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sources of energy, origins of the power used for transportation, for heat and light in dwelling and working areas, and for the manufacture of goods of all kinds, among other applications. The development of science and civilization is closely linked to the availability of energy in useful forms. Modern society consumes vast amounts of energy in all forms: light, heat, electrical, mechanical, chemical, and nuclear. The rate at which energy is produced or consumed is called power, although this term is sometimes used in common speech synonymously with energy.

Types of Energy

Chemical and Mechanical Energy

An early source of energy, or prime mover, used by humans was animal power, i.e., the energy obtained from domesticated animals. Later, as civilization developed, wind power was harnessed to drive ships and turn windmills, and streams and rivers were diverted to turn water wheels (see water power). The rotating shaft of a windmill or water wheel could then be used to crush grain, to raise water from a well, or to serve any number of other uses. The motion of the wind and water, as well as the motion of the wheel or shaft, represents a form of mechanical energy. The source of animal power is ultimately the chemical energy contained in foods and released when digested by humans and animals. The chemical energy contained in wood and other combustible fuels has served since the beginning of history as a source of heat for cooking and warmth. At the start of the Industrial Revolution, water power was used to provide energy for factories through systems of belts and pulleys that transmitted the energy to many different machines.

Heat Energy

The invention of the steam engine, which converts the chemical energy of fuels into heat energy and the heat into mechanical energy, provided another source of energy. The steam engine is called an external-combustion engine, since fuel is burned outside the engine to create the steam used inside it. During the 19th cent. the internal-combustion engine was developed; a variety of fuels, depending on the type of internal-combustion engine, are burned directly in the engine's chambers to provide a source of mechanical energy. Both steam engines and internal-combustion engines found application as stationary sources of power for different purposes and as mobile sources for transportation, as in the steamship, the railroad locomotive (both steam and diesel), and the automobile. All these sources of energy ultimately depend on the combustion of fuels for their operation.

Electrical Energy

Early in the 19th cent. another source of energy was developed that did not necessarily need the combustion of fuels—the electric generator, or dynamo. The generator converts the mechanical energy of a conductor moving in a magnetic field into electrical energy, using the principle of electromagnetic induction. The great advantage of electrical energy, or electric power, as it is commonly called, is that it can be transmitted easily over great distances (see power, electric). As a result, it is the most widely used form of energy in modern civilization; it is readily converted to light, to heat, or, through the electric motor, to mechanical energy again. The large-scale production of electrical energy was made possible by the invention of the turbine, which efficiently converts the straight-line motion of falling water or expanding steam into the rotary motion needed to turn the rotor of a large generator.

Nuclear Energy

The development of nuclear energy made available another source of energy. The heat of a nuclear reactor can be used to produce steam, which then can be directed through a turbine to drive an electric generator, the propellers of a large ship, or some other machine. In 1999, 23% of the electricity generated in the United States derived from nuclear reactors; however, since the 1980s, the construction and application of nuclear reactors in the United States has slowed because of concern about the dangers of the resulting radioactive waste and the possibility of a disastrous nuclear meltdown (see Three Mile Island; Chernobyl; Fukushima).

Environmental Considerations

The demand for energy has increased steadily, not only because of the growing population but also because of the greater number of technological goods available and the increased affluence that has brought these goods within the reach of a larger proportion of the population. For example, despite the introduction of more fuel-efficient motor vehicles (average miles per gallon increased by 34% between 1975 and 1990), the consumption of fuel by vehicles in America increased by 20% between 1975 and 1990. The rise in gasoline consumption is attributable to an increase in the number of miles the average vehicle traveled and to a 40% increase in the same period in the number of vehicles on the road. Since 1990 average fuel efficiency has changed relatively little, while the number of vehicles, the number of miles they travel, and the total amount of fuel consumed has continued to increase.

As a result of the increase in the consumption of energy, concern has risen about the depletion of natural resources, both those used directly to produce energy and those damaged during the exploitation of the fuels or as a result of contamination by energy waste products (see under conservation of natural resources). Most of the energy consumed is ultimately generated by the combustion of fossil fuels, such as coal, petroleum, and natural gas, and the world has only a finite supply of these fuels, which are in danger of being used up. Also, the combustion of these fuels releases various pollutants (see pollution), such as carbon monoxide and sulfur dioxide, which pose health risks and may contribute to acid rain and global warming. In addition, environmentalists have become increasingly alarmed at the widespread destruction imposed on sensitive wildlands (e.g., the tropical rain forests, the arctic tundra, and coastal marshes) during the exploitation of their resources.

The Search for New Sources of Energy

The environmental consequences of energy production have led many nations in the world to impose stricter guidelines on the production and consumption of energy. Further, the search for new sources of energy and more efficient means of employing energy has accelerated. The development of a viable nuclear fusion reactor is often cited as a possible solution to our energy problems. Presently, nuclear-energy plants use nuclear fission, which requires scarce and expensive fuels and produces potentially dangerous wastes. The fuel problem has been partly helped by the development of breeder reactors, which produce more nuclear fuel than they consume, but the long-term hopes for nuclear energy rest on the development of controlled sources using nuclear fusion rather than fission. The basic fuels for fusion are extremely plentiful (e.g., hydrogen, from water) and the end products are relatively safe. The basic problem, which is expected to take decades to solve, is in containing the fuels at the extremely high temperatures necessary to initiate and sustain nuclear fusion.

Another source of energy is solar energy. The earth receives huge amounts of energy every day from the sun, but the problem has been harnessing this energy so that it is available at the appropriate time and in the appropriate form. For example, solar energy is received only during the daylight hours, but more heat and electricity for lighting are needed at night. Despite technological advances in photovoltaic cells, solar energy has not become a more significantly more financially competitive source of energy. Although several solar thermal power plants are now in operation in California, they are not yet able to compete with conventional power plants on an economic basis.

Some scientists have suggested using the earth's internal heat as a source of energy. Geothermal energy is released naturally in geysers and volcanoes. In California, some of the state's electricity is generated by the geothermal plant complex known as the Geysers, which has been in production since 1960, and in Iceland, which is geologically very active, roughly 90% of the homes are heated by geothermal energy. Still another possible energy source is tidal energy. A few systems have been set up to harness the energy released in the twice-daily ebb and flow of the ocean's tides, but they have not been widely used, because they cannot operate turbines continuously and because they must be built specifically for each site.

Another direction of research and experimentation is in the search for alternatives to gasoline. Possibilities include methanol, which can be produced from wood, coal, or natural gas; ethanol, an alcohol produced from grain, sugarcane, and other agriculture plants and currently used in some types of U.S. motor fuel (e.g., gasohol and E85, a mixture of 85% ethanol and 15% gasoline); compressed natural gas, which is much less polluting than gasoline and is currently used by a 1.5 million vehicles around the world; and electricity, which if ever practicable would be cheaper and less polluting, especially if derived from solar energy, rather than gasoline.


See G. R. Harrison, The Conquest of Energy (1968); F. Barnaby, Man and the Atom: The Uses of Nuclear Energy (1971); W. G. Steltz and A. M. Donaldson, Aero-Thermodynamics of Steam Turbines (1981); T. N. Veziroglu, ed., Alternative Sources of Energy (1983 and 1985) and Renewable Energy Sources (Vol. 4, 1984); G. L. Johnson, Wind Energy Systems (1985).

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Natural Resources, Nonrenewable


It is common to subdivide natural resources into the non-renewable and renewable categories, respectively. The former, predominantly metals and fossil fuels, are derived from a limited stock, whose ultimate size is unknown. The supply of the latter, primarily of biological origin, relies on regeneration that can be repeated in perpetuity. This difference leads to frequent assertions that sustainability requires more reliance on renewables, to avoid, or at least delay, an impending and unavoidable depletion of nonrenewable resources.

The differences in the conditions of long-term supply between the two categories are often exaggerated. Everything being equal, the supply of both tends to become more costly with expanded use, for that necessitates the employment of more meager mineral deposits and more marginal soils. Everything is not equal, however, and technological progress has more than compensated for this upward push, so that the real cost of mineral as well as agricultural output has tended to fall over time. Furthermore, examples of dramatic exhaustion are easier to quote from the renewable category. Witness how the forests disappeared in antique Italy and in seventeenth-century England, or the virtual extinction of cod in the worlds oceans in the late twentieth century.

The fear of depletion of exhaustible resources is almost as old as humankind, but the available experience suggests that painful scarcity is less of an immediate threat than ever in history. Despite impressive growth rates in usage, which have raised present world consumption to many times that of the early or mid-twentieth century, the reserves of virtually all metal minerals and fossil fuels have expanded at even faster rates, through a combination of discovery and subsequent appreciation of the newfound deposits. Extraction costs show a falling trend in real terms, and the prices of most exhaustible resources have declined in parallel. All this is counter to the predictions of a dire future made by the Club of Rome in the early 1970s. These predictions completely missed the point, primarily because they neglected technological progress in exhaustible resource exploration and exploitation. There are no indications that the benign trends caused by technological innovation are in the process of reversal.

Though in most cases, declining costs have resulted in falling prices, there are important exceptions. The price of oil has followed an upward trend in real terms ever since the Organization of Petroleum Exporting Countries (OPEC) took effective command of the oil market in the early 1970s. The cartel has been able to exercise market management to its advantage because its members control the worlds largest and most economical reserves, those in the Middle East. The most potent tool for maintaining monopolistic pricing in the oil market has been a virtual arrest since the late 1970s in the cartels expansion of capacity to exploit this resource wealth. The prices of petroleum have spilled over to other fossil fuels, since the latter can substitute for oil in many cases. Monopolistic market conditions are likely to be maintained so long as the cartel remains in charge.

The prices of virtually all primary materials, exhaustible as well as renewable, rose impressively in the first half of the 2000s. The price of oranges and rice increased by 50 percent between 2002 and 2005, coffee went up by 68 percent, and rubber by 95 percent. The price of oil doubled while the prices of nickel and copper increased by even more. This was the third powerful and general commodity boom since World War II (19391945). As was the case with commodity booms during the time periods between 1950 and 1951 and between 1973 and 1974, this boom was triggered by a sudden and sizable demand expansion at a time when inventories were small and no slack capacity existed to satisfy the surge. As on previous occasions, the rising prices were temporarily decoupled from the costs of production.

The demand shock centered on 2004 was primarily due to a very fast growth in world gross domestic product (GDP). The new phenomenon was that the economies of several large developing countries, notably China and India but also Brazil and Indonesia, expanded at voracious rates, and contributed strongly to the global boom. The successful growth performance in those nations was primarily due to the economic liberalization measures implemented during preceding decades. An intensified participation in the integration of the global economy was a key factor behind these countries impressive growth rates. At the present stage of their economic development, involving industrialization, urbanization, and the buildup of infrastructure, these economies are very intensive resource users. This accentuated the demand shock in the raw materials markets.

Normality will likely return to these markets before the end of the 2000s, just as it did a few years after the outbreak of the earlier commodity booms. The year 2004 was exceptional in terms of global growth, unlikely to be repeated in the near future. The profitability of the natural resource industries at the prevailing prices is exceedingly high, so the incentive to invest in capacity expansion is strong. Sizable investment efforts are also under implementation. Building new capacity will take several years to complete, but once that capacity becomes operational, and the supply can increase, prices are bound to fall, to reflect once more the cost of production. Oil is an exception in this regard. The cartels efforts to keep capacity constrained may permit it to continue extracting monopolistic prices.

Successful globalization could well result in higher world economic growth than was attained in past decades. But there is no reason to believe that this will compromise the nonrenewable natural resources availability. The world is still very far from the bottom of the barrel of the resource wealth, and with continued cost-reducing technological progress, it is uncertain whether that bottom will ever be seen. Faster growth in the demand for natural resource commodities can easily be accommodated by a more speedy supply expansion, but producers must be given a sufficiently early warning of what to expect in order to adjust their production capacity. Successful globalization brings prospects for a speedier increase in the incomes of the poor in this world, which should be seen as a blessing and not a resource threat.


Radetzki, Marian. 2002. Is Resource Depletion a Threat to Human Progress? Oil and Other Critical Exhaustible Materials. Energy Sustainable Development: A Challenge for the New Century (Energex2002 ). Krakow: Mineral and Energy Economy Research Institute, Polish Academy of Sciences.

Tilton, John. 2003. On Borrowed Time? Assessing the Threat of Mineral Depletion. Washington, DC: Resources for the Future.

Marian Radetzki

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energy sources Naturally occurring substances, processes and phenomena from which we obtain energy. The vast majority of energy derives from the Sun. Fossil fuels are the remains of life that depended for growth on solar energy. Hydroelectricity also derives from solar energy, which maintains the Earth's hydrological cycle, while uneven heating of the atmosphere generates wind, whose energy harnessed by wind farms. The movements of the oceans, namely waves and tides, controlled by wind and the pull of the Sun and Moon, have been used successfully in some regions to create energy. Increasingly, solar energy is being used to heat some domestic water supplies directly, and for providing electricity from photoelectric cells. Geothermal energy is energy obtained from underground hot rocks. See also nuclear energy; renewable energy

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nonrenewable energy sources Sources of energy that use up the earth's finite mineral resources; these include fossil fuels. Concern about the exhaustion of nonrenewable energy sources, together with the fact that burning fossil fuels contributes to air pollution and the greenhouse effect, is leading to increased use or investigation of renewable energy resources, which are not exhaustible. These include the sun (for solar heating and solar cells), wind power (for aerogenerators) and water (for hydroelectric generators).

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non-renewable resource (finite resource) Resource that is concentrated or formed at a rate very much slower than its rate of consumption and thus, for all practical purposes, is non-renewable. Compare RENEWABLE RESOURCE.

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non-renewable resource(finite resource) A resource that is concentrated or formed at a rate very much slower than its rate of consumption. Compare renewable resource.