CLIMATE AND ENERGY: A COMPARATIVE ASSESSMENT OF THE SATELLITE POWER SYSTEM (SPS) AND ALTERNATIVE ENERGY TECHNOLOGIES January 1980 U.S. Department of Energy Office of Energy Research Satellite Power System Project Division DOE/NASA SATELLITE POWER SYSTEM Concept Development and Evaluation Program DOE/FR-0050
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DOE/ER-0050 Dist. Category (JC-11, 13, 34b, 97c CLIMATE AND ENERGY: A COMPARATIVE ASSESSMENT OF THE SATELLITE POWER SYSTEM (SPS) AND ALTERNATIVE ENERGY TECHNOLOGIES January 1980 Prepared by David A. Kellermeyer Integrated Assessments and Policy Evaluations Group Energy and Environmental Systems Division Argonne National Laboratory Argonne, Illinois 60439 Under Contract No. 31-109-ENG-38 Prepared for: U.S. Department of Energy Office of Energy Research Satellite Power System Project Division Washington, D.C. 20545 DOE/NASA SATELLITE POWER SYSTEM Concept Development and Evaluation Program
ACKNOWLEDGMENTS This report was prepared for the Satellite Power System Project Office (SPSPO) of the Office of Energy Research of the U.S. Department of Energy. The author is grateful to all those who contributed to the report through their comments and suggestions. Harry Moses of DOE, Lester Machta of NOAA, Ralph Rotty of ORNL Institute of Energy Analysis, George D. Robinson of the Center for Environment and Man, Ralph Llewellyn of Indiana State University, and William Lowry of the University of Illinois submitted valuable comments and suggestions through their reviews of the report. Tom Wolsko and Ron Whitfield of Argonne National Laboratory provided guidance during the preparation of the report and the response to review comments. Michael Riches of DOE/SPSPO served as program manager and provided much useful input and direction.
DEFINITIONS OF UNIT SYMBOLS Btu: British thermal unit °C: degrees centigrade cm: centimeter GW: gigawatt (i.e., 10$ watts) GWe: gigawatt (electric) GW-yr: gigawatt-year J: joule K: Kelvin (unit of temperature) kg: kilogram km: kilometer kW: kilowatt kWe: kilowatt (electric) kWt: kilowatt (thermal) m: meter min: minute mm: millimeter m/s: meter per second mW: milliwatt MW: megawatt MWe: megawatt (electric) MWt: megawatt (thermal) MW-yr: megawatt-year pm: micrometer ppm: part per million (by weight) ppmv: part per million (by volume) t: metric ton (1,000 kg) W: watt
TABLE OF CONTENTS EXECUTIVE SUMMARY ......................................................... ix ABSTRACT................................................................... 1 1 INTRODUCTION .......................................................... 1 2 ANTHROPOGENIC IMPACTS ON CLIMATE ..................................... 5 2.1 Waste Heat......................................................... 5 2.1.1 Sources of Waste Heat....................................... 5 2.1.2 Global Impacts ............................................ 8 2.1.3 Regional Impacts .......................................... 10 2.1.4 Local Impacts................................................ 15 2.2 Atmospheric Particles...............................................17 2.2.1 Sources and Sinks of Atmospheric Particles ................ 17 2.2.2 Potential Climatic Response.................................. 20 2.3 Carbon Dioxide....................................................... 21 2.3.1 Increase of Atmospheric CO2..................................22 2.3.2 Global Carbon Budget ...................................... 22 2.3.3 Projected Future CO2 Levels..................................27 2.3.4 Climatic Response to Increased CO2 Levels................... 28 2.3.5 Possible Mitigating Measures ............................. 31 2.4 Uncertainties Concerning Climatic Change............................32 2.4.1 Feedback Mechanisms.......................................... 32 2.4.2 Natural Climatic Fluctuations................................33 2.4.3 Other Forcing Parameters .................................. 34 3 ENERGY TECHNOLOGY IMPACTS ON CLIMATE ................................... 37 3.1 Coal Technologies................................................... 37 3.1.1 Waste Heat Impacts..........................................37 3.1.2 Impact of Particle Releases................................. 38 3.1.3 CO2 Impacts.................................................. 39 3.1.4 Other Impacts................................................41 3.2 Nuclear Technologies.................................................41 3.2.1 Waste Heat Impacts..........................................41 3.2.2 Other Impacts................................................ 42 3.3 Satellite Power System............................................... 42 3.3.1 Rectenna Waste Heat Effects..................................42 3.3.2 Microwave Transmission Impacts ........................... 43 3.3.3 Impact of Rocket Effluents ............................... 43
3.3 Projected Annual Emissions of CO2 from U.S. Utility Coal. Combustion Compared with Projected Annual World Emissions of CO2........................................................40 3.4 Contribution of Energy Technologies to Potential Climatic Impacts........................................................48 LIST OF TABLES
LIST OF FIGURES 2.1 World Energy Use Between 1925 and 1971........................... 7 2.2 Anthropogenic Energy Densities Compared to Net Surface Radiation over Various Areas .................. 11 2.3 Annual Production of CO2 from Fossil Fuels and Cement....................................................23 2.4 Atmospheric CO2 Concentrations.......................................23 2.5 Major Reservoirs and Exchanges in the CO2 Cycle......................24 LIST OF TABLES 1 Energy Released per Unit of Useful Energy Produced by Different Technologies ........................ x 2 Annual Primary Particulate Emissions from U.S. Coal-Fired Utilities Compared with Annual Particulate Emissions from All Sources........................................... xi 3 Projected Annual Emissions of CO2 from U.S. Utility Coal Combustion Compared with Projected Annual World Emissions of CO2.......................................................xii 2.1 Current and Projected Global Anthropogenic Energy Release......... 7 2.2 Projections of Future Global Energy Release and Resulting Surface Temperature Response ........................... 9 2.3 Summary of Urban Effects on Summer Precipitation at Nine Locations...................................................... 13 2.4 Hail-Day Increases for Eight Cities.................................. 13 2.5 Energy Production Rates of Natural Atmospheric Processes and Anthropogenic Sources..................................... 15 2.6 Estimates of Source Contributions to Atmospheric Particulate Matter ......................................... 18 2.7 Atmospheric Response to Fossil Fuel CO2 Input....................... 26 2.8 Predictions by Different Models of Surface Temperature Response to a Doubling of CO2.................................29 2.9 Major Climatic Feedback Mechanisms ................................ 33 2.10 Greenhouse Effect Arising From Increases in Various Trace Atmospheric Constitutents...............................35 3.1 Energy Use in Coal-Fired Utilities in the United States and Global Energy Use......................................... 38 3.2 Annual Primary Particulate Emissions from U.S. Coal-Fired Utilities Compared to Annual Particulate Emissions from All Sources....................................................39
3.3 Projected Annual Emissions of CO2 from U.S. Utility Coal Combustion Compared with Projected Annual World Emissions of CO2........................................................40 3.4 Contribution of Energy Technologies to Potential Climatic Impacts........................................................48
The potential climatic impacts of five electrical energy techologies — coal combustion, light water nuclear reactors, the satellite power system (SPS), terrestrial photovoltaics (TPV), and fusion were assessed. The objectives of this assessment were to identify major issues surrounding the effect of technology deployment on climate and to assess the degree to which these five technologies might contribute to significant climatic changes. In the course of this work, the state of the art of climate study was reviewed and is described in this report. Particular focus is placed on the impacts of waste heat rejection, emissions of atmospheric aerosols, and emissions of carbon dioxide (CO2). Impacts are identified as being global, regional, or local in scale, and the tremendous uncertainties of attempting to predict the future climate are discussed. The potential impacts of the energy technologies on the climate were evaluated by comparing the emissions of heat or pollutants from each technology to the amount of such emissions currently considered necessary to produce significant climatic perturbations. Only operating emissions were considered, except for the SPS, which would involve emissions from heavy-lift launch vehicles (HLLV). Also considered were impacts resulting from individual facilities, clusters of facilities on a regional scale, and widespread utilization of technologies on a national or global scale. The major results of this comparative assessment appear in Sec. 3 (Table 3.4, p. 48) and are discussed in the following paragraphs. Waste Heat On a global scale, waste heat will not produce any detectable climatic change until world energy use increases by at least two orders of magnitude; thus, global waste heat will not be an issue for any of the technologies considered. On a regional scale, waste heat from energy facilities may produce some noticeable impacts on temperature, cloudiness, and precipitation patterns, particularly if facilities are sited close together, as in power parks. Due to its large size (100 km^),* an SPS rectenna may produce small temperature increases comparable to those occurring in a typical suburban area. The most noticeable waste heat impacts will occur on a local level, *See p. iv, "Definitions of Unit Symbols."
within a few kilometers from large heat releases. Heat and moisture released from cooling towers have been shown to increase the occurrence of fog, clouds, and precipitation. The extent of these impacts depends on the amount of heat released, how much heat is released in the sensible and latent forms, the height of release, and the ambient meteorological conditions. A comparison of the heat released per unit of energy produced by each technology appears in Table 1. Although the figures in this table do not represent the comparative magnitudes of impacts, it is apparent that coal and nuclear technologies are the most likely to produce noticeable impacts, particularly because of unit capacity. Atmospheric Particles The climatic effect of changes in atmospheric particulate loading has not been clearly established. Emissions of primary particles as well as of gases such as sulfur oxides (S0x) and nitrogen oxides (N0x), which are converted to particles in the atmosphere (secondary particles) are responsible for the increases in the anthropogenic input to particulate levels. An increased particulate loading in the atmosphere affects the climate by changing the radiative properties of the atmosphere. However, whether an increase or decrease in global temperature will occur depends on the optical properties of the particles emitted as well as on their vertical distribution. Particulate emissions can also affect regional climate by contributing to the number of condensation and freezing nuclei in the atmosphere, thus influencing clouding and precipitation processes. In addition, an abundance of particles can block solar radiation. Table 1. Energy Released per Unit of Useful Energy Produced by Different Technologies3^
Of the energy systems considered, only coal technologies will produce primary and secondary atmospheric particles. HLLV launches associated with the SPS may produce small amounts of secondary particles, and these emissions may contribute slightly to regional climatic modification. The contribution of coal-combustion particles to any global warming or cooling should be small. Table 2 shows that the primary particulate emissions from coal-fired utilities constitute a very small fraction of total particulate emissions in the U.S. However the contribution of coal combustion to secondary particulate loadings by emission of S0x and N0x may be more important than the emission of primary particles, but the increasing use of emission control devices should limit these impacts. CO2 Impacts Gaseous CO2 is transparent to incoming solar radiation, but is a strong absorber of terrestrial radiation. Hence, an increase in atmospheric CO2 can produce an increase of absorbed terrestrial radiation in the troposphere, which is the portion of the atmosphere that is below the stratosphere and extends 10 to 15 kilometers from the earth's surface. The net effect has been shown to be tropospheric warming and a slight stratospheric cooling. Table 2. Annual Primary Particulate Emissions from U.S. Coal-Fired Utilities Compared with Annual Particulate Emissions from All Sources
Measurements have indicated a steady increase of CO2 content since the late 1800s, most of which is due to increased use of fossil fuels. If trends in fossil fuel use persist, the atmospheric CO2 content will be double the preindustrial levels of about 300 ppm by the mid 21st century. Recent atmospheric models predict a global temperature increase of 2-3°C for a doubling of atmospheric CO2, and increases near the poles of the earth may be considerably larger. Of the technologies considered, only coal combustion will result in substantial emissions of CO2. Space vehicle launches for SPS construction will emit some CO2, but these emissions should be two orders of magnitude smaller than the coal emissions per unit of energy produced. Coal combustion can contribute substantially to global CO2 levels. Table 3 compares the current and predicted CO2 emissions from U.S. coal combustion alone to current and projected global CO2 emissions. This comparison indicates that coal- fired energy generation may have a major impact on climate. Other Contributions to Climate Change In addition to the waste heat, particle, and CO2 influences, other parameters can affect climate. Natural climatic fluctuations may either augment or mask an anthropogenic effect. The current cooling trend of the earth is probably due to natural fluctuations and may obscure CO2 wanning Table 3. Projected Annual Emissions of CO2 from U.S. Utility Coal Combustion Compared with Projected Annual World Emissions of CO2
effects for a few decades. The increasing levels of chlorofluoromethanes (FC) and nitrous oxide (N2O) in the stratosphere may deplete the ozone layer, which could result in either surface warming or cooling depending on the vertical distribution of ozone (O3). A number of industrial gases such as nitrous oxide (N2O), methane (CH4), ammonia (NH3), and sulfur dioxide (SO2) can act as greenhouse gases by absorbing terrestrial radiation in the troposphere. The magnitude of their effect is uncertain, although some investigators believe that the collective effect of these gases may be comparable in magnitude to the effect of CO2. Conclusions The CO2 warming effect has the greatest potential for altering global climate over the next few centuries, and this greenhouse effect may be augmented somewhat by other industrial gases. The impact on climate of particulate emissions should be minimal, particularly if they are controlled to meet health standards. Compared to the CO2 effect, wanning due to waste heat should not be an issue of global proportions. Local and regional ’’hotspots" of heat release may produce some local or regional modifications in climate.* As indicated in Table 3.4 (p. 48), coal appears to be the technology most likely to have an impact on global climate because of large CO2 emissions. SPS launchings may affect global climate somewhat by altering the stratosphere, but significant changes are currently not predicted. All of the technologies appear capable of causing some local or regional climatic perturbations from heat release; however, such impacts will be principally site specific. The impacts of energy on climate, particularly from CO2 emissions, could be substantial in the next century or two. Unfortunately, knowledge of climate change and response to anthropogenic (man-induced) influences is still limited. Much important information regarding sources (e.g., combustion of fossil fuels, decomposition of biomass) and sinks (e.g., oceans, vegetation) of CO2, atmospheric feedback mechanisms, and natural climatic fluctuations must be gathered. Thus, although the possibility of energy-related climatic effects should be considered in the formulation of long-term energy policy, global climatic change per se cannot at this time be used as a decision criterion. *Weinberg, W.M., and R.P. Hammond, Limits to the Use of Energy, In: Is There an Optimum Level of Population?, S.F. Singer, ed., McGraw-Hill, New York, pp. 42-56 (1971).
ABSTRACT The potential effects of five energy technologies on global, regional, and local climate were assessed. The energy technologies examined were coal combustion, light water nuclear reactors, satellite power systems, terrestrial photovoltaics, and fusion. The assessment focused on waste heat rejection, production of particulate aerosols, and emissions of carbon dioxide. The current state of climate modeling and long-range climate prediction introduces considerable uncertainty into the assessment, but it may be concluded that waste heat will not produce detectable changes in global climate until world energy use increases 100-fold, although minor effects on local weather may occur now; that primary particulate emissions from coal combustion constitute a small percentage of total atmospheric particulates; that carbon dioxide from coal combustion in the U.S. alone accounts for about 30% of the current increase in global atmospheric CO2, which may, by about 2050, increase world temperature 2-3°C, with pronounced effects on world climate; that rocket exhaust from numerous launches during construction of an SPS may affect the upper atmosphere, with uncertain consequences; and that much research in climatology is needed before potential effects can be quantitatively predicted with any confidence. Although climatic impact is an appropriate concern in formulating long-term energy policy, the level of uncertainty about it suggests that it is not currently useful as a decision criterion. 1 INTRODUCTION It is becoming increasingly evident that human activities have the potential for significantly perturbing the global as well as the local environment. Of particular importance is the extent to which human activities are inadvertently modifying the earth's climate. The worldwide population explosion has created increasing demands for the production of food, and as population pressures increase, the competition for finite food supplies could severely threaten world peace and stability. Relatively small global climatic changes can substantially alter patterns of agricultural production as well as affect the total amount of biological production. Therefore, it is apparent that the potential of human activities for changing the earth's climate is a global issue of enormous proportions. Man has the ability to change the earth's environment in several different ways. The increase in size and distribution of human populations
has changed the characteristics of its surface. Excessive destruction of forests and grasslands in conjunction with the urbanization of large land areas has resulted in changes in the surface radiation balance, as well as changes in the fluxes of moisture to and from the surface. Of greater impact on a global scale, have been the direct anthropogenic releases of heat and various pollutants into the atmosphere. These releases have affected the transmissivity of the atmosphere and have changed the radiation balance of the earth-atmosphere system. Although the magnitude of these man-induced changes in the atmosphere has been thus far too small for them to be reliably measured and identified as global climatic changes, it is possible that this situation can change within the next 50 to 100 years. The major human activity that releases pollutants into the atmosphere is the satisfaction of energy demands. Use of fossil fuels as the principal source of energy has been the major anthropogenic contribution to the steady increase of atmospheric carbon dioxide (CO2) levels. Additionally, fossil fuel utilization has contributed to the increasing global levels of atmospheric aerosols. Both CO2 and aerosols play important roles in the radiation balance of the earth-atmosphere system and thus can substantially affect global climate. Many atmospheric models predict that the increasing use of fossil fuels could result in a measurable global climate change by the year 2000 due to increased atmospheric CO2 levels. It has been suggested that, to avoid substantial changes in climate beyond 2000, the use of fossil fuels must be curtailed and other sources of energy must be sought. However, uncertainties still exist about the nature of climate change and the magnitude of man's role in it. These uncertainties effectively prevent the direct consideration of impacts on climate in energy policy decisions at the present. What is certain, however, is that man's contribution to climatic change is a global problem. Thus, any effort to reduce man's inadvertent modification of climate must occur on a global scale and involve the energy policies of all nations. This report has several objectives. The first is to describe the possible anthropogenic contributions to global climate change, particularly from energy production. The current state of knowledge concerning energy and climatic change is reviewed, with particular attention to assessing the unknowns and uncertainties surrounding climatic change and the likelihood
that these unknowns can be clarified in the near future. An attempt is made to rank climatic issues in the order of their potential magnitude of impact. Climate issues on a global, regional, and local scale are addressed. The role of various energy technologies in contributing to climatic impacts on these three scales is examined from a standpoint of large-scale application of these technologies as well as from that of individual energy facilities. Some of the options for future energy supply and their implications are discussed. Finally, recommendations are made for future work to be performed concerning the SPS assessment, as well as for research needed to develop a better understanding of future climate.
2 ANTHROPOGENIC IMPACTS ON CLIMATE 2.1 WASTE HEAT Almost every human activity results in the dissipation of heat. The release of heat to the atmosphere directly affects its temperature and thus the local climate. Rejection of heat to the lower atmosphere can also result in a change of atmospheric stability, which directly affects precipitation and cloud formation. As population growth continues, man’s energy needs will increase, as will the amount of heat released to the environment. This increased anthropogenic heat rejection may play a role in shaping the future climate of the earth. It is appropriate to look at the climatic effects of waste heat on three different geographic scales. The release of a large amount of heat at one or a few major sources could produce local perturbations (withing a few kilometers of the source) in climate. Extremely large heat releases from several closely grouped sources or moderate heat release over a larger region, such as from a metropolitan area, can affect the climate on a regional scale (out to about 50 km). The impact of all of the heat released by man can be examined in terms of its possible contribution to changes in global climate. The severity of waste heat impacts varies considerably, depending on the geographic scale of interest. 2.1.1 Sources of Waste Heat Although man’s release of heat to the environment is generally referred to as waste heat, it is important to note that all anthropogenic heat dissipated to the atmosphere will contribute to potential climatic change. An example is a coal-fired electrical generating plant with a conversion efficiency of about 34%. Of the energy input to the plant, approximately two- thirds will be released on the premises as waste heat and one-third will be converted into useful energy. However, almost all of this useful energy, in the form of electricity, will eventually be dissipated to the atmosphere in the form of waste heat from homes, industries, and other locations. Therefore, it is the total energy input to the system that is important in assessing the impact on the global climate. Waste heat should be considered as all heat released to the atmosphere that would not be there as a result of natural sources such as the solar radiation balance or volcanic activity.
Although most of man's activities release heat to the environment, the vast preponderance of the heat released comes from the production or consumption of energy. The human body gives off waste heat at the rate of approximately 100 W (thermal), but this is two orders of magnitude smaller than the per capita energy use of the United States (10,000 W). About 20% of U.S. energy use goes to the production of electricity; other major energy uses include transportation (20%), space heating (15%), and industrial use of heat (20%).l The per capita energy consumption for the entire world is currently one-sixth of that in the United States, and the distribution of energy uses in the U.S. is also substantially different from that in less-developed nations. World energy use has increased substantially over the past century. Figure 2.1 displays an estimate of the growth of the world's consumption of energy between 1925 and 1971. Between 1925 and 1968, world energy consumption increased at a rate of about 3.5% per year. However, the growth rate itself increased from 2% per year between 1925 and 1938 to 5.5% per year after 1960.2 This increase is a function of both an increasing world population and an increasing per capita energy demand, although the rise in per capita consumption is probably the dominant of the two factors.^ In the United States alone, increased population has accounted for only about 20% of the increased electric power consumption. The other 80% of the increase is a result of increases in per capita demand.^ The growth rate of per capita energy use in the United States is estimated at 2-3% per year.5 As less-developed countries become more modernized, substantial increases in energy use can be expected. Furthermore, as supplies of natural resources become depleted, it is likely that energy-intensive substitutes will have to be developed, which will further increase worldwide per capita energy use. Weinberg and Hammond^ project future energy needs in an industrial society to be as much as 20 kWt* per capita, which is double the current U.S. consumption. It is obvious that energy use and the resulting heat rejection to the environment will continue to increase. How large these increases will be and what the ultimate heat rejection of the earth might be are the important issues. Table 2.1 contains some estimates of 1970-71 energy use and projections for the future.1»6“10 There is some disagreement on exactly what the present world energy use is, but most estimates predict increases by a factor of five over current levels by the year 2000. *See p. iv, "Definitions of Unit Symbols."
Fig. 2.1. World Energy Use Between 1925 and 1976 Table 2.1. Current and Projected Global Anthropogenic Energy Release
2.1.2 Global Impacts Although it is apparent that anthropogenic heat rejection to the environment on a global scale will increase severalfold by the year 2000, the important issue is whether this increase may have significant climatic implications. If noticeable climatic impacts do not occur by the year 2000, it is quite possible that they will occur beyond 2000 when heat rejection may be two orders of magnitude greater than it is at present. Thus, it is important to establish the magnitude of waste heat rejection at which climatic impacts may become an issue and the point in time at which this magnitude might be achieved. Perkins-Ll attempted to put global heat rejection into perspective by comparing global energy use with the solar input to the earth-atmosphere system. Solar input is estimated at 17.3 x 10^-^ W, of which about 35% is reflected back to space, leaving a net solar input of 11.2 x 10^^ W.$ In comparison to this number, the energy figures in Table 2.1 are quite small. A crude estimate of the atmospheric response to these heat inputs can be made by considering that thermal radiation from a black body is proportional to the fourth power of the absolute temperature: If the black-body radiation temperature of the earth-atmosphere system is taken as 255 K, then the impact of a heat rejection of 3.35 x lO^ W by the year 2000 can be calculated to produce a global warming of 0.019 K. This is far below the magnitude of natural climatic fluctuations and would not be a noticeable impact. Weinberg and Hammond'si ultimate heat rejection estimate of 4 x 10^ W would produce an estimated warming of 0.22 K. Although this is not a substantial global warming, it approaches the magnitude necessary to produce a noticeable change in global climate. Rottyl^ also estimated that noticeable climatic change from thermal pollution can occur with a heat rejection of approximately Other estimates of the global impact of heat rejection have been made, and several are summarized in Table 2.2. Kellogg^ compared the heat released by human activities to the amount of solar energy absorbed at the earth’s surface. Although man currently releases only 0.01% of the solar
Table 2.2. Projections of Future Global Energy Release and Resulting Surface Temperature Response energy absorbed at the surface, Kellogg predicted a 100-fold increase in heat release by the year 2100. He also suggested, on the basis of a consensus of climate models, that a 1% increase in available heat at the earth's surface translates to a 1° to 4°C increase in surface temperature. This can certainly be classified as a significant climatic perturbation. General atmospheric circulation models have been used to simulate atmospheric response to man-made heat release. Washington^ assumed a geographical distribution of energy use on the basis of current population density, and assumed a per capita energy use of 15 kW by an ultimate population of 20 x 10$ people. Based on a simulation of positive thermal pollution and a control run, Washington's results (for a time-averaged January simulation) showed temperature changes of up to 10°C in the northern hemisphere and 1-2°C in the tropics. However, further experiments with the model showed that the atmospheric effects of thermal pollution could not be separated from the natural fluctuations of the model over the averaging period used. A number of simulations have been carried out to investigate the impacts of extremely large energy releases over relatively small areas, to assess, for example, the impacts of intense regional development or of an extremely large energy park. The results of Llewellyn and Washington^ and Williams et al.l? show large increases in temperature close to the heat
release and substantial variations in global circulation patterns for extremely large heat releases. However, the simulations represented extreme cases, and the ability of models to give statistically significant results for more realistic experiments is currently limited. It is possible that the magnitude of heat release impacts is dependent on the season. During the winter, when more stable atmospheric conditions prevail, the impacts of waste heat occur mainly in the boundary layer and have a larger impact on surface temperature. In the summer, an increased vertical mixing of the excess heat and a smaller perturbation of surface temperature is likely. Thermal pollution cannot be examined in isolation when one is considering global climate changes.® Certainly, other climate-forcing parameters play important roles. Carbon dioxide and atmospheric aerosols will be discussed later in this report, and natural climatic fluctuations must also be taken into account. In addition, it is not possible to calculate reliably an atmospheric temperature increase due to added heat without considering the total response of the atmosphere and potential feedback mechanisms. For example, if the surface temperature increases because of heat added to the atmosphere, evaporation will increase, and this could lead to increased global cloudiness. The clouds could provide negative feedback by reflecting more incoming solar radiation into space. On the other hand, a warming of the earth's surface could result in a decrease of surface albedo due to melting of snow and ice cover. This would lead to increased surface absorption of solar radiation and enhance the warming trend. It is not clear from current knowledge whether anthropogenic heat rejection at any time in the future will significantly alter global climate. It can be said with reasonable confidence that significant global impacts from waste heat are unlikely in the next 50 to 100 years. Beyond that time frame, if energy use continues to grow, global impacts of a noticeable, if not substantial, magnitude are possible. 2.1.3 Regional Impacts Although it is apparent that man's worldwide energy release is not particularly large in comparison to the incoming solar flux, this is not
always the case for smaller geographic scales, as Figure 2.2 illustrates. The figure is a plot of energy density versus area for different locations. Net surface radiation is shown on the graph for comparison. Some highly developed urban areas of 100-1000 km^ are currently releasing more energy to the environment than the net surface radiation. In the future, energy releases of such magnitudes may not be limited to urban areas. Some consideration has been given to the future construction of large energy centers or parks in which 20,000 to 50,000 MW of electrical energy will be produced on one 100-km^ site. This would result in substantial savings in construction costs, maintenance, safeguards, and transmission lines compared to dispersed individual facilities. However, the waste heat rejection from such a power park would be 4 to 10 times the global average net radiation at the surface. It is apparent that man is capable of, and in fact is currently, releasing as much or more energy to the environment in certain regions than Fig. 2.2. Anthropogenic Energy Densities Compared to Net Surface Radiation over Various Areas
the earth is receiving from the sun. As population and energy demand increase, the number and sizes of these areas will likely increase substantially. The question of concern is whether or not these perturbations of the heat balance of the lower atmosphere will produce significant climatic perturbations . Considerable work has been done to evaluate and describe the impact of large urban areas on weather and climate. Man-made heat islands have been studied by Landsberg and Maisel,18 Ludwig,1$ Clarke,20 and others. The urban heat island exists during both the day and the night but is much stronger at night. In large urban areas, temperatures can be as much as 5°C to 10°C warmer than nearby rural areas. Studies have indicated that the mean annual minimum temperature of a city may be as much as 2°C higher than surrounding rural areas.21>22 However, this temperature increase is not due solely to the waste heat released from the cities. Urbanization results in the replacement of natural vegetated surfaces with brick, asphalt, and concrete, which store heat much more effectively than vegetation and release more stored heat to the environment at night. In addition to the effects of waste heat on temperature, it has been observed that urban areas can affect precipitation patterns. There are several causal factors that increase precipitation around an urban center; these include combustion vapor added to the atmosphere, greater surface roughness to enhance mechanical turbulence, the presence of greater concentrations of condensation and ice nuclei in the urban atmosphere, and higher temperatures to increase thermal convection. Table 2.3 summarizes the urban effects on summer rainfall in nine metropolitan areas. In addition to increasing precipitation, cities quite possibly influence the occurrence of severe weather in their vicinities. Table 2.4 displays the increase in hail-days at several cities, where increases in thunderstorm occurrences of up to 50% at a given point have also been observed.23 Although these precipitation increases appear to be real, the exact causes have not been quantified. It is likely that waste heat has a role, although not a major one, in climatic change. The contribution of energy production to creation of urban heat islands and their precipitation impacts is somewhat less certain.
Table 2.3. Summary of Urban Effects on Summer Precipitation at Nine Locations3 Table 2.4. Hail-Day Increases for Eight Cities The effects of waste heat rejection from large nuclear power centers or parks will become more important for energy production in the future. Because of the increasing difficulties in finding suitable sites for power
plants and the problems of handling radioactive waste materials, consideration has been given in the United States to locating more and more generating capacity on a given site. These envisioned power parks would consist of 20,000 to 50,000 MWe of generating capacity on a land area of 20-100 km^. A number of studies have been conducted to assess the possible impacts of the dissipation of waste heat from large electric power centers.24-27 The impacts most often studied include heat-island formation, initiation of convective clouds, increased humidity and precipitation, fog formation, and vorticity concentration. The potential for climate and weather modification in the vicinity of power parks can be visualized by examining the energy density of the waste heat being rejected from them. Table 2.5 compares the energy production of natural atmospheric events to that from three groups of existing power plants and three hypothetical energy-park configurations. The table shows that the heat released from an energy park will greatly exceed the solar flux at the ground and may even approach the latent heat release of a thunderstorm that covers approximately the same geographical area. It should be noted that if evaporative cooling towers were used in the energy park, only about 20% of the waste heat would be rejected as sensible heat and the rest as latent heat. Nevertheless, the heat release from an energy park is of the same magnitude as the energy of many natural phenomena. At the least, power parks will produce sizable heat islands or thermal mountains that can increase cloudiness and precipitation by triggering or enhancing convective activity. The increase in convective precipitation produced by such a power park depends on the local climate. Increases would probably be most significant in the southern and southwestern United States.24,27 The production and enhancement of ground fog is also considered an important impact of power parks and is expected to be most common for parks located in the Northwest and in the Appalachian Mountain regions.27 potentially serious consequence of energy parks could be the release of large amounts of waste heat, which could concentrate atmospheric vorticity and increase the possibility of severe weather. Vorticity concentrations from power-park energy releases would be most probable in areas where, and during seasons when, convective vortices are most likely to occur naturally.
Table 2.5. Energy Production Rates of Natural Atmospheric Processes and Anthropogenic Sources 2.1.4 Local Impacts Noticeable atmospheric modifications are currently occurring within a few kilometers of large, industrial emitters of heat and moisture. In particular, large electric generating facilities, which reject large amounts of heat to the environment by means of cooling towers, cooling ponds, or other means, have been shown to alter the local climate. The geographical extent
and severity of these local climatic impacts appear to be largely a function of site-specific criteria such as local meteorology, the magnitude of heat release, and the means of heat rejection. A considerable amount of work has been done to characterize the atmospheric impacts of cooling towers. Most cooling towers are, and most likely will continue to be, "wet" towers, in which heat exchange occurs by evaporation from countless water droplets generated by splashing warm water over successive barriers. There are two major types of cooling towers in use today: mechanical-draft and natural-draft. In mechanical-draft towers, large fans force the vertical air flow, whereas in natural-draft towers, the great size of the tower causes vertical air flow to develop without a fan because of density gradients. Of the two types of cooling towers, the natural-draft tower appears to cause less serious local impacts. In the United Kingdom, it is felt that the impact of these towers on local climate has been negligible throughout 50 years of operational experience.29 Although visible plumes of water droplets frequently occur near natural-draft cooling towers, ground fog due to downwash occurs infrequently.30-32 fact, £n many cases, downwind measurements of ground-level relative humidity have shown no measurable increase.29 The output of heat and moisture from natural-draft cooling towers is believed to enhance development of cumulus clouds, particularly when the atmosphere is unstable or conditionally unstable. In several cases, anomalous precipitation events have been observed within a few kilometers of large heat and moisture releases from natural-draft towers.33-35 However, measurements from local weather stations taken over several years have not shown that statistically significant increases in precipitation occur near large cooling towers.36,37 Drops of cooling water can be carried out of the top of the tower as water splashes over the heat exchange surfaces. These drops can contain inpurities such as salts and fungicides and can damage local vegetation. This phenomenon, called "drift deposition," may be an important environmental impact but should not significantly change the local climate. Mechanical-draft cooling towers are much more likely to produce fog because they are not so tall as natural-draft towers. Fog is common within a few kilometers of these towers at wind speeds of 3-5 m/s or greater, due to
downwash effects. Increases in relative humidity and decreases in sunshine duration have also been measured within a few kilometers of mechanical-draft towers.38 Currently, the sun shading produced by cooling tower plumes is of great concern in Europe. Over a period of several years, changes in solar radiation can cause changes in natural vegetational cover.30 Fog frequently occurs over and near cooling ponds, especially during meteorological conditions that normally produce fog, such as cool, calm mornings.39 in the winter, such fog can produce light icing on vertical objects; however, both the fog and icing are limited to within a few hundred meters of the cooling pond. In general, it appears that although the atmospheric impacts of waste heat rejection at an individual site are often noticeable, these impacts will be confined to an area close to the site. Thus, site selection and the selection of the appropriate cooling technology will be important in minimizing the adverse impacts of these local atmospheric perturbations. 2.2 ATMOSPHERIC PARTICLES Suspended particles, chiefly in the size range of 0.01-10 pm, are abundant in the atmosphere. The properties of these particles affect weather and climate in two ways. First, particles act as condensation and freezing nuclei for the formation of cloud droplets and ice crystals in the atmosphere. Thus, particles play an important role in cloud and precipitation processes. Second, because of their optical properties, particles interact with both solar and terrestrial radiation. Atmospheric aerosols (i.e., the suspension of particles in the atmosphere) can scatter and absorb incoming solar radiation and absorb and re-emit terrestrial infrared radiation. The proportion of the anthropogenic contribution to the total amount of atmospheric particles has increased over the past century. The particles produced by man may be currently influencing weather and climate and may play an important role in future weather and climatic change. 2.2.1 Sources and Sinks of Atmospheric Particles Sources Atmospheric particles are generated by both natural and anthropogenic sources. They can be injected into the atmosphere as primary particles or be
formed in the atmosphere by chemical reaction of anthropogenic or natural gaseous emissions. The major natural emissions of primary particles occur as a result of wind-raised dust and wind-raised sea salt. However, the contribution of particles through gas-to-particle conversion of natural emissions of H2S, N0x, NH3 , and organic compounds may be as great as that from dust and salt. Anthropogenic primary emissions occur from industrial and utility combustion, cement and metals manufacturing, agricultural operations, and several other sources. However, the most important anthropogenic contribution derives from the conversion to sulfates and nitrates of SO2 and N0x emissions. Estimates of the source contributions to atmospheric particles are contained in Table 2.6, which reveals that the anthropogenic contribution to global particle emissions is only about 10% of the total. Mitchell^O estimates a somewhat higher percentage of anthropogenic input (28%) . The major energy inputs to this contribution occur as a result of fly ash from Table 2.6. Estimates of Source Contributions to Atmospheric Particulate Matter
coal combustion and emission of N0x and SO2 from fossil fuel combustion. The uncertainties in these estimates are fairly substantial; probably, the estimate of natural emissions in Table 2.6 is high. However, the natural component is definitely the dominant one. Worldwide particulate loading produced by human activity has increased significantly in this century.40 Increasing population and energy consumption in the future portend increased atmospheric levels of particulates. However, in recent decades many nations have taken steps to control pollutant emissions to protect public health: for example, air quality measurements in the United States indicate that in the past decade urban SO2 and total suspended particulate levels have decreased.41 Therefore, it is conceivable that in some locations the anthropogenic contribution to global particle loading could remain fairly constant or even decrease in the future despite increasing population and energy use. However, the potential exists for several-fold increases in world anthropogenic particle emissions in the next 50 to 100 years.10,40 Sinks Despite the extremely large input of particles into the atmosphere, they are removed quite efficiently, which prevents a large, cumulative buildup of particles in the global atmosphere. The mean residence time of a particle in the troposphere is of the order of a few days to a few weeks. There are two major mechanisms by which atmospheric particles are removed. The first is the gravitational fallout of particles, which are eventually deposited on a surface (dry deposition). The second is referred to as wet deposition, which occurs when water vapor condenses on a particle, forming a cloud droplet, which eventually falls as precipitation (rainout). Wet deposition also occurs when a particle is captured by falling rain or snow and is carried to the ground (washout). The residence time of any given particle in the atmosphere is dependent on the characteristics of the particle and its location in the atmosphere. Particles capable of acting as cloud condensation nuclei or freezing nuclei are much more likely to be removed by cloud and precipitation processes. Particles emitted in or injected into the stratosphere, such as those from aircraft or volcanoes, may remain in the atmosphere for considerable periods
because they are physically separated from the immediate influence of precipitation processes. 2.2.2 Potential Climatic Response Mesoscale Response The role of particles in cloud and precipitation processes may be significant to weather and climate over a mesoscale (50 km) area where pollutant emissions have created an abundance of condensation and freezing nuclei. Numerous studies have shown an increase in precipitation in the vicinity of large urban areas such as St. Louis42 and Chicago^ where there is an abundance of particles. The cause of precipitation anomalies around cities has not been established. Particles may play an important or a negligible role in comparison to waste heat and mechanical turbulence caused by cities. At this time, it is impossible to link an excess of particles with any local or mesoscale precipitation increase. Certainly this would apply as well to any energy facility or energy park. Particles can substantially alter radiation processes over a mesoscale area. Measurements have indicated that many cities have experienced an attenuation of 10 to 30% in surface solar radiation,21 and a large portion of this attenuation is caused by particles in the atmospheric boundary layer. The attenuation is made up of a scattering component and an absorption component. Calculations have shown that aerosol absorption can cause warming at the surface of up to a few degrees centigrade in a polluted atmosphere.44,45 Global Response Currently, the effect of changes in atmospheric particle concentration cannot be clearly identified. The impact of volcanic activity on tropospheric and stratospheric temperatures appears to exist in the measured records but cannot be interpreted as a causal relation. The backscatter and absorption components of the total attenuation by particles have competing effects on atmospheric temperature. The back- scattered radiation is unavailable for heating of the earth's surface and atmosphere and is lost to space. On the other hand, the solar radiation absorbed by particles is not available to heat the surface but does heat the atmosphere.
The determination of whether or not increased particle concentrations will cause a warming or cooling effect depends on several considerations. Two important factors are the earth's surface albedo and surface water content, which determine how much of the radiation lost to the surface due to absorption and backscatter would have been used for heating if particles were not present. The vertical location of particles is also important. Particles in the stratosphere will result in surface cooling due to attenuation of solar radiation and the fact that heating due to absorption will occur in the stratosphere and have minimal effect on the surface. Possibly the most important factor is the efficiency of atmospheric particles as backscatterers as opposed to their efficiency as absorbers. Unfortunately, this cannot be reliably measured or inferred. The direction of the effect of increased particle loadings on the global climate is uncertain. An increase in the albedo of the earth-atmosphere system would probably lead to surface cooling. However, depending on particle distribution and characteristics, and underlying ground reflectivity, a net global warming may be favored. In fact, Bryson^^ suggests that the atmospheric warming effect of CO2 has been more than offset by the cooling effect of increased particle loading of the atmosphere over the past few decades. The calculations of Rasool and Schneider^? would tend to support this view. However, more recent evidence suggests that the ratio of absorption to back-scatter in atmospheric aerosols is likely to be high and thus they may create a warming rather than a cooling effect.^^ Another viewpoint is that the effect of increased particle loading will be very small^$ on either the increase or the decrease of temperature. The emphasis of researchers today on the CO2 issue rather than the particle issue would tend to support the latter opinion. 2.3 CARBON DIOXIDE The steadily increasing level of carbon dioxide in the atmosphere is a potential cause of near-term global climate change that is currently being given the most attention by investigators. Most of these investigators expect the so-called "greenhouse effect" of CO2 will result in much warmer global temperatures. Depending on the magnitude of the atmospheric response to increased CO2, this warming could have serious implications for future climate and society.
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