Overview and Recommendations

INTRODUCTION

Worldwide industrial civilization may face a major decision over the next few decades—whether to continue reliance on fossil fuels as principal sources of energy or to invest the research and engineering effort, and the capital, that will make it possible to substitute other energy sources for fossil fuels within the next 50 years. The second alternative presents many difficulties, but the possible climatic consequences of reliance on fossil fuels for another one or two centuries may be so severe as to leave no other choice.

A decision that must be made 50 years from now ordinarily would not be of much social or political concern today, but the development of the scientific and technical bases for this decision will require several decades of lead time and an unprecedented effort. No energy sources alternative to fossil fuels are currently satisfactory for universal use, and, in any case, conversion to other sources would require many decades. Similarly, finding ways to make reliable estimates of the climatic changes that may result from continued use of fossil fuels could very well require decades.

The climatic questions center around the increase in atmospheric carbon dioxide that might result from continuing and increasing use of fossil fuels. Four questions are crucial:

  1. What concentrations of carbon dioxide can be expected in the atmosphere at different times in the future, for given rates of combustion of fossil fuels?



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Studies in Geophysics: Energy and Climate Overview and Recommendations INTRODUCTION Worldwide industrial civilization may face a major decision over the next few decades—whether to continue reliance on fossil fuels as principal sources of energy or to invest the research and engineering effort, and the capital, that will make it possible to substitute other energy sources for fossil fuels within the next 50 years. The second alternative presents many difficulties, but the possible climatic consequences of reliance on fossil fuels for another one or two centuries may be so severe as to leave no other choice. A decision that must be made 50 years from now ordinarily would not be of much social or political concern today, but the development of the scientific and technical bases for this decision will require several decades of lead time and an unprecedented effort. No energy sources alternative to fossil fuels are currently satisfactory for universal use, and, in any case, conversion to other sources would require many decades. Similarly, finding ways to make reliable estimates of the climatic changes that may result from continued use of fossil fuels could very well require decades. The climatic questions center around the increase in atmospheric carbon dioxide that might result from continuing and increasing use of fossil fuels. Four questions are crucial: What concentrations of carbon dioxide can be expected in the atmosphere at different times in the future, for given rates of combustion of fossil fuels?

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Studies in Geophysics: Energy and Climate What climatic changes might result from the increased atmospheric carbon dioxide? What would be the consequences of such climatic changes for human societies and for the natural environment? What, if any, countervailing human actions could diminish the climatic changes or mitigate their consequences? NATURE OF THE PROBLEM Three by-products of energy production and consumption—heat, particulate matter, and gases—were recognized at the start of the work of the Panel as having the potential for inadvertent modification of global climate. It has been known for some time that cities create their own microclimate (see Chapters 5 and 6). At first, the Panel speculated that increasing urbanization, large power-generating compounds (power parks), and similar developments might, by their output of heat and particles, disturb rainfall or influence other meteorological phenomena on a global scale. However, our study showed that the simple combustion product carbon dioxide has the greatest apparent potential for disturbing global climate over the next few centuries (see Chapters 4 and 10). Carbon dioxide, although virtually transparent to shortwave solar radiation (visible light), strongly absorbs long-wave radiation (heat) at certain wavelengths where other atmospheric gases are transparent. In the atmosphere, it impedes radiation of heat from the earth’s surface into space. An increase in carbon dioxide concentration in the atmosphere could disturb the balance between incoming solar radiation and the radiation of heat from the earth into space with a resulting increase in the temperature of the lower atmosphere. Because glass in a greenhouse traps the sun’s heat, although mainly by preventing convection, this phenomenon has come to be known as the greenhouse effect. In emphasizing questions related to increased atmospheric carbon dioxide we do not imply that serious consequences might not arise also from an increase in the load of particulates in the atmosphere or the growth of large “hot spots” resulting from the uneven distribution of human energy use. It is clearly possible, although expensive, to control the level of atmospheric particulates produced by human activity, and there are other reasons for doing so than the possible effects of high particulate concentrations on climate (see Chapter 3). Present climatic models are not adequate to predict reliably possible large-scale climatic changes resulting from the uneven geographic distribution of heat released by human energy use. But the greater understanding of climate required to answer questions about the effect of carbon dioxide could make it possible to give useful estimates of the effects of uneven heat releases. Even a future world population of ten billion people, with a per capita energy use several times greater than at present, would release an amount of heat equivalent to only one thousandth of the global net radiation received from the sun. The short residence times of tropospheric aerosols limit the threat that they pose because the atmosphere can be cleansed of them in a matter of weeks. The average global temperature is only one of a constellation of dynamically related variables that, taken together, describe climate. Others include statistical properties of temperature, cloudiness, precipitation, and wind. The possibility that a moderate change in one of these variables could lead to a major shift in global climate cannot be ruled out. Historical records and indirect indices of past climates do indeed show marked shifts in temperature, precipitation, and ice volume. About 60 million years ago, the warm Mesozoic era ended and a gradual cooling began, leading to the present glacial age. The last 2 million years have been characterized by ice ages relieved by warm interglacial periods. The most recent ice age,

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Studies in Geophysics: Energy and Climate during which average midlatitude temperatures were 5 to 10°C below those we presently enjoy, ended about 10,000 years ago. Some of the basic processes governing climatic change are poorly understood. It is not known whether climate changes occur in steplike transitions from one dynamically stable steady state to another or whether they represent a more gradual passage through a continuum of climate states. Either kind of change could be induced by variations in external parameters, such as the amount of radiation coming from the sun, or by spontaneous internal redistributions of energy within the physical components of the climate system (see Chapter 2). If changes in climate are steplike, then a disturbance of climate such as would be produced by a large increase in carbon dioxide production would be especially worrisome; a slow change might be the forerunner of a comparatively abrupt transition to a new climatic regime. If, on the other hand, changes in climate are gradual, then the effects of increasing carbon dioxide in the atmosphere would build steadily to produce a more gradual global shift in climate. In either case, agricultural belts would be shifted by changing seasonal precipitation and temperature patterns. For some countries with marginal agriculture, the impact on food production could be severe. For this and other reasons, the prospect of a man-made modification of global climate must be taken seriously. If the potential for climatic change discussed in this report is further substantiated, then it may be necessary to reverse the trend in consumption of fossil fuels. Alternatively, carbon dioxide emissions will somehow have to be controlled or compensated for (no practical means of doing so seem to be readily at hand). In the face of so much uncertainty regarding climatic change, it might be argued that the wisest attitude would be laissez-faire. Unfortunately, it will take a millennium for the effects of a century of use of fossil fuels to dissipate. If the decision is postponed until the impact of man-made climate changes has been felt, then, for all practical purposes, the die will already have been cast. MAGNITUDE OF THE PROBLEM Man’s use of energy has increased manyfold since the industrial revolution, yet large-scale effects on climate are not readily apparent. One should, therefore, look ahead for significant relationships. Thus estimates of future world population, future energy uses, and future sources of energy are central to an assessment of future climatic impact. Harry Perry and Hans H. Landsberg have undertaken to produce such estimates,* which, as they note, are intended simply as plausible springboards for analysis and discussion—not as forecasts. Nevertheless, the model they present sets forth vividly the implications of growing population and a continuing demand for energy. They envision a world population of some 10 billion by the latter part of the next century and total energy consumption over 5 times current levels. Perhaps surprisingly, all this energy could be provided by fossil fuels, mainly coal. On this basis, annual heat and carbon dioxide production would also be over 5 times current levels, while annual production of particles (because of the need to use dirtier fuels) could be perhaps 20 times current values. Thus considerable man-made heat would be released into the environment, but it would still be only a small fraction of the natural energy flows on a global or regional scale; local concentrations, however, could be much greater. While particulate production might be very high, there is no reason to expect that release of particulates to the environment would be correspondingly high. On the contrary, there is every reason to suppose that present * These estimates are discussed in Appendix A at the end of this chapter and in Chapter 1.

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Studies in Geophysics: Energy and Climate means of controlling particle emissions will be improved to a high degree. Certainly a twentyfold increase in the emission of particles would be intolerable because of hazards to human health. Perry and Landsberg have calculated that in 1973, energy use w as 7.6 billion metric tons of coal equivalent or 5.8 × 1016 kilocalories. This is about 0.01 percent of the incoming solar radiation. Their figures for 2075 indicate that the total energy used by human beings may correspond by then to about 0.1 percent of the incoming solar energy. On a worldwide basis, the climatic effect of the added heat would be small. On a local scale, however, it might be significant. Over Japan, for example, the heat released by human energy use could be nearly 2.6 percent of the solar radiation absorbed near the earth’s surface, and over Western Europe it could be about 0.6 percent. Even with a population of 20 billion people and a per capita energy demand 10 times the present world average (twice that of the United States in 1975) the total energy release would be 400 Gt of coal equivalent, or about 0.3 percent of the absorbed solar radiation. Current general circulation models indicate that, if the heat release were uniformly distributed on the earth’s surface, the corresponding increase in average surface temperature would be about 0.6°C, and at latitudes above 50° perhaps 2–3°C. According to the data and estimates in Chapters 4 and 10, somewhat less than half of the carbon dioxide released by man since the industrial revolution has remained in the atmosphere. During that time, about a 13 percent rise in atmospheric concentration of carbon dioxide has taken place. Most of the remainder is inferred to have been taken up by the oceans and by the terrestrial biosphere. One can estimate the amount of carbon dioxide that may be released through the middle of the next century and, by the use of models of the carbon cycle, the amount that may be expected to remain in the atmosphere, It is not implausible that the peak atmospheric concentration occurring in A.D. 2150 to A.D. 2200 might be four to eight times the preindustrial level. Moreover, concentrations much higher than today’s may persist for many centuries thereafter. Manabe and Wetherald (1975) have constructed a three-dimensional climatic model of the general circulation of the atmosphere that simulates the effects of a doubling in atmospheric carbon dioxide. This model, although recognized to be imperfect in a number of significant ways, is the most complete one yet devised. For a doubling of carbon dioxide in the atmosphere, the model predicts about a 2–3°C rise in the average temperature of the lower atmosphere at middle latitudes and a 7 percent increase in average precipitation. The temperature rise is greater by a factor of 3 or 4 in polar regions (see Chapter 9). For each further doubling of carbon dioxide, an additional 2–3°C increase in air temperature is inferred. The increase in carbon dioxide anticipated for A.D. 2150 to A.D. 2200 might lead to an increase in global mean air temperature of more than 6°C—comparable with the difference in temperature between the present and the warm Mesozoic climate of 70 million to 100 million years ago. CONCLUSIONS It does not now appear that the direct generation of heat from the production and consumption of energy over the next few centuries will cause a rise of more than 0.5°C in global average air temperature, although it may have substantial effects on local climates. If the correspondingly increased particulate emissions are properly controlled, there should be little global effect on climate from an increased atmospheric burden of aerosols. The climatic effects of carbon dioxide release may be the primary limiting

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Studies in Geophysics: Energy and Climate factor on energy production from fossil fuels over the next few centuries. The prospect of damaging climatic changes may thus be the stimulus for greater efforts at conservation and a more rapid transition to alternate energy sources than is justified by economic considerations alone. The potential effect of carbon dioxide on climate could be exacerbated by fluorocarbons, nitrous oxide, and other industrial gases. The natural variability of climate could increase or reduce the impact of such man-made effects. There are profound uncertainties regarding the carbon cycle, climate, and their interdependence. These uncertainties can be resolved only by a well-coordinated effort of extraordinarily interdisciplinary character. The focus for such an effort is not provided by any existing institutional mechanisms. RECOMMENDATIONS The possibility of modification of the world’s climate by carbon dioxide released in the production of energy from fossil fuels should be given serious prompt consideration by concerned national and international organizations and agencies. Two kinds of action are needed: organization of a comprehensive worldwide research program and new institutional arrangements. A worldwide comprehensive research program should be undertaken. It should include studies of the carbon cycle, climate, future population changes, and energy demands and ways to mitigate the effects of climatic change on world food production. Research on climate. The development and verification of climatic models should continue. Adequate means to monitor climate should be provided both to verify models and to give warning of climatic change. Further studies of the sensitivity of climate to disturbances in the radiation balance should be carried out using advanced climate models. Paleoclimatology should be pursued in the interest of understanding past climate changes as well as to provide data for verification of models, both of climate and of biogeochemical cycles. Studies of world population and energy demands. These studies should include estimates of the contribution to our energy requirements that can be made by renewable resources. Investigation of energy sources that do not release waste gases and particles and minimize the release of heat should be intensified. The problems associated with energy supply and demand call for the further study of conservation measures and their prompt implementation. Food. In view of the prospective impact of man’s activities on climate as well as the natural variability of climate, greater attention must be given to agriculture and water resources from the point of view of mitigating the effects of climatic change. Carbon dioxide and the atmosphere-ocean-biosphere system. A better understanding of the partitioning of carbon among the biosphere, oceans, and atmosphere is essential and might be obtained by the following measures: Measurements of variations with time in the ratio of the two stable isotopes of carbon (13C and 12C) in the atmosphere are needed to determine the net flux of carbon between the atmosphere and the biosphere. Past variations in this ratio can be obtained from measurements of these two isotopes in tree-ring sequences from trees in isolated locations—as distant as possible from major biological and industrial sources of carbon dioxide. Changes in the 13C–12C ratio are likely to be small relative to random measurement errors, and consequently many measurements are needed over a wide range of geographic locations. Better estimates should be made of the area of land annually cleared for

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Studies in Geophysics: Energy and Climate agricultural and other purposes. From 1972 onward, these estimates can be obtained from earth-resources satellite data. To obtain estimates for the period before 1972, a historical study of the growth of cultivated areas in all continents from the early part of the nineteenth century should be made. Attempts should be made to estimate changes in forest biomass throughout the world, particularly in tropical and subtropical areas. The principal component of this biomass consists of wood in living trees; measurements of differences in the thickness of successive tree rings might indicate changes in the rate of net primary production of trees, at least in temperate latitudes. Many tree-ring sequences (of the order of several thousand) would be necessary for an adequate sample. Efforts should also be made to estimate time variations in the quantity of foliage and other organs of trees that participate actively in photosynthesis and in the rate of fall of “litter” (dead leaves and branches) from trees. Better estimates are needed of the fraction of soil humus from which carbon dioxide is released to the atmosphere. Changes in this quantity should be determined in agricultural and other cleared areas. Surveys of the present distribution of humus in soils throughout the world are needed to serve as a baseline for comparison with future measurements. Intercomparable mean monthly values of the partial pressure of atmospheric carbon dioxide should be obtained from continuous measurements at a number of carefully selected stations in different latitudes in both the northern and southern hemispheres. One of the principal objectives of such a network of stations would be to study year-to-year variations in the airborne fraction of carbon dioxide released to the atmosphere by fossil-fuel combustion and land clearing. These variations appear to be related to fluctuations in carbon dioxide uptake and release by near-surface ocean waters, and their elucidation should give us greater insight into oceanic processes affecting the partitioning of carbon dioxide between the ocean and the atmosphere. Further insight into these processes might be gained by time sequences of measurements of the total carbon dioxide content and partial pressure of free carbon dioxide at a global network of observing stations in surface and subsurface ocean waters. These quantities vary widely with local biological and other ocean processes, and hence it may not be possible to make useful interpretations of the measurements from the standpoint of the global carbon dioxide problem. Further analysis of the desirability of this type of measurement should be undertaken. Better estimates are needed of the quantity of carbon dioxide released by fossil-fuel combustion. International statistics on the consumption of fossil fuels should be supplemented by estimates of the carbon content of the fuels consumed each year. The present uncertainty in the amount of carbon dioxide released is of the order of 10 to 15 percent because the estimates of fuel consumption are given in terms of fuel energy rather than carbon content. A series of measurements of the dispersal of tritium from atmospheric nuclear-weapons tests in subsurface ocean waters should be made at approximately five-year intervals following the lines of the GEOSECS expeditions of the early 1970’s. Such measurements of time variations in the oceanic distribution of tritium appear to be the most satisfactory experimental means of studying “stirring” processes (advection, convection, and turbulent mixing) in the upper thousand or so meters of the ocean waters. These processes are critically important in estimating partitioning of fossil-fuel carbon dioxide between the ocean and the atmosphere. In principle, an independent check on oceanic stirring processes could be obtained if the Suess effect (the decrease in the radiocarbon content of the atmosphere from the beginning of the nineteenth century to 1950 resulting from injection of 14C-free fossil-fuel carbon dioxide into the atmosphere) were more accurately

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Studies in Geophysics: Energy and Climate known. The present uncertainty in the Suess effect is about ±25 percent. Many more measurements of 14C in tree rings covering the time span from 1800 to 1950 in trees from carefully selected locations are needed. The following kinds of observations should be given consideration for future studies but with a lower priority than the above recommendations relating to carbon dioxide. Knowledge of rates of interchange between the interstitial waters of calcareous sediments and the bottom waters overlying the sediments would allow better estimates of probable rates of solution of calcium carbonate and the corresponding increase in the capacity of the ocean to absorb carbon dioxide. More data on the distribution of aragonite (the more soluble of the two crystalline forms of calcium carbonate) in shallow and deep calcareous sediments are needed for better estimates of the possible solution of calcium carbonate. Whether solution of calcium carbonate has actually occurred and if so to what extent can be determined directly by measurement of changes in the alkalinity of seawater. New methods of measuring the alkalinity have a precision of about 1 part in 10,000, corresponding to a change in atmospheric carbon dioxide of about 0.1 percent, Carbon dioxide could be extracted from the atmosphere-subsurface ocean system if the rate of fallout of particulate organic matter from the subsurface layer into the deep ocean waters could be accelerated. This might be possible if the photosynthetic production of organic matter in the near-surface ocean waters could be increased. Photosynthetic production in these waters appears to be determined by the supply of dissolved phosphorus and nitrogen compounds. In the future, it might be possible to disperse large quantities of industrially produced phosphorus and nitrogen over extended areas in the oceans, at a cost that would be relatively small compared with the total cost of carbon dioxide-producing fossil fuels. The effectiveness of this tactic can probably be determined by comparative measurements of the rate of fallout of organic matter in both presently highly productive and unproductive ocean areas. In principle, fertilization of ocean waters with 10 million tons of phosphorus would produce fallout of about 300 million tons of organic carbon. All the foregoing recommendations for research relate to global concerns and therefore the cooperation of such international agencies as the World Meteorological Organization, the Intergovernmental Oceanographic Commission, and the International Council of Scientific Unions should be sought in responding to them. The necessary research will be expensive in terms of scientific and technical manpower and research facilities and must by continued over many years. Consequently, it must be fostered and supported by governments. A high degree of international governmental cooperation is called for because of the need for a worldwide set of measurements and network of observing stations. Consideration should be given to the establishment at the national level of a mechanism to weave together the interests and capabilities of the scientific community and the various agencies of the federal government in dealing with climate-related problems. Solutions to those problems will involve coordination of research in many scientific disciplines and are likely to require adjustments in national policy or the formulation of new legislation. Such a mechanism might be embodied in a Climatic Council with the following functions: To serve as the focal point within the United States for the development of a global research and action program. To coordinate activities that cross disciplinary, institutional, and organizational boundaries.

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Studies in Geophysics: Energy and Climate To serve as a link with international mechanisms that guide international research and action programs concerned with carrying out aspects of the above recommendations. POTENTIAL CONSEQUENCES OF CLIMATIC CHANGES WARMING OF THE OCEAN WATERS A warmer atmosphere could not persist without a comparable warming of the upper layers of the oceans. The effects would be several: a reduction in the amount of sea ice, a rise in sea level, a flux of carbon dioxide from the ocean to the atmosphere, a reduction in the vertical stirring of the oceans, and a poleward shift in marine ecosystems including the fish population. Reduction of sea ice should decrease albedo and lead to further warming, higher precipitation, and possibly a new buildup of snow and ice poleward. An increase by 5°C in the average temperature of the top 1000 m of ocean water would raise sea level by about 1 m, because of the expansion of water volume. Such an increase in ocean temperature would raise the partial pressure of carbon dioxide in the water by about 30 percent. After equilibration with the atmosphere, which would probably take place within a few years, the carbon dioxide content of the air would be increased by about 17 percent. The expected polar warming would affect the rate of ventilation of all subsurface waters. A “lid” of relatively warm water would be formed over the colder deep waters, thereby increasing the vertical density stratification of the oceans. This would inhibit vertical mixing and stirring processes, which would in turn reduce the rate of nutrient supply to the near surface ocean waters and hence the productivity of marine plants. The quantity of dead organic carbon falling from the surface layers to the deep water would be lower, and consequently the rate of uptake of carbon dioxide by the deep sea would also be lower. According to our models, atmospheric and presumably oceanic near-surface temperatures would increase much more at high than at low latitudes. Circulation of the deep waters and vertical exchange between the deep and near-surface waters might be profoundly altered by reduction or even cessation of present vertical convection and formation of deep water in the north Atlantic. Experience in previous periods of ocean warming indicates that the area of sea ice would be substantially reduced, probably so much that both the Northwest and Northeast Passages would be open for shipping throughout most of the year. During earlier decades of this century, the slight rise in average air temperature over the northern hemisphere, and the concomitant warming of surface-water layers of the ocean, brought about a marked shift in the locations of certain commercially important fish populations, notably the North Atlantic cod. Much of the cod fishery shifted to the waters off Greenland and north of Iceland. Hence an abnormally large warming of the atmosphere would surely have significant effects in the geographic extent and location of important commercial fisheries. Because different marine organisms respond differently to temperature changes, marine ecosystems might be seriously disrupted. EFFECTS ON THE POLAR ICE CAPS In the present state of understanding, it is impossible to forecast what might happen to the Greenland and Antarctic ice caps as a result of a rise of several degrees in global average air temperature. It is likely that the temperature in the Antarctic

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Studies in Geophysics: Energy and Climate would still remain below the freezing point, so that melting at or near the surface of the ice probably would not occur. On the other hand, a substantial change in climate might greatly increase the annual snowfall in Antarctica and Greenland, resulting in a substantial increase in the thickness of the ice. This, in turn, would increase horizontal stresses at the base of the ice caps, which might result in surges or slides of ice masses into the sea. If these surges resulted in destruction of the West Antarctic ice cap, there might be a corresponding rise in sea level of about 5 m within 300 years (Hughes, 1974, 1977). EFFECTS ON WORLDWIDE AGRICULTURE Far-reaching consequences of a large increase in atmospheric carbon dioxide would be felt in agriculture—mankind’s basic industry. With our present level of understanding, we cannot specify these consequences completely, let alone quantitatively. We can only suggest some of the possible effects. A few of these would be beneficial; others would be disruptive. Five factors must be considered: the effect of high levels of carbon dioxide on plant metabolism; higher annual average temperatures; spatial shifts in agroclimatic regions, especially in the precipitation patterns in different regions; the possibilities of greater or less variability from year to year in different regions; and the effects of possible increased cloudiness on the growth of crops. Effects on Photosynthesis Both theory and experiment show that raising the carbon dioxide content of the air in contact with plants increases the photosynthetic production of organic matter, provided other requirements for plant growth—nutrients, water, and sunshine—are present in abundance and the plants are not under stresses caused by too low or too high temperatures, soil acidity or alkalinity, lack of oxygen in the root zone, diseases, or other factors. With modern farming technology it is possible to provide adequate supplies of water and major and minor nutrients and to eliminate most causes of stress. Atmospheric carbon dioxide, incoming solar radiation, and the genetic potential of crop plants can then become the limiting factors of agricultural production. Under normal farming conditions, the net photosynthetic product, that is, the organic matter remaining after the plant has used some of its own product in respiration, will not increase so rapidly as the atmospheric carbon dioxide (Waggoner, 1969). For the terrestrial biosphere as a whole, we have estimated that the factor of proportionality (designated as β) is about 30 percent, but it can be much higher for agricultural crop plants. Future agronomic and genetic research might bring this factor close to 1 (Waggoner, 1969; Hardman and Brun, 1971). Other changes that might be brought about by higher atmospheric carbon dioxide would work in an opposite direction. If average air temperatures increase significantly, plant respiration is also likely to increase (Waggoner, 1969; Botkin et al., 1973), The net photosynthetic product may be reduced even though gross photosynthesis is raised. If average cloudiness (the proportion of the land area covered by clouds) rises, the quantity of incoming solar radiation will be lowered, and the energy available to crop plants for photosynthesis will diminish. Excessive cloudiness during the monsoon season in India and Bangladesh already limits crop yields, compared with those obtained on the same farms in the sunnier months of October through March.

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Studies in Geophysics: Energy and Climate Poleward Shift of Agroclimate Zones A rise in average annual global air temperature, increasing toward higher latitudes as predicted in the model of Manabe and Wetherald (1975) would result in a general poleward movement of agroclimatic zones. At higher latitudes, there would be a longer frost-free growing season than at present, and the boundaries of cultivation could be extended northward in the northern hemisphere. At the same time, summer temperatures might become too high for optimum productivity of the crops presently grown at middle latitudes, such as corn and soy beans in Iowa, Illinois, Indiana, and Missouri, and it might be necessary to shift the Corn Belt toward the north. But the acid podzol soils over large areas in these higher latitudes are badly leached, and extensive and expensive soil amendments would be required even to approach the yields now obtained in the remarkable soils of the Corn Belt. The model predicts a global rise in average annual precipitation, which at first glance would seem to benefit agriculture. But the accompanying higher temperatures would also increase evapotranspiration from cultivated lands, and some part, perhaps all, of the benefits from the additional water supply would be lost. In some regions, higher evapotranspiration might exceed the increase in precipitation; in others, the reverse might be true (Manabe and Wetherald, 1975). In general, the most serious effects on agriculture would arise not from changes in global average conditions but from shifts in the location of climatic regions and changes in the relationships of temperature, evapotranspiration, water supply, cloudiness, and radiation balance within regions. Present cropping patterns, crop varieties, and farming technology in different climatic regions are based on cumulative experience over many years in the selection of appropriate crop species and varieties for each region and in adapting both the plants and their physical environment to each other in as nearly an optimal fashion as possible. These adaptations have remained fairly satisfactory over the relatively narrow range of climatic changes that have occurred in the historic past. But large changes in climatic relationships within regions such as might be brought about by a doubling or quadrupling of atmospheric carbon dioxide would almost certainly exceed the adaptive capacity of presently grown crop varieties. The regional changes in temperature-precipitation relationships that can accompany even comparatively small excursions in global average temperatures are illustrated by paleoclimatic studies. For example, during the so-called climatic optimum of several thousand years ago, when the average temperature was perhaps 1.5°C higher than at present, precipitation probably increased over southern Europe, northern Africa, southern India, and eastern China, while over large parts of the United States, Canada, and Scandinavia, the climate was drier (Kellogg, 1977). It cannot be expected that regional climatic changes resulting from a large rise in atmospheric carbon dioxide would be simply an exaggerated replica of past changes. Both the seasonal and latitudinal effects of added carbon dioxide should be different from, for example, the effects of a global change in incoming solar radiation. Since both water vapor and carbon dioxide absorb and reradiate infrared energy, the effect of added carbon dioxide will be relatively more important in the dry air of high latitudes, in the upper troposphere, and in the stratosphere than in the moist air of the tropics. Similarly, because absolute humidity in winter is less than in summer, the effects of added carbon dioxide will be relatively more significant in the winter months. These latitudinal and altitudinal differences in the role of carbon dioxide are taken into account in the model of Manabe and Wetherald (1975); and they must form an integral part of future three-dimensional dynamic models that attempt to specify regional climatic changes in temperature, precipitation, evapotranspiration, and cloudiness.

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Studies in Geophysics: Energy and Climate Studies of oxygen and carbon isotope ratios in deep-sea cores suggest that the higher temperatures of the climatic optimum may have been due to a temporary increase in atmospheric carbon dioxide resulting from the changes in ocean circulation that followed the melting of the ice cap. If this suggestion can be substantiated, further paleoclimatic studies of seasonal differences in temperature-precipitation relationships during the climatic optimum should provide valuable insights into the future effects of increased atmospheric carbon dioxide (Berger and Garner, 1975; Berger and Killingley, 1977). Serious Effects in Arid and Semiarid Regions The most serious effects of possible future climatic changes could be felt along the boundaries of the arid and semiarid regions in both hemispheres. These are the zones of atmospheric subsidence where precipitation is scanty and highly variable: the southwestern United States and northern Mexico; the belt of relatively dry lands extending from southern Europe and northern Africa (including the Sahara), eastward across Arabia and south Asia to Pakistan and northwestern India; northeastern Brazil, northern Chile and southern Peru, western Argentina, southwest Africa, and Australia. We need to be able to estimate whether these belts of aridity and semiaridity will move toward or away from the poles and whether they will expand or contract in area. Short-term variations in climate, especially in rainfall, often persisting for several years, are characteristic of the semiarid regions. The human disasters caused by drought in these regions are familiar and dramatic. But the variations are also closely related to destruction of the resource base through processes of desertification—wind and water erosion and sedimentation—which make large areas unfit for agriculture or pasturage, deterioration in soil and groundwater quality through salinization, and destruction of natural vegetation and its replacement by plants unfit for grazing. The effects of relatively short-term climatic variations in the semiarid zone are worsened by the seemingly inevitable behavior patterns of farmers and pastoralists, who, during relatively wet periods, expand their cultivated areas and drive their livestock into marginal lands beyond the region’s carrying capacity. During dry periods, these marginal lands, with their natural protective cover destroyed by cultivation and grazing, are eroded at rates exceeding by orders of magnitude those that had prevailed before. From this discussion of the human consequences of a marked climatic change that might be brought about by the addition of large quantities of carbon dioxide to the atmosphere, it may be concluded that world society could probably adjust itself, given sufficient time and a sufficient degree of international cooperation. But over shorter times, the effects might be adverse, perhaps even catastrophic. COUNTERVAILING MEASURES Two kinds of countervailing measure against the possible climatic effects of added carbon dioxide can be visualized: measures to reduce possible climatic changes themselves and measures to reduce the impact on human affairs. In the first category, it is possible to conceive of ways of reversing the changes in the radiation balance of the earth that might result from added carbon dioxide or ways of removing the added carbon dioxide from the air. In the second category, we are concerned primarily with ways to increase the robustness and flexibility of the world’s food-supply systems. We shall consider these first because they are less problematic and largely within the range of present technology.

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Studies in Geophysics: Energy and Climate bonate. Their content of “free” carbon dioxide is on the average ten times higher (and their CO32− concentration correspondingly lower) than that at equilibrium with present atmospheric carbon dioxide, while the average calcium content is somewhat lower than the saturation value for water with a CO2 content at equilibrium with the present pressure of CO2 in the atmosphere (Garrels et al., 1975). The marked undersaturation of calcium carbonate in present rivers is demonstrated by the close correlation between the contents of calcium and bicarbonate in different rivers and the total dissolved solids. If the rivers were saturated with calcium carbonate, their calcium and bicarbonate concentrations would be relatively constant regardless of the total quantities of dissolved solids. Garrels et al. (1975) examined the content of “free” carbon dioxide in 17 different rivers covering a wide range of latitudes, rock types in the drainage basins, river sizes and stages, and total dissolved solids. The CO2 pressures were 3–30 times higher than that in the present atmosphere and were nearly independent of all the above river characteristics. The average CO2 pressure was about the same as that of the interstitial waters of soils. Apparently the CO2 pressure in the world’s rivers depends on microbiological oxidation processes that are relatively independent of the carbon dioxide pressure in the atmosphere. It seems reasonable to conclude that even with a quadrupling of atmospheric carbon dioxide, the annual loss of carbon in river waters would not exceed 500 Mt, less than 0.03 percent of the additional carbon in the atmosphere. Organic carbon is deposited in marine sediments at a rate, according to Broecker (1974), about one fourth of that of carbon as calcium carbonate, and this represents a net loss of atmospheric carbon that must, on a geologic time scale, be counterbalanced by other processes. The rate of deposition of organic matter is apparently determined by the amount of phosphorus carried by rivers from the land to the sea, which may be related to the atmospheric carbon dioxide concentration through weathering processes. Photosynthetic reduction of carbon dioxide by plants and the subsequent deposition of a small fraction of the plant remains in marine sediments, leaving the photosynthetically produced oxygen in the air, is probably the chief process that, over geologiceons, has resulted in our planet having an atmosphere with free oxygen. But the present annual rate of deposition is probably not more than 20 to 50 Mt. This is negligible compared with the rate of addition of carbon dioxide to the air. A process of greater potential significance could be the dissolution of calcium carbonate in marine sediments. The upper water layers of the sea in the tropics and subtropics appear to be markedly oversaturated with respect to both calcite and aragonite, the two crystalline forms of calcium carbonate. Carbonate-rich sediments, including coral reefs and atolls and deposits that may be formed inorganically, are widespread at shallow depths. In the deeper waters of low latitudes and midlatitudes, pelagic sediments containing a high percentage of calcareous skeletons of marine animals and plants occur above a “compensation depth,” at which, because of the combined effects of pressure and temperature, the water appears to be about saturated with calcium carbonate. Above the compensation depth, the waters are supersaturated; below it, they are undersaturated, and the fraction of calcium carbonate in pelagic sediments sharply diminishes. The compensation depth is different in different oceans, because of their differing carbonate ion concentrations, being about 4500 and 1000 m for calcite and aragonite, respectively, in the Atlantic (and probably the Indian Ocean), and perhaps as shallow as 500 and 300 m for these two mineral species in the North Pacific north of 10° N. South of 10° N, the saturation depth for calcite in the Pacific is probably between 3500 and 4000 m, judging by the distribution of calcium carbonate in the pelagic sediments (Sverdrup et al., 1942).

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Studies in Geophysics: Energy and Climate When some of the carbon dioxide produced by fossil-fuel combustion and forest clearing reaches the deep sea, the carbonate ion concentration in the deep water will diminish and consequently the compensation depth will rise. Calcium carbonate on the surface of the sediments should dissolve at depths between the old and new compensation depths. At a depth of the order of 10 cm below the sediment surface (beneath the zone of burrowing organisms), calcium carbonate will be effectively insulated from the overlying waters and will dissolve very slowly, if at all. Between 1 and 10 cm below the sediment surface, the rate of solution of sedimentary calcium carbonate is limited by the rates of exchange between the interstitial water in the sediment and the overlying seawater. Experimental data summarized by Guinasso and Schink (1975) indicate that this rate is several orders of magnitude lower than the rate of molecular diffusion in water. Calculations based on the data suggest that the rate of solution of calcium carbonate, even if the superjacent waters become more acid, is likely to correspond to less than 1 Gt of carbon a year, a relatively small proportion of the anticipated increase in atmospheric carbon. The alkalinity of the seawater, and hence its ability to absorb carbon dioxide, will increase in proportion to the quantity of calcium carbonate dissolved. If the compensation depth rose to the sea surface, the ultimate result could be, as Keeling and Bacastow show (see Chapter 4), that the carbon dioxide content of the atmosphere in the early twenty-second century would, ceteris paribus, be only five times the preindustrial value, instead of eight times if carbonate solution did not occur, and it would drop off to twice the preindustrial value a thousand years from now. However, this would require solution of a layer of shallow-water carbonate sediments several meters thick, which probably could not occur without massive human intervention. Observed mixing rates resulting from the activities of burrowing organisms in shallow water sediments (Guinasso and Schink, 1975; Guinasso, 1976; Sundquist et al., 1977; Goreau, 1977; Berger, 1977) indicate that the diffusion of interstitial waters between these sediments and the superjacent waters is slow, although much more rapid than in deep-sea sediments, and hence the rate of solution of calcium carbonate in undisturbed sediments will result in only a small rate of increase in the capacity of the ocean to absorb carbon dioxide. Up to the present, this effect is probably negligible. The carbon dioxide added from the air has not penetrated to sufficient depths to raise the compensation depth, except in the North Pacific, where the compensation depth may have become a few meters shallower. But the total quantity of carbon dioxide in the top meter of sediments in the uppermost thousand meters of the entire Pacific Ocean corresponds only to 230 Gt of carbon (Sverdrup et al., 1942), and perhaps 90 percent of this lies south of 10° N where the compensation depth has almost certainly not been affected. An upper limit to the quantity of sedimentary calcium carbonate dissolved up to the present is probably about 1 Gt of carbon, less than one fifth of the addition from fossil fuels in the single year 1973. We conclude that none of the geologic processes described above would significantly affect the increase in atmospheric carbon dioxide from fossil-fuel combustion that is likely to occur during the next few centuries. CLIMATE Any useful prediction of the effect of carbon dioxide added to the air must depend on an understanding of the physical processes that determine climate. In general, we know that both carbon dioxide and water vapor in the air absorb and reradiate infrared radiation. Hence the temperature of the lower air must be at the level where the fraction of the infrared radiation passing outward to space is equal to the total incoming radiation from the sun, less the amount reflected from clouds

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Studies in Geophysics: Energy and Climate and from the earth’s surface. Because of this greenhouse effect produced by carbon dioxide and water vapor, the average temperature at the earth’s surface is about 30°C higher than it would be in the absence of these two gases. As mentioned above, Manabe and Wetherald (1975) have calculated the magnitudes of the effects of a doubling of the atmospheric carbon dioxide—it would result in about a 2– 3°C rise in the earth’s average air temperature, about a 2 percent increase in relative humidity, and a 7 percent increase in average precipitation. The temperature rise would be greater at high latitudes, about 10°C at latitude 80° N. Temperatures in the stratosphere would decrease. At a height of 30 km, this decrease would be about 5°C. The increase in average air temperatures near the ground would be about 4–6° for a fourfold increase in CO2 and 6–9° for an eightfold increase (see Chapter 9). A global average rise of 6°C would be comparable with the extreme changes of global temperature believed to have occurred in geologic history of the last billion years. Although the model used by Manabe and Wetherald is the most sophisticated that can be constructed at present, it does not take account of four climatic feedback mechanisms that could change the calculated results: atmosphere-ocean carbon dioxide interaction, cloud reactions, ocean temperature and heat transport changes, and aerosol reactions. Atmospheric-Ocean Carbon Dioxide Interactions If an increase in atmospheric carbon dioxide raises the air temperature over the sea it will also warm the waters near the surface and thereby reduce the solubility of carbon dioxide. Some carbon dioxide will be driven from the sea into the air, or conversely less carbon dioxide will be absorbed. A more important effect will be the increase in the vertical density gradients in the ocean, which may significantly change interactions between the air and deep-ocean circulation. Cloud Reactions An increase in the water vapor content of the air could result in an increase in low-level clouds. This might be expressed as a larger area of the earth’s surface being covered by clouds and also by changes in the heights of cloud tops, which determine their temperature and hence their radiative properties. An increase in the surface area covered by clouds would result in a proportional increase in albedo—that is, in the reflectivity of the earth. A higher albedo in turn would reduce the percentage of solar radiation reaching the earth’s surface and thus would cause a lowering of air temperatures. This could partly compensate for the rise in temperature that would otherwise be produced by the rise in atmospheric carbon dioxide, although Manabe and Wetherald find in some of their numerical experiments that increases in low cloudiness are offset from the standpoint of radiation balance by changes in middle and high cloudiness. Ocean Temperature and Heat Transport Changes The Manable-Wetherald model assumes a swamplike ocean with no heat capacity but with the ability to provide water vapor to the atmosphere. Their result would have been completely different if a constant sea-surface temperature had been assumed, implying an ocean of infinite heat capacity. This would greatly diminish the response of the ocean-atmosphere system to changes in the carbon dioxide content or even to changes in solar radiation. In fact, the ocean has a large but finite heat capacity, and it surrounds continental land masses that have very low

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Studies in Geophysics: Energy and Climate heat capacity. This fact is particularly important in considering seasonal cycles of heating and cooling, because of the long lag time and persistence of changes in ocean temperatures near the surface. The ocean also transports heat from low latitudes to high latitudes. The quantity of heat transported poleward by the oceans is about equal to that transported by the air. Any model that attempts to predict atmospheric temperature changes, let alone the diffusive mixing in the oceans that determines the amount of carbon dioxide absorbed, must take into account possible changes of the ocean circulation. That is, it must be a coupled ocean-atmosphere model. The construction of such a model is difficult at present, because the main motions of the sea appear to be in eddies of the order of 200 km in diameter (much smaller than the main components of the atmospheric circulation), and satisfactory methods for arriving at even a statistical description of these oceanic motions have not yet been developed. Ways of expressing the effects of these eddies in terms of larger-scale oceanic parameters are needed. Aerosol Interactions Aerosol particles absorb and scatter sunlight, and they also absorb and reradiate infrared radiation. The backscattering of solar radiation tends to increase the net albedo, while the absorption and reradiation of sunlight in effect reduce the net albedo. Thus, “dark” particles, which have a high ratio of absorption to backscatter, tend to decrease the albedo over a light surface such as a snow field, a low cloud deck, or desert areas. Aerosols over the ocean, which has a low albedo, tend to increase the net albedo. Modeling the interaction of aerosols such as dust, sea salts, or sulfates cannot be done very well at present (see Chapter 3) because their introduction into the atmosphere is either not coupled to the dynamics of climate (fires, volcanoes) or is coupled in a very complex way (wind-raised dust and sea spray). OUTLOOK We now summarize what will be needed to improve our understanding of the phenomena involved in the carbon dioxide problem and indicate some of the elements that should be included in planning to close gaps in our knowledge, so that future decisions regarding the exploitation of energy resources can be made on as sound a basis as possible. CARBON CYCLE Further work is needed to understand the carbon cycle that takes into account buffering by the biosphere, rock weathering, and calcium carbonate precipitation and solution in lakes and the oceans. A program of measurement of tracers that indicate the mixing rates of the upper oceans (e.g., tritium), and also of oceanic carbon dioxide content both near the surface and at a series of depths below the surface, should be undertaken. Present efforts to develop better methods of studying the ocean circulation in three dimensions should be broadened and intensified. Research on the biological and chemical processes in ocean banks and reefs, and in the calcareous oozes of the deep seafloor, should be encouraged. Baseline measurements of soil humus and of the other living and dead components of the terrestrial organic pool should be made on a worldwide basis, and these measurements should be repeated at suitable intervals to allow direct estimates of the net uptake or net release of carbon from this reservoir.

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Studies in Geophysics: Energy and Climate CLIMATE Clearly, a fundamental understanding of the mechanisms and dynamics of climate is needed. The question of how to meet that need has been addressed in a number of recent reports (U.S. Domestic Council, 1974; Matthews et al., 1971; GPS No. 16, 1975; U.S. Committee for the Global Atmospheric Research Program, 1975). Broadly speaking, these reports agree that modeling is the most promising approach to understanding climate. They document the considerable gains achieved through modeling but point out that much remains to be done. Further progress will require new observations, both to point the way to new advances and to test models, and technological innovation in observational and data-gathering systems, more powerful computers, and perhaps new institutions through which to plan, organize, and execute research programs and to provide access to the results of these programs to the widest possible audience (see Chapter 8). Problems that will have to be considered in improving our understanding of energy-related aspects of climate include the following. Ocean-Atmosphere Interaction The oceans play an important part in storing and transporting heat involved in climate dynamics. Coupled ocean-atmosphere models, including mechanisms of sea-ice formation and its effect on radiation balance and of the exchange of heat between the ocean and the atmosphere, are needed (for further discussion see Ocean Science Committee, 1975). Radiation Balance The physical and dynamical mechanisms of cloud formation are not well understood. Cloud formation in turn affects the radiation balance. This is one of the most challenging problems in climatic modeling. Fluorocarbons and oxides of nitrogen from fertilizers can, like carbon dioxide, cause a greenhouse effect. Global warming due to the use of chlorofluoromethanes and the increase in atmospheric content of nitrous oxide has been predicted (Committee on Impacts of Stratospheric Change, 1976; Chapter 4). Thus, carbon dioxide and other atmospheric gases may act together to produce a global warming trend. Monitoring The principal requirement for improvement of general circulation climatic models is an integrated program of measurements of the distribution in space and time of key physical properties and processes in the ocean and the atmosphere—key properties indicated as essential by the models themselves. These include many kinds of observation that can be made from satellites, such as those of total solar flux, net radiation budget, cloud cover, albedo, extent of snow, sea ice and polar ice sheets, tropospheric and stratospheric aerosols, and atmospheric turbidity. Other properties and processes must be measured in situ, including river runoff, soil moisture (to some extent measurable from space), subsurface ocean temperatures, precipitation, sea level, carbon dioxide, and ozone. Many of the necessary measurements are included in the Global Atmospheric Research Program under the joint aegis of the World Meteorological Organization and the International Council of Scientific Unions. Almost as important as the actual measurements are methods of data compilation and processing that will compress the enormous amounts of data that will be obtained into usable information that can be handled in practical models of the ocean-atmosphere system (see Chapter 8).

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Studies in Geophysics: Energy and Climate The benefits to be gained from establishing a global monitoring system are not only scientific but also practical, for such a system can provide us with early warning of climatic change. Climate cannot be predicted in the sense that weather can (see Chapter 9). Weather is determined by the short-term behavior of the atmosphere and oceans, which is, in turn, determined primarily by initial conditions. The statistical properties that define climate are determined primarily by boundary conditions and the basic parameters of the system; initial conditions are not likely to be as relevant to these properties. The potential climate changes discussed in this report are largely responses to a change in one of those basic parameters: the total quantity of carbon dioxide in the air, waters, and organic matter of the earth. An effective global monitoring system, through the observation of regional and local climatic changes as well as other changes in physical parameters as outlined above under Recommendations, may be expected to provide evidence of such responses before their consequences become unpleasantly obvious. APPENDIX A: ENERGY CONSUMPTION IN 2075 Hans H. Landsberg and Harry Perry, Resources for the Future, Inc. INTRODUCTION The following calculations require a preliminary note. Anyone having engaged in projections for even a decade ahead is aware of the fragility of such estimates. Vulnerability tends to increase with time horizons as well as with widening geographic scope. Thus a 100-year projection must offhand seem foolhardy. It probably is. As the only excuse for having engaged in it the authors offer the insistent demand for it by those asked to speculate on the consequences of energy consumption far enough into the future to enable them to deal with significant cumulative effects. Undertaking a methodical projection then has the advantage of being subject to inspection and scrutiny but does not bring one any closer to a “forecast.” In this context it is desirable to proceed with the least sophistication. Thus the reliance on population and per capita energy consumption in preference to any more complex formula. Both involve arbitrariness and provide fuel for disagreement. As providing orders of magnitude, however, they seem serviceable and keep the discussion on the level of simplicity that matches their merit. It is hoped that no reader or user will be tempted to elevate them to any higher status or divorce them from their sole intended function as tools for the calculations that utilize them. ASSUMPTIONS CONCERNING POPULATION World population is expected to stabilize at some time in the future, but the net reproduction rate (NRR) should reach 1.0 at different times for different regions. Table A.1 indicates the five-year range when the NRR is estimated to reach 1.0 for each region of the world and the population that would exist in each region in 2075 as a consequence. The year range selected for the NRR to reach 1.0 was a “most probable” estimate for each region. Based on these estimates, world population would be about 10.7 billion in 2075. ASSUMPTION CONCERNING ENERGY PER CAPITA CONSUMPTION Annual per capita energy consumption now varies widely among regions. For the world as a whole, it is about 52.5 × 106 Btu. For the United States the annual per

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Studies in Geophysics: Energy and Climate TABLE A .1 World Population in 2075a Region Year Range NRR Equals 1.0 Population in 2075 (millions) United States 1975–1980 285 North America (excluding United States) 1975–1980 36 Western Europe 1975–1980 579 Oceania 1985–1990 31 Latin America 2010–2015 989 Japan 1995–2000 139 Other Asia 2019–2024 4901 Africa 2020–2025 1430 Soviet Union 1975–1980 332 Communist East Europe 1990–1995 139 Communist Asia 2000–2005 1835 TOTAL WORLD   10696 aSource: T. Frojkn (1973). capita consumption is 306 × 106 Btu, while for Africa it is only 9.2 × 106 Btu, or 3 percent of the level of the United States. Estimates of future world per capita energy consumption were made by Weinberg and Hammond (1971). They projected that annual world per capita consumption would stabilize at about twice the current U.S. level, or about 600 × 106 Btu. In a more recent article, Puiseux (1975) estimated that an “advanced civilization” could be achieved with a world per capita energy consumption of 185 × 106 Btu to 264 × 106 Btu. He also estimated a world population of 10 billion people. Table A.2 shows an estimate of the levels of energy consumption that might be reached in different regions by 2075. For the regions that now have large per capita energy consumptions, the values shown in Table A.2 are the maximum that is believed will be used in any future year. Values of per capita consumption below 265 × 106 Btu per year are for regions that would not yet have reached a maximum per capita consumption by 2075 since they currently have such a small base of energy use. North American values already exceed the maximum and have been allowed to increase at a moderate pace. TABLE A.2 Per Capita Consumption and Total Energy Consumption by Regions, 2075 Region Per Capita Consumption (Btu × 106) Total Consumption (Btu × 1015) United States 741 211 North America (excluding United States) 623 23 Western Europe 290 168 Oceania 577 18 Latin America 130 128 Japan 497 69 Other Asia 40 194 Africa 64 92 Soviet Union 760 252 Communist East Europe 580 81 Communist Asia 58 107 TOTAL WORLD   1343

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Studies in Geophysics: Energy and Climate LEVELS OF ENERGY CONSUMPTION AND HEAT RELEASE By combining Table A.1 with column 1 of Table A.2, it is possible to determine the heat released annually in 2075 for each of the regions shown on the tables. These data are shown in column 2 of Table A.2. The heat released per km2 for each region in 2025 and 2075 can be calculated and is shown and compared with the heat that each region would receive from solar energy in those years. These data are shown in Table A.3. Table A.4 shows the projected world consumption of fuels for 1973, 2025, and TABLE A.3 Estimated Energy Densities by Region   Btu × 109/km2 Man-made Heat Release as Percentage of Solar Energy Region 2025 2075 2025 2075 United States 20.93 22.56 0.289 0.311 North America (excluding United States) 1.56 1.87 0.022 0.026 Western Europe 33.60 44.03 0.464 0.608 Oceania 1.76 2.13 0.024 0.029 Latin America 5.54 6.24 0.077 0.087 Japan 182.80 186.29 2.523 2.571 Other Asia 10.65 12.50 0.147 0.172 Africa 2.57 3.03 0.036 0.042 Soviet Union 10.89 11.26 0.150 0.155 Communist Eastern Europe 60.39 63.65 0.834 0.879 Communist Asia 6.28 9.08 0.087 0.126 TOTAL WORLD 8.63 9.89 0.119 0.136 TABLE A.4 World Heat Releasea and Carbon Dioxide and Particulate Inputsb   1973 2025 2075 2090c 2170d Ultimate Total 1. Heate             Gt of coal equivalent per year 7.6 42 48     7500 Quadrillion (1015) Btu per year 220 1170 1340     210000 Cumulative percent of total recoverable reserves of fossil fuels 2.5 17 42     100 2. Carbon Dioxidef             Annual production, Gt of carbon 4.8 16   37 13 5000 Annual increase in air (airborne portion), Gt of carbon 3.0 9   21 0 900 Airborne portion/production, percent 56g 53   57 0 18 Annual increase of atmospheric carbon relative to 1860, percent 0.5 1.3   3.4 0 — Total atmospheric carbon, Gt 700 945   1950 2900 1500 3. Particulatese             Emissions, Mt 140 800 2800       aIncluding all nonrenewable energy forms. bIncluding coal, oil, and natural gas for carbon dioxide and particulate calculations. cYear of peak carbon dioxide production in Revelle-Munk model (see Chapter 10). dYear of peak atmospheric carbon dioxide in Revelle-Munk model (see Chapter 10). eCalculated with Perry-Landsberg model (see Chapter 1). fCalculated with Rovelle-Munk model (see Chapter 10). gAverage airborne fraction from 1959 to 1973 inclusive.

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Studies in Geophysics: Energy and Climate 2075. Comparing these values with those in Table A.3 using a total inhabited surface area of 136 × 106 km2 indicates that by 2075 all the energy needed could still be provided by fossil fuels, mostly from the production of coal. REFERENCES Bacastow, R. B., and C. D. Keeling (1973). Atmospheric carbon dioxide and radio carbon in the natural carbon cycle: Changes from A.D. 1700 to 2070 as deduced from a geochemical model, in G. M. Woodwell and E. V. Pecan (1973). Baes, C. F., Jr., H. E. Goeller, J. S. Olson, and R. M. Rotty (1976). The Global Carbon Dioxide Problem, ORNL-5194, August. Avail, from NTIS. Berger, W. H. (1977). Benthic Processes and Geochemistry of Interstitial Waters of Marine Sediments, K. A. Fanning and F. T. Manheim, eds., Joint Oceanographic Congress, Edinburgh. Berger, W. H., and J. V. Garner (1975). On the determination of Pleistocene temperatures from planktonic foraminifera. J. Foraminifera Res. 5, 102. Berger, W. H., and J. S. Killingley (1977). Glacial-Holocene transition in deep-sea carbonates: selective dissolution and the stable isotope signal, Science 197, 563. Bohn, H. L. (1976). Estimate of organic carbon in world soils, Soil Sci. Soc. Am. J. 40, 468. Bolin, B. (1977). Changes of land biota and their importance for the carbon cycle, Science 196, 613. Botkin, D. B., J. F. Janak, and J. R. Wallis (1973). Estimating the effects of carbon fertilization on forest composition by ecosystem simulation, in G. M. Woodwell and E. V. Pecan (1973). Bowen, H. J. M. (1966). Trace Elements in Biochemistry, Academic Press, New York. Broecker, W. S. (1974). Chemical Oceanography, Harcourt Brace Jovanovich, Inc., New York. Broecker, W. S. (1977). The fate of fossil fuel CO2–a research strategy (to be published). Presented at WMO Scientific Workshop on CO2, Washington, D.C., 1976. Committee on Impacts of Stratospheric Change (1976). Halocarbons: Environmental Effects of Chlorofluoromethane Release. National Academy of Sciences, Washington, D.C. Dryssen, D., and D. Jagner, eds. (1972). The Changing Chemistry of the Oceans (Nobel Symposium 20), Wiley-Interscience, New York. FAO (1976), Paper presented at the 12th session of the Latin American Forestry Commission, Havana. FAO-UNESCO (1971). FAO (Food and Agr. Org.), United Nations, Soil Map of the World, 1:5,000,000, UNESCO, Paris. Frejka, T. (1973). Reference Tables to the Future of Population Growth—Alternative Paths to Equilibrium, The Population Council. Garrels, R. M., F. T. Mackenzie, and C. Hunt (1975). Chemical Cycles and the Global Environment, W. Kauffman, Los Altos, California. Goreau, T. J. (1977). Nature 265, 525. GPS No. 16 (1975). Report of the Study Conference on the Physical Basis of Climate and Climate Modeling. Wijk, Sweden. WMO, Geneva, Switzerland. Guinasso, N. L., Jr., and D. R. Schink (1975). Quantitative estimates of biological mixing rates in abyssal sediments, J. Geophys. Res. 80, 3032. Guinasso, N. L. (1976). EOS 57, 150. Hardman, L. L., and W. A. Brun (1971). Effect of atmosphere enriched with carbon dioxide on different developmental stages from growth and yield components of soybeans, Crop Sci. 11, 886. Hughes, T. J. (1974). ISCAP Bulletin No. 3: Study of Unstable Ross Sea Glacial Episodes, Institute for Quaternary Studies, Orono, Maine. Hughes, T. J. (1977). West Antarctic ice streams, Rev. Geophys. Space Phys. 15, 1. Kellogg, W. W. (1977). Global influences of mankind on the climate, in Climate Change, J. Gribbin, ed., Cambridge University Press, Cambridge, England, in press. Manabe, S., and R. Wetherald (1975). The effects of doubling the CO2 concentration on the climate of a general circulation model, J. Atmos. Sci. 32, 3. Matthews, W. H., W. W. Kellogg, and G. D. Robinson, eds. (1971). Inadvertent Climate Modification, Study of Man’s Impact on Climate (SMIC), MIT Press, Cambridge, Mass. Michel, R. L., and H. E. Suess (1975). Bomb tritium in the Pacific Ocean, J. Geophys. Res. 80, 4139. Ocean Science Committee (1975). The Ocean’s Role in Climate Prediction, NRC Ocean Affairs Board, National Academy of Sciences, Washington, D.C. Östlund, H. G., M. O. Rinkel, and C. G. Rooth (1969). Tritium in the equatorial Atlantic current system, J. Geophys. Res. 74, 4535. Östlund, H. G., H. G. Dorsey, and C. G. Rooth (1974). GEOSECS North Atlantic radiocarbon and tritium results, Earth Planet. Sci. Lett. 23, 69.

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Studies in Geophysics: Energy and Climate Persson, R., (1976). Forest Resources in Africa, Part II, Regional Analysis, Department of Forest Survey, Royal College of Forestry, Stockholm. Proceedings of the Dahlem Workshop on Global Chemical Cycles and Their Alteration by Man (1977). To be published. Proceedings of the ERDA Workshop on Significant Environmental Concerns, Miami, Fla., March 7–11 (1977). To be published. Proceedings of the SCOPE Workshop on Biogeochemical Cycling of Carbon (1977). To be published. PSAC (1965). President’s Science Advisory Committee. Restoring the Quality of Our Environment, The White House, Washington, D.C., p. 127. Puiseux, L. (1975). World energy consumption and production over the next 50 years, Pugwash Newsletter 12, 3 (Jan.) Revelle, R. R. (1976). The resources available for agriculture, Sci. Am. 235, 164. Sundquist, E., D. K. Richardson, W. S. Broecker, and T. H. Peng (1977). The Fate of Fossil Fuel CO2 in the Ocean, N. R. Anderson and A. Malahoff, eds., Plenum Press, New York. Sverdrup, H. U., M. W. Johnson, and R. H. Fleming (1942). The Oceans, Prentice-Hall, New York. Swedish Royal College of Forestry (1974). Forest Resources in Southeast Asia, Department of Forest Survey, Royal College of Forestry, Stockholm. U.S. Committee for the Global Atmospheric Research Program (1975). Understanding Climatic Change: A Program for Action, National Academy of Sciences, Washington, D.C. U.S. Domestic Council (1974). A United States Climate Program, Environmental Resources Committee, Subcommittee on Climate Change. Waggoner, P. E. (1969). Environmental manipulation for higher yields, in Physiological Aspects of Crop Yield, Am. Soc. Agron. and CSSA, Madison, Wisconsin. Weinberg, A. M., and R. P. Hammond (1972). Global effects of increased use of energy, in Peaceful Uses of Atomic Energy, Proceedings of the Fourth International Conference on the Peaceful Uses of Atomic Energy, jointly sponsored by the United Nations and the International Atomic Energy Agency (IAEA, Vienna), Vol 1. Whittaker, R. H., and G. E. Likens (1975). The biosphere and man, in Primary Productivity of the Biosphere, H. Lieth and R. H. Whittaker, eds., Springer Verlag, New York. Wilson, C. L., and W. H. Matthews, eds. (1970). Man’s Impact on the Global Environment, Study of Critical Environmental Problems (SCEP), MIT Press, Cambridge, Mass. Woodwell, G. M., and E. V. Pecan (1973). Carbon and the Biosphere, Proceedings of the 24th Brookhaven Symposium on Biology, Technical Information Center, Office of Information Services, USAEC.

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