energy and environmental impacts: present and future perspectives
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Energy and Environmental Impacts: Present and FuturePerspectivesIBRAHIM DINCER aa TUBITAK-Marmara Research Center , Gebze, Kocaeli, TurkeyPublished online: 02 Aug 2007.
To cite this article: IBRAHIM DINCER (1998) Energy and Environmental Impacts: Present and Future Perspectives, EnergySources, 20:4-5, 427-453, DOI: 10.1080/00908319808970070
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Energy and Environmental Impacts: Present and Future Perspectives
IBRAHIM DINCER TUBITAK-Marmara Research Center Gebze, Kocaeli-Turkey
Today, world energy consumption contributes to pollution, environmental deteriora- tion, and global greenhouse emissions. Increases in energy consumption are driven by population growth and economic development that tend to increase energy use per capita. Thus the inevitable increase in population in the near future and the economic development that must necessarily occur in many countries pose serious implications for the environment. Since the early 1980s the relationship between energy use and environmental impacts has received much attention, and a number of international activities have focused on this topic. In this article, four important aspects that are related to the present and future patterns of environmental impacts, energy consumption, energy conservation, and fuel substitution are introduced and discussed in detail. We conclude that further political, economic, and institutional changes from the standpoint of environmental impacts are necessaly for the future energy policies. To this end, renewable energy resources can play an important role in controlling and reducing environmental impact.
Keywords acid rain, air pollution, energy, energy efficiency, environment, environmental impacts, greenhouse effect, ozone layer, renewable energy
Environmental problems associated with energy use span a growing spectrum of pollutants, hazards, and accidents and degradation of environmental quality and natural ecosystems. Over the past few decades, the increasing use of energy has expanded our concerns from what were once primarily local or regional issues, to a growing awareness of the international and global nature of major energy-related environmental problems. Particularly in developing or newly industrialized coun- tries, where energy growth rates are typically extremely high and where environ- mental management has not yet been fully incorporated into the infrastructure, emerging environmental problems are becoming apparent. In some cases these are worsening chronic problems, but in many cases they represent acute or severe situations.
The industrialized countries are mainly responsible for air pollution, ozone depletion, and carbon emissions because of the small contribution of the develop- ing countries. In developing countries there is a great potential to use energy efficiently because energy use is much less efficient than in more developed countries. It is clear that there is a need to make major changes in the production and use of energy. For this reason some national and international programs are
Received 2 May 1997; accepted 27 May 1997. Address correspondence to Dr. Ibrahim Dincer, associate professor, Department of
Mechanical Engineering, KFUPM, Box 127, Dharan 31261, Saudi Arabia. E-mail: [email protected]
Energy Sources, 20:427-453,1998 Copyright O 1998 Taylor & Francis
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taken into account, such as promotion of energy transition, increase of energy efficiency in terms of conservation, promotion of renewable energy technologies, and promotion of sustainable transport systems.
At present, developing countries, with a population of around 4 billion, represent some 77% of the world's population, but use only a quarter of its global energy budget. Demographers predict that the total population will top 8 billion by 2005. Roughly three quarters of these people will live in developing countries. It is obvious that the energy service requirements of the developing world must grow considerably to meet the extra demand and to ensure that the development process is not constrained. The developing world lacks the financial resources or technol- ogy to supply its burgeoning populations with energy to meet its basic needs. Moreover, the world is becoming increasingly aware of the damage to global environmental systems caused by the production and consumption of energy (Strong, 1992).
In the 1970s the primary focus was on the relationship between energy and economics. At that time, the linkage between energy and the environment did not receive as much attention. An institutional structure to deal with environmental problems emerged after the 1970s in each country in the world. In the academic community, concern about problems of pollution and the wasteful use of raw materials and energy, of course, arose much earlier. Unfortunately, the institutions that became responsible for environmental matters also held other conflicting responsibilities. Since the late 1970s, parliaments have adopted a number of laws on environmental and management policies that were supposed to be the basis of central government decisions relating to economic development and environmental impacts. Different government agencies were charged with carrying out economic and legal measures for environmental protection.
As environmental concerns such as pollution, ozone depletion, and global climate change became major issues in the 1980s, interest in the link between energy utilization and the environment became more pronounced. Since then, there has been increasing attention to this linkage. Many scientists suggest that the impact of energy resource utilization on the environment is best addressed by considering exergy. The exergy of a quantity of energy or a substance is a measure of usefulness, quality, or potential to cause change. Exergy appears to be an effective measure of the potential of a substance to impact the environment. In practice, the author feels that a thorough understanding of what exergy is and how it provides insights into the efficiency and performance of energy systems is required for the engineer or scientist working in the area of energy systems and the environment. In spite of many studies concerning the close relationship between energy and the environment, there have been limited works on the link between exergy and environmental concepts (Rosen & Dincer, 1996).
It is well known that there is always an environmental cost associated with the thermal, chemical, and/or nuclear emissions that are a necessary consequence of carrying out the processes that give benefits to mankind. The environmental impact of emissions is reduced by increasing the efficiency of resource utilization. Some- times, in practice, this is referred to as "energy conservation." However, increasing efficiency generally entails greater use of materials, labor, and more complex devices. The additional cost may be justified by the added security associated with a decreased dependence on energy resources and by the social peace obtained through increased productive employment.
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If we briefly look at the environmental problems associated with the use of various energy sources, the major concern is the greenhouse effect due to carbon dioxide (CO,) emissions from burning of fossil fuels, which play a leading role. Also, sulfur dioxide (SO,) and nitrogen oxides (NO,) emitted by fossil fuel burning contribute to acid rain and to air pollution. However, nuclear energy is associated with health risks to nuclear industry workers and to the people living around the power stations, as well as with the long-lasting waste disposal problems and the hazards of disastrous accidents. Hydro-energy can cause enormous disruption to the natural environment and is by no means an altogether benign form of energy. The burning of traditional biomass fuels, e.g., wood, crop residues, and dung, contributes a big share to air pollution along with coal and oil, especially in developing countries. Beyond the year 2000, there is much room for debate. Not least are the public's perceptions that environmental damage may have reached the point where, despite lack of leadership from those in power, policy initiatives are introduced to encourage increased energy efficiency programs in terms of energy conservation and more environmentally benign forms of energy, and these may begin to have an important effect. It is expected that energy consumption will grow but at a relatively low rate. A concerted effort in using energy efficiently could, however, considerably reduce the total energy consumed; a massive promotion of new energy sources could capture a sizable segment of the market for renewable energy.
It is well known that emissions such as CO,, SO,, and NO, from thermal power plants contribute to long-range and global environmental damage through the greenhouse effect and acid rain. Although SO, and NO, emissions have been gradually reduced through technological improvements in power plants, the global warming issue associated with fossil fuel CO, emissions continues to be a serious and controversial issue. It is axiomatic that a rise in atmospheric CO, concentra- tions is caused by human activities, such as the combustion of fossil fuels and deforestation. At present, attention is being focused on devising strategies for reducing CO, emissions (Arnagai, 1991).
The main purpose of this article is to address four important aspects, namely, environmental impacts, energy consumption, energy conservation, and fuel substi- tution, and to discuss the current situations and possible future developments.
Environmental Impact
The risk and reality of environmental degradation have become more apparent. Growing evidence of environmental problems is due to a combination of factors. During the last two decades, the environmental impact of human activities has grown dramatically because of the sheer increase of world population, consump- tion, and industrial activity. Throughout the 1970s, most environmental analysis and legal control instruments concentrated on conventional pollutants such as SO,, NO,, particulates, and carbon monoxide (CO). Recently, environmental concern has extended to the control of micropollutants or hazardous air pollutants, which are usually toxic chemical substances harmful in small doses, as well as to that of globally significant pollutants such as CO,. Aside from advances in environmental science, developments in industrial processes and structures have led to new environmental problems. For example, in the energy sector, major shifts
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to the road transport of industrial goods and to individual travel by cars has led to an increase in road traffic and hence a shift in attention paid to the effects and sources of NO, and volatile organic compound (VOC) emissions. A brief discus- sion on these gases and particulates is given below (Hollander & Brown, 1992).
CO, an odorless and colorless gas, is a significant polluter of urban air, where it arises mostly from the incomplete combustion of automobile fuels. The human health risk from inhaled CO arises from the fact that it enters the bloodstream and disrupts the delivery of oxygen to the body's tissues by combining with hemoglobin, the molecule that normally carries oxygen. At very high concentrations (e.g., those that occur with unvented combustion in enclosed spaces), CO is a deadly poison. At lower concentrations it can lead to angina, blurred vision, and impaired physical and mental coordination.
SO,, a corrosive gas hazardous to human health and harmful to the natural environment, is emitted worldwide by natural processes such as volcanoes and sea spray, and by human activities, notably combustion of sulfur-containing fuels (mainly coal and fuel oil) and smelting of nonferrous metal ores, oil refining, and pulp and paper manufacturing. Electricity generation from fossil fuels is the main source of SO, emissions in industrialized countries. Its main health effects are breathing difficulty, lung damage, and aggravation of respiratory and cardiovascu- lar disease; it also damages the plant foliage and is a precursor of acid precipita- tion.
NO, is produced wherever combustion occurs at temperatures high enough for oxygen and nitrogen (contained in air) to react. It is also formed from nitrogen in the fossil fuels themselves (e.g., coal). NO, can irritate lungs and lower resistance to respiratory infections such as influenza. A key ingredient in ozone formation, it also forms acids that can damage structures and natural systems. Controlling NO, emissions is more challenging than controlling SO,. SO, emissions come almost exclusively from large facilities such as power plants, which are relatively easy to identify and control. On the other hand, NO, sources-mostly motor vehicles-are smaller, more mobile, and much more numerous and varied.
VOCs are petroleum and solvent vapors that damage the formation of ozone. For this reason, efforts have focused on cutting VOC emissions. For example, in the United States, tailpipe emissions of unburned fuel have been cut by 90% since the 1970s through the use of catalytic converters.
Particles in the air-fly ash, sea salt, dust, metals, liquid droplets, and soot-come from a variety of sources, natural and human made. They are emitted by factories, power plants, vehicles, fires, windblown dust, and the like, or they are formed in the atmosphere by condensation or chemical transformation of emitted gases including SO,, NO,, and VOCs. Acted on by other substances in the air and by sunlight, particles are transformed into a variety of nitrate, sulfate, and carbona- ceous solid suspensions called aerosols or particulates. Particulates have a variety of health and environmental effects that matches their chemical diversity. The nitrate and sulfate particulates are themselves acidic and deposited downwind, with or without precipitation, where they may cause serious harm to plant life and human structures. Visibility problems are due mainly to airborne particles. Particu- lates may also be human health hazards, since they are breathed deeply into lungs and many have toxic or mutagenic components. Recently, it has been found that nonaccidental death rates rise and fall in near lock step with daily levels of particulates-even at very low levels (Hollander & Brown, 1992).
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Environmental problems span a continuously growing range of pollutants, hazards, and ecosystem degradation over ever wider areas. The major areas of environmental concern are (International Energy Agency, 1989)
major environmental accidents water pollution maritime pollution land-use and siting impact radiation and radioactivity solid waste disposal hazardous air pollutants ambient air quality acid rain ozone depletion global climate change
The interface between energy and the environment is complex and constantly evolving. Increasing awareness of the environmental consequences of economic activities in general and energy activities in particular means that many areas of environmental concern are quite recent. Knowledge of the mechanisms involved in the impacts of these activities may still be incomplete and in some cases specula- tive. For each of these items, Table 1 presents the pollutants and hazards involved, as well as the cause-and-effect linkage between energy activities, pollutants, and environmental effects.
Major Environmental Pollution
Recently, concern has focused on the risk of major environmental accidents. Some examples are onshore and offshore blowouts, explosions, and fires at refineries, oil rigs, tanks, and pipelines due to the production, treatment, transport, and use of oil and gas; hydroelectric dam failures causing flooding and landslides; and explosions in mines. There has been increased public awareness of the fact that developments in industrial structures have resulted in an increase in production and flows of hazardous substances. Urbanization and demographic concentration have also played a part in worsening the gravity of major accidents in terms of human lives lost and injured or displaced people. Consequently, major industrial accidents do not always result in large-scale environmental damage. Awareness of the risk of disaster-scale ecological accidents affecting ecosystems rather than human health has become more acute.
Water Pollution
Both the quality and quantity of water resources are increasingly important issues, particularly in the case of groundwater, if only because of its role in supplying drinking and irrigation water. Efforts are still being made to control energy-related pollution problems, e.g., geothermal fluids containing toxic chemicals, acid drainage from mines, coal wastes, effluent containing hazardous chemicals from power plants and refineries, and thermal pollution from the discharges of cooling systems of power plants. There is still considerable lack of information and associated uncertainty about the level of groundwater pollution and identification of energy- related sources.
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Table 1 Importance of energy activities in the generation of air pollutants
Energy activities Man-made
as % of As % of As % of Contributions as % of energy Pollutant total total man-made related releases
so2 45" 40" 90" 8ob coal combustion, 20b oil combustion
NO, 75" 64" 85" 51b transport, 49b stationary sources CO 50" 15-25" 30-50" 75b transport, 25b stationary sources Lead 100" 90" 9ob 8od transport, 20d combustion in
stationary sources PM 11.4" 4.5" 40b 17b transport, 5b electric utilities,
1 2 ~ wood combustion VOC 5b 2.8" 5sb oil industry, l o b gas industry,
75b mobile sources Radionuclides 10" 2.5" 25" 25d mining and uranium milling,
75d nuclear power and coal combustion
co2 4' 2.2-3.2" 55-80" 15b natural gas, 45b oil, 40b solid fuels
N2O 37-58" 24-43" 65-75" 60-75" fossil fuel combustion, 25-40" biomass burning
CH4 60" 9-24" 15-40" 20-40" natural gas losses, 30-50" biomass burning
Source: International Energy Agency (1989). "Global estimates. b~stimates for OECD countries. 'Global estimates of contribution of anthropogenic C 0 2 to increases in CO, concentra-
tions and to global warming is much larger. d~stirnates for the United States.
Maritime Pollution
Much concern has concentrated on maritime pollution resulting from large acci- dental oil spills. However, the main source of marine-based pollution remains shipping operations. I t is estimated that 1 tonne is discharged for every 1000 tonnes of oil transported by sea. Therefore 1.1 million tonnes yr-' a re the result of regular discharge of oil by ships at sea, and the remainder (about 400,000 tonnes) comes from tanker accidents. Spills are considered the most dangerous maritime pollution, and much work needs to be done in this area (International Energy Agency, 1989).
Land-Use and Siting Impact
Land-use pressure exerted by economic activities gives rise to concerns that land particularly suited for sustaining agriculture, housing, o r natural ecosystems could be lost. In the energy sector, mining sites and hydroelectric reservoirs have attracted the most public attention. Concern has also been focused on the large -
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land surfaces that might be needed for large-scale exploitation of renewable energy forms, e.g., solar power, wind power stations, or biomass production, which would complete with other land uses. Other energy-related activities involving large facilities or complex industrial processes, e.g., fuel refining or electric power generation, are subject to, inter alia, environmental concerns about siting some- times in addition to land-use concerns. Increased siting problems are occurring for the disposal of solid wastes, ranging from those generated in pollution control operations to high-level radioactive waste containing long-lived radionuclides.
Radiation and Radioactivity
About 90% of exposure to radiation is due to natural causes. Also, supplementary man-made radiation causes considerable concern. Energy activities contribute about 25% to total man-made radioactivity (International Energy Agency, 1989). Though fossil fuel combustion releases radionuclides, ongoing debate about man- made energy-related radiation centers mainly on the nuclear fuel cycle and its various stages. Radon, which is released in uranium mining and milling, is one of the potential occupational hazards and may cause groundwater contamination. Nuclear waste disposal involves varying degrees of hazards, depending on the characteristics of the wastes. There has been increasing wony that the risk of exposure to radiation would be high throughout the dismantling of the compo- nents, particularly the reactor vessel.
Solid Waste Disposal
Disposal of solid waste can pose environmental problems of two types. First, if the waste is classified as hazardous, that is, considered to be a potential threat to health and environment, it may release hazardous pollutants and result in air, water, and soil pollution, which constitute major issues in themselves. Most of the solid waste considered hazardous is generated by chemical and metal industries. Second, though the waste may not be considered hazardous, e.g., bottom ash from power plants, it can still pose disposal problems merely because of questions of space and appropriate containment. A major and growing source of waste has developed along with air pollution control. The commercial use of wastes from pollution control as products for the building industry and transportation surfaces is limited by the size of the market. It requires large tracts of land for disposal and adequate containment practices to avoid water contamination.
Hazardous Air Pollutants
Hazardous air pollutants are usually emitted in smaller quantities than those that are the focus of ambient air quality concerns. Lead is the main hazardous air pollutant, and most of the world's lead pollution comes from the use of lead-based gasoline additives to increase octane ratings. Lead exposure may cause neurologi- cal damage, most notably in children and fetuses, whose nervous systems are still developing. The results can be mental retardation, learning disabilities, or hyperac- tivity. Since the 1970s, many countries recognizing the health risks of lead have taken steps to phase out these lead-based additives. For example, Japan began to reduce the lead content of gasoline in 1970; lead-free gasoline was introduced in
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1975; nearly all gasoline sold in Japan today is lead free. The European Commu- nity reduced the allowable lead content of gasoline from 0.4 g/L in 1978 to 0.013 g/L in 1989. In the United States, lead emissions fell by 90% in the 1980s, and emissions from lead smelter and battery factories have been substantially reduced (Hollander & Brown, 1992). Additionally, the number of suspected hazardous pollutants is very large, and knowledge of sources, emissions, and effects is still developing. Concerns involve both localized effects, where micropollutants are discharged, and regional effects due to toxic pollutants, e.g., cadmium, mercury, and polycyclic aromatic hydrocarbons (PAHs). Many energy-related activities emit hazardous air pollutants, e.g., hydrocarbons (such as benzene) emitted fugitively from oil and gas extraction and processing industries; hydrocarbon and dioxin emissions caused by the use and combustion of petrol and diesel oil for transport; small quantities of arsenic, mercury, beryllium, and radionuclides released during the combustion of coal and heavy fuel oil; and mercury, chlorinated dioxin, and furan emissions from municipal waste incinerators.
In the United States the Environmental Protection Agency (EPA) proposed a new set of measures on September 1, 1994, that would require municipal incinera- tors to upgrade systems and thus limit a host of toxins, including dioxin, lead, cadmium, mercury, particulates, sulfur dioxide, nitrogen dioxide, and carbon diox- ide. The proposed regulations, required under the Clean Air Act Amendment of 1990, were phased in over 3 years. The regulations are expected to reduce emissions by as much as 145,000 tons ~ r - ' at a cost upward of $450 million ~ r - ' , adding about $12 ton-' to the cost of burning refuse. This translates to a monthly charge of $2 in garbage collection costs per household (Anon, 1994).
Ambient Air Quality
Air pollution is caused by emissions of toxic gases such as SO,, NO,, CO, VOC, and particulate matter (e.g., fly ash and suspended particles). This can pose a serious health threat and cause a high incidence of respiratory problems. Excessive concentrations of these pollutants and of ozone have demonstrated health, welfare, and ecological effects felt locally and sometimes regionally. VOC and NO, are well known to be responsible for photochemical smog. In principle, these problems are soluble through the enforcement of clean air regulations. There is, however, a cost associated with such measures, and a program of cleaning up the air requires concerted action by governments if it is to succeed. For example, SO, emissions in eastern Canada were reduced by 45% between 1970 and 1985 (Dincer & Dost, 1996). NO, emissions have not shown any remarkable decrease and are set to increase over the coming decades. Air pollutants, as well as precursors of photo- chemical oxidants, are emitted from a variety of stationary and mobile fuel consumption sources, and energy-related activities contribute significant quantities of all of these pollutants. For example, recent estimates show that stationary combustion facilities are a major source of SO, and NO, emissions, and in Organization for Economic Cooperation and Development (OECD) countries the mobile sources (e.g., transport vehicles) account for 75% CO emissions and transportation causes 13% of man-made particulate matter emissions, 20% of which is due to stationary combustion sources (International Energy Agency, 1989).
The simplest and cheapest way of alleviating localized air pollution is to build high chimney stacks, so that some of the fumes are transported elsewhere. The
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pollutants do not simply vanish in the sky, however, and this practice in North America and Europe has merely led to the more intractable problem of acid rain.
Recently, there has been great interest in indoor air pollution due to increas- ing energy-related activities. Here we give detailed information on this topic. Energy use in buildings produces a variety of air pollutants, including CO, CO,, smoke from stoves and fireplaces, and various gaseous oxides of nitrogen and sulfur from furnaces, as well as stray natural gas and heating-oil vapors. The radioactive gas radon, present in small quantities in natural gas, is emitted by gas-burning appliances. Especially in well-insulated, tightly sealed, energy-efficient homes, these pollutants and others-such as cigarette smoke, formaldehyde from plywood and glues, radon from the surrounding soil, and asbestos-can build up to significant levels. Highly energy-efficient buildings may be so tightly sealed that they experience a complete air change only once every 2-10 hours, compared to once every hour or half hour for older, leaky buildings. While many of these pollutants can be eliminated at the source-for example, by not smoking or not using wood stoves or unvented gas heaters-others are so much a part of modern life (or, in some cases, the natural world) as to be nearly inescapable. Ventilation is the key. Exhaust fans are used to change the air in many energy-efficient buildings. Often air-to-air heat exchangers are used to recapture the heat that would otherwise go out with the indoor air (Hollander & Brown, 1992). A more troubling and far more widespread problem of indoor pollution is the use of so-called traditional fuels in the Third World. Smoke from wood, crop residues, and dung contains a variety of carcinogens, mutagens, and other toxic substances in the form of easily respirable particles. Health risks are particularly great among those who spend long hours cooking over fires in enclosed spaces. Knowledge of indoor pollutant dose-response relationships is still incomplete. Despite much research on indoor air pollution, relevant control strategies are still at the developmental stage.
Acid Rain
Acids produced by the combustion of fossil fuels and the smelting of nonferrous ores can be transported long distances through the atmosphere and deposited on Earth in ecosystems that are exceedingly vulnerable to damage from excessive acidity. This is referred to as the acid rain problem that has been found to be mainly related to emissions of SO, and NO,. These pollutants have caused only local concern in the past, largely for health reasons. However, as awareness of their contribution to the regional and transboundary problem of acid rain has grown, concern is now also focusing on other substances such as VOC, chlorides, ozone, and trace metals that may participate in the complex set of chemical transforma- tions in the atmosphere resulting in acid rain and the formation of other regional air pollutants. The well-known effects are acidification of lakes, streams, and groundwater, resulting in damage to fish and aquatic life; damage to forests and agricultural crops; and deterioration of materials, e.g., buildings, metal structures, and fabrics. Some energy-related activities are a major source of acid rain. For example, electric power stations, residential heating, and industrial energy use account for 80% SO, emissions, with coal alone producing about 70%. Another source is sour gas treatment, which produces H,S, which then reacts to form SO, when exposed to air. Road transport is an important source of NO, emissions, with 48% of total emissions in OECD countries (International Energy Agency, 1989).
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Most of the remainder is due to fossil fuel combustion in stationary sources. Additionally, VOCs are generated by a variety of sources and comprise a large number of very diverse compounds.
A major problem with acid rain is that its effects are diffuse and often found in a different country than its source. This makes it exceptionally difficult to apply the principle of "the polluter pays" and has already led to some acrimony between governments. Coal and high-sulfur fuel oil are the materials most responsible for producing acid rain, and considerable research is being undertaken on clean coal technology. Possible solutions include cleaning the coal before combustion, as well as actually burning it more cleanly, through the use of techniques, e.g., fluidized bed technology. As mentioned above, vehicle exhaust is a major contributor, and it is expected that the number of vehicles worldwide will be over 500 million by early 2000. Three-way catalytic converters can reduce emissions of some pollutants, but unfortunately, the increase in the quantity of fuel consumed will hence increase the amount of carbon dioxide released into the atmosphere. It is well known that the effective solution is to limit the number of vehicles through promoting efficient public transport and to enforce the use of more fuel-efficient vehicles.
Ozone Depletion
It is well known that the ozone present in the stratosphere, roughly between altitudes of 12 and 25 km, protects us from incoming ultraviolet radiation. A global environmental problem is the distortion and regional depletion of the stratospheric ozone layer, which was shown to be caused by chlorofluorocarbons (CFCs), halons (chlorinated and brominated organic compounds), and N,O emissions. Ozone depletion can lead to increased levels of damaging ultraviolet radiation, which could cause a rise in skin cancer, eye damage, and harm to many biological species. Energy-related activities are only partially (directly or indirectly) responsible for these emissions. Energy activities, e.g., fossil fuel and biomass combustion, account for 65-75% of anthropogenic N,O emissions. CFCs, which are used in air condi- tioning and refrigerating equipment as refrigerants and in foam insulation as a blowing agent, play the most important role in ozone depletion. Scientific debate on ozone depletion has gone on for over a decade; only in 1987 was an interna- tional protocol signed in Montreal-an historical landmark-to reduce production of CFCs and halons. Conclusive scientific evidence of the destruction of strato- spheric ozone by CFCs and halons has recently been gathered, and commitments for a more drastic reduction of their production were undertaken at the 1990 London Conference. Replacement products and technologies without CFCs are gradually coming to the fore and should make a total ban of these obnoxious products less painful. One important aspect is the need to distribute fairly the economic burdens derived from a ban of CFCs, particularly with respect to developing countries, some of which have invested heavily in CFC-related tech- nologies.
Global Climate Change
The potentially most important environmental problem relating to energy is global climate change (global warming or the greenhouse effect). The increasing concen- tration of greenhouse gases such as CO,, CH,, CFCs, halons, N20, ozone, and
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peroxyacetylnitrate in the atmosphere is acting to trap heat radiated from Earth's surface and is raising the surface temperature of Earth. The surface temperature increased about 0.6"C over the last century, and as a consequence, sea level is estimated to have risen by perhaps 20 cm (Colonbo, 1992). Such changes have wide-ranging effects on human activities all over the world. Currently, it is estimated that CO, contributes about 50% to the anthropogenic greenhouse effect. In Table 2, current knowledge of the role of various greenhouse gases is given. Humankind is contributing with a great many economic activities to the increase atmospheric concentration of various greenhouse gases. CO, from fossil fuel combustion, methane from increased human activity, CFCs, and deforestation all contribute to the greenhouse effect. Most scientists agree that there is a cause-effect relationship between the observed emission of greenhouse gases and global warming. Furthermore, they predict that if the atmospheric concentration of greenhouse gases continues to increase, as the present trends of fossil fuel consumption indicate, Earth's temperature may increase in the next century by another 2°C and perhaps 4°C. If this prediction comes true, sea level could rise between 30 and 60 cm before the end of the 21st century. The impact on coastal settlements could be dramatic; there could be a displacement of fertile zones for agriculture and food production toward higher latitudes; and the decreasing availability of fresh water for irrigation and other essential uses could seriously jeopardize the survival of entire populations (Colonbo, 1992).
Present and Future Patterns of Energy Consumption and the Environment
The world population was about 5.3 billion in 1990. It has doubled in the past 40 years, and it is likely to double again by the middle of the 21st century. The first expectation is that the world's population will rise to about 7:0 billion in 2010. Even if birth rates were to fall so that the world population became stable by 2050, the total would then be about 10.5 billion. Population growth is greater in developing countries than in industrialized countries, which include the OECD group, the former USSR, and Eastern Europe. In 1960, developing countries accounted for less than 70% of the total world population. Today this share has risen to 77%, and by the year 2050 it is expected to reach about 85% (Eden, 1993).
Energy is the key item in our relation with our environment. Energy consump- tion determines how much and how severely we can affect our environment and how damaging or healing our interactions with it are. Therefore this section will concentrate entirely on energy production, consumption, and use.
Globally, energy consumption in developing countries results in significant emissions of greenhouse gases. Energy-related activities contribute half of the gases that are involved in global warming, with other industrial emissions, defor- estation, and agriculture making up the remainder. Industrialized countries cur- rently emit 11 times as much greenhouse gases as developing countries, with the Third World accounting for 15% of cumulative CO, output between 1870 and 1986. However, with population growth and accelerated industrialization, develop ing countries will account for both greater per capita and overall output. Much of this will come from metrpolitan areas, where there is a concentration of vehicles. industries, urban deforestation, and other sources of high emissions (Leitmann, 1994).
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Tab
le 2
R
oles
of
diff
eren
t su
bsta
nces
in t
he g
reen
hous
e ef
fect
Abi
lity
to r
etai
n in
frar
ed r
adia
tions
Su
bsta
nce
com
pare
d to
CO
,
Prei
ndus
tria
l co
ncen
trat
ion
(PP
~)
Pres
ent
conc
entr
atio
n (P
P~
)
Ann
ual
grow
th
rate
(%
)
Shar
e in
the
gre
enho
use
Shar
e in
the
gre
enho
use
effe
ct d
ue to
hum
an
incr
ease
due
to
hum
an
activ
ities
(%)
activ
ities
(%)
Sour
ce: A
ebisc
her
et a
l. (1
989)
.
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Energy and Environmental Impacts 439
Energy demand growth has been very rapid since the sharp fall in oil prices in 1986, and world energy demand grew by 17% from 1986 to 1992, while oil demand in 1994 was more than 12 million barrels d-' higher than in 1985. While the abundance of potential energy resources is not in dispute, the present combination of energy demand growth and energy prices may not be sustainable. According to macroeconomic and population growth assumptions, the projected demand for oil, natural gas, and coal, as well as for electricity, grows very rapidly. For example, if crude oil prices were not to exceed $18 per barrel and if the recent slowing in the rate of improvement of energy intensity continued, the world demand for oil could exceed 100 million barrels d-' by 2010. This would represent an increase in average consumption of about 2 million barrels d-', every year throughout the next 15 years. Equally fast growth rates for coal and gas demand result from these assumptions.
The International Energy Agency (IEA) uses two important cases for energy analyses and future projections, namely, the capacity constraints case and the energy savings case. In the first case, trends in past behavior are assumed to continue to dominate future energy consumption patterns. In this respect, growth in world energy demand proves too fast for production to keep up. In the second case, exogenously imposed additional energy efficiency improvements are assumed to be greater than those suggested by past behavior. In Tables 3 and 4, general energy perspectives of the world based on these cases are given (OECD/IEA, 1995). As can be seen in Table 3, in the capacity constraints case, world total primary energy demand is projected to increase by more than 44% between now and 2010, or at an average annual rate of about 2.1%, to 11,489 million tonnes of oil equivalent (Mtoe). This compares with average annual growth in primary energy use of 2.4% from 1971 to 1992. Natural gas is expected to be the fastest growing fossil fuel with an average of 2.5% yr-' through this period. In the energy savings case, world energy demand grows by less than 35% from now to 2010, with rates of growth in all regions being lower than those in the capacity constraints case. World consumption of coal and other solid fuels in the period up to 2010 is expected to increase at an annual average rate of 2% (to 3280 Mtoe) in the first case and 1.6% in the second case (to 3067 Mtoe). Therefore, energy demand in this case increases by only an average of 1.7% per year. By 2010, primary energy demand is projected to reach 10,686 Mtoe (Table 4). Additionally, Tables 3 and 4 present the final energy consumptions, net transformation and other losses, electricity outputs, gross domestic product (GDP) values, energy per capita, and energy intensities, as well as CO, emissions and their future projections. Further information about these cases and energy analyses can be found in World Energy Outlook (OECD/IEA, 1995).
World energy use, after years of slow growth, began rising rapidly in the mid-1980s. Between 1980 and 1986, energy use rose at an annual rate of only 1.5% (mainly because of near zero growth in the major industrialized countries). How- ever, 1987 saw a 3.1% increase, and in 1988 the figure was 3.7%. Most of the growth in energy demand for years has been in developing countries. Between 1973 and 1987, their energy use grew at an annual average of 5.1%. Their share of the world's commercial energy use rose from 14% in 1970 to 23% in 1985. Developing countries are expected to continue to account for most of the growth in energy use. The newly industrializing countries of Southeast Asia show the fastest growth of all: an 11.4% increase in 1988. Japan's energy use rose by 6.2% in that year, and
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Tab
le 3
G
ener
al e
nerg
y de
man
d pe
rspe
ctiv
e of
the
wor
ld a
ccor
ding
to th
e ca
paci
ty c
onst
rain
ts c
ase
Pot
enti
al
Ann
ual g
row
th ra
te (
%)
Fue
l sha
re (%
)
1971
19
92
2000
20
10
1971
-199
2 19
92-2
000
2000
-201
0 19
92-2
010
1971
19
92
2000
20
10
Prim
ary
ener
gy (M
toe)
So
lids
Oil
Gas
N
ucle
ar
Hyd
ro
Geo
/oth
er (
rene
wab
les)
T
otal
Fi
nal e
nerg
y So
lids
a
Oil
a o
Gas
E
lect
rici
ty
Tot
al
Tra
nsfo
rmat
ion
and
loss
es
Ele
ctri
city
out
put (
TW
h)
Solid
s O
il G
as
Nuc
lear
H
ydro
G
eo/o
ther
(re
new
able
s)
Tot
al
CO
, em
issi
ons (
Mt)
C
hang
e si
nce
1990
(%I
GD
P p
er c
apit
a (1
987
US$
) E
nerg
y pe
r ca
pita
(toe
) E
nerg
y in
tens
ity (t
oe/1
000$
)
Sour
ce:
OE
CD
/IE
A (
1995
).
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442 I. Dincer
that of the United States rose by 4%, reaching its highest level (~o l l ande r & Brown, 1992).
Oil is expected to keep the leadership role in the next century, and therefore problems will continue to arise as periodic shocks and fluctuations cause demand to adjust within a supply limit. The limit will probably remain about 4000 Mtoe yr-' and will begin a slow decline in the middle third of the next century. With an average production of 1000 Mtoe ~ r - ' , supplies could last for about 90 years. It is projected that production could continue close to this level throughout the 21st century. Production elsewhere currently totals more than 2200 Mtoe, but the reserve/production ratio is only 21 years. Using improved technologies in many countries will help to maintain production close to 2000 Mtoe for several years. It is known that resources of unconventional oil are much larger than those of conventional oil and this will help to maintain the total world oil production close to 3000 Mtoe yr-' through the 21st century (Eden, 1993).
Proven natural gas reserves equal 100,000 Mtoe, which is two thirds of proven oil reserves. It is likely that ultimate resources of conventional gas are comparable with those of oil at a production rate of 3000 Mtoe yr-' to be maintained throughout most of the 21st century. The present demand is 1700 Mtoe ~ r - ' , and it is likely to increase steadily as natural gas is used to substitute for oil, especially for electricity generation. The use of natural gas in competition with oil will help to stabilize world oil demand close to current levels. The longer term transport of gas from production wells to markets will include three cases, namely, pipelines, liquefied natural gas (LNG), and conversion to liquids. The development of these transport facilities for natural gas will introduce additional flexibility and help to restrain prices for the next one or two decades. World natural gas consumption is projected to increase rapidly early in the 21st century, and hence the total energy supply from natural gas is forecast to be about 3000 Mtoe yr-'. Therefore global demand for natural gas is projected to grow considerably less, and by less than the demand for total primary energy.
The contribution of solid fuels to the world energy potential is expected to remain substantial and close to the present 29%. The relative abundance and physical attributes of solid fuels indicate that the bulk of the consumption of most countries is satisfied by indigenous resources. This is certainly the case, especially for lignite, whose low thermal content makes large distance transportation uneco- nomical. For example, in 1992, hard coal had the largest share of solid fuel consumption, with about 70%, while lignite accounted for 12.3% and other solid fuels for 15.5% (Eden, 1993). The energy supply of coal and solid fuels to world energy in the 21st century is expected to reach 8000 Mtoe under normal circum- stances. If some environmental constraints appear, supply would be less.
Hydropower will continue to increase, especially in developing countries, but its growth will slow as options become more costly and/or more distant from major markets, and as environmental protection is given high priority. It is projected that hydro energy will rise to the equivalent of 1000 Mtoe yr-' by 2050.
Currently, nuclear energy generated, especially by industrialized countries, is about 80%. However, a continued slowdown in the rate of nuclear power growth is expected up to the early 21st century because of cost, regulatory and pricing regimes, long design and construction times, and environmental and safety con- cerns. Many countries have abandoned their nuclear programs, put them on hold, or have stated long-term plans to eliminate nuclear power from their fuel base. It is
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Energy and Environmental Impacts 443
expected that nuclear energy production, currently equivalent to 450 Mtoe yr-' will grow by about 1.5% to 2010 and in the 21st century will fall slightly to 200 Mtoe. For the future of nuclear power, as known, one of the strongest arguments driving a revival of nuclear energy is the fact that it can substitute for fossil fuels and reduce their most undesirable environmental impacts, such as acid precipita- tion and potential for C0,-induced climate change. While many environmentalists argue that conservation is preferable, the role of nuclear energy in mitigating the greenhouse effect has become an undeniable issue worldwide. Therefore it is important to examine the necessary conditions for a significant nuclear revival.
The potential from new renewable energy sources, e.g., biomass, solar, wind, geothermal, wave, is expected to reach about 100 Mtoe by 2010. If growth continues at an average rate of 7% yr-', it will be reached 1500 Mtoe by 2050.
World electricity demand increased at an average annual rate of 4.5% from 1971 to 1992 and doubled to 4800 TWh. By 2010, it is projected to increase more rapidly to 20,323 TWh. World electricity generation is projected to grow by an average rate of 2.5% in the 21st century. Briefly, investment in electricity supply will remain a problem for many developing countries, where there is a conflict between social needs for low-priced electricity and investment requirements for an adequate return on capital. This will lead to slower growth in the use of electricity in developing countries, though its growth is likely to remain higher than in the industrialized countries.
In recent years, the issue of global warming and energy-related CO, emissions has been at the forefront of environmental policy. It can be seen in Tables 3 and 4 that CO, emissions were 14,707 and 21,114 Mt in 1971 and 1992. The growth rate from 1971 to 1992 was 43.5%. Carbon emissions are expected to rise 45.5% for the capacity constraints case and 33.7% for the energy savings case by 2010. In spite of many countries that have announced their intention to stabilize emissions at 1990 levels by 2000, there are many uncertainties that make this aim unreachable. Increased energy consumption will have direct impacts on the environment and yield high carbon emissions. For developing countries, there is a difficult dilemma due to the conflict between development, which traditionally has led to greater energy demand, and environmental protection, which seeks to limit the use of fossil fuels.
It is useful to explain that there is an argument about the fact that CO, levels are rising in the atmosphere, although the complex global balance of emission and absorption of carbon is not well understood; there is also great uncertainty about the quantitative linkage between atmospheric CO, levels and global climate change (Cockshutt, 1993).
In view of the fact that energy consumption is a major contributor to environ- mental degradation, decisions regarding energy policy alternatives require compre- hensive environmental analysis. To the extent that it is practical, environmental impact data must be developed for all aspects of energy systems and must not be limited to separate components.
Energy consumption is intimately bound up with the natural environment. The environmental consequences of the growth in world energy demand would indeed be catastrophic, with far-reaching economic consequences. The use of renewable energy sources and alternative fuel substitution can offer a partial solution, but it is believed that the easiest, most effective, and cheapest way is the use of energy conservation technologies.
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Somewhat expensive equipment can minimize the environmental effects of pollutants such as SO,, but combustion of all fossil fuels produces CO,, and no means exist to prevent this situation. A massive reforestation program is called for, but this alone is not able to absorb the projected increase in CO,. Consequently, any increase in world consumption of fossil fuels adds to the already measured climatic effects of greenhouse warming Earth's atmosphere.
Energy Conservation and the Environment
For too long now, energy has been considered a limitless commodity. Without any consideration whatever, energy was continuously wasted simply because it was so abundant and cheap, or so we thought. This situation has now completely reversed itself. No longer will refuse and other solid wastes-all potential sources of energy -simply be buried. Instead, they have been used to supplement fuel supplies. No longer are valuable reusable items disposed of. Recycling (resource recovery), which inherently has extended the lifetime of many natural resources, is both more profitable and more compatible with environmental aims.
Energy conservation became popular in the 1970s and has been called "the fifth energy source." The advantage of conservation is that it not only postpones shortages of energy sources, especially fossil fuels, and reduces environmental damage, it can also save considerable amounts of money, even when energy costs are low. Conservation, however, is only slowly reaching a wide range of users. The efficient use of energy is also of paramount importance to developing countries, as it can forestall the need for very large capital investments in additional and unnecessary energy infrastructure.
In the early 1980s, priority was given to the following measures in order to achieve successfully conservation results:
strong regulations and standards, particularly for cars and buildings incentive schemes to stimulate energy conservation investments (for exam- ple, insulation schemes or industrial investment incentives) energy auditing and reporting schemes, especially for energy-intensive indus- tries measures to encourage the use of waste heat from power stations and from industries, e.g., cogeneration of heat and electricity promotion of research and development in conservation techniques
Since the late 1980s, the "environment" has been taken into consideration as part of these criteria, and much attention has been paid to energy conservation and the environment.
It is clear that there is an undoubtedly enormous potential for energy conser- vation, which could considerably decrease total world energy consumption and, thereby, the effects of energy consumption on the environment. One problem is that implementing a program to encourage energy conservation and efficient energy use requires a myriad of small changes in consumption patterns. Unlike a fuel substitution program, a conservation program is somewhat open-ended and may even seem intangible. However, the cumulative effect of apparently small measures can bring remarkable fuel savings. An important point is that many of these simple efficiency measures could be implemented in a relatively short time,
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Energy and Environmental Impacts 445
since there is a rapid stock turnover for light bulbs, cars, and refrigerators, unlike power stations.
A number of analysts have reached the important conclusion that despite high capital costs, some efficiency measures can result in considerable net savings of cash as well as energy. This is true for individual consumers and is even more true for economies as a whole, where one can, for example, count into the equation the savings on power stations that no longer need to be built, or on energy distribution infrastructure that is not required. Such savings are worthwhile to any economy but may be particularly attractive to developing countries that suffer from acute shortage of capital. The growth in energy demand in developing countries requires enormous amounts of foreign exchange, both to invest in power stations and infrastructure and to buy imported fuels. This in itself has an environmental impact, since one way of earning foreign exchange is to increase shares of good agricultural land to be turned into cash export crops. This in turn leads to cultivation of increasingly marginal land for growing staple food supplies, and to progressive erosion of soils and eventual desertification. It is evident that develop ing countries have an advantage over industrialized countries, in that investment in new efficient technology is typically much cheaper than retrofitting old plants. It is therefore important that the expansion of developing economies, especially the introduction of new industries, is based on the latest technology available, bypass- ing the inefficient and wasteful technologies that have been used in industrialized countries.
Scheraga (1994) points out numerous examples of negative environmental externalities associated with energy use: greenhouse gas emissions that contribute to global climate change, environmental damage due to the process of extracting energy resources from the ground, and competition for water between hydropower and other uses (e.g., agriculture and recreational activities) and associated damage to water quality. Externalities other than environmental impacts may also exist, such as the national security concerns that arise from increasing dependence on foreign oil.
It is obvious that energy conservation reduces the environmental impact from several energy systems. In addition to reducing environmental damage, conserva- tion will enhance the reliability of future energy supplies. By slowing the rate of growth of energy demand, we can improve the longevity of our supplies, allowing more flexibility in developing systems for meeting long-term energy needs. There is tremendous potential for conservation at both the energy production and consump- tion stages. For example, only about 30% of the oil in a reservoir is extracted from onshore wells; offshore extraction is somewhat more efficient. As the price of crude oil rises, more extensive use of secondary recovery techniques (e.g., flooding, thermal stimulation), which conserve oil resources and reduce some of the damage of oil extraction, will become evident. Another example is that in deep mining of coal, less than 60% of the resource in place is recovered and more than 10% of the energy in coal can be lost in cleaning. Briefly, much of the environmental damage from our use of energy comes from systems that provide energy to the consumer. If the systems for providing energy were to function more efficiently, then the adverse environmental effects of energy production would be reduced: Similarly, if the consumer were to use energy more efficiently, that is, if he could expend less energy while achieving his desired ends, then both energy production and environ- mental damage will be reduced.
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Recently, the term efficiency has been used in at least two different ways, namely, first-law efficiency and second-law efficiency. The former, which merely reflects the standard laws of energy conservation, is defined as the ratio of useful energy output to total energy output, for any process. For chains of processes such that the output of one is the input of the next, first-law efficiencies are multiplica- tive.
'The laws of thermodynamics allow a sufficiently accurate description of the impact of conservation measures on energy production and consumption. In thermodynamics, it is often convenient to consider a hypothetical body sufficiently great in size that it can supply or absorb finite amounts of heat without undergoing any change in temperature. Such a body is called a thermal energy reservoir. In practice, large bodies of water such as oceans, lakes, and rivers as well as the atmosphere can be modeled accurately as thermal energy reservoirs. For instance, the atmosphere does not warm up as a result of heat losses from residential buildings in winter. Likewise, megajoules of waste energy dumped in large rivers by power plants do not cause any significant change in water temperature (Rosen & Dincer, 1996).
As indicated by Rosen (1986), the second law of thermodynamics is instrumen- tal in providing insights into environmental impact. It is well known that heat transfer from industrial devices to the environment is of major concern to engi- neers and scientists working on energy and environment issues. Irresponsible management of waste energy can significantly increase the temperature of portions of the environment, resulting in thermal pollution. If not carefully controlled, thermal pollution can seriously disrupt marine life in lakes and rivers. However, by careful design and management, the waste energy dumped into large bodies of water can sometimes be used to significantly improve the quality of marine life by keeping the local temperature increases within safe and desirable levels.
Exergy analysis is a method that uses the conservation of mass and conserva- tion of energy principles together with the second law of thermodynamics for the design and analysis of energy systems. The exergy method can be suitable for furthering the goal of more efficient energy-resource use, for it enables the locations, types, and true magnitudes of wastes and losses to be determined. Therefore exergy analysis can reveal whether or not and by how much it is possible to design more efficient energy systems by reducing the sources of inefficiency in existing systems (Egrican & Dincer, 1992).
An understanding of the relations between exergy and the environment may reveal the underlying fundamental patterns and forces affecting changes in the environment, and help researchers to deal better with environmental damage. ~ h e s e relationships between exergy and environmental impact have been intro- duced previously (Rosen & Dincer, 1996; Rosen, 1986).i
Increasing efficiency is one of the key strategies for achieving sustainable development. Increasing energy efficiency means greater output with the same amount of input. Increase in energy efficiency brings about a decrease in pollution.
The primary energy sources are fossil fuels such as coal, oil, and gas. Typical analyses are shown in Table 5 (Darby, 1990). Following combustion, CO, is discharged by an amount related to the quantity of carbon in fuel, which could be in the range 2.8-3.2 g, of CO, per gram of fuel. The quantity of CO, and water vapor for a given heat output from fossil fuel is also shown in Table 5. The combustion of oil discharges only about 70% of CO, and about half that from
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Energy and Environmental Impacts
Table 5 Typical constituents of fossil fuels, and the products of combustion
Coal (%) Oil (%) Natural gas (%)
Constituent (dry wt.) Carbon Hydrogen oxygen Nitrogen Sulfur Ash Carbon dioxide
Energy per kg of fuel 29.0 42.0 53.0 burnt (MJ)
Quantities for an output of 1000 MJ (kg)
Fuel needed 34.0 24.0 19.0 Carbon content 27.0 20.5 14.0 Hydrogen content 1.7 2.6 5 .O Carbon dioxide produced 99.0 75.0 51.0 Water produced 14.0 21.0 40.0
Source: Darby (1990).
natural gas compared with coal. CO is produced primarily during incomplete combustion of hydrocarbon fuels. The emission of NO, arises from two sources: the oxidation of nitrogen in the combustion air and the oxidation of nitrogen contained in the fuel. SO, arises from oxidation of sulfur in the fuel, and all the sulfur is normally converted to the oxide. Sulfur occurs naturally in coal and oil but not in natural gas. There is no realistic means available for recovering CO, at the point of discharge. Technologies are available for reducing the other emissions, either by redesign of burners, by use of catalytic converters, or by chemical routes.
It is axiomatic that conservation leading to a reduction in the usage of fossil fuels will directly or indirectly also cause a reduction in chemical emissions. This effect on chemical emissions can be brought about by the following situations (Darby, 1990):
those that arise during the mining, extraction, or transport of the primary source the efficiency with which the fossil fuel is cornbusted and the products of combustion utilized the means taken, with either the thermal or electrical energy generated, to minimize the losses and to recycle and reutilize waste energy streams the application of more efficient techniques, especially in the field of power generation
Successful efforts have been made to improve process energy utilization and hence reduce the usage of primary fuels and their associated emissions. Innovative
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methods of yesterday have become standard production methods of today. Further, innovations arising from a specific process or industry have been transferred successfully to other industries.
Energy and environment studies that lead to increased energy efficiency can reduce environmental impact by reducing energy losses. Within the scope of exergy methods, such activities lead to increased exergy efficiency. In practice, efficiency improvements can be identified by means of modeling and computer simulation studies. Increased efficiency can often contribute in a major way to achieving energy security in an environmentally acceptable way by the direct reduction of emissions that might otherwise have occurred. Increased efficiency also reduces the requirement for new facilities for the production, transportation, transformation, and distribution of the various energy forms; these additional facilities all carry some environmental impacts. To control environmental pollution, efficiency im- provement actions often need to be supported by pollution control technologies or fuel substitution. It is through regional or national actions, rather than through individual projects, that improved exergy efficiency can have a major impact on environmental protection.
Fuel Substitution
Substituting fuels to further the achievement of environmental objectives has involved the following: (1) permanent shifts to energy alternatives (e.g., from fossil fuels to nuclear or renewable energy sources); (2) temporay fuel switching to minimize seasonal or short-term environmental impacts (e.g., from gasoline to natural gas); and/or (3) the use of higher quality (less polluting) forms of the same fuel (e.g., from high- to low-sulfur coal). More recently, the growing recognition of environmental problems has affected fuel choices. In order to determine the comparative effects on the environment of different fuel choices, it is imperative to look at the fuel cycle and the environmental impacts at all stages (International Energy Agency, 1989). Reddy (1995) indicated that urbanization is a growing trend in the developing countries and that rising urban energy demand has to be addressed as part of national development plans. However, this cannot be done without understanding the fuel shifts that are taking place, particularly in the domestic sector.
Notable alterations in fuel choice occurred in the late 1970s, largely as a result of energy security and environmental objectives explicitly supported by government policy makers and uncertainty about future fuel costs. The greatest shift took place in the utility sector and through changes in space heating of residential and commercial buildings. The observed shifts in the industrial sector were less marked and often were the result of structural changes and not of fuel substitution. Both siting constraints and a number of fuel use restrictions played some part. Here, we present some details and specific information on substituting fuels.
Natural Gas
Natural gas is preferable to coal and oil in terms of SO, and particulate matter. There is therefore some interest in substituting natural gas for coal in power
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Energy and Environmental Impacts 449
generation, particularly as an increasing share of future energy demand will be for electricity.
Natural gas is distributed through an inconspicuous, pervasive, and efficient system of pipes. Its capillaries reach right to the kitchen. It provides an excellent hierarchy of storage, remaining safe in geological formations until shortly before use. Natural gas can be easily and highly purified, permitting complete combustion. For gas, the next decades should be a time of relative and absolute growth. With estimates of the gas resource base having more than doubled over the past 20 years to very large volumes, we should encourage its adoption in the transportation sector as well as for electric power. There are already upward of 700,000 natural gas vehicles in the world. Italy's fleet leads the way, but numbers are growing from Brooklyn to New Zealand. Natural gas can do a great deal to clear the skies over many cities. Steps should be taken to make it easier to build and access gas pipelines (Ausubel, 1991).
Current U.S. regulations focus on market approaches to reduce SO2, NO,, and CO, pollution, allowing affected firms to choose the least cost compliance alterna- tive. Natural gas, a relatively benign fuel from an environmental perspective, could realize a substantial increase in demand if it is competitive. The viability of gas as an alternative has been questioned because of its high forecast prices and unstable supply. Potential efficiency gains in the completion and production of natural gas wells may lower production costs and increase recoverable reserves. Coupled with the premium that can be paid for its environmentally desirable qualities, gas can potentially be a feasible alternative. However, the window of opportunity is limited because many industries, such as electric power generation, require decisions involving up-front capital expenditures that lock firms into a specific compliance mechanism and fuel type (Chernak, 1994).
Despite the clean fuel image of natural gas, it should be noted that natural gas still produces significant quantities of greenhouse gases such as NO, and CO,. Leaks of methane during gas production, transportation, and burning also pose a considerable threat to the environment. However, the combustion of natural gas produces no SO, emissions and substantially less NO, and CO, than its two major competing fuels, e.g., oil and coal (Table 6). It was previously mentioned that world natural gas consumption is projected to increase rapidly early in the 21st century, and hence the total energy supply from natural gas is forecast to be about 3000 Mtoe yr-'. Therefore global demand for natural gas is projected to grow consider- ably less, and by less than the demand for total primary energy. Some important
Table 6 Substances emitted from coal, petroleum, and natural gas sources
Substance Coal Petroleum Natural gas
co2 X X X co X X NO, X X X so2 X X CH4 X X X HCl x
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steps have already been taken to promote natural gas, primarily for energy security reasons.
Nuclear Energy
Because of the greenhouse effect from burning fossil fuels, along with acid rain and air pollution, nuclear energy was considered a new opportunity, and some environmentalists have even begun to view nuclear power in a more favorable way. On the other hand, its political acceptability has been doubtful. While those in the industry are convinced that nuclear power is safe, the general public remains far from convinced. In the past, nuclear accidents such as Chernobyl have proved the nuclear advocates wrong, and the long-term effects of these accidents are still being felt. Along with the risks associated with plants while they are operating and their regular discharges of low-level waste, the long-term problem of waste disposal remains unsolved.
It is expected that the growth rate of nuclear energy generated by the industrialized countries will continuously decrease up to the early 21st century because of cost, regulatory and pricing regimes, long design and construction times, and environmental and safety concerns. Many countries have abandoned nuclear power programs, have put them on hold, or have stated long-term plans to eliminate nuclear power from their fuel bases. As mentioned earlier, it is expected that nuclear energy production, currently equivalent to 450 Mtoe yr-' will grow by about 1.5% to 2010, and will fall slightly to 200 Mtoe in the 21st century. It is well known that one of the strongest arguments driving a revival of nuclear energy is the fact that it can substitute for fossil fuels and reduce their most undesirable environmental impacts, such as acid precipitation and potential for C0,-induced climate change. While many environmentalists argue that conservation is prefer- able, the role of nuclear energy in mitigating the greenhouse effect has become an undeniable issue worldwide. Therefore it is important to examine the necessary conditions for a significant nuclear revival.
Hydropower
Hydropower, which is a clean and renewable energy source with enormous poten- tial, will continue to increase, especially in developing countries, but its growth will slow as options become more costly and/or more distant from major markets, and as environmental protection is given high priority. It is projected that hydro energy will rise to the equivalent of 1000 Mtoe yr-' by 2050. It is clear that hydroelectric- ity brings its own problems, e.g., enormous unused capacity and ecological damage. In tropical climates the creation of large hydro lakes is associated with increases in water-borne diseases such as bilharzia. Also, the flooding of large areas of land inevitably means the destruction of agricultural land and/or tropical rain forest and, often, the displacement of large populations. For example, over 1 million people were displaced because of the Ataturk dam project in Turkey-the third largest dam in the world. But hydropower is a mature technology, and the largest exploited resources are now in the developing countries. Consequently, increasing political pressure from environmentally concerned groups on funding organizations (e.g., World Bank) make it unlikely that large hydro schemes will receive much support.
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Renewable Energy
The main renewable energy resources are biomass, solar, wind, geothermal, wave, and small hydro, and the renewable energy technologies produce marketable energy by converting natural phenomena into useful energy forms. These technolo- gies utilize the energy inherent in sunlight and its direct and indirect impacts on Earth (photons, wind, falling water, heating effects, and plant growth), gravitational forces (the tides), and the heat of Earth's core (geothermal) as the resources from which they produce energy. These resources represent an energy potential that is incredibly massive, dwarfing that of equivalent fossil resources, and hence their magnitude has no key constraints on energy production. However, they are generally diffuse and not fully accessible, some are intermittent, and all have distinct regional variabilities. These aspects give rise to difficult, but solvable, technical, institutional, and economic challenges inherent in their development and use (Hartley, 1991).
Over the past two decades, extensive research and development activities have focused serious attention on renewables as potential alternative energy resources. Today, significant progress continues to be made in improving collection and conversion efficiencies, lowering costs, improving reliability, and understanding where and how these technologies can be most beneficial. Given the current encouraging pace of technological advances in renewable energy technologies and the increasing cost of conventional energy supplies, the use and mix of these resources are expected to greatly expand over the next several decades.
Renewable energy technologies generally should be expected to reduce envi- ronmental impacts below those of energy systems based on fossil or nuclear sources. It is important to note that the atmospheric benefit resulting from renewable energy resources depends greatly on the type of fossil fuel displaced (Table 6). The potential from new renewable energy resources, e.g., biomass, solar, wind, geothermal, wave, is expected to reach about 10% by 2010, depending on such factors as advances in technology, the world energy supply and demand situation, and worldwide public policy (Hartley, 1991). If the growth continues at an average rate of 7% yr-', it will reach 1500 Mtoe by 2050.
Conclusions
Methods are available for reducing environmental pollutant emissions from the use of energy resources. This reduction will be offset by the predicted increase in the requirements for energy. The implementation of the required methods has so far been generally governed by the market forces based on the price of energy. Recently, there have been moves to prohibit or constrain various emissions. Aside from environmental implications, some renewables have reached the stage where they are economically viable. The extraction of energy from wastes is now an established technology. The availability and use of natural gas, which is a clean premium fuel, lead not only to reduction in chemical emissions by substitution for other fuels, but also allows the employment of much improved energy-efficient systems. Thus improved energy efficiency worldwide and incentives to use renew- ables are the key elements of a global energy strategy aimed at reducing CO, emissions. For this reason, a coordinated attack on the world's energy problem is essential if environmental impacts are to be contained.
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Energy consumption continues to increase. Energy efficiency and conservation can offer the potential for rapid improvements in the level of pollution and CO, emissions. Admittedly, most of the actual measurements need to be carried out by consumers rather than by governments, and there is also a useful role for other bodies in educating consumers about the need for energy efficiency and conserva- tion and the benefits it will bring. There remains an important role that can most effectively, if not solely, be played by governments. The areas for government action fall under the following main areas: more research and development into methods of energy efficiency and conservation, immediate implementation of energy efficiency and conservation techniques, and promotion of renewable energy sources.
Over the next several decades, it is expected that the use of renewable energy technologies will greatly expand as these technologies mature, as the cost of conventional energy supply increases, and as the environmental impact of fossil fuel usage is better understood.
The most promising approach is undoubtedly the development and implemen- tation of technologies for increasing the efficiency of energy production and consumption. The adoption of these kinds of technologies will be promoted to the extent that these technologies are also cost-effective. The possibility of a further shift away from fossil fuels in the mix of alternative energy sources deserves more attention and effort. In the short term, such efforts will meet considerable resistance from inertia and entrenched interests.
Another factor is that not all assets of a healthy environment can be expressed in market prices. The reform of a centrally planned economic system follows its own dynamics and will be more determined by ideological and economic factors than by global environmental considerations.
What is important in the final instance is the translation of knowledge into effective policies and actions in terms of energy and the environment. These solutions are completely dependent on the close relationship between policy makers, decision makers, scientists, and the greater society. In this arena, scientists in this highly socially relevant and significant field of the global environment should pay greater attention to their role in society and their contribution to energy and environmental impacts, and the relevant decision-making processes.
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