The Technology of Two Degrees

Transcription

1 The Technology of Two Degrees Jae Edmonds and Steven J. Smith Pacific Northwest National Laboratory, Joint Global Change Research Institute, at the University of Maryland, College Park, MD Abstract This paper examines the technology implications of limiting the change in mean global surface temperature (GMST) to two degrees Celsius (2 o C) relative to preindustrial temperatures. Understanding the implications of this goal is clouded by uncertainty in key physical science parameters, particularly the climate sensitivity. If the climate sensitivity is 2.5 o C then stabilization implies stabilization of CO 2 concentrations at less than 500 parts per million (ppm) with a peak in global CO 2 emissions occurring in the next 15 years and with a decline in emissions to 3.1 petagrams of carbon per year (PgC/y) by Under such circumstances the value of technology improvements beyond those assumed in the reference case is found to be exceptionally high, denominated in trillions of 1990 USD. The role of non-co 2 greenhouse gases is important. Aerosols could produce significant feedbacks, though uncertainty is significant. If the climate sensitivity is 3.5 o C or greater, it may be impossible to hold GMST change below 2 o C. On the other hand if the climate sensitivity is 1.5 o C, limiting GMST change to 2 o C may be a trivial matter requiring little deviation from a reference emissions path until after the middle of the 21 st century.

2 Introduction The European Union has set as its goal, limiting the change in global mean surface temperature (GMST) to two degrees Celsius (2 o C) relative to preindustrial. This paper makes no attempt to assess the merits of this goal. The purpose of this paper is to ask, what are the implications for energy technology of establishing such a goal? And what implications do energy technologies have for the economic cost of pursuing this goal? This paper utilizes an integrated assessment model, MiniCAM, to examine the implications for energy technology of limiting climate change to 2 o C. The MiniCAM is an integrated assessment model that considers the sources of emissions of a suite of greenhouse gases 1 (GHG's), emitted in 14 globally disaggregated regions 2, the fate of emissions to the atmosphere, and the consequences of changing concentrations of greenhouse related gases for climate change 3. The MiniCAM begins with a representation of demographic and economic developments in each of the 14 regions and combines these with assumptions about technology development to describe an internally consistent representation of energy, agriculture, land-use, and economic developments that in turn shape global emissions and concentrations of GHGs. GHG concentrations in turn determine radiative forcing and climate change. The MiniCAM was one of the models employed to develop the IPCC emissions scenarios described in the Special Report on Emissions Scenarios (SRES) [4]. In this paper we update the MiniCAM B2 scenario contained in [4] 1 MiniCAM tracks emissions of 15 greenhouse related gases: CO 2, CH 4, N 2 O, NO x, VOCs, CO, SO2, carbonaceous aerosols, HFCs, PFCs, and SF 6. Each is associated with multiple human activities that are tracked in MiniCAM. 2 The United States, Canada, Latin America, Western Europe, Eastern Europe, the Former Soviet Union, the Mideast, Africa, India, China, Other South and East Asia, Australia and New Zealand, Japan and Korea. 3 The equation structure of the MiniCAM model is described in [1]. Its energy-economy roots can be traced back to [2]. The model has been continuously revised and updated to include an expanded set of processes, such as endogenous agriculture and land-use determination, which is in turn linked to changes in natural system stocks and transient emissions fluxes. Its natural system representation utilizes MAGICC, which has its origins in [3].

3 to include a number of model enhancements[smith et al. 2005], and the inclusion of a full suite of greenhouse gases, aerosols, and criteria air pollutants [Smith and Wigley 2005]. Briefly, the reference case is one in which global population grows to 9 billion people by the year 2050 and reaches 9.5 billion by the year Global GDP increases from 30 trillion 2002 USD in 1990 to more than 250 trillion USD 4 in the year The global energy system increases in scale from about 375 exajoules per year (EJ/y) in 1990 to more than 1200 EJ/y by Fossil fuel CO 2 emissions increase from approximately 6 PgC/y in 1990 to approximately 20 PgC/y in Emissions of other CO 2 from industrial applications increase steadily throughout the century. Emissions of high GWP gases also increase significantly on a percentage basis. Other gases such as CH 4 and N 2 O increase during the first half of the century but exhibit limited growth thereafter. Emissions of carbonaceous aerosols and sulfur dioxide decline over the course of the scenario. Reference case emissions trajectories for anthropogenic greenhouse related gases, concentrations for CO 2, CH 4, and N 2 O, and GMST are recorded in Figure 1, panels A, B, and C respectively. Non-CO2 Tgas/year 1,200 1, Panel A: Reference Case Emissions for Five Gases, CO2 (Right Axis) and CO, CH4, VOCs, and NOx (Left Axis) VOC CO CH4 CO CO2 TgC/yr CH4 NOx VOC CO2 NOx ,000 20,000 15,000 10,000 5,000 CO2 T C/year ppb Panel B: Reference Case Concentrations of CO2, CH4, and N2O CH4Conc N2OConc CO2Conc CO2 ppm degrees C Panel C: Reference Case Global Mean Temperature Change Relative to Pre-industrial Figure 1: Reference Case Emissions (Panel A), Concentrations of CO 2, CH 4, and N 2 O (Panel B) and GMST for a Climate Sensitivity of 2.5 o C (Panel C). 4 Measured using purchasing power parity exchange rates.

4 The Technology of the Reference Case Technology assumptions play a central role in shaping emissions. While fossil fuels are the backbone of the present global energy system, it is energy services that consumers ultimately desire. Fossil fuels are presently the most cost-effective way of delivering energy services to society under most circumstances. Reference case emissions trajectories presume that even in the absence of explicit policies to limit GHG emissions, technologies will evolve substantially. For example, the scenario, IS92a [5], assumed that by the end of the 21 st century electric power production would already be more than seventy-five percent non-emitting, and that a commercial biomass industry would develop that was as large as the present global oil and gas enterprise. This study is also characterized by assumed advances in technology over the course of the study given in Table (Ref. Case) 2095 (Adv. Tech) Technology Units 1990 Electric Power Generation (fuel + non-fuel cost) 5 Solar 1990 USD/kWh Wind 1990 USD/kWh CO 2 Capture and Storage 7 Coal power output loss Percent 25 Unavailable 15 Coal added capital cost % non-capture capital cost 88 Unavailable 63 Gas power output loss Percent 13 Unavailable 10 Gas added capital cost % non-capture capital cost 89 Unavailable 72 CO 2 capture efficiency Percent 90 Unavailable 90 CO 2 storage cost 1990 USD/tC 37 Unavailable 37 Transportation Service per unit final energy (unitless) Agricultural Biomass 5 Nuclear technology is also subject to technological improvement which we have not explored in this study. Gen III and Gen IV reactor technologies could dramatically reduce costs and enhance performance. The economic implications of advanced reactor and fuel cycle designs will be explored in future work. Solar power is represented as one aggregate technology in this model version. PV costs are used as a marker in the table, recognizing that costs vary significantly for different solar technologies. Work explicitly addressing solar technologies is underway. 7 Note that incremental capital costs do not include the cost of CO 2 storage, which is included as a separate cost entry.

5 Biofuels crop Average annual productivity growth rate (%.y) Conventional crops Average annual productivity growth rate (%.y) Hydrogen Production Natural gas to H 2 Percent efficiency 70 Unavailable 80 Natural gas to H 2 + CCS Percent efficiency 58 Unavailable 71 Coal to H 2 Percent efficiency 62 Unavailable 66 Coal to H 2 + CCS Percent efficiency 52 Unavailable 58 Electrolysis Percent efficiency 87 Unavailable 94 Biofuels Percent efficiency 60 Unavailable 80 Table 1 Technology Assumptions in the Reference and Advanced Technology Cases The assumptions given in Table 1 are not intended to be predictions about the future or future technology developments. The changes hypothesized are used for illustrative purposes. They are intended to show the sensitivity of the system to technology assumptions. And, therefore it is the qualitative response of cost and other variables to technology that is of primary interest. The system is sensitive to assumptions not articulated in Table 1 as well. For example, later in this paper we demonstrate the sensitivity of results to end-use energy technology assumptions. The intent of this paper is to initiate consideration of the role of technology in stabilizing climate change, and future work will continue and expand the investigations we have begun here. Stabilizing Temperature Limiting GMST change not to exceed 2 o C, the Temperature Stabilization Case (TSC), means limiting emissions of the suite of greenhouse gases. Note that stabilizing GMST differs from stabilizing GHG concentrations, the goal of the UNFCCC [6], due to dynamic physical processes such as ocean thermal lag. As a consequence, stabilization of temperature can require that GHG concentrations peak and then decline, sometimes called concentration overshoot scenarios. GMST

6 is stabilized in the MiniCAM by imposing a common global emissions tax rate denominated in USD/tC equivalent 8 so as to minimize cost. As all parties participate from the start, this trajectory is unrealistic. Any real-world trajectory would encounter greater costs than those reported here owing to heterogeneous timing of regional and national emissions limitations and to the employment of potentially inefficient policy instruments. The estimates of the value of technology improvements are therefore likely biased low. The CO 2 emissions pathway in the TSC departs dramatically from that of the reference case, Figure 2 Panel A. TSC industrial carbon emissions peak in 2020 at 7.6 PgC/y and decline rapidly thereafter. By 2095 industrial emissions have declined to 2.6 PgC/y. The emissions mitigation is accomplished in the reference case by creating a massive commercial biomass industry (more than 400EJ/y production), deploying additional nuclear power, improving energy efficiency and reducing the use of all fossil fuels. Commercial biomass production plays a major role in providing energy in the TSC. In the reference case the bulk of biomass energy production is traditional fuels and modern fuels derived from waste products, Figure 3 Panel A. In the TSC vast tracts of land are devoted to Panel A: Fossil Fuel Carbon Emissions Panel B: CO 2 Concentration Panel C: GMST Change from Pre-industrial PgC/y Reference Case ppm Reference Case TSC degrees C Reference Case TSC , 7.6 PgC/y TSC energy crop production, Figure 3 Panel C. This in turn leads to dramatic increases in food prices, transfer of resources to the agriculture sector, transfer of financial resources to producing regions, 8 In this study we employ 100-year Global Warming Potentials [7] to convert carbon prices to prices for other GHG's.

7 largely in the south, and a dramatic increase in deforestation rates and associated carbon emissions, Figure 3 Panel B. Figure 2: Fossil Fuel CO 2 Emissions (Panel A), CO 2 Concentrations, (Panel B) and GMST for a Climate Sensitivity of 2.5 o C (Panel C). Figure 3: Land Use in the Reference Case (Panel A), Land-use Change Emissions (Panel B) and Land Use in the 2 o C GMST Change Limit Case (Panel C). 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% Panel A: Reference Case Unmgd Forest Pasture Crops 0% Biofuels Crop Land PgC/year C Panel B: Land-Use Change Carbon Emissions Reference Case 2 o C GMST Change Limit C % 90% 80% 70% 60% 50% 40% 30% 20% 10% Panel C: 2 o C GMST Change Limit Case Unmgd Forest Pasture Crops 0% Biofuels Crop Land Cumulative emissions mitigation in the period 2005 to 2095 is more than 600 PgC. It must be noted that emissions mitigation would be still larger were it not for advances in technology assumed to occur in the reference case. While emissions mitigation in the period to 2020 is significant, more than 15 PgC, the bulk of emissions mitigation, approximately 650 PgC, occurs after the year 2050 as opposed to before 2050, 200 PgC. Thus, near-term emissions mitigation is merely an overture to the dramatic reductions required in the second half of the 21 st century. This in turn implies dramatic value

8 to the improvement of technologies even if the bulk of their deployment occurs after the middle of the century. The rapid reductions in carbon emissions limit CO 2 concentrations to less than 475 ppm, Figure 2 Panel B. Reductions in emissions of fossil fuel CO 2 simultaneously reduce emissions of aerosols and thereby increase GMST prior to 2050, Figure 2 Panel C. This effect coupled with ocean thermal inertia is potentially large enough to make achieving the TSC impossible for climate sensitivities of 4.5 o C, because the simultaneous reductions in aerosol emissions with carbon emission reductions produces a realized temperature increase that exceeds 2 o C. The assumed climate sensitivity plays a major role in determining the emissions path. Climate sensitivity values ranging from 1.5 o C Figure 4: Carbon Emissions Pathways for Three Alternative Climate Sensitivity Values Fossil Fuel Carbon Emissions to 4.5 o C have long been cited as encompassing a significant portion of overall uncertainty in climate sensitivity 9. We examine three climate sensitivities: 1.5 o C, 2.5 o C 10, and 3.5 o C 11. The associated pathways are displayed in Figure 4. For a PgC/ry Reference Case Climate Sensitivity 2.5 Degrees C Climate Sensitivity 3.5 Degrees C Climate Sensitivity 1.5 Degrees C climate sensitivity of 3.5 o C emissions must decline to virtually zero by the year For a climate sensitivity of 1.5 o C substantial emissions reductions begin only after Thus, policy 9 See, for example [7], section This is the same climate sensitivity employed in Figures 1 and It is impossible to prevent GMST from exceeding 2 o C for a climate sensitivity greater than 3.5 o C. Thus, we do not show results for the full range of climate sensitivities ranging between 1.5 o C and 4.5 o C.

9 decisions must be taken today in the context of profound uncertainty, a feature which highlights the usefulness of framing the problem in terms of risk management. From this perspective the presence of uncertainty is not a reason for inaction, but rather shapes the nature of near-term actions and recommends policies that provide flexibility in future actions. The uncertainty virtually guarantees that today s decisions will eventually be deemed inappropriate, but it is impossible to determine before the fact whether their inadequacy will be in too aggressively preserving other socially desirable resources at the expense of climate or climate at the expense of other socially desirable resources. Under the assumed suite of technologies (Table 1), the assumed cost-minimizing behavior of human societies and values for physical parameters (e.g. the 2.5 o C climate sensitivity), the present discounted economic cost 12 of holding GMST change below 2 o C is approximately 18 trillion 1990 constant USD. Costs are calculated for a fixed suite of technologies and profile of technology developments. No attempt has been made to impose a particular model of induced technological change 13. We do this so as to allow a comparison between alternative technology regimes and thereby to value technology developments in terms of their contribution to meeting the particular temperature change limit. The value of technology is independent of the source of technological change, and yields a metric for the value of potential technological progress on a variety of fronts. 12 A discount rate of 5 percent per year was employed. 13 While it is popular to impose some simple model such as an experience curve (often mislabeled as a learning curve ) the long history of research in the field of induced technological change finds no simple model to provide a satisfying explanation of the process by which technologies are created and transformed. See Weyant and Olavson [8] and Clarke and Weyant [9] for reviews of this literature.

10 The Technology Gap The imposition of a constraint on climate change implies the deployment of IS92a (frozen 1990 technology) different technologies than in a case without the constraint. Edmonds [10] showed that while it may be convenient to think of the required technological change to meet the environmental constraint as merely the change in technology deployment relative to PgC/yr Technological change assumed in the reference case Incremental technology gap IS92a WRE 550 the reference case, that framing of the issue ignores the potentially huge contribution of Figure 5: Carbon Emissions Pathways for Three Alternative Climate Sensitivity Values technological change incorporated by assumption into the reference case. Figure 5 shows a comparison between assumed emissions associated with the IPCC emissions scenario, IS92a [11], and the same scenario run with energy technologies frozen at 1990 levels to illustrate the degree of presumed technological change embedded in the reference scenario 14. But, the reference case technological improvements are a matter of assumption. They presume the successful execution of a variety of public and private sector long-term energy R&D programs around the world. That success is not guaranteed. When considering improvements in technology and the change in technology deployment necessary to shift global emissions away from a reference case and onto a climate stabilization trajectory, both the incremental technology gap and the technological change assumed in the reference case must be jointly considered. A failure to develop emissions mitigating technology in the 14 The intent of this calculation is not to construct a plausible alternative scenario, but rather to illustrate the degree to which technological change is embedded in the reference scenario and thereby taken for granted.

11 reference case implies a larger incremental technology gap. Conversely, assuming that technologies will be developed and deployed that reduce emissions in the reference case may shrink the expected incremental technology gap, but that reduced incremental technology gap is accompanied by an obligation to deliver the technologies in the reference case technology suite. The concept of technology gaps and the role of technological development and deployment have been explored in detail in Battelle [12]. The notion of an incremental gap is therefore a contingent concept. The Value of Technology in Limiting GMST Change to 2 o C To illustrate the economic value associated with achieving reference case technology performance, we consider two simple sensitivities we change the rate of improvement in end-use energy technologies by ±0.25 percent per year. Reference case emissions change by approximately ±5PgC/y by 2095 with CO 2 concentrations changing by approximately ±75ppm and GMST changing by approximately ±0.25 o C. The value of technological change in stabilizing GMST to less than 2 o C (the TSC) is computed as the difference in the cost of the TSC using reference case technology and the cost for each sensitivity case. The benefit of improved end-use energy efficiency in meeting the climate change limitation is approximately 6 trillion 1990 USD present discounted value (PDV). The economic cost of a lower assumed rate of end-use energy efficiency improvement exceeds 8.5 trillion 1990 USD PDV. We have hypothesized a variety of alternative technology changes, Table 1. While all of the technologies listed in Table 1 exist, in that some version of the technology is currently available somewhere in some form 15, mere existence is insufficient to insure significant global market penetration, even when greenhouse gas emissions have economic value. The principal virtue of technology is not that it makes it possible to achieve a particular environmental goal. That can be 15 This is the sense employed in [13] and [14].

12 accomplished trivially if costs are irrelevant. The great virtue of technology is that it holds the potential for reducing the cost of achieving an environmental goal. We use cost here not in its financial sense, but in the sense of requiring a lesser diversion of scarce social resources from other pursuits. To explore the value of technology improvement in managing the cost of the TSC, we re-solve the model constrained to hold GMST change below 2 o C with each technology change listed in Table 1 and record the cost. We then return to original values in Table 1 and move on to the next technology. After examining the sensitivity of cost to hypothesized individual technology changes we next explore the same sensitivity with combinations of two technologies, and then with more than two technologies at a time. Results are reported in Figure 6. The technology changes hypothesized in Table 1 s 2095 (Adv. Tech.) column are significant, but not beyond the realm of possibility. Some appear closer to deployment than others at the moment. But, the history of technology development is nothing if not a lesson in forecaster humility. Technologies that were expected to develop have proved more difficult than expected, and technologies that were never envisioned have evolved to play a central role in the economy. We therefore approach the problem of technology analysis not as a forecasting exercise, but rather as a value of technology exercise. We ask the far more tractable question, what is the value of achieving specific cost and performance changes in terms of meeting a specific environmental constraint, imposed in an economically efficient manner, against a prescribed reference case background and a specific set of natural system parameters. Results are therefore highly contingent. Changes hypothesized in Table 1 s 2095 (Adv. Tech.) column explore only a subset of potential technology options and improvements. Many important options are left for future work to explore including the potential role of nuclear power. The partial nature of the suite of technology improvements does not negate the qualitative insights regarding the role of technology in managing

13 the economic and environmental risks of climate change. Model representations can also play a role. The impact of wind and solar technologies, for example, are likely understated in this version of the model. Cost (Trillion 1990 USD) $30.0 $25.0 $20.0 $15.0 $10.0 $5.0 $ % EEffic Base_Stab Wind & Solar BioTech (ag productivity and biofuels, no H2) Individual Technology Sensitivity Geol Carb CCS +0.25% EEffic Minimum Total Cost H2 End Uses H2 Wind&Solar Binary Cominations, Technology Sensitivity +0.25% EEffic H2 Carb CCS & H2 H2 & BioTech +0.25% EEffic H2 Wind&Solar Multiple Cominations, Technology Sensitivity H2 & CCS & BioTech +0.25% EE H2 CCS Bio W&S Figure 6: Minimum Total Cost of Limiting MGST Change to 2 o C Relative to Preindustrial. First, the more technologies that are successfully advanced, the lower the cost of implementing the TSC. But, all technologies are not equal. Technologies interact in important ways. Some are substitutes for one another. That is, the lower the cost of one technology, the smaller the deployment of the second. Hydrogen (H 2 ) and end-use energy efficiency improvements have this property in this analysis. Some technologies are complements and therefore lowering the cost of one technology leads to increased deployment of a second. Carbon dioxide capture and storage (CCS) and cost-competitive H 2 technologies (fuel cells as well as H 2 production, transportation, and storage technologies) are complementary technologies. The availability of CCS implies that H 2 derived from electricity generated by fossil powered utilities as well as H 2 derived from fossil fuels can reduce emissions more

14 effectively. CCS could also complement commercial biomass crops, implying an ability to produce fuels with negative emissions per unit of end-use energy supply. Second, important interactions in the global energy-economy system must be considered. For example, crop productivity, biofuels, and land-use-change emissions interact strongly. The package of assumptions associated with biotechnology include, increased productivity growth rates for food and fiber as well as energy crops. Furthermore, a hypothetical technology is assumed that employs a biological process to transform input streams such as for example, waste energy and water, to produce H 2 on insignificant (or currently unused) land areas. A technology with performance characteristics outlined in Table 1 reduces the human footprint on land, lowers prices for crops, livestock, and forest products, reduces land-use change emissions to levels below those in the reference case, and reduces the cost of the TSC by between 3.4 and 14.3 trillion 1990 USD, depending upon complementary technology availability (e.g. CCS and H 2 ). Realized economic value and impact on emissions will depend on technology performance and availability. Similarly, CCS interacts strongly with other technologies. CCS can be deployed in electric power generation, but capture is incomplete, and the process diverts significant power resources to the capture process and requires significant capital investments. The captured CO 2 must be transported and stored (both temporarily and long-term). CCS technology can also be associated with the conversion of hydrocarbons from one form to another, for example coal to liquids, coal to gas, gas, coal, or bioenergy crops to H 2, or bioenergy crops to gas or liquids. Volumes associated with the successful development and deployment of CCS technology are potentially huge. In this analysis up to 45 PgC were captured and stored in the period between 2005 and 2050 but up to an additional 200

15 PgC were captured and stored in the period between 2050 and While annual global capture and storage did not exceed 0.5 PgC/y in 2020, this rate could be as high as 2.5 PgC/y by 2050 and to more than 6 PgC/y by The period between 2005 and 2050 is a preparatory period in which technologies that eventually become core components of the global energy system develop and experience initial deployment. The scale of the enterprise changes dramatically in the post-2050 period. A similar story can be told for other technologies such as biotechnology, hydrogen, wind, nuclear, solar or energy efficiency. The requirements of the post-2050 period cast a long shadow back to present technology research and development decision making. Concluding Remarks In this paper we have explored some of the technology implications of limiting GMST change to 2 o C relative to preindustrial. Climate change is a century scale problem. In this paper analysis has been carried out to the year Analysis at this time scale yields important insights unavailable in an examination of shorter scope. While the technical and economic challenges of the emissions trajectory between 2005 and 2050 are daunting under the assumption of a 2.5 o C climate sensitivity, they are far more modest than the challenges of the 2050 to 2095 period. We also examined the implications of uncertainty in climate sensitivity for policy and technology development and deployment. In light of the profound uncertainty implied by variation in the climate sensitivity parameter, options which provide flexibility in managing both economic and environmental 16 The question of storage is an important one. Present understanding of potential reservoir capacity suggests that the global storage resource is more than adequate for the volumes suggested by this analysis. Edmonds, Freund and Dooley [15] estimated storage volumes as follows: Deep Saline Reservoirs, 87 to 2,727 PgC; Depleted Gas Reservoirs, 136 to 300 PgC; Depleted Oil Reservoirs, 41 to 191 PgC; and Unminable Coal Seams, >20 PgC, based on Herzog et al. [16] and Freund and Ormerod [17]. The more recent estimate by Dooley and Friedman [18] indicate that resource volumes are: Coal Basins, 48; Depleted Oil Plays, 31 PgC; Gas Basins, 190; Deep Saline Formation On-shore, 1,608; Deep Saline Formation Off-shore, 1,374. Edmonds et al. [19] explore the implication of the heterogeneous regional distribution of storage resources for technology deployment and find that resource distribution has little impact on aggregate global technology deployment. Permanence of storage is another important issue. We have assumed no significant losses from reservoirs. Any real world system will be imperfect. Characterization of real world systems is an important research priority and is a prerequisite to large-scale deployment of CCS technology.

16 risks are attractive. One of the attractions of technology development is the flexibility it provides in managing both types of risk. If the climate sensitivity is 2.5 o C then limiting GMST to 2 o C implies stabilization of CO 2 concentrations at less than 500 parts per million (ppm) with a peak in global CO 2 emissions occurring in the next 15 years and with a decline in emissions to 3.1 petagrams of carbon per year (PgC/y) by Under such circumstances the value of technology improvements beyond those assumed in the reference case is denominated in trillions of 1990 USD. The role of non-co 2 greenhouse gases is important. Aerosols could produce significant feedbacks in addition to their impacts as local pollutants, though uncertainty is significant. If the climate sensitivity is 4.5 o C or greater, it may be impossible to limit climate GMST change to 2 o C. On the other hand if the climate sensitivity is 1.5 o C, limiting GMST change to 2 o C may be a trivial matter requiring little deviation from a reference emissions path until after the middle of the 21st century. References 1. Edmonds J, Clarke K, Dooley J, Kim SH, Smith SJ Stabilization of CO 2 in a B2 world: insights on the roles of carbon capture and storage, hydrogen, and transportation technologies, Energy Economics, 26(2004): Edmonds, J. and J. Reilly Global Energy: Assessing the Future, Oxford University Press, Oxford, United Kingdom. 3. Hulme, M., Raper, S.C.B. and Wigley, T.M.L., 1995: An integrated framework to address climate change (ESCAPE) and further developments of the global and regional climate modules (MAGICC). Energy Policy 23, Nakicenovic, N., et al Special Report on Emissions Scenarios. Cambridge University Press, Cambridge, United Kingdom.

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18 13. IPCC (Intergovernmental Panel on Climate Change), Climate Change 2001: Mitigation. The Contribution of Working Group III to the Third Assessment Report of the Intergovernmental Panel on Climate Change. B. Metz, O. Davidson, R. Swart, and J. Pan (eds.). Cambridge University Press, Cambridge, UK. 14. Pacala, S. and R. Socolow Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies. Science 305: Edmonds JA, PF Freund, and JJ Dooley "The Role of Carbon Management Technologies in Addressing Atmospheric Stabilization of Greenhouse Gases." In Greenhouse Gas Control. Proceedings of the Fifth International Conference on Greenhouse Gas Control Technologies, GHCT-5, ed. David Williams, Bob Durie, et. al., pp CSIRO Publishing, Collingwood, Australia. 16. Herzog, H., E. Drake, and E. Adams CO 2 Capture, Reuse, and Storage Technologies for Mitigating Global Climate Change. Energy Laboratory, Massachusetts Institute of Technology, Cambridge, MA. 17. Freund, P and Ormerod, WG Progress Toward Storage of Carbon Dioxide. Energy Conversion and Management. 38:S199-S Dooley JJ and Friedman SJ A Regionally disaggregated global accounting of CO 2 storage capacity: data and assumptions. Battelle Pacific Northwest Division Technical Report Number PNWD Edmonds, J., J. Dooley, S. Kim, S. Friedman, and M. Wise Technology in an Integrated Assessment Model: The Potential Regional Deployment of Carbon Capture and Storage in the Context of Global CO 2 Stabilization. Submitted to Human-Induced Climate Change: An Interdisciplinary Perspective, Cambridge University Press.