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## Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base (1992) Committee on Science, Engineering, and Public Policy (COSEPUP)

### Citation Manager

. "Q Geoengineering Options." Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base. Washington, DC: The National Academies Press, 1992.

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### Appendix Q Geoengineering Options

This appendix is divided into four sections: (1) naval rifle system, (2)- balloon system, (3) multiple balloon system, (4) changing cloud abundance. Each section either describes the system or indicates how the costs were computed.

#### Naval Rifle System

The current cost of a naval projectile weighing 1900 pounds (lb) is \$7000 to \$8000. The cost of propellant alone (if the shell is furnished) is \$900. It seems that a reasonable estimate for a 1-t shell, dust (commercial aluminum oxide can be obtained for \$0.25/lb), and a propellant for each shot is \$10,000. An efficiency of one-half is assumed: one-half of the shell is dust, and the other half consists of the packaging, dispersal mechanisms, and so on, necessary to make the shell function. Thus the cost of the ammunition for 40 years will be

The number of shots required in the 40 years is

If a single rifle can fire 5 shots per hour (naval rifles can fire faster than this, but cooling intervals between shots can lengthen the barrel life) and the rifle operates 250 working days per year, then a rifle can fire 5 shots/hour × 24 hours/day × 250 days/yr = 3 × 104 shots/yr per rifle.

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 Front Matter (R1-R26) Part One: Synthesis (1-2) 1 Introduction (3-4) 2 Background (5-11) 3 The Greenhouse Gases and Their Effects (12-28) 4 Policy Framework (29-35) 5 Adaptation (36-47) 6 Mitigation (48-64) 7 International Considerations (65-67) 8 Findings and Conclusions (68-72) 9 Recommendations (73-83) Individual Statement by a Member Of The Synthesis Panel (84-86) Part Two: The Science Base (87-88) 10 Introduction (89-90) 11 Emission Rates and Concentrations Of Greenhouse Gases (91-99) 12 Radiative Forcing and Feedback (100-110) 13 Model Performance (111-116) 14 The Climate Record (117-134) 15 Hydrology (135-139) 16 Sea Level (140-144) 17 A Greenhouse Forcing and Temperature Rise Estimation Procedure (145-152) 18 Conclusions (153-154) Part Three: Mitigation (155-156) 19 Introduction (157-170) 20 Framework for Evaluating Mitigation Options (171-200) 21 Residential and Commercial Energy Management (201-247) 22 Industrial Energy Management (248-285) 23 Transportation Energy Management (286-329) 24 Energy Supply Systems (330-375) 25 Nonenergy Emission Reduction (376-413) 26 Population (414-423) 27 Deforestation (424-432) 28 Geoengineering (433-464) 29 Findings and Recommendations (465-498) Part Four: Adaptation (499-500) 30 Findings (501-507) 31 Recommendations (508-514) 32 Issues, Assumptions, and Values (515-524) 33 Methods and Tools (525-540) 34 Sesitivities, Impacts, and Adaptations (541-652) 35 Indices (653-656) 36 Final Words (657-658) Individual Statement by a Member of the Adaptation Panel (659-660) Appendixes (661-662) A Questions and Answers About Greenhouse Warming (663-691) B Thinking About Time in the Context of Global Climate Change (692-707) C Conservation Supply Curves for Buildings (708-716) D Conservation Supply Curves for Industrial Energy Use (717-726) E Conservation Supply Data for Three Transportation Sectors (727-758) F Transportation System Management (759-766) G Nuclear Energy (767-774) H A Solar Hydrogen System (775-778) I Biomass (779-785) J Cost-Effectiveness of Electrical Generation Technologies (786-791) K Cost-Effectiveness of Chlorofluorocarbon PhaseoutÂ—United States and Worldwide (792-797) L Agriculture (798-807) M Landfill Methane Reduction (808-808) N Population Growth and Greenhouse Gas Emissions (809-811) O Deforestation Prevention (812-813) P Reforestation (814-816) Q Geoengineering Options (817-835) R Description of Economic Estimates of the Cost of Reducing Greenhouse Emissions (836-839) S Glossary (840-846) T Conversion Tables (847-848) U Prefaces from the Individual Panel Reports (849-854) V Acknowledgments from the Individual Panel Reports (855-857) W Background Information on Panel Members and Professional Staff (858-868) Index (869-918)

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Page 817 Appendix Q Geoengineering Options This appendix is divided into four sections: (1) naval rifle system, (2)- balloon system, (3) multiple balloon system, (4) changing cloud abundance. Each section either describes the system or indicates how the costs were computed. Naval Rifle System The current cost of a naval projectile weighing 1900 pounds (lb) is \$7000 to \$8000. The cost of propellant alone (if the shell is furnished) is \$900. It seems that a reasonable estimate for a 1-t shell, dust (commercial aluminum oxide can be obtained for \$0.25/lb), and a propellant for each shot is \$10,000. An efficiency of one-half is assumed: one-half of the shell is dust, and the other half consists of the packaging, dispersal mechanisms, and so on, necessary to make the shell function. Thus the cost of the ammunition for 40 years will be The number of shots required in the 40 years is If a single rifle can fire 5 shots per hour (naval rifles can fire faster than this, but cooling intervals between shots can lengthen the barrel life) and the rifle operates 250 working days per year, then a rifle can fire 5 shots/hour × 24 hours/day × 250 days/yr = 3 × 104 shots/yr per rifle.

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Page 818 Thus are required. Therefore, operating inventory of 4 × 102 riflescan be assumedat any time. A gun barrel will have to be replaced approximately every 1500 shots; thus over the 40 years, will be needed. A gun barrel probably would cost (in continuous production several hundred thousand dollars—say a million dollars. The total cost of rifle barrels is thus3 × 105 barrels × 106 \$/barrel = \$3 ×1011 for barrels. If the rifles are organized into 10-barrel stations, on land or at sea, and a billion dollars is allocated for the capital cost of each station, one might expect to buy 40 10-barrel stations to keep 350 barrels operating at a time, thus giving a cost for stations of 40 stations × 109 \$/station = \$4 × 1010. This should probably be doubled, at least; to allow for overhead, power, maintenance, replacement, and so on. Multiplying by 5 gives \$2 × 1011 for stations. Finally, people are needed to operate the system. Although the system would probably be highly automated, assume that it will work like current operations. Then allocate 10 people/barrel × 4 × 102 barrels × 3 shifts × \$105/person/yr × 40 years = \$48 × 109 \$5 × 1010, which can be doubled to include indirect personnel, overhead, and so on, giving \$1011 for operators. Therefore, 24,000 people are assumed to be involved at any time. To sum up, Ammunition \$4 × 1012 = 4.0 × 1012 Rifle barrels \$3 × 1011 = 0.3 × 1012 Stations \$2 × 1011 = 0.2 × 1012 People \$1 × 1011 = 0.1 × 1012   TOTAL \$4.6 × 1012 \$5 × 1012 for 40 years, giving an annual undiscounted cost of \$50/40 × 1011 = \$100billion.

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Page 819 Clearly, the cost of the project is dominated by ammunition, and the number of stations and rifles is reasonable, as is the amount of activity, considered on a large industrial scale. The rifles could be deployed at sea or in empty areas (e.g., military reservations) where the noise of the shots and the fallback of expended shells could be managed. Balloon System Consider a hydrogen balloon floating at 20 km, using the Archimedes principle and noting that the density of hydrogen-gas is one-fourteenth that of air: md(isplaced) = mg(as inside balloon) + mb(alloon) + mp(ayload) 4/3pr3ro=4/3pr31/14ro + 4pr2Drrs(kin) + mp mp=4/3pr3ro13/14-4pr2Drrs =4pr3[13/(3x14)ro-(Dr/)/rs] If r = 100 m (radius of balloon) ro = 88 g/m3 = 8.8 × 10-2 kg/m3 (density of air at 20 km) Dr = 1 mm = 10-3 m (thickness of balloon skin) ro = 1.15 g/cm3 (nylon) × 10-3 kg/g × [102 cm/m]3 = 1.15 × 103 kg/m3. Then mp = 1.26 × 107 (2.7 × 10-2 - 1.15 × 10-2) = 1.26 × 105 (1.55) = 1.95 × 105 2 × 105 kg. The mass of the balloon for a 1-mm thickness is 4pr2Drr = 12.6 × 104 × 10-3 × 1.15 × 103 = 1.26 × 1.15 × 105 × 10-3 × 103 kg = 1.5 × 105 kg. If the balloon is 2/3-mm-thick (assumed for convenience), its mass from the previous computation is 1.5 × 105 kg and the mass of dust lifted, if a 50 percent efficiency factor is used to account for instruments, dust dispenser, container, and so on (this is conservative), is 105 kg. Nylon of the appropriate gauge for weaving into a 2/3-mm-thick fabric (1050 denier is about 0.3 mm) costs \$2/lb = \$4.4/kg. If this is tripled for fabric and balloon manufacture

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Page 820 (the cost of parachute fabric is about 3 times the cost of the yarn, based on information from a colleague at Du Pont Industrial Fabrics), cost of controls, dust dispensing, and so on, \$15/kg can be estimated or 1.5 × 105 kg/balloon × \$15/kg = 2.25 × 106 \$/balloon. Twenty lifts are necessary in 40 years: 2 × 106 balloons × 2.25 × 106\$/balloon = \$4.25 × 1012. Consider the additional costs of infrastructure and support: there will be 2 × 106 lifts in 40 years or If there are 100 crews (each responsible for 2 lifts per day on 250 days a year) and each crew has 100 people, 104 people × 105 \$/person/yr × 40 years = \$4 × 1010 \$1011 with an overhead of 150%. If each station is capitalized at \$109, another \$1011 is required, but this infrastructure barely affects costs, as does the cost of dust even at \$0.50/kg or hydrogen at \$10/kg. Hydrogen can currently be purchased as liquid hydrogen in 1500-gallon lots (equivalent to 169,000 standard cubic feet) for \$2.5/100 ft3. For conversion, 1 kg of hydrogen = 432.3 standard cubic feet. Thus the cost is In quantities of 100 × 106 ft3/day, Ogden and Williams (1989) quote costs lower than \$30/GJ. This is Each balloon has a mass of 4.2 × 106 m3 × 1/14 × 8.8 × 10-2 kg/m3 = 2.6 × 104 kg of hydrogen. At 5 × 104 balloon lifts per year, the annual quantity is 13.2 × 108 kg 109 kg = 423 × 109 ft3 109 ft3/day = 102 × 106 ft3/day.

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Page 821 The total mass of hydrogen required for 40 years is 2.6 × 104 kg/balloon × 2 × 106 balloons = 5.2 × 1010 kg. At \$10/kg, this costs \$5.2 × 1011 = \$0.52 × 1012. [Design note: The breaking strength of 1200 denier ( 0.4 mm) nylon is over 25 lb (Du Pont, 1988). The equatorial circumference of the balloon is 2pr = 6.3 × 102 m × 103 mm/m = 6.3 × 105 mm; therefore, the payload will be suspended from a double (actually 2.5) set of nylon strings 0.4 mm in diameter: 6.3 × 105 mm × [25 lb/(2.2 lb/kg)] × 2 = 142 × 105 kg. Because the payload weighs 1.18 × 105 kg, the safety factor = 121 times!] By using hydrogen at \$10/kg, costs may be summarized as Balloons \$4.25 × 1012 Infrastructure and personnel \$0.10 × 1012 Capital for launch stations \$0.10 × 1012 Hydrogen \$0.52 × 1012   TOTAL \$4.97 × 1012     \$5 × 1012. This mitigates 1012 t of carbon or 4 × 1012 t of CO2. An undiscounted cost the same as that for the naval rifle system is obtained: \$5/t C = \$1.25/t CO2 \$5/40/t C/yr = \$0.125/t C/yr = \$0.03/t CO2/yr. All of the above material assumes no reuse of balloons, and no allowance is made for the automation of launch, and so on. The possibility of some reuse, and of automation, probably reduces the total cost. If not controlled to land for reuse, balloons could be "chased" and controlled to land for collection and disposal, or to land in the deep ocean and sink promptly. Consider hot air balloons. Again by using the Archimedes principle, mdisplaced = mgas + mballoon + mpayload Vro = Vri + mballoon + mpayload Using the perfect gas law piVi = miRTi pi = RriTi poVo = moRTo po = RroTo where m = mass, V = volume, po = outside pressure, pi = inside pressure, ro = density of air outside, and ri = density of gas inside. At floating equilibrium,po=pri, because the balloon is limp. Therefore,

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Page 822 If r and dr are expressed in meters, and roand rs are in each r must be multiplied by 1/10-3 = 103: mp = 12.6 × 103 r3 { (ro/3)[(Ti - To)/Ti] - (Dr/r)rs} = 1.26 × 104 r3 { (ro/3)[(Ti - To)/Ti] - (Dr/r)rs} where r (specific gravity) is expressed in grams per cubic centimeter, r in meters, and mp in kilograms. At 20 km, ro = (88 g/m3)(102 cm/m)3 = 88 × 10-6 g/cm3 for To = -58.5°C = 217 K (Kelvin) Ti = 104°C = 377 K (Kelvin) r = 102 m Dr = 1 mm r s = 1.15 = 1.26 × 1010 (1.23 × 10-5 - 1.15 × 10-5) = 0.1 × 105 kg = 104 kg. If 2/3-mm nylon is used, mp = 6 ×4 kg. Thus the costs of a hot air balloon system can be expected to be at least 4 to 10 times higher than the cost of a hydrogen balloon system. These costs

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Page 823 could be decreased by running the balloon at higher temperature, but to get 105 kg of payload per balloon with 1-mm nylon a temperature of 658 K (385°C) is required, and with 2/3-mm nylon 475 K (202°C), which seems difficult to manage. The breaking strength of nylon goes to zero percent of its room temperature value by 250°C. While the skin temperature of a hot air balloon is well below the core gas temperature, the management of temperature to guarantee skin strength with so large a differential between average and skin temperature seems rather difficult, although the skin might be insulated as some weight penalty. The results are sensitive to the factors. Hot air balloons seem to be nearly competitive with hydrogen balloons. This question would have to be explored further before choices between hydrogen and hot air systems could finally be made. Multiple Balloon System The mass of a bubble filled with hydrogen is one-fourteenth the mass of the air displaced. The total mass of the hydrogen-filled balloon will be (at any altitude) At floating equilibrium, we have 1/14·4/3pr3ra=4pr2Drrs=4/3pr3ra Drrs=13/14rra Drrs=13/3x14rra=3x10-1 rra If plastic with density of 1 g/cm3 and a skin thickness of Dr = 10-1 mm = 10-4 m = 10-2 cm (which is plausible) is used, then At 19 km = 12 miles 62,000 feet, ra 10-4 and r3x10-2/10-4=300cm=3. Such a balloon has a disk area of pr2 = 9p = 28 m2 = 3 × 10 m2. Thus, 5x1012/3x10 2x1011 = 200x109 balloons of 3 -m radius

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Page 824 are required. If the balloon is 10-mm material, a balloon of 3 × 10-1 m (30-cm) radius is obtained and 20,000 × 109 balloons are needed. Hydrogen will diffuse through the skin of the balloons, which probably means that the system must be refreshed annually. The fall of collapsed balloons might be an annoying form of trash rain. Because the area of the material required for a balloon is 4pr2, the material requirement is of material for any size balloon. At \$0.10/m2 (20 m2 of wrapping plastic can be bought in the supermarket for about \$2), this is \$2 × 1012. Over 40 years, this amounts to \$80 × 1012. It offsets 1012 t of carbon, so the cost is \$80/t C or \$80/40 = \$2/t C/yr or \$0.50/t CO2/yr. A reasonable cost range of \$0.50 to \$5/t CO2/yr can be assumed. Changing Cloud Abundance A study was undertaken to consider the various factors that would be required to increase the albedo effect of global cloud cover sufficiently to balance the temperature increase that is projected to occur with a doubling of CO2. Toward this end, the temperature sensitivity to different (high, middle, and low) cloud layer properties was calculated by using a radiative-convective atmospheric model. In addition, cost estimates have been made. These amelioration processes are reversible and inexpensive. If they were determined to be deleterious or if cost-competitive programs were developed, these measures could be discontinued immediately. At the outset it cannot be emphasized too strongly that there are tremendous uncertainties associated with these intellectual exercises. As a case in point, circumstantial evidence teaches that we have a very limited understanding of the role of cloud abundance because a warming accompanied the measured increase in cloud coverage over the past century. Consequently, a much better understanding of the system is necessary before any large-scale operations could reasonably be proposed. The Climatic Effect of Clouds Earlier, Reck (1978) studied the effect of increases in cloud cover and, using a radiative-convective atmospheric model, found that a 4 to 5 percent increase in low-level cloud cover would be sufficient to offset the warming predicted from a doubling of preindustrial CO2. This value is in reasonable agreement with Randall et al. (1984), who estimated that a 4 percent increase was required in the amount of marine stratocumulus, which comprises the bulk of the low clouds on a global basis. Unfortunately, many

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Page 825 assumptions are contained in these estimates, and to understand those assumptions and the role that clouds could play, cloud sensitivity calculations have been made to illustrate the range of surface temperature for various assumptions of cloud properties. In these calculations, the Mitigation Panel used the assumed abundances and optical properties shown in Table Q.1 and a global surface albedo of 15.4 percent. The model has three layers of clouds under global average conditions. It is assumed that clouds, once formed, will have the same effects over their entire lifetimes and that they will have optical properties identical to those of current low-level clouds, which are assumed to be unchanging during the seeding process. Unfortunately, these assumptions contain many uncertainties. These sensitivity calculations show that the effects of clouds depend not only on the fraction of a given cloud type, but also on the surface albedo beneath the clouds. The special role of the low-level cloud and its varying effect as the surface albedo changes add considerable complication because the surface albedo varies from about 4 to 20 percent over some water to as high as 90 percent over pure snow or ice (Hummel and Reck, 1979). This means that once a cloud is formed it may start with a cooling effect and end up in an area where it could produce either greater or lesser cooling, with the slight possibility of even a heating effect. Albrecht (1989) (see also Twomey and Wojciechowski, 1969) suggests that the average low-cloud reflectivity would increase if the abundance of cloud condensation nuclei (CCN) were to increase through emission of SO2. TABLE Q.1 Assumed Properties of Average Global Clouds   Cloud Type   High Middle Low Cloud Abundances       Fraction of shortwave cloud cover 0.181 0.079 0.302 Fraction of longwave cloud cover 0.181 0.079 0.302 Cloud Optical Properties       Solar albedo of cloud cover 0.21 0.48 0.69 Solar absorptivity of cloud cover 0.005 0.02 0.035 Infrared absorptivity of cloud cover 0.50 1.00 1.00

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Page 826 To test for the sensitivity to this part of the problem, the surface temperature changes with varying optical properties were calculated and are shown in Table Q.2. For comparison purposes the sensitivity of high and middle clouds was also included. Clearly, the estimate depends strongly on the value of assumed low-cloud solar reflectivity. For example, a change of 4 percent in the reflectivity value (low-cloud abundance—see Table Q.2) would be sufficient to cause the calculated surface temperature to change by 3°C. With a sensitivity of this magnitude, clearly a large potential exists for forced changes provided they could be controlled, and provided large regional anomalies and uncontrolled long-distance effects are not created. There is also a height dependence in the radiation field that varies greatly with latitude and altitude (Ramanathan et al., 1987). The cloud fraction variation with latitude is shown in Table Q.3. In the present environment, there is a greater probability of having clouds over water than over land, with more clouds over land in the afternoon and more clouds over water in the morning. This occurs because cloud height and optical properties are intimately related to humidity and physical conditions. For example, the role of a cloud at a given latitude is controlled by the zenith angle of the sun. If the cloud were to move to a more northern latitude, its cooling effect would be expected to diminish in proportion to the change in the cosine of the sun's zenith angle. As can be noted from the cosines listed in Table Q.3, a cloud at 5° latitude could have about twice as large a contribution as the same cloud at 65° latitude. Many less predictable features are also crucial (such as the degree of evaporation). Reck (1978, 1979), using a model based on that of Manabe and Wetherald (1967), has also illustrated cloud height effect. These calculations show heating from high-level clouds and cooling from middle- and lower-level TABLE Q.2 Calculated Surface Temperature Sensitivity to Changes in Cloud Properties   Cloud Type   High Middle Low Sensitivity (°C) per percent change in cloud abundance 0.36 -0.35 -0.66 Sensitivity (°C) per percent change in cloud albedo -0.16 -0.06 -0.35 Sensitivity (°C) per percent change in cloud absorptivity -0.062 0.048 0.045

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Page 827 TABLE Q.3 Latitudinal Variation of Assumed Annual Cloud Cover     Fraction of Cloud Cover Latitude (degrees) Cosine of Zenith Angle Upper Cloud Middle Cloud Lower Cloud 5 0.61 0.225 0.075 0.317 15 0.593 0.181 0.064 0.264 25 0.560 0.160 0.063 0.248 35 0.512 0.181 0.079 0.302 45 0.450 0.210 0.110 0.388 55 0.381 0.242 0.131 0.438 65 0.309 0.254 0.119 0.444 75 0.259 0.252 0.111 0.424 85 0.243 0.205 0.092 0.375 ones. One possible error in the estimates presented here is the assumptionof either a fixed cloud altitude or a fixed cloud temperature. Reck (1979)has shown a greater model sensitivity to a fixed cloud temperature. Mixedbehavior might be observed in the real atmosphere. Clearly with all thepossible heating or cooling effects, the presence of naturally occuring cloudscould complicate the analysis of data obtained to test the role of humanintervention. See, for example, the cloud experiments suggested below. With all the above assumptions in mind, it is proposed both that CCN emissions should be done over the oceans at an altitude that will produce an increase in the stratocumulus cloud albedo only, and that the clouds will remain at the same latitudes over the ocean where the surface albedo is relatively constant and low. As noted in Figure Q.1, an increase in surface albedo, should the cloud float over land, would only enhance its cooling effect. This is true provided the latitude of the cloud does not change, as discussed previously. How Cloud Condensation Nuclei Can Change Climate Despite the lack of knowledge about cloud processes, the possibility of altering clouds has been considered for a long time. The idea of cloud seeding for agricultural purposes became popular in the 1950s and 1960s, but because of the lack of precision and the litigation that resulted, it has not been very succesful (see, for example, Todd and Howell, 1985; and Kerr, 1982). Changes in cloudiness on a regional scale were also proposed some time ago by Russian scientist, who considered decreasing the cloudiness

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Page 828 FIGURE Q.1 Calculated surface temperature variation with changes in low-cloud cover and surface albedo. in the arctic region to promote ice melting and improved growing conditions in Siberia. Before the more recent satellite measurements, most of what was known about cloud processes and how they contribute to the global radiative balance came from climate modeling, and in climate models, most of the details of the cloud processes were not included. Certainly, no individual clouds were included on the grid scale of the general circulation models (GCM); thus specific details of the microphysics, as it might involve seeding or CCN, could not be studied within the concept of GCMs. Proposed Change in Low-Cloud Albedo Through Emissions of Cloud Condensation Nuclei In a recent paper, Albrecht (1989), following a hypothesis of Twomey and Wojciechowski (1969), grossly estimated the additional CCN that would be necessary to increase the fractional cloudiness or albedo of marine stratocumulus clouds by 4 percent. He estimates that this increase in low-level fractional cloudiness would be equivalent to that attributed to a 30 percent increase in CCN. As noted from Table Q.3, this 4 percent increase, if it were strictly in lower-level cloud abundance at global average conditions (35° latitude), would be more or less equivalent to the cloudiness at 4° latitude further north. Albrecht's idealized stratocumulus cloud, which he argues is typical, has a thickness of 375 m, a drizzle rate of 1 mm per day,

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Page 830 420 × 106 oz/yr × 28.35 g/oz × 1 t/106 g = 11.9 × 103 t/yr of Ag, or = 25.5 × 103 t/yr AgI. Clearly there is not enough silver or AgI to consider this experiment. For H2SO4, with a density of 1.841 g/cm3, the total weight to be added per day = 1.841/5.7 × 1.5 × 105 t/day = 48 × 103 t/day H2SO4 = 31 × 103 t/day SO2, if all the SO2 is converted to H2SO4 CCN. To put this number in perspective, a medium-sized coal-fired U.S. power plant emits about this much SO2 in a year; the equivalent emissions of 365 U.S. coal-burning power plants (50 percent of present U.S. SO2 emissions) would produce sufficient CCN. To estimate the value of the sulfur directly, the total weight of SO2 to be added per day is 32 × 103 t or about 16 × 103 t of sulfur, which is equivalent to about 6 megatons (Mt; 1 Mt = 1 million tons) of sulfur per year. Given the average market price of sulfur for 1983–1987 (f.o.b. mine or plant)—\$96.90 (U.S. Bureau of the Census, 1988)—the minimum yearly cost would be at least \$580 × 106/yr. Equating this yearly cost to the 300 parts per million by volume (ppmv) of CO2 necessary for full compensation gives \$580 × 106/(2840 Mt C/ppmv CO2 × 300 ppmv CO2), or about a fraction of a cent per ton of CO2. To obtain an equivalence to conserved carbon, known emissions of carbon in 1978, 1979, and 1980 have been compared with the total measured increase of CO2 to obtain the equivalence: 3890 Mt C 1 ppmv CO2. A 4 percent increase in cloudiness was then equated to a 300-ppmv CO2 decrease, which translates into a reduction of 1200 gigatons (Gt; 1 Gt = 1 billion tons) of carbon, or 4400 Gt of CO2. The primary cost of this process involves the mechanism for distributing SO2 in the atmosphere at the correct location. Assume a fleet of ships each carrying sulfur and a suitable incinerator. The ships are dedicated to roaming the subtropical Pacific and Atlantic oceans far upwind of land while they burn sulfur. They are vectored on paths to cloud-covered areas by a control center that uses weather satellite data to plan the campaign. In addition to choosing areas that contain clouds, it is important to distribute the ships and their burning pattern so as not to create major regional changes, or the kind of change with a time or space pattern likely to force unwanted wave patterns. These restrictions (which we may not know how to define) could be a difficult problem for such a system to solve. From the above, 16 × 103 t/day, or 6 Mt/yr of sulfur must be burned. If 102 t per ship per day are allocated, and a ship stays out 300 days each year, roughly 200 ships of 10,000-ton capacity are needed (one reprovisioning stop every 150 days). At a cost of \$100 × 106 per ship (surely generous),

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Page 831 the capital cost of the fleet is \$2 × 1010. Amortized over 20 years, an annual capital cost of \$1 × 109 may be used. The sulfur will cost another \$0.6 × 109 per year, and \$2 × 106 per ship per year may be allocated for operating costs (\$10,000 per operating day), to give a total cost of \$2 × 109 annually. Over 40 years (until 2030) this means \$8 × 1010, or \$1011. This continuously mitigates ˜103 Gt = 1012 t for a cost of \$0.10/t of CO2. Of course, this continues to be a yearly cost of \$1 × 109/yr. The SO2 could also be emitted from power plants. These plants could be built in the Pacific Ocean near the equator (hopefully on small deserted islands) and would serve to furnish power for nearby locations (e.g., South America). Transmission or use of the power in the form of refined materials could be considered, or possibly the use of superconducting power transmission systems. It is estimated that eight large power plants using spiked coal would be required (with 4 times the normal amount of sulfur) at a cost of \$2 to \$2.5 × 106 per plant. Most of the cost would be borne by those buying the power, so the cost might be at most 10 percent per year (the interest on the investment), or a total of \$2 × 109 per year (with the above conversion, \$2 × 109/3890 × 106 \$0.0005/t CO2). Comparison of the Cloudiness and Proposed Cloud Condensation Nuclei Emissions with Current Estimates in the Real Atmospher Total U.S. SO2 emissions are 65.7 × 103 t per day, which is roughly 2 times the amount calculated in the previous paragraph. Consequently, there should already be some cloud-enhancing effects evident in the northern hemisphere if Twomey and Wojciechowski's hypothesis, as implemented by Albrecht, is correct. An examination of available CCN data shows that the mean CCN concentration at oceanic locations in the northern Atlantic is about 5 times higher than at remote locations in the southern Pacific (see Schwartz (1988), who, however, concludes that there is no discernible contribution of anthropogenic SO2 emissions to the global cloud cover effect on planetary albedo or temperature). Furthermore, several studies have examined trends in cloudiness in the northern hemisphere and have all come to the same conclusion: The total cloud amount has been increasing in the northern hemisphere (study areas include United States, North America, the North Atlantic, and Europe) since the early 1900s (Henderson-Sellers, 1986, 1989; Changnon, 1981; Angell et al., 1984; Warren et al., 1988). The largest increases in cloudiness in the United States occurred from the 1930s to about 1950 and from the mid-1960s to about 1980. The first period corresponds to a period of rapid growth of U.S. SO2 emissions after the Depression and extends to the end of World War II; the second period corresponds to the proliferation of tall stacks. From 1965 to 1980 the mean effective stack height (physical height of stack plus plume rise) of SO2

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