Intergovernmental Panel on Climate Change (IPCC ... - ipcc-wg3

More documents

Recommendations

Info

292 IPCC Special Report on Carbon dioxide Capture and Storage variety of ways. These different ways of reporting result in very different numerical values (Box 6.3). Over several centuries, CO 2 released to the deep ocean would be transported to the ocean surface and interact with the atmosphere. The CO 2 -enriched water would then exchange CO 2 with the atmosphere as it approaches chemical equilibrium. In this chemical equilibrium, most of the injected CO 2 remains in the ocean even though it is no longer isolated from the atmosphere (Table 6.1; Figure 6.3). CO 2 that has interacted with the atmosphere is considered to be part of the natural carbon cycle, much in the way that CO 2 released directly to the atmosphere is considered to be part of the natural carbon cycle. Such CO 2 cannot be considered to be isolated from the atmosphere in a way that can be attributable to an ocean storage project. Loss of isolation of injected CO 2 does not mean loss of all of the injected CO 2 to the atmosphere. In chemical equilibrium with an atmosphere containing 280 ppm CO 2 , about 85% of any carbon injected would remain the ocean. If atmospheric CO 2 partial pressures were to approach 1000 ppm, about 66% of the injected CO 2 would remain in the ocean after equilibration with the atmosphere (Table 6.1). Thus, roughly 1/5 to 1/3 of the CO 2 injected into the ocean will eventually reside in the atmosphere, with this airborne fraction depending on the long-term atmosphere-ocean CO 2 equilibrium (Kheshgi, 1995, 2004b). The airborne fraction is the appropriate measure to quantify the effect of ocean storage on atmospheric composition. 6.3.3 Estimation of fraction retained from ocean observations Observations of radiocarbon, CFCs, and other tracers indicate the degree of isolation of the deep sea from the atmosphere (Prentice et al., 2001). Radiocarbon is absorbed by the oceans from the atmosphere and is transported to the deep-sea, undergoing radioactive decay as it ages. Radiocarbon age (Figure 6.16) is not a perfect indicator of time since a water parcel last contacted the atmosphere because of incomplete equilibration with the atmosphere (Orr, 2004). Taking this partial equilibration into account, the age of North Pacific deep water is estimated to be in the range of 700 to 1000 years. Other basins, such as the North Atlantic, have characteristic overturning times of 300 years or more. This data suggests that, generally, carbon injected in the deep ocean would equilibrate with the atmosphere over a time scale of 300 to 1000 years. 6.3.4 Estimation of fraction retained from model results Ocean models have been used to predict the isolation of injected CO 2 from the atmosphere. Many models are calibrated using ocean radiocarbon data, so model-based estimates of retention of injected CO 2 are not completely independent of the estimates based more directly on observations (Section 6.3.3). A wide number of studies have used three-dimensional ocean general circulation models to study retention of CO 2 injected into the ocean water column (Bacastow and Stegen, 1991; Bacastow et al., 1997; Nakashiki and Ohsumi, 1997; Dewey et al., 1997, 1999; Archer et al., 1998; Xu et al., 1999; Orr, 2004; Hill et al., 2004). These modelling studies generally confirm inferences based on simpler models and considerations of ocean chemistry and radiocarbon decay rates. In ocean general circulation simulations performed by seven modelling groups (Orr, 2004), CO 2 was injected for 100 years at each of seven different locations and at three different depths. Model results indicate that deeper injections will be isolated from the atmosphere for longer durations. Figure 6.17 shows the effect of injection depth on retained fraction for the mean of seven ocean sites (Orr, 2004). Ranges of model results indicate some uncertainty in forecasts of isolation of CO 2 released to the deep ocean, although for all models the time extent of CO 2 isolation is longer for deeper CO 2 release, and isolation is nearly complete for 100 years following CO 2 release at 3000 m depth (Figure 6.18 and 6.19). However, present-day models disagree as to the degassing time scale for particular locations (Figure 6.19). There seems to be no simple and robust correlation of CO 2 retention other than depth of injection (Caldeira et al., 2002), however, there is some indication that the mean fraction retained for stored carbon is greater in the Pacific Ocean than the Atlantic Ocean, but not all models agree on this. Model results indicate that for injection at 1500 m depth, the time scale of the partial CO 2 degassing is sensitive to the location of the injection, but at 3000 m, results are relatively insensitive to injection location. Model results have been found to be sensitive to differences in numerical schemes and model parameterizations (Mignone et al., 2004). 6.4 Site selection 6.4.1 Background Figure 6.16 Map of radiocarbon ( 14 C) age at 3500 m (Matsumoto and Key, 2004). There are no published papers specifically on site selection for intentional ocean storage of CO 2 ; hence, we can discuss only general factors that might be considered when selecting sites for
Chapter 6: Ocean storage 293 Box 6.3 Measures of the fraction of CO 2 retained in storage Different measures have been used to describe how effective intentional storage of carbon dioxide in the ocean is to mitigate climate change (Mueller et al., 2004). Here, we illustrate several of these measures using schematic model results reported by Herzog et al. (2003) for injection of CO 2 at three different depths (Figure 6.17). Fraction retained (see Chapter 1) is the fraction of the cumulative amount of injected CO 2 that is retained in the storage reservoir over a specified period of time, and thereby does not have the opportunity to affect atmospheric CO 2 concentration (Mignone et al., 2004). The retained fraction approaches zero (Figure 6.17) over long times, indicating that nearly all injected CO 2 will interact with the atmosphere (although a small amount would interact first with carbonate sediments). Airborne Fraction is the fraction of released CO 2 that adds to atmospheric CO 2 content (Kheshgi and Archer, 2004). For atmospheric release, airborne fraction is initially one and decays to roughly 0.2 (depending on atmospheric CO 2 concentration) as the added CO 2 is mixed throughout the ocean, and decays further to about 0.08 as CO 2 reacts with sediments (Archer et al., 1997). For deep-sea release, airborne fraction is initially zero and then approaches that of atmospheric release. Note that the asymptotic airborne fraction depends on the concentration of CO 2 of surface waters (Figure 6.3). Fraction retained is used throughout this report to indicate how long the CO 2 is stored. In addition the following measures can be used to compare the effectiveness of ocean carbon storage with other options, for example: • The Net Present Value (NPV) approach (Herzog et al., 2003) considers temporary storage to be equivalent to delayed emission of CO 2 to the atmosphere. The value of delaying CO 2 emissions depends on the future costs of CO 2 emission and economic discount rates. There is economic value to temporary storage (i.e., delayed emission) if the cost of CO 2 emissions increases at a rate that is less than the discount rate (Herzog et al., 2003). • The Global-Warming Potential (GWP) is a measure defined by the IPCC to compare the climatic effect of different greenhousegas emissions. It is computed by accumulating the radiative climate forcing of a greenhouse-gas emission over a specified time horizon. This measure has been applied to compare the radiative forcing from oceanic and atmospheric releases of carbon dioxide (Kheshgi et al., 1994, Ramaswamy et al., 2001). Haugan and Joos (2004) propose a modification to the GWP approach that compares the climate effects of the airborne fraction of a CO 2 release to the ocean with those from a release to the atmosphere. Table 6.2 compares these measures for results from a schematic model at three depths. Figure 6.17 Fraction of carbon in the ocean from injection at three different depths and the atmosphere illustrated with results from a schematic model (Herzog et al., 2003). Calculations assume a background 280 ppm of CO 2 in the atmosphere. Table 6.2 Evaluation of measures described in the text illustrated using schematic model results shown in Figure 6.17. For the Net Present Value measure, the percentage represents the discount rate minus the rate of increase in the cost of CO 2 emission. (If these are equal, the Net Present Value of temporary carbon storage is zero) Two significant digits shown for illustration exceed the accuracy of model results. Measure Atmospheric release Injection depth 1000 m 2000 m 3000 m Effective at 20 years 0 0.96 1.00 1.00 Retained at 100 years 0 0.63 0.97 1.00 Fraction at 500 years 0 0.28 0.65 0.85 Airborne at 20 years 0.61 0.03 6×10 -6 7×10 -10 Fraction at 100 years 0.40 0.19 0.02 9×10 -4 at 500 years 0.24 0.20 0.12 0.06 Net Present 5% per year 0 0.95 1.00 1.00 Value (constant 1% per year 0 0.72 0.95 0.99 emissions cost) 0.2% per year 0 0.41 0.72 0.85 Global 20 year horizon 1 0.01 1×10 -6 6×10 -10 Warming 100 year horizon 1 0.21 0.01 4×10 -4 Potential 500 year horizon 1 0.56 0.20 0.06
Page 1:
CARBON DIOXIDE CAPTURE AND STORAGE
Page 5 and 6:
IPCC Special Report on Carbon Dioxi
Page 7:
Contents Foreword Preface .........
Page 10 and 11:
viii IPCC Special Report on Carbon
Page 12 and 13:
IPCC Special Report on Carbon dioxi
Page 14 and 15:
Summary for Policymakers Contents W
Page 16 and 17:
Summary for Policymakers Figure SPM
Page 18 and 19:
Summary for Policymakers Figure SPM
Page 20 and 21:
Summary for Policymakers 10. Indust
Page 22 and 23:
10 Summary for Policymakers emissio
Page 24 and 25:
12 Summary for Policymakers 18. Ava
Page 26 and 27:
14 Summary for Policymakers for use
Page 28 and 29:
16 Summary for Policymakers
Page 30 and 31:
18 Technical Summary Contents 1. In
Page 32 and 33:
20 Technical Summary Figure TS.1. S
Page 34 and 35:
22 Technical Summary Major issues f
Page 36 and 37:
24 Technical Summary Figure TS.2b.
Page 38 and 39:
26 Technical Summary Figure TS.3. O
Page 40 and 41:
28 Technical Summary Table TS.3. Su
Page 42 and 43:
30 Technical Summary In some situat
Page 44 and 45:
32 Technical Summary Figure TS.7. M
Page 46 and 47:
34 Technical Summary Table TS.6. St
Page 48 and 49:
36 Technical Summary leakage of CO
Page 50 and 51:
38 Technical Summary There is no pr
Page 52 and 53:
40 Technical Summary Figure TS.10.
Page 54 and 55:
42 Technical Summary Table TS.9. 20
Page 56 and 57:
44 Technical Summary Reference Plan
Page 58 and 59:
46 Technical Summary For CO 2 stabi
Page 60 and 61:
48 Technical Summary detecting the
Page 62 and 63:
50 Technical Summary
Page 64 and 65:
52 IPCC Special Report on Carbon di
Page 66 and 67:
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
Page 86 and 87:
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
100 IPCC Special Report on Carbon d
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120 and 121:
Page 122 and 123:
Page 124 and 125:
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Page 154 and 155:
Page 156 and 157:
Page 158 and 159:
Page 160 and 161:
Page 162 and 163:
Page 164 and 165:
Page 166 and 167:
Page 168 and 169:
Page 170 and 171:
Page 172 and 173:
Page 174 and 175:
Page 176 and 177:
Page 178 and 179:
Page 180 and 181:
Page 182 and 183:
Page 184 and 185:
Page 186 and 187:
Page 188 and 189:
Page 190 and 191:
Page 192 and 193:
Page 194 and 195:
Page 196 and 197:
Page 198 and 199:
Page 200 and 201:
Page 202 and 203:
Page 204 and 205:
Page 206 and 207:
Page 208 and 209:
Page 210 and 211:
Page 212 and 213:
Page 214 and 215:
Page 216 and 217:
Page 218 and 219:
Page 220 and 221:
Page 222 and 223:
Page 224 and 225:
Page 226 and 227:
Page 228 and 229:
Page 230 and 231:
Page 232 and 233:
Page 234 and 235:
Page 236 and 237:
Page 238 and 239:
Page 240 and 241:
Page 242 and 243:
Page 244 and 245:
Page 246 and 247:
Page 248 and 249:
Page 250 and 251:
Page 252 and 253:
Page 254 and 255: 242 IPCC Special Report on Carbon d
Page 354 and 355:
Page 356 and 357:
Page 358 and 359:
Page 360 and 361:
Page 362 and 363:
Page 364 and 365:
Page 366 and 367:
Page 368 and 369:
Page 370 and 371:
Page 372 and 373:
Page 374 and 375:
Page 376 and 377:
Page 378 and 379:
Page 380 and 381:
fig 9-1 368 IPCC Special Report on
Page 382 and 383:
Page 384 and 385:
Page 386 and 387:
Page 388 and 389:
Page 390 and 391:
Page 392 and 393:
Page 394 and 395:
Page 396 and 397:
Page 398 and 399:
Page 400 and 401:
Page 402 and 403:
Page 404 and 405:
Page 406 and 407:
Page 408 and 409:
Page 410 and 411:
Page 412 and 413:
Page 414 and 415:
Page 416 and 417:
Page 418 and 419:
Page 420 and 421:
Page 422 and 423:
Page 424 and 425:
Page 426 and 427:
Page 428 and 429:
Page 430 and 431:
Page 432 and 433:
Page 434 and 435:
Page 436 and 437:
Page 438 and 439:
Page 440 and 441:
Page 442 and 443:
show all

Intergovernmental Panel on Climate Change (IPCC ... - ipcc-wg3

Create successful ePaper yourself

Delete template?

Save as template?