). This meeting, at which the United States took a leading role, was controversial because many developing countries were fearful that a focus on environmental protection was a means for the developed world to keep the undeveloped world in an economically subservient position. The most important outcome of the conference was the creation of the United Nations Environmental Programme (UNEP).

UNEP was designed to be “the environmental conscience of the United Nations,” and, in an attempt to allay fears of the developing world, it became the first UN agency to be headquartered in a developing country, with offices in Nairobi, Kenya. In addition to attempting to achieve scientific consensus about major environmental issues, a major focus for UNEP has been the study of ways to encourage sustainable development—increasing standards of living without destroying the environment. At the time of UNEP’s creation in 1972, only 11 countries had environmental agencies. Ten years later that number had grown to 106, of which 70 were in developing countries.

A growing number of international agreements have been reached in an effort to improve the world’s environmental status. In 1975 the Convention on International Trade in Endangered Species of Wild Fauna and Flora(CITES) went into effect with the goal of reducing commerce in animals and plants on the edge of extinction. In 1982 the International Whaling Commission agreed to a moratorium on all commercial whaling. Perhaps the most important international agreement was the 1987 Montréal Protocol on Substances that Deplete the Ozone Layer. For the first time, an international pact was signed that set specific targets for reducing emissions of chemicals responsible for the destruction of the earth’s ozone layer. The international community again came together in 1989 to limit the movement of hazardous wastes among countries.

Twenty years after the Stockholm Conference, the UN Conference on Environment and Development was held in Rio de Janeiro, Brazil, in 1992. Popularly known as the Earth Summit, this meeting was the largest gathering of world leaders in history. The conference produced two major treaties. The first was an agreement to reduce emission of gases leading to global warming, and the second was a pact on biodiversity requiring countries to develop plans to protect endangered species and habitats. At the insistence of the United States, however, the final version of the global warming treaty was dramatically scaled back. The United States was also one of the very few countries that refused to sign the biodiversity treaty. United States representatives objected to a part of the treaty that specified that money to come from the use of natural resources from protected ecosystems, such as rain forests, should be shared equally between the source country and the corporation or institution removing the materials.

The 1992 agreement on global warming limits each industrialized nation to emissions in the year 2000 that are equal to or below 1990 emissions. However, these limits are voluntary and no enforcement provisions were included in the agreement. By 1997 the fact that the goals would not be met was clear. At a follow-up conference in Kyōto, Japan, representatives from 160 countries signed a new agreement, known as the Kyōto Protocol. This agreement calls for the industrialized nations to reduce emissions to an average of about 5 percent below 1990 emission levels and to reach this goal between the years 2008 and 2012.

A desire for environmental change led to the creation of various political parties around the world whose emphasis was largely on environmental protection. The first of these organizations, collectively known as green parties, was the Values Party in New Zealand, created in 1972. By far the most successful has been the green party of West Germany, Die Grunen, which in 1983 won nearly 6 percent of the seats in the West German Parliament. Green parties have developed in almost all countries that have open elections, but they have had the largest impact in those nations where proportional representation within a parliamentary system occurs. Thus, the green parties have not played a significant role in American politics. In 1993, 23 green parties from eastern and western Europe came together to form the European Federation of Green Parties, with the hope that together they would have the leverage necessary to demand that environmental issues such as pollution control, population growth, and sustainable development be more fully addressed by various national governments and international bodies.

VI

CURRENT ISSUES

In November 1992 a document entitled Warning to Humanity was released. This alarm was signed by 1500 scientists from around the world, including 99 Nobel laureates, a dozen national academies of science, the Pontifical Academy of Science, and the director general of the United Nations Educational, Scientific and Cultural Organization (UNESCO). The document was bold and clear, stating that “human beings and the natural world are on a collision course,” which “may so alter the living world that it will be unable to sustain life in the manner that we know.”

The problems facing the environment are vast and diverse. Destruction of the world’s rain forests, global warming, and the depletion of the ozone layer are just some of the problems that will reach critical proportions in the coming decades. Their rates will be directly affected by the size of the human population.

A

Population Growth

Human population growth may be seen to be at the root of virtually all of the world’s environmental problems. Increasingly large numbers of people are being added to the world every year. As the number of people increases, more pollution is generated, more habitats are destroyed, and more natural resources are used up. Even if new technological advances were able to cut in half the environmental impact that each person had, as soon as the world’s population size doubled, the earth would be no better off than before.

The Population Division of the United Nations predicts that the 5.63 billion humans alive in 1994 will increase to 6.23 billion in the year 2000, 8.47 billion in 2025, and 10.02 billion in 2050. The UN’s estimate assumes that population will peak and stabilize at 11.6 billion in 2200. Others predict that numbers will continue to rise into the foreseeable future, to as many as 19 billion people in 2200.

Although it is true that rates of population increase are now much slower in the developed world than in the developing world, it would be a mistake to assume that the population growth problem is primarily a problem of developing countries. In fact, because larger amounts of resources per person are used in the developed nations, each citizen from the developed world has a much greater environmental impact than does a citizen from a developing country. Conservation strategies that would not alter lifestyles but would greatly lessen environmental impact are essential in the developed world.

Evidence now exists suggesting that the most important factors necessary to lower population growth rates in the developing world are democracy and social justice. Studies show that population growth rates have fallen in areas where several social conditions have been met. In these areas, literacy rates have increased, and women are given economic status equal to that of men and thus are able to hold jobs and own property; also, birth control information is more widely available, and women are free to make their own reproductive decisions.

B

Global Warming

Like the glass panes in a greenhouse, certain gases in the earth’s atmosphere permit the sun’s radiation to heat the earth but retard the escape into space of the infrared energy radiated back out by the earth. This process is referred to as the greenhouse effect. These gases, primarily carbon dioxide, methane, nitrous oxide, and water vapor, insulate the earth’s surface, helping to maintain warm temperatures. Without these gases, the earth would be a frozen planet with an average temperature of about -18° C (about 0° F) instead of a comfortable 15° C (59° F). If the concentration of these gases were higher, more heat would be trapped within the atmosphere, and worldwide temperatures would rise.

Within the last century, the amount of carbon dioxide in the atmosphere has increased dramatically, largely because of the practice of burning fossil fuels—coal and petroleum and its derivatives. Global temperature has also increased 1° C (about 1.8° F) within the past century. Atmospheric scientists have now concluded that at least half of that increase can be attributed to human activity, and they have predicted that unless dramatic action is taken, temperature will continue to rise by between 1° and 3.5° C (between 1.8° and 6.3° F) over the next century. Although this may not seem like a great difference, global temperature was only 2.2° C (4° F) cooler during the last ice age than it is presently. The consequences of such a modest increase in temperature may well be devastating. Sea levels will rise, completely inundating a number of low-lying island nations and flooding many coastal cities such as New York and Miami. Many plant and animal species will probably be driven into extinction, agricultural regions will be disrupted, and the frequency of severe hurricanes and droughts is likely to increase.

C

Depletion of the Ozone Layer

The ozone layer, a thin band in the stratosphere (a layer in the upper atmosphere), serves to shield the earth from the sun’s harmful ultraviolet rays. In the 1970s, scientists discovered that the layer was being attacked by chlorofluorocarbons (CFCs), chemicals used in refrigeration, air-conditioning systems, cleaning solvents, and aerosol sprays. CFCs release chlorine into the atmosphere; chlorine, in turn, breaks ozone down into its constituent parts of oxygen. Because chlorine is not affected by its interaction with ozone, each chlorine molecule has the ability to destroy a large amount of ozone for an extended period of time.

The consequences of the depletion of the ozone layer are dramatic. Increased ultraviolet radiation will lead to a growing number of skin cancers and cataracts and also reduce the ability of people’s immune systems to respond to infection. Additionally, the growth rates of the world’s oceanic plankton, the base of most marine food chains, will be negatively affected, perhaps leading to increased atmospheric carbon dioxide and thus to global warming. Even if the manufacture of CFCs was immediately banned, the chlorine already released into the atmosphere would continue to destroy the ozone layer for many decades. Additionally, the latest studies suggest that global warming may increase the amount of ozone destroyed.

Predicting the rate of ozone depletion is difficult. Optimists claim that if international agreements for the phasing out of ozone-depleting chemicals agreed to in Montréal in 1987 are followed, ozone loss will peak in the year 2000. With many of the world’s fastest growing countries in the process of industrializing and modernizing, there is reason to believe that destruction will continue to increase well beyond that year.

D

Air Pollution

A significant portion of industry and transportation is based on the burning of fossil fuels, such as gasoline. As these fuels are burned, chemicals and particulate matter are released into the atmosphere. Although a vast number of substances contribute to air pollution, the most common contain carbon, sulfur, and nitrogen. These chemicals interact with one another and with ultraviolet radiation in sunlight in various dangerous ways. Smog, usually found in urban areas with large numbers of automobiles, is formed when nitrogen oxides react with hydrocarbons in the air to produce aldehydes and ketones. Smog can cause serious health problems. When sulfur dioxide and nitrous oxide are transformed into sulfuric acid and nitric acid in the atmosphere and come back to earth in precipitation, they form acid rain. Acid rain is a serious global problem because few species are capable of surviving in the face of such acidic conditions. Acid rain has made numerous lakes so acidic that they no longer support fish populations. Acid rain is also thought to be responsible for the decline of many forest ecosystems worldwide. Germany’s Black Forest has suffered dramatic losses, and recent surveys suggest that similar declines are occurring throughout the eastern United States.

E

Water Pollution

Estimates suggest that nearly 1.5 billion people lack safe drinking water and that at least 5 million deaths per year can be attributed to waterborne diseases. Water pollution may come from point or nonpoint sources. Point sources discharge pollutants at specific locations—from, for example, factories, sewage treatment plants, or oil tankers. The technology exists for point sources of pollution to be monitored and regulated, although political factors may complicate matters. Nonpoint sources—runoff water containing pesticides and fertilizers from acres of agricultural land, for example—are much more difficult to control. Pollution arising from nonpoint sources accounts for a majority of the contaminants in streams and lakes.

With almost 80 percent of the planet covered by oceans, people have long acted as if those bodies of water could serve as a limitless dumping ground for wastes. Raw sewage, garbage, and oil spills have begun to overwhelm the diluting capabilities of the oceans, and most coastal waters are now polluted. Beaches around the world are closed regularly, often because of high amounts of bacteria from sewage disposal, and marine wildlife is beginning to suffer.

F

Groundwater Depletion

Water that seeps through porous rocks and is stored beneath the ground is called groundwater. Worldwide, groundwater is 40 times more abundant than fresh water in streams and lakes, and although groundwater is a renewable resource, reserves are replenished relatively slowly. In the United States, approximately half the drinking water comes from groundwater. Presently, groundwater in the United States is being withdrawn approximately four times faster than it is being naturally replaced. The Ogallala Aquifer, a huge underground reservoir stretching under eight states of the Great Plains, is being drawn down at rates exceeding 100 times the replacement rate, suggesting that agricultural practices depending on this source of water may have to change within a generation. When groundwater is depleted in coastal regions, oceanic salt water commonly intrudes into freshwater supplies. Saltwater intrusion is threatening the drinking water of many areas along the Gulf and Atlantic coasts.

The EPA has estimated that, on average, 25 percent of usable groundwater is contaminated, although in some areas as much as 75 percent is contaminated. Contamination arises from leaking underground storage tanks, poorly designed industrial waste ponds, and seepage from the deep-well injection of hazardous wastes into underground geologic formations. Because groundwater is recharged and flows so slowly, once polluted it will remain contaminated for extended periods.

G

Habitat Destruction and Species Extinction

It is difficult to estimate the rate at which humans are driving species extinct because scientists believe that only a small percentage of the earth’s species have been described. What is clear is that species are dying out at an unprecedented rate; minimum estimates are at least 4000 species per year, although some scientists believe the number may be as high as 50,000 per year. The leading cause of extinction is habitat destruction, particularly of the world’s richest ecosystems—tropical rain forests and coral reefs. At the current rate at which the world’s rain forests are being cut down, they may completely disappear by the year 2030. If growing population size puts even more pressure on these habitats, they might well be destroyed sooner.

Since European colonization, North America has been transformed: Approximately 98 percent of tall-grass prairies, 50 percent of wetlands, and 98 percent of old-growth forests have been destroyed. This loss is critical from several perspectives. The economic value of species lost and of natural products and drugs that never will be discovered or produced is incalculable. Similarly, it is impossible to place either a moral or an aesthetic value on our growing list of extinct species. As habitats are destroyed and species lost, the world is increasingly losing threads from the interconnected fabric of life.

H

Chemical Risks

Pesticide residues on crops and mercury in fish are examples of toxic substances that may be encountered in daily life. Many industrially produced chemicals may cause cancer, birth defects, genetic mutations, or death. Although a growing list of chemicals has been found to pose serious health risks to humans, the vast majority of substances have never been fully tested. In recent studies, a wide range of chemicals has been found to mimic estrogen, the hormone that normally controls the development of the female reproductive system in a large number of animal species. Preliminary results indicate that these chemicals, in trace amounts, may disrupt development and lead to a host of serious problems in both males and females, including infertility, increased mortality of offspring, and behavioral changes such as increased aggression. Numerous studies have found that the amount of sperm produced by men has decreased precipitously over the past 50 years.

I

Environmental Racism

Studies have shown that not all individuals are equally exposed to pollution. For example, toxic waste sites are more prevalent in poorer communities, and the single most important factor in predicting the location of hazardous-waste sites in the United States is the ethnic composition of a neighborhood. Three of the five largest commercial hazardous waste landfills in America are in predominantly black or Hispanic neighborhoods, and three out of every five black and Hispanic Americans live in the vicinity of an uncontrolled toxic waste site. The fact that the wealth of a community is not nearly as good a predictor of hazardous-waste locations as is the ethnic background of the residents reinforces the conclusion that racism is involved in the selection of sites for hazardous-waste disposal.

Environmental racism takes international forms as well. Dangerous chemicals banned in the United States often continue to be produced and shipped to developing countries. Additionally, the developed world has shipped large amounts of toxic waste to developing countries for less-than-safe disposal.

J

Energy Production

The world cannot continue to rely on the burning of fossil fuels for much of its industrial production and transportation. Fossil fuels are in limited supply; in addition, when burned they contribute to global warming, air pollution, and acid rain.

Nuclear energy as an alternative is opposed by many because of the massive devastation an accident can cause. The accident at the Chernobyl’ nuclear power plant in 1986 scattered radioactive contamination over a large part of Europe (see Chernobyl’ Accident). Approximately 135,000 people were evacuated, and human health has been dramatically affected. The World Health Organization released a report in late 1995 attributing the “explosive increase” in childhood thyroid cancer in Belarus, Ukraine, and Russia directly to the accident.

One reasonable solution is to combine conservation strategies with the increased use of solar energy. The price of solar energy relative to traditional fuels has been dropping steadily, and if environmental concerns were factored into the cost, solar power would already be significantly cheaper. Although it is desirable to have a wider range of energy options, other alternative sources of power (such as wind, geothermal, or hydroelectric) are not likely to provide large-scale solutions in the forseeable future.

K

Other Issues

Global environmental collapse is not inevitable. But the developed world must work with the developing world to ensure that new industrialized economies do not add to the world’s environmental problems. Politicians must think of sustainable development rather than economic expansion. Conservation strategies have to become more widely accepted, and people must learn that energy use can be dramatically diminished without sacrificing comfort. In short, with the technology that currently exists, the years of global environmental mistreatment can begin to be reversed.

Contributed By: Michael Zimmerman

Microsoft ® Encarta ® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved.

Greenhouse Effect

I

INTRODUCTION

Greenhouse Effect, the capacity of certain gases in the atmosphere to trap heat emitted from the Earth’s surface, thereby insulating and warming the Earth. Without the thermal blanketing of the natural greenhouse effect, the Earth’s climate would be about 33 Celsius degrees (about 59 Fahrenheit degrees) cooler—too cold for most living organisms to survive.

The greenhouse effect has warmed the Earth for over 4 billion years. Now scientists are growing increasingly concerned that human activities may be modifying this natural process, with potentially dangerous consequences. Since the advent of the Industrial Revolution in the 1700s, humans have devised many inventions that burn fossil fuels such as coal, oil, and natural gas. Burning these fossil fuels, as well as other activities such as clearing land for agriculture or urban settlements, releases some of the same gases that trap heat in the atmosphere, including carbon dioxide, methane, and nitrous oxide. These atmospheric gases have risen to levels higher than at any time in the last 420,000 years. As these gases build up in the atmosphere, they trap more heat near the Earth’s surface, causing Earth’s climate to become warmer than it would naturally.

Scientists call this unnatural heating effect global warming and blame it for an increase in the Earth’s surface temperature of about 0.6 Celsius degrees (about 1 Fahrenheit degree) over the last nearly 100 years. Without remedial measures, many scientists fear that global temperatures will rise 1.4 to 5.8 Celsius degrees (2.5 to 10.4 Fahrenheit degrees) by 2100. These warmer temperatures could melt parts of polar ice caps and most mountain glaciers, causing a rise in sea level of up to 1 m (40 in) within a century or two, which would flood coastal regions. Global warming could also affect weather patterns causing, among other problems, prolonged drought or increased flooding in some of the world’s leading agricultural regions.

II

HOW THE GREENHOUSE EFFECT WORKS

The greenhouse effect results from the interaction between sunlight and the layer of greenhouse gases in the Earth's atmosphere that extends up to 100 km (60 mi) above Earth's surface. Sunlight is composed of a range of radiant energies known as the solar spectrum, which includes visible light, infrared light, gamma rays, X rays, and ultraviolet light. When the Sun’s radiation reaches the Earth’s atmosphere, some 25 percent of the energy is reflected back into space by clouds and other atmospheric particles. About 20 percent is absorbed in the atmosphere. For instance, gas molecules in the uppermost layers of the atmosphere absorb the Sun’s gamma rays and X rays. The Sun’s ultraviolet radiation is absorbed by the ozone layer, located 19 to 48 km (12 to 30 mi) above the Earth’s surface.

About 50 percent of the Sun’s energy, largely in the form of visible light, passes through the atmosphere to reach the Earth’s surface. Soils, plants, and oceans on the Earth’s surface absorb about 85 percent of this heat energy, while the rest is reflected back into the atmosphere—most effectively by reflective surfaces such as snow, ice, and sandy deserts. In addition, some of the Sun’s radiation that is absorbed by the Earth’s surface becomes heat energy in the form of long-wave infrared radiation, and this energy is released back into the atmosphere.

Certain gases in the atmosphere, including water vapor, carbon dioxide, methane, and nitrous oxide, absorb this infrared radiant heat, temporarily preventing it from dispersing into space. As these atmospheric gases warm, they in turn emit infrared radiation in all directions. Some of this heat returns back to Earth to further warm the surface in what is known as the greenhouse effect, and some of this heat is eventually released to space. This heat transfer creates equilibrium between the total amount of heat that reaches the Earth from the Sun and the amount of heat that the Earth radiates out into space. This equilibrium or energy balance—the exchange of energy between the Earth’s surface, atmosphere, and space—is important to maintain a climate that can support a wide variety of life.

The heat-trapping gases in the atmosphere behave like the glass of a greenhouse. They let much of the Sun’s rays in, but keep most of that heat from directly escaping. Because of this, they are called greenhouse gases. Without these gases, heat energy absorbed and reflected from the Earth’s surface would easily radiate back out to space, leaving the planet with an inhospitable temperature close to –19°C (2°F), instead of the present average surface temperature of 15°C (59°F).

To appreciate the importance of the greenhouse gases in creating a climate that helps sustain most forms of life, compare Earth to Mars and Venus. Mars has a thin atmosphere that contains low concentrations of heat-trapping gases. As a result, Mars has a weak greenhouse effect resulting in a largely frozen surface that shows no evidence of life. In contrast, Venus has an atmosphere containing high concentrations of carbon dioxide. This heat-trapping gas prevents heat radiated from the planet’s surface from escaping into space, resulting in surface temperatures that average 462°C (864°F)—too hot to support life.

III

TYPES OF GREENHOUSE GASES

Earth’s atmosphere is primarily composed of nitrogen (78 percent) and oxygen (21 percent). These two most common atmospheric gases have chemical structures that restrict absorption of infrared energy. Only the few greenhouse gases, which make up less than 1 percent of the atmosphere, offer the Earth any insulation. Greenhouse gases occur naturally or are manufactured. The most abundant naturally occurring greenhouse gas is water vapor, followed by carbon dioxide, methane, and nitrous oxide. Human-made chemicals that act as greenhouse gases include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs).

Since the 1700s, human activities have substantially increased the levels of greenhouse gases in the atmosphere. Scientists are concerned that expected increases in the concentrations of greenhouse gases will powerfully enhance the atmosphere’s capacity to retain infrared radiation, leading to an artificial warming of the Earth’s surface.

A

Water Vapor

Water vapor is the most common greenhouse gas in the atmosphere, accounting for about 60 to 70 percent of the natural greenhouse effect. Humans do not have a significant direct impact on water vapor levels in the atmosphere. However, as human activities increase the concentration of other greenhouse gases in the atmosphere (producing warmer temperatures on Earth), the evaporation of oceans, lakes, and rivers, as well as water evaporation from plants, increase and raise the amount of water vapor in the atmosphere.

B

Carbon Dioxide

Carbon dioxide constantly circulates in the environment through a variety of natural processes known as the carbon cycle. Volcanic eruptions and the decay of plant and animal matter both release carbon dioxide into the atmosphere. In respiration, animals break down food to release the energy required to build and maintain cellular activity. A byproduct of respiration is the formation of carbon dioxide, which is exhaled from animals into the environment. Oceans, lakes, and rivers absorb carbon dioxide from the atmosphere. Through photosynthesis, plants collect carbon dioxide and use it to make their own food, in the process incorporating carbon into new plant tissue and releasing oxygen to the environment as a byproduct.

In order to provide energy to heat buildings, power automobiles, and fuel electricity-producing power plants, humans burn objects that contain carbon, such as the fossil fuels oil, coal, and natural gas; wood or wood products; and some solid wastes. When these products are burned, they release carbon dioxide into the air. In addition, humans cut down huge tracts of trees for lumber or to clear land for farming or building. This process, known as deforestation, can both release the carbon stored in trees and significantly reduce the number of trees available to absorb carbon dioxide.

As a result of these human activities, carbon dioxide in the atmosphere is accumulating faster than the Earth’s natural processes can absorb the gas. By analyzing air bubbles trapped in glacier ice that is many centuries old, scientists have determined that carbon dioxide levels in the atmosphere have risen by 31 percent since 1750. And since carbon dioxide increases can remain in the atmosphere for centuries, scientists expect these concentrations to double or triple in the next century if current trends continue.

C

Methane

Many natural processes produce methane, also known as natural gas. Decomposition of carbon-containing substances found in oxygen-free environments, such as wastes in landfills, release methane. Ruminating animals such as cattle and sheep belch methane into the air as a byproduct of digestion. Microorganisms that live in damp soils, such as rice fields, produce methane when they break down organic matter. Methane is also emitted during coal mining and the production and transport of other fossil fuels.

Methane has more than doubled in the atmosphere since 1750, and could double again in the next century. Atmospheric concentrations of methane are far less than carbon dioxide, and methane only stays in the atmosphere for a decade or so. But scientists consider methane an extremely effective heat-trapping gas—one molecule of methane is 20 times more efficient at trapping infrared radiation radiated from the Earth’s surface than a molecule of carbon dioxide.

D

Nitrous Oxide

Nitrous oxide is released by the burning of fossil fuels, and automobile exhaust is a large source of this gas. In addition, many farmers use nitrogen-containing fertilizers to provide nutrients to their crops. When these fertilizers break down in the soil, they emit nitrous oxide into the air. Plowing fields also releases nitrous oxide.

Since 1750 nitrous oxide has risen by 17 percent in the atmosphere. Although this increase is smaller than for the other greenhouse gases, nitrous oxide traps heat about 300 times more effectively than carbon dioxide and can stay in the atmosphere for a century.

E

Fluorinated Compounds

Some of the most potent greenhouse gases emitted are produced solely by human activities. Fluorinated compounds, including CFCs, HCFCs, and HFCs, are used in a variety of manufacturing processes. For each of these synthetic compounds, one molecule is several thousand times more effective in trapping heat than a single molecule of carbon dioxide.

CFCs, first synthesized in 1928, were widely used in the manufacture of aerosol sprays, blowing agents for foams and packing materials, as solvents, and as refrigerants. Nontoxic and safe to use in most applications, CFCs are harmless in the lower atmosphere. However, in the upper atmosphere, ultraviolet radiation breaks down CFCs, releasing chlorine into the atmosphere. In the mid-1970s, scientists began observing that higher concentrations of chlorine were destroying the ozone layer in the upper atmosphere. Ozone protects the Earth from harmful ultraviolet radiation, which can cause cancer and other damage to plants and animals. Beginning in 1987 with the Montréal Protocol on Substances that Deplete the Ozone Layer, representatives from 47 countries established control measures that limited the consumption of CFCs. By 1992 the Montréal Protocol was amended to completely ban the manufacture and use of CFCs worldwide, except in certain developing countries and for use in special medical processes such as asthma inhalers.

Scientists devised substitutes for CFCs, developing HCFCs and HFCs. Since HCFCs still release ozone-destroying chlorine in the atmosphere, production of this chemical will be phased out by the year 2030, providing scientists some time to develop a new generation of safer, effective chemicals. HFCs, which do not contain chlorine and only remain in the atmosphere for a short time, are now considered the most effective and safest substitute for CFCs.

F

Other Synthetic Chemicals

Experts are concerned about other industrial chemicals that may have heat-trapping abilities. In 2000 scientists observed rising concentrations of a previously unreported compound called trifluoromethyl sulphur pentafluoride. Although present in extremely low concentrations in the environment, the gas still poses a significant threat because it traps heat more effectively than all other known greenhouse gases. The exact sources of the gas, undisputedly produced from industrial processes, still remain uncertain.

IV

OTHER FACTORS AFFECTING THE GREENHOUSE EFFECT

Aerosols, also known as particulates, are airborne particles that absorb, scatter, and reflect radiation back into space. Clouds, windblown dust, and particles that can be traced to erupting volcanoes are examples of natural aerosols. Human activities, including the burning of fossil fuels and slash-and-burn farming techniques used to clear forestland, contribute additional aerosols to the atmosphere. Although aerosols are not considered a heat-trapping greenhouse gas, they do affect the transfer of heat energy radiated from the Earth to space. The effect of aerosols on climate change is still debated, but scientists believe that light-colored aerosols cool the Earth’s surface, while dark aerosols like soot actually warm the atmosphere. The increase in global temperature in the last century is lower than many scientists predicted when only taking into account increasing levels of carbon dioxide, methane, nitrous oxide, and fluorinated compounds. Some scientists believe that aerosol cooling may be the cause of this unexpectedly reduced warming.

However, scientists do not expect that aerosols will ever play a significant role in offsetting global warming. As pollutants, aerosols typically pose a health threat, and the manufacturing or agricultural processes that produce them are subject to air-pollution control efforts. As a result, scientists do not expect aerosols to increase as fast as other greenhouse gases in the 21st century.

V

UNDERSTANDING THE GREENHOUSE EFFECT

Although concern over the effect of increasing greenhouse gases is a relatively recent development, scientists have been investigating the greenhouse effect since the early 1800s. French mathematician and physicist Jean Baptiste Joseph Fourier, while exploring how heat is conducted through different materials, was the first to compare the atmosphere to a glass vessel in 1827. Fourier recognized that the air around the planet lets in sunlight, much like a glass roof.

In the 1850s British physicist John Tyndall investigated the transmission of radiant heat through gases and vapors. Tyndall found that nitrogen and oxygen, the two most common gases in the atmosphere, had no heat-absorbing properties. He then went on to measure the absorption of infrared radiation by carbon dioxide and water vapor, publishing his findings in 1863 in a paper titled “On Radiation Through the Earth’s Atmosphere.”

Swedish chemist Svante August Arrhenius, best known for his Nobel Prize-winning work in electrochemistry, also advanced understanding of the greenhouse effect. In 1896 he calculated that doubling the natural concentrations of carbon dioxide in the atmosphere would increase global temperatures by 4 to 6 Celsius degrees (7 to 11 Fahrenheit degrees), a calculation that is not too far from today’s estimates using more sophisticated methods. Arrhenius correctly predicted that when Earth’s temperature warms, water vapor evaporation from the oceans increases. The higher concentration of water vapor in the atmosphere would then contribute to the greenhouse effect and global warming.

The predictions about carbon dioxide and its role in global warming set forth by Arrhenius were virtually ignored for over half a century, until scientists began to detect a disturbing change in atmospheric levels of carbon dioxide. In 1957 researchers at the Scripps Institution of Oceanography, based in San Diego, California, began monitoring carbon dioxide levels in the atmosphere from Hawaii’s remote Mauna Loa Observatory located 3,000 m (11,000 ft) above sea level. When the study began, carbon dioxide concentrations in the Earth’s atmosphere were 315 molecules of gas per million molecules of air (abbreviated parts per million or ppm). Each year carbon dioxide concentrations increased—to 323 ppm by 1970 and 335 ppm by 1980. By 1988 atmospheric carbon dioxide had increased to 350 ppm, an 8 percent increase in only 31 years.

As other researchers confirmed these findings, scientific interest in the accumulation of greenhouse gases and their effect on the environment slowly began to grow. In 1988 the World Meteorological Organization and the United Nations Environment Programme established the Intergovernmental Panel on Climate Change (IPCC). The IPCC was the first international collaboration of scientists to assess the scientific, technical, and socioeconomic information related to the risk of human-induced climate change. The IPCC creates periodic assessment reports on advances in scientific understanding of the causes of climate change, its potential impacts, and strategies to control greenhouse gases. The IPCC played a critical role in establishing the United Nations Framework Convention on Climate Change (UNFCCC). The UNFCCC, which provides an international policy framework for addressing climate change issues, was adopted by the United Nations General Assembly in 1992.

Today scientists around the world monitor atmospheric greenhouse gas concentrations and create forecasts about their effects on global temperatures. Air samples from sites spread across the globe are analyzed in laboratories to determine levels of individual greenhouse gases. Sources of greenhouse gases, such as automobiles, factories, and power plants, are monitored directly to determine their emissions. Scientists gather information about climate systems and use this information to create and test computer models that simulate how climate could change in response to changing conditions on the Earth and in the atmosphere. These models act as high-tech crystal balls to project what may happen in the future as greenhouse gas levels rise. Models can only provide approximations, and some of the predictions based on these models often spark controversy within the science community. Nevertheless, the basic concept of global warming is widely accepted by most climate scientists.

VI

EFFORTS TO CONTROL GREENHOUSE GASES

Due to overwhelming scientific evidence and growing political interest, global warming is currently recognized as an important national and international issue. Since 1992 representatives from over 160 countries have met regularly to discuss how to reduce worldwide greenhouse gas emissions. In 1997 representatives met in Kyôto, Japan, and produced an agreement, known as the Kyôto Protocol, which requires industrialized countries to reduce their emissions by 2012 to an average of 5 percent below 1990 levels. To help countries meet this agreement cost-effectively, negotiators are trying to develop a system in which nations that have no obligations or that have successfully met their reduced emissions obligations could profit by selling or trading their extra emissions quotas to other countries that are struggling to reduce their emissions. Negotiating such detailed emissions trading rules has been a contentious task for the world community since the signing of the Kyôto Protocol. A ratified agreement is still not yet in force, and ratification received a setback in 2001 when newly elected U.S. president George W. Bush renounced the treaty on the grounds that the required carbon-dioxide reductions in the United States would be too costly. He also objected that developing nations would not be bound by similar carbon-dioxide reducing obligations. However, many experts expect that as the scientific evidence about the dangers of global warming continues to mount, nations will be motivated to cooperate more effectively to reduce the risks of climate change.

Contributed By: Michael Mastrandrea Stephen H. Schneider

Microsoft ® Encarta ® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved.

Global Warming

I

INTRODUCTION

Global Warming, increase in the average temperature of the atmosphere, oceans, and landmasses of Earth. The planet has warmed (and cooled) many times during the 4.65 billion years of its history. At present Earth appears to be facing a rapid warming, which most scientists believe results, at least in part, from human activities. The chief cause of this warming is thought to be the burning of fossil fuels, such as coal, oil, and natural gas, which releases into the atmosphere carbon dioxide and other substances known as greenhouse gases. As the atmosphere becomes richer in these gases, it becomes a better insulator, retaining more of the heat provided to the planet by the Sun.

The average surface temperature of Earth is about 15°C (59°F). Over the last century, this average has risen by about 0.6 Celsius degree (1 Fahrenheit degree). Scientists predict further warming of 1.4 to 5.8 Celsius degrees (2.5 to 10.4 Fahrenheit degrees) by the year 2100. This temperature rise is expected to melt polar ice caps and glaciers as well as warm the oceans, all of which will expand ocean volume and raise sea level by an estimated 9 to 100 cm (4 to 40 in), flooding some coastal regions and even entire islands. Some regions in warmer climates will receive more rainfall than before, but soils will dry out faster between storms. This soil desiccation may damage food crops, disrupting food supplies in some parts of the world. Plant and animal species will shift their ranges toward the poles or to higher elevations seeking cooler temperatures, and species that cannot do so may become extinct. The potential consequences of global warming are so great that many of the world's leading scientists have called for international cooperation and immediate action to counteract the problem.

II

THE GREENHOUSE EFFECT

The energy that lights and warms Earth comes from the Sun. Most of the energy that floods onto our planet is short-wave radiation, including visible light. When this energy strikes the surface of Earth, the energy changes from light to heat and warms Earth. Earth’s surface, in turn, releases some of this heat as long-wave infrared radiation.

Much of this long-wave infrared radiation makes it all the way back out to space, but a portion remains trapped in Earth’s atmosphere. Certain gases in the atmosphere, including water vapor, carbon dioxide, and methane, provide the trap. Absorbing and reflecting infrared waves radiated by Earth, these gases conserve heat as the glass in a greenhouse does and are thus known as greenhouse gases. As the concentration of these greenhouse gases in the atmosphere increases, more heat energy remains trapped below. All life on Earth relies on this greenhouse effect—without it, the planet would be colder by about 33 Celsius degrees (59 Fahrenheit degrees), and ice would cover Earth from pole to pole. However, a growing excess of greenhouse gases in Earth’s atmosphere threatens to tip the balance in the other direction—toward continual warming.

III

TYPES OF GREENHOUSE GASES

Greenhouse gases occur naturally in the environment and also result from human activities. By far the most abundant greenhouse gas is water vapor, which reaches the atmosphere through evaporation from oceans, lakes, and rivers.

Carbon dioxide is the next most abundant greenhouse gas. It flows into the atmosphere from many natural processes, such as volcanic eruptions; the respiration of animals, which breathe in oxygen and exhale carbon dioxide; and the burning or decay of organic matter, such as plants. Carbon dioxide leaves the atmosphere when it is absorbed into ocean water and through the photosynthesis of plants, especially trees. Photosynthesis breaks up carbon dioxide, releasing oxygen into the atmosphere and incorporating the carbon into new plant tissue.

Humans escalate the amount of carbon dioxide released to the atmosphere when they burn fossil fuels, solid wastes, and wood and wood products to heat buildings, drive vehicles, and generate electricity. At the same time, the number of trees available to absorb carbon dioxide through photosynthesis has been greatly reduced by deforestation, the long-term destruction of forests by indiscriminate cutting of trees for lumber or to clear land for agricultural activities.

Ultimately, the oceans and other natural processes absorb excess carbon dioxide in the atmosphere. However, human activities have caused carbon dioxide to be released to the atmosphere at rates much faster than that at which Earth’s natural processes can cycle this gas. In 1750 there were about 281 molecules of carbon dioxide per million molecules of air (abbreviated as parts per million, or ppm). Today atmospheric carbon dioxide concentrations are 368 ppm, which reflects a 31 percent increase. Atmospheric carbon dioxide concentration increases by about 1.5 ppm per year. If current predictions prove accurate, by the year 2100 carbon dioxide will reach concentrations of more than 540 to 970 ppm. At the highest estimation, this concentration would be triple the levels prior to the Industrial Revolution, the widespread replacement of human labor by machines that began in Britain in the mid-18th century and soon spread to other parts of Europe and to the United States.

Methane is an even more effective insulator, trapping over 20 times more heat than does the same amount of carbon dioxide. Methane is emitted during the production and transport of coal, natural gas, and oil. Methane also comes from rotting organic waste in landfills, and it is released from certain animals, especially cows, as a byproduct of digestion. Since the beginning of the Industrial Revolution in the mid-1700s, the amount of methane in the atmosphere has more than doubled.

Nitrous oxide is a powerful insulating gas released primarily by burning fossil fuels and by plowing farm soils. Nitrous oxide traps about 300 times more heat than does the same amount of carbon dioxide. The concentration of nitrous oxide in the atmosphere has increased 17 percent over preindustrial levels.

In addition, greenhouse gases are produced in many manufacturing processes. Perfluorinated compounds result from the smelting of aluminum. Hydrofluorocarbons form during the manufacture of many products, including the foams used in insulation, furniture, and car seats. Refrigerators built in some developing nations still use chlorofluorocarbons as coolants. In addition to their ability to retain atmospheric heat, some of these synthetic chemicals also destroy Earth’s high-altitude ozone layer, the protective layer of gases that shields Earth from damaging ultraviolet radiation. For most of the 20th century these chemicals have been accumulating in the atmosphere at unprecedented rates. But since 1995, in response to regulations enforced by the Montréal Protocol on Substances that Deplete the Ozone Layer and its amendments, the atmospheric concentrations of many of these gases are either increasing more slowly or decreasing.

Scientists are growing concerned about other gases produced from manufacturing processes that pose an environmental risk. In 2000 scientists identified a substantial rise in atmospheric concentrations of a newly identified synthetic compound called trifluoromethyl sulfur pentafluoride. Atmospheric concentrations of this gas are rising quickly, and although it still is extremely rare in the atmosphere, scientists are concerned because the gas traps heat more effectively than all other known greenhouse gases. Perhaps more worrisome, scientists have been unable to confirm the industrial source of the gas.

IV

MEASURING GLOBAL WARMING

As early as 1896 scientists suggested that burning fossil fuels might change the composition of the atmosphere and that an increase in global average temperature might result. The first part of this hypothesis was confirmed in 1957, when researchers working in the global research program called the International Geophysical Year sampled the atmosphere from the top of the Hawaiian volcano Mauna Loa. Their instruments indicated that carbon dioxide concentration was indeed rising. Since then, the composition of the atmosphere has been carefully tracked. The data collected show undeniably that the concentrations of greenhouse gases in the atmosphere are increasing.

Scientists have long suspected that the global climate, the long-term average pattern of temperature, was also growing warmer, but they were unable to provide conclusive proof. Temperatures vary widely all the time and from place to place. It takes many years of climate observations to establish a trend. Records going back to the late 1800s did seem to show a warming trend, but these statistics were spotty and untrustworthy. Early weather stations often were located near cities, where temperature measurements were affected by the heat emitted from buildings and vehicles and stored by building materials and pavements. Since 1957, however, data have been gathered from more reliable weather stations, located far away from cities, and from satellites. These data have provided new, more accurate measurements, especially for the 70 percent of the planetary surface that is ocean water (see Satellite, Artificial). These more accurate records indicate that a surface warming trend exists and that, moreover, it has become more pronounced. Looking back from the end of the 20th century, records show that the ten warmest years of the century all occurred after 1980, and the three hottest years occurred after 1990, with 1998 being the warmest year of all.

Greenhouse gas concentrations are increasing. Temperatures are rising. But does the gas increase necessarily cause the warming, and will these two phenomena continue to occur together? In 1988 the United Nations Environment Program and the World Meteorological Organization established a panel of 200 leading scientists to consider the evidence. In its Third Assessment Report, released in 2001, this Intergovernmental Panel on Climate Change (IPCC) concluded that global air temperature had increased 0.6 Celsius degree (1 Fahrenheit degree) since 1861. The panel agreed that the warming was caused primarily by human activities that add greenhouse gases to the atmosphere. The IPCC predicted in 2001 that the average global temperature would rise by another 1.4 to 5.8 Celsius degrees (2.5 to 10.4 Fahrenheit degrees) by the year 2100.

The IPCC panel cautioned that even if greenhouse gas concentrations in the atmosphere ceased growing by the year 2100, the climate would continue to warm for a period after that as a result of past emissions. Carbon dioxide remains in the atmosphere for a century or more before nature can dispose of it. If greenhouse gas emissions continue to increase, experts predict that carbon dioxide concentrations in the atmosphere could rise to more than three times preindustrial levels early in the 22nd century, resulting in dramatic climate changes. Large climate changes of the type predicted are not unprecedented; indeed, they have occurred many times in the history of Earth. However, human beings would face this latest climate swing with a huge population at risk.

V

EFFECTS OF GLOBAL WARMING

Scientists use elaborate computer models of temperature, precipitation patterns, and atmosphere circulation to study global warming. Based on these models, scientists have made several predictions about how global warming will affect weather, sea levels, coastlines, agriculture, wildlife, and human health.

A

Weather

Scientists predict that during global warming, the northern regions of the Northern Hemisphere will heat up more than other areas of the planet, northern and mountain glaciers will shrink, and less ice will float on northern oceans. Regions that now experience light winter snows may receive no snow at all. In temperate mountains, snowlines will be higher and snowpacks will melt earlier. Growing seasons will be longer in some areas. Winter and nighttime temperatures will tend to rise more than summer and daytime ones.

The warmed world will be generally more humid as a result of more water evaporating from the oceans. Scientists are not sure whether a more humid atmosphere will encourage or discourage further warming. On the one hand, water vapor is a greenhouse gas, and its increased presence should add to the insulating effect. On the other hand, more vapor in the atmosphere will produce more clouds, which reflect sunlight back into space, which should slow the warming process (see Water Cycle).

Greater humidity will increase rainfall, on average, about 1 percent for each Fahrenheit degree of warming. (Rainfall over the continents has already increased by about 1 percent in the last 100 years.) Storms are expected to be more frequent and more intense. However, water will also evaporate more rapidly from soil, causing it to dry out faster between rains. Some regions might actually become drier than before. Winds will blow harder and perhaps in different patterns. Hurricanes, which gain their force from the evaporation of water, are likely to be more severe. Against the background of warming, some very cold periods will still occur. Weather patterns are expected to be less predictable and more extreme.

B

Sea Levels

As the atmosphere warms, the surface layer of the ocean warms as well, expanding in volume and thus raising sea level. Warming will also melt much glacier ice, especially around Greenland, further swelling the sea. Sea levels worldwide rose 10 to 25 cm (4 to 10 in) during the 20th century, and IPCC scientists predict a further rise of 9 to 88 cm (4 to 35 in) in the 21st century.

Sea-level changes will complicate life in many coastal regions. A 100-cm (40-in) rise could submerge 6 percent of The Netherlands, 17.5 percent of Bangladesh, and most or all of many islands. Erosion of cliffs, beaches, and dunes will increase. Storm surges, in which winds locally pile up water and raise the sea, will become more frequent and damaging. As the sea invades the mouths of rivers, flooding from runoff will also increase upstream. Wealthier countries will spend huge amounts of money to protect their shorelines, while poor countries may simply evacuate low-lying coastal regions.

Even a modest rise in sea level will greatly change coastal ecosystems. A 50-cm (20-in) rise will submerge about half of the present coastal wetlands of the United States. New marshes will form in many places, but not where urban areas and developed landscapes block the way. This sea-level rise will cover much of the Florida Everglades.

C

Agriculture

A warmed globe will probably produce as much food as before, but not necessarily in the same places. Southern Canada, for example, may benefit from more rainfall and a longer growing season. At the same time, the semiarid tropical farmlands in some parts of Africa may become further impoverished. Desert farm regions that bring in irrigation water from distant mountains may suffer if the winter snowpack, which functions as a natural reservoir, melts before the peak growing months. Crops and woodlands may also be afflicted by more insects and plant diseases.

D

Animals and Plants

Animals and plants will find it difficult to escape from or adjust to the effects of warming because humans occupy so much land. Under global warming, animals will tend to migrate toward the poles and up mountainsides toward higher elevations, and plants will shift their ranges, seeking new areas as old habitats grow too warm. In many places, however, human development will prevent this shift. Species that find cities or farmlands blocking their way north or south may die out. Some types of forests, unable to propagate toward the poles fast enough, may disappear.

E

Human Health

In a warmer world, scientists predict that more people will get sick or die from heat stress, due less to hotter days than to warmer nights (giving the sufferers less relief). Diseases now found in the tropics, transmitted by mosquitoes and other animal hosts, will widen their range as these animal hosts move into regions formerly too cold for them. Today 45 percent of the world’s people live where they might get bitten by a mosquito carrying the parasite that causes malaria; that percentage may increase to 60 percent if temperatures rise. Other tropical diseases may spread similarly, including dengue fever, yellow fever, and encephalitis. Scientists also predict rising incidence of allergies and respiratory diseases as warmer air grows more charged with pollutants, mold spores, and pollens.

VI

DEBATES OVER GLOBAL WARMING

Scientists do not all agree about the nature and impact of global warming. A few observers still question whether temperatures have actually been rising at all. Others acknowledge past change but argue that it is much too early to be making predictions for the future. Such critics may also deny that the evidence for the human contribution to warming is conclusive, arguing that a purely natural cycle may be driving temperatures upward. The same dissenters tend to emphasize the fact that continued warming could have benefits in some regions.

Scientists who question the global warming trend point to three puzzling differences between the predictions of the global warming models and the actual behavior of the climate. First, the warming trend stopped for three decades in the middle of the 20th century; there was even some cooling before the climb resumed in the 1970s. Second, the total amount of warming during the 20th century was only about half what computer models predicted. Third, the troposphere, the lower region of the atmosphere, did not warm as fast as the models forecast. However, global warming proponents believe that two of the three discrepancies have now been explained.

The lack of warming at midcentury is now attributed largely to air pollution that spews particulate matter, especially sulfates, into the upper atmosphere. These particulates, also known as aerosols, reflect some incoming sunlight out into space. Continued warming has now overcome this effect, in part because pollution control efforts have made the air cleaner.

The unexpectedly small amount of total warming since 1900 is now attributed to the oceans absorbing vast amounts of the extra heat. Scientists long suspected that this was happening but lacked the data to prove it. In 2000 the U.S. National Oceanic and Atmospheric Administration (NOAA) offered a new analysis of water temperature readings made by observers around the world over 50 years. Records showed a distinct warming trend: World ocean temperatures in 1998 were higher than the 50-year average by 0.2 Celsius degree (0.3 Fahrenheit degree), a small but very significant amount.

The third discrepancy is the most puzzling. Satellites detect less warming in the troposphere than the computer models of global climate predict. According to some critics, the atmospheric readings are right, and the higher temperatures recorded at Earth’s surface are not to be trusted. In January 2000 a panel appointed by the National Academy of Sciences to weigh this argument reaffirmed that surface warming could not be doubted. However, the lower-than-predicted troposphere measurements have not been entirely explained.

VII

EFFORTS TO CONTROL GLOBAL WARMING

The total consumption of fossil fuels is increasing by about 1 percent per year. No steps currently being taken or under serious discussion will likely prevent global warming in the near future. The challenge today is managing the probable effects while taking steps to prevent detrimental climate changes in the future.

Damage can be curbed locally in various ways. Coastlines can be armored with dikes and barriers to block encroachments of the sea. Alternatively, governments can assist coastal populations in moving to higher ground. Some countries, such as the United States, still have the chance to help plant and animal species survive by preserving habitat corridors, strips of relatively undeveloped land running north and south. Species can gradually shift their ranges along these corridors, moving toward cooler habitats.

There are two major approaches to slowing the buildup of greenhouse gases. The first is to keep carbon dioxide out of the atmosphere by storing the gas or its carbon component somewhere else, a strategy called carbon sequestration. The second major approach is to reduce the production of greenhouse gases.

A

Carbon Sequestration

The simplest way to sequester carbon is to preserve trees and to plant more. Trees, especially young and fast-growing ones, soak up a great deal of carbon dioxide, break it down in photosynthesis, and store the carbon in new wood. Worldwide, forests are being cut down at an alarming rate, particularly in the tropics. In many areas, there is little regrowth as land loses fertility or is changed to other uses, such as farming or building housing developments. Reforestation could offset these losses and counter part of the greenhouse buildup.

Many companies and governments in the United States, Norway, Brazil, Malaysia, Russia, and Australia have initiated reforestation projects. In Guatemala, the AES Corporation, a U.S.-based electrical company, has joined forces with the World Resources Institute and the relief agency CARE to create community woodlots and to teach local residents about tree-farming practices. The trees planted are expected to absorb up to 58 million tons of carbon dioxide over 40 years.

Carbon dioxide gas can also be sequestered directly. Carbon dioxide has traditionally been injected into oil wells to force more petroleum out of the ground or seafloor. Now it is being injected simply to isolate it underground in oil fields, coal beds, or aquifers. At one natural gas drilling platform off the coast of Norway, carbon dioxide brought to the surface with the natural gas is captured and reinjected into an aquifer from which it cannot escape. The same process can be used to store carbon dioxide released by a power plant, factory, or any large stationary source. Deep ocean waters could also absorb a great deal of carbon dioxide. The feasibility and environmental effects of both these options are now under study by international teams.

In an encouraging trend, energy use around the world has slowly shifted away from fuels that release a great deal of carbon dioxide toward fuels that release somewhat less of this heat-trapping gas. Wood was the first major source of energy used by humans. With the dawn of the Industrial Revolution in the 18th century, coal became the dominant energy source. By the mid-19th century oil had replaced coal in dominance, fueling the internal combustion engines that were eventually used in automobiles. By the 20th century, natural gas began to be used worldwide for heating and lighting. In this progression, combustion of natural gas releases less carbon dioxide than oil, which in turn releases less of the gas than do either coal or wood.

Nuclear energy, though controversial for reasons of safety and the high costs of nuclear waste disposal, releases no carbon dioxide at all. Solar power, wind power, and hydrogen fuel cells also emit no greenhouse gases. Someday these alternative energy sources may prove to be practical, low-pollution energy sources, although progress today is slow.

B

National and Local Programs

The developed countries are all working to reduce greenhouse emissions. Several European countries impose heavy taxes on energy usage, designed partly to curb such emissions. Norway taxes industries according to the amount of carbon dioxide they emit. In The Netherlands, government and industry have negotiated agreements aimed at increasing energy efficiency, promoting alternative energy sources, and cutting down greenhouse gas output.

In the United States, the Department of Energy, the Environmental Protection Agency, product manufacturers, local utilities, and retailers have collaborated to implement the Energy Star program. This voluntary program rates appliances for energy use and gives some money back to consumers who buy efficient machines. The Canadian government has established the FleetWise program to cut carbon dioxide emissions from federal vehicles by reducing the number of vehicles it owns and by training drivers to use them more efficiently. By 2004, 75 percent of Canadian federal vehicles are to run on alternative fuels, such as methanol and ethanol.

Many local governments are also working against greenhouse emissions by conserving energy in buildings, modernizing their vehicles, and advising the public. Individuals, too, can take steps. The same choices that reduce other kinds of pollution work against global warming. Every time a consumer buys an energy-efficient appliance; adds insulation to a house; recycles paper, metal, and glass; chooses to live near work; or commutes by public transportation, he or she is fighting global warming.

C

International Agreements

International cooperation is required for the successful reduction of greenhouse gases. In 1992 at the Earth Summit in Rio de Janeiro, Brazil, 150 countries agreed to meet again to translate their good intentions into a treaty.

In 1997 in Japan, 160 nations drafted a much stronger agreement known as the Kyōto Protocol. This treaty, which has not yet been implemented, calls for the 38 industrialized countries that now release the most greenhouse gases to cut their emissions to levels 5 percent below those of 1990. This reduction is to be achieved no later than 2012. Initially, the United States voluntarily accepted a more ambitious target, promising to reduce emissions to 7 percent below 1990 levels; the European Union, which had wanted a much tougher treaty, committed to 8 percent; and Japan, to 6 percent. The remaining 122 nations, mostly developing nations, were not asked to commit to a reduction in gas emissions.

But in 2001 newly elected U.S. president George W. Bush renounced the treaty saying that such carbon-dioxide reductions in the United States would be too costly. He also objected that developing nations would not be bound by similar carbon-dioxide reducing obligations. The Kyōto Protocol will not be binding until nations accounting for 55 percent of 1990 greenhouse gas emissions have ratified it. Most countries are waiting for ratification by the United States, at present the source of one-fifth of greenhouse gas emissions.

Some critics find the Kyōto Protocol too weak. Even if it were enforced immediately, it would only slightly slow the buildup of greenhouse gases in the atmosphere. Much stronger action would be required later, particularly because the developing nations exempted from the Kyōto rules are expected to produce half the world’s greenhouse gases by 2035. The most influential opponents of the protocol, however, find it too strong. Opposition to the treaty in the United States is spurred by the oil industry, the coal industry, and other enterprises that manufacture or depend on fossil fuels. These opponents claim that the economic costs to carry out the Kyōto Protocol could be as much as $300 billion, due mainly to higher energy prices. Proponents of the Kyōto sanctions believe the costs will prove more modest—$88 billion or less—much of which will be recovered as Americans save money after switching to more efficient appliances, vehicles, and industrial processes.

Behind the issue of cost lies a larger question: Can an economy grow without increasing its greenhouse gas emissions at the same time? In the past, prosperity and pollution have tended to go together. Can they now be separated, or decoupled, as economists say? In nations with strong environmental policies, economies have continued to grow even as many types of pollution have been reduced. However, limiting the emission of carbon dioxide has proved especially difficult. For example, The Netherlands, a heavily industrialized country that is also an environmental leader, has done very well against most kinds of pollution but has failed to meet its goal of reducing carbon dioxide output.

Representatives have met regularly to negotiate a consensus about certain unresolved issues of the Kyōto Protocol, such as the rules, methods, and penalties that should be enforced in each country to slow greenhouse emissions. A particularly contentious issue is a proposed system for trading in pollution “rights” or credits. Negotiators are working to design a system in which nations with successful cleanup programs could profit by selling unused pollution rights to other nations. Nations that find further improvement difficult, such as The Netherlands, could buy pollution credits on the market, or perhaps earn them by helping reduce greenhouse gas emissions in less developed countries, where more can be achieved at less expense. Treaty representatives at a meeting held at The Hague, The Netherlands, in November 2000 came close to an agreement on this and other treaty issues, but the talks ultimately failed. Negotiators plan to continue discussions periodically through 2001.

Microsoft ® Encarta ® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved.