THE CO2-CLIMATE PROBLEM¹

The CO₂-climate problem is not new. Although for many of us this topic appeared only yesterday, you may judge its age by reading a few of the beautifully written reports of the 1960s and 1970s. Restoring the Quality of Our Environment (President's Science Advisory Committee, 1965) has a chapter on CO₂ and climate that demonstrates the problem in its modern form. The report first analyzes the growth of atmospheric CO₂ by comparing the Keeling record of accurate concentration measurements (initiated in 1958) with estimates of global fossil fuel combustion and then makes crude estimates of future concentrations. It then combines concentration estimates with early radioactive connective models to estimate temperature change, and compares estimated changes to observed changes with consideration given to intrinsic climate variability. Finally, it speculates about possible impacts beyond temperature such as the CO₂ fertilization of plant growth.

The National Academy of Sciences 1977 report on Energy and Climate serves as another demonstration of the consistency in our understanding of the climatic implications of transferring large quantities of carbon from fossil reservoirs to the atmosphere. When compared to recent Intergovernmental Panel on Climate Change (IPCC) reports, these older studies show that although there is a wealth of new science, what is really new is the growing will toward real action—and sadly an unambiguous trend to toward increasing in the length and opacity of climate assessment reports.

Are we seeing an anthropogenic climate signal yet? What signal will we see if we double or triple CO₂ concentrations? These are the two crucial scientific questions. Although they are often deliberately blurred in public debate, they are sharply distinct. On the first, my answer is we cannot yet claim to have seen an unambiguous anthropogenic signal. Although we can measure the signal (the climate record) reasonably well, the crux of this so-called detection and attribution problem is our uncertainty about the climate's unforced variability over decade-to-century time scales—the climate's noise spectrum—and our uncertainty about the magnitude of natural forcing such as solar variability. Without robust understanding of the noise we can't calculate the signal-to-noise ratio very confidently and thus cannot yet answer the detection question unequivocally.

It is the second question, however, that ought to matter for policy: If we double or triple CO₂, will we see a big signal? Here the answer is an unequivocal yes. With the exception of a few outspoken individuals, there is essentially no serious scientific dissent on this question.

When you move beyond the climate science to consider the impacts of climate change, the answer bifurcates again. If you ask, “will there be substantial impacts on many lightly managed ecosystems and on some human populations?” the answer is unequivocally yes. Examples include the ecosystems of the high Arctic and the inhabitants of low-lying islands.

If, however, you want to know about the net economic impacts of climate change, the answer is much less certain. Most economic modeling studies suggest that if we do nothing to abate climate change, we will suffer a loss of a few percent of global gross domestic product (GDP) by 2100 and that modest efforts at abatement are capable of reducing this loss (e.g., the benefits of abatement can outweigh the costs). Modeling our economic future on 100-year time scales is, however, an uncertain and untested art; both the costs of mitigation and the estimates of impact are highly uncertain.

When judged in gross economic terms, climate change will not be catastrophic and is in fact (arguably) minor compared to other economic uncertainties such as the rate of technological change or the evolution of the inequality in distribution of the world's wealth. Despite some overheated rhetoric, our civilization will not collapse if we fail to act aggressively to counter climate change. Humans are very robust. Nevertheless, climate change poses very serious environmental problems. If we double or triple carbon dioxide—as many business-as-usual projections suggest we will within this century—we will see substantial climate change and very substantial changes to many natural ecosystems. Many of us value these ecosystems and value the rights of human communities that will be most affected. We have shown by other actions that we are willing to pay a price to protect such values. I hope and expect that we will take strong action to stabilize CO₂ concentrations. The history of pollution control technologies gives reason to hope that the price of achieving deep cuts in CO₂ emissions will be lower than we predict. The topic of this meeting gives us an explicit basis for that hope.

INDUSTRIAL CARBON MANAGEMENT

Use of fossil fuels with minimal emissions of CO₂ requires two steps. The energy content of the fuels must first be separated from their carbon content in a process that takes a fuel with high carbon-to-energy ratio as input and produces a low-or zero-carbon output along with a carbonaceous stream with low free energy to be sequestered away from the atmosphere. In practice, this generally means a system that uses coal or gas to produce electricity or hydrogen with sequestration of the resulting CO₂, but other options may prove important (Figure 8.1). Separation and sequestration together comprise industrial carbon management.

FIGURE 8.1

Industrial carbon management: a schematic illustrating the definitions of sequestration and separation adopted here. The output stream is labeled carbon free for simplicity; separation includes processes that take a high-carbon stream in and produce a (more...)

These technologies are not laboratory theory; on the contrary, many of the required components exist at the largest industrial scales. Among the most important such technologies are the gasification of coal, the capture of CO₂ using aqueous amines, the steam reforming of methane, and finally, the longrange transport of CO₂ by pipeline and its injection into geological formations. We have, in essence, a sizable basket of component parts out of which we might assemble a system for carbon management.

Although ICM makes sense only as part of a broad portfolio of greenhouse gas mitigation technologies, it may nevertheless transform the politics of the CO₂-climate problem. By lowering the cost of emissions mitigation, ICM may enable stabilization of atmospheric concentrations at acceptable cost. By weakening the link between fossil energy and atmospheric CO₂ emissions, ICM makes it feasible to consider a fossil-based global economy through the next century. By reducing the severity of the threat that emission reduction poses to fossil industries and fossil-rich nations, ICM may ease current dead-locks in both domestic and international abatement policy.

There are, however, no magic bullets with which to slay the CO₂-climate problem. All current options—ICM included—either are impracticably expensive or involve significant environmental risks. Moreover, global energy systems are highly heterogeneous, making it implausible that any single technology will triumph everywhere. Finally, the history of energy policy is full of technologies that seemed to their advocates to be too cheap to meter, yet are now irrelevant. Thus, although I will tell you a (mostly) optimistic story about the potential role of ICM in mitigating CO₂ emissions, skepticism is wise. The very fact that ICM was not on the energy policy agenda even a decade ago should make one cautious about any predictions for the next century.

SEPARATION

There are three broad paths to separation:²

1. Postcombustion capture (PCC): Burn the fuel in air then capture CO₂ from the combustion products.
2. Oxyfuel. Separate oxygen from air, burn the fuel in pure oxygen, and then capture CO₂ from the combustion products.
3. Precombustion decarbonization. (PCDC). Reform fuel to make hydrogen and CO₂.

The first two, PCC and oxyfuel, involve complete combustion to CO₂ and water and so are limited to producing electricity and heat, whereas PCDC produces hydrogen that may be combusted in an integrated system to produce electricity and heat or may be distributed for use elsewhere.

Most discussion of ICM has focused on large-scale electricity generation, where PCC is perhaps the most obvious route to separation because it is closely analogous to existing environmental control technologies, such as flue gas desulfurization, that remove pollutants from power plant exhaust streams. Amine solvents are now used to capture CO₂ from power plant exhaust streams for commercial uses such as the carbonation of beverages. Using current technology, amine systems are able to capture about 90% of the CO₂, but the energy cost of solvent regeneration reduces plant electrical output by about 15%. A host of other capture methods have been proposed, and there is evidence that amine technologies can be significantly improved. In comparison to other routes to separation, PCC has the great advantage that it requires little modification to existing power plants and so could in principle be applied as a retrofit; its disadvantage is that the separation is performed at atmospheric pressure on a gas stream that is only 4 to 15% CO₂ and contains a multitude of reactive combustion products. From a coal-fired plant, for example, the exhaust gas is at most about 15% CO₂ and contains SO_x, NO_x, and various metals so that a CO₂ separation system must either be tolerant of impurities or the impurities must be removed. Significant opportunities exist for co-optimization of the multiple emissions control technologies that must be applied to coal-fired plants.

Instead of separating CO₂ from the combustion gases, you can first separate the O₂ from air and then do the combustion in pure O₂, producing an exhaust stream that is CO₂, H₂O, and impurities from which the water can easily be removed by condensation. Compared to PCC, Oxyfuel schemes offer the advantage of doing the primary separation step on a clean gas mixture (air) that is free from the many reactive impurities in combustion gases. The leading disadvantage of Oxyfuel is the high energy and capital cost associated with oxygen production. Oxyfuel systems also offer higher combustion temperatures that yield higher Carrot efficiencies. The flame temperature from pure Oxyfuel is too high, however, so all Oxyfuel schemes must use a diluent to reduce the temperature and increase the volume of working fluid. The leading choices are direct injection of water or recycle CO₂. The direct (i.e., without reforming to produce H₂) use of methane in high-temperature fuel cells may be considered an Oxyfuel route to separation because an oxygen-permeable membrane is used to transport O₂ to CH₄ for oxidation. This analogy is particularly apt because one of the leading methods to produce O₂ in combustion-based Oxyfuel schemes involves the use of air separation membranes that are closely related to the membranes used in solid oxide fuel cells.

PCDC is most obviously accomplished by steam reforming of methane followed by the water-gas shift reaction to produce a CO₂-H₂ mixture. Separation of CO₂ from such gas streams is much easier than it is from combustion air in PCC systems because of the higher working pressures and higher fraction of CO₂. As described below, this method is now used to produce hydrogen from methane at very large scale. Many other methods are possible. For methane, one can, for example, produce synthetic gas using partial oxidation instead of steam reforming. For coal, a multitude of gasification reactions are possible including, for example, H₂ rather than O₂-blown gasification. Even in a electric power plant, PCDC systems appear to be competitive with other methods whether the fuel is coal or natural gas. In addition, PCDC has the important advantage that a power plant could sell zero-CO₂-emission hydrogen “over the fence” to support the development of a hydrogen infrastructure (Ogden, 1999).

GEOLOGICAL SEQUESTRATION³

Although much is uncertain about geological sequestration, the essence of current knowledge is easily stated: (1) it is possible to put very large volumes of CO₂ underground at comparatively low cost; (2) it appears that a capacity of greater than 1,000 gigatonnes carbon (GtC) exists in reasonably well understood geological structures; and, (3) while the fate of CO₂ is highly dependent on the specific geological character of the injection site, it seems highly likely that a large fraction of CO₂ could be confined underground for time scales in excess of a thousand years.

As we now envision it, the CO₂ would be injected into geological formations similar or identical to the formations from which we now extract oil and gas, and the technologies employed would be readily derived from current systems used in the oil and gas industry. The most likely sequestration sites and their estimated capacities are shown in Figure 8.2.

FIGURE 8.2

Carbon reservoirs and sinks. The resource base (the sum of reserves and resources) is used for fossil fuels [Rogner, 1997]. The consumption box shows worldwide cumulative consumption of fossil fuels. The upper section of the atmosphere box shows the increase (more...)

While geological sequestration will build generally on the totality of experience with fossil fuel extraction, it will be most directly built on current practice of CO₂ injection for enhanced oil recovery (EOR). Conventional extraction methods typically leave substantial oil in place. This oil may be extracted using EOR. Carbon dioxide injection (or “flooding” in industry jargon) is particularly effective because, as an organic solvent, the CO₂ acts to reduce the viscosity of the residual oil and in addition causes the oil to expand thus helping to free it from the porous rock in which it is embedded. Typical EOR floods operate at pressures above the critical point of CO₂ so that fluid flow is facilitated by the absence of a liquid-gas interface.

The use of CO₂ for EOR will provide early sequestration opportunities at negative cost as EOR operations pay of order $50/tC for CO₂. Most assessments suggest that absent EOR, the cost of geological sequestration will be of order $10-25/tC. At this price, the overall cost of ICM is dominated by the cost of separation. There are reasons, however, to expect that these estimates may be too optimistic and that sequestration cost will consume a rising fraction of the total cost of ICM. Costs of CO₂ sequestration may be higher than predicted from the EOR experience due to the additional costs involved in monitoring and verification. Depending on our experience with CO₂ injection and on the regulatory framework that is adopted (which will likely be different for current regulation of CO₂ EOR) the costs of monitoring could be very high. Moreover, sequestration cost estimates have tended to assume injection into previously characterized high-permeability structures, but in the long run these will be saturated and we will have to turn to lower permeability structures and to include the full cost of subsurface characterization. Arguably this could drive sequestration costs closer to the cost of natural gas extraction (currently of the order $100/tC).

Carbon need not be sequestered as CO₂; instead, it can be sequestered as a stable and immobile carbonate. The process mimics the natural weathering of magnesium and calcium silicates that ultimately react to form carbonate deposits. Integrated power plant designs have been proposed, in which a fossil fuel input would be converted to carbon-free power (electricity or hydrogen), with simultaneous reaction of the CO₂ with serpentine rock (magnesium silicate) to form carbonates (Lackner et al., 1995). Carbonate formation is exothermic; thus, in principle, the reaction requires no input energy. Ample reserves of the required serpentine rocks exist at high purity. The size of the mining activities required to extract the serpentine rock and dispose of the carbonate are comparable to the mining activity needed to extract the corresponding quantity of coal. The difficulty is in devising an inexpensive and environmentally sound industrial process to perform the reaction.

The importance of geochemical sequestration lies in the permanence with which it removes CO₂ from the biosphere. Unlike carbon that is sequestered in organic matter or as CO₂ in geological formations, once carbonate is formed the only important route for it to return to active biogeochemical cycling is by thermal dissociation following the subjection of the carbonate-laden oceanic crust beneath the continents, a process with a time scale of more than 10⁷ years.

THE ICM TOOL BOX

Industrial carbon management will be built atop the existing fossil fuel infrastructure. Building an effective ICM system will require adaptation and improvement of existing technologies as well as the development of new technologies to fill the gaps. We have a box of tools that have been proved by previous experience. We could assemble these tools today, with minimum modification, to build an ICM infrastructure for the production of electricity and hydrogen, but the cost of CO₂ mitigation would be relatively high, perhaps $100 to $250/tC. With the design of a few new components and careful optimization of components in integrated systems, it seems reasonable to suppose that the cost could fall substantially.

One can argue that the costs of many low-CO₂-emission technologies could be reduced with a bit more R&D, so how is ICM different? The answer lies in the close connection between ICM and the existing energy infrastructure and consequently in the scale at which the enabling technologies already exist. Consider four key examples:

1. Coal gasification. Integrated gasification combined cycle (IGCC) electric generation, a point of departure for many coal-based ICM designs, has not been adopted commercially despite decades of R&D; nevertheless, there is a large fleet of gasifiers now in operation with a worldwide syngas capacity equivalent to 50 GW thermal.
2. Hydrogen production. Steam methane reforming to produce hydrogen now consumes almost 2% of U.S. primary energy. Leading uses for the hydrogen are the production of ammonia and the reformulation of gasoline. Some current applications involve the long-range transport of hydrogen in pipelines.
3. EOR. In the United States about 7 MtC per year of CO₂ is used for enhanced oil recovery, most of it is supplied by pipeline from natural CO₂ formations. The longest pipeline runs 800 km. If the CO₂ were derived from fossil fuels, it would account for about 0.5% of U.S. primary energy.
4. CO2 capture with MEA. Monoethanolamine (MEA) solvents are used today for CO₂ capture from exhaust gases in more than 10 facilities worldwide and are also widely used for striping CO₂ from natural gas.

In addition to these enabling technologies, several integrated systems are important examples of nascent ICM. The first large project that sequesters CO₂ to avoid emissions is in Norway, where Statoil operates one of largest gas fields in Europe in which the produced gas contains about 10% CO₂, which must be reduced to 2.5% for sale to customers. The CO₂ is separated on an offshore platform and injected into a high-permeability aquifer under the seabed. The offshore capture and sequestration project was developed in response to Norway's offshore carbon tax of $170/tC. Statoil has sequestered about 0.3 MtC per year of CO₂ since 1996, and the transport of the sequestered CO₂ is now being monitored by an international research team (Herzog et al., 2000). A similar project planned in Indonesia at the Natuna field will inject 30 MtC per year, roughly 0.5% of present global emissions.

A project using the CO₂ from the Dakota Gasification plant to enhance oil recovery at Pan Canadian's Weyburn field is (arguably) the existing project that most resembles ICM. The Dakota plant has produced synthetic natural gas from coal since 1984. It is the largest facility of its kind and was a product of the Synfuels programs of the 1970s. Weyburn is a large oil field in Saskatchewan that is nearing the end of conventional production; with CO₂ EOR, the amount of recoverable oil will be increased by about 30%. A 325-km pipeline now transports 0.5 MtC of CO₂ per year from the gasification plant to Weyburn (Hattenback et al., 1999).

It is instructive to compare the scale of these technologies with current low-CO₂-emission alternatives. Nuclear and biomass are both used at very large scale, accounting for 9% and 3% of U.S. primary energy, respectively, but solar and wind are much smaller—0.08% and 0.04% respectively (Energy Information Administration, 1998). In comparison the Dakota Weyburn project alone sequesters 0.03% of U.S. CO₂ emissions, and all of the key enabling technologies listed above are in use at scales that far exceed the current scale of wind and solar.

ICM AND MITIGATION OF CO2 EMISSIONS: TECHNICAL AND ECONOMIC BARRIERS

Industrial carbon management may be used to mitigate CO₂ emissions throughout most of the energy system; however, the heterogeneity of energy distribution and use means that the comparative advantage of ICM over other CO₂ mitigation technologies will vary widely. Most analysis of ICM has focused on electricity generation, but ICM can also be used to produce hydrogen, enabling deep reductions in CO₂ emissions via the substitution of hydrogen for natural gas or petroleum.

There are several good reasons to focus on electricity generation as an early application of ICM technologies:

• Electric power plants are among the largest point sources of CO₂.
• New electric generating technologies can be introduced without affecting the end user (other than by changing the cost of production).
• Most coal is used for electric generation (93% in the United States), and coal has the highest carbon-to-energy ratio of the fossil fuels.

Given existing technologies, the cost of electricity with ICM is estimated to be about 5-7 cents/kWh, about 2-3 cents/kWh more that the cost from current technologies (Herzog et al., 1997), and roughly comparable to the cost of electricity from wind, biomass, or nuclear power. Figure 8.3 illustrates the relationship between cost of electricity and intensity of CO₂ emissions for various technologies. For new coal plants, the cost of reducing CO₂ emission is about $100/tC. It is difficult, however, to estimate the real cost of reducing emissions from static cost comparisons because in real electric markets the introduction of ICM competes with fuel switching (coal to natural gas) and depends on the dynamics of plant dispatch. Figure 8.4 illustrates the cost of emissions reduction in a simple dynamic electric supply model.

FIGURE 8.3

The cost of electricity versus carbon intensity. The x-axis shows CO₂ emissions (in kilograms of carbon per unit of electricity generation [in gigajoules]). The y-axis shows the approximate cost of electricity from new generating units including costs (more...)

FIGURE 8.4

Carbon mitigation supply curves. These results are derived from the author's dynamic optimization model applied to a representative U.S. electricity market. Each point on the graph reflects the decrease in carbon emissions compared to a baseline scenario (more...)

Given open competition between electricity technologies under a carbon tax (or equivalent regulatory mechanism) and the assumption that carbon sequestration can meet environmental permitting requirements, there are significant structural reasons to expect sequestration to be adopted in preference to nonfossil alternatives even if the cost of electricity were similar. Unlike wind power and other distributed renewables, ICM plants would match the existing distribution system with respect to sizing and ease of dispatch. Moreover, ICM plants with likely be constructed with existing suppliers, and established upstream fossil energy companies (the oil majors) could provide both fuel and CO₂ sequestration. While nuclear power could, in principle, play a central role in reducing CO₂ emissions, absent sweeping changes in the industry, its regulators, and public perception, it seems likely that utilities would find ICM less risky.

In sharp contrast to the introduction of new electric generating technologies, the introduction of hydrogen into dispersed stationary uses requires the development of a hydrogen distribution infrastructure—a serious challenge—while the introduction of hydrogen into transportation requires the development of effective hydrogen-fueled vehicles and a refueling infrastructure—likely an even greater challenge. Yet as a means to mitigate CO₂ emissions, the potential advantage of ICM over nonfossil energy sources (other than biomass) is due to the intrinsic advantages of thermochemical over electrochemical production of hydrogen. A crude comparison of energy costs serves to illustrate the point. At current prices, coal and natural gas, likely the most important fuels for ICM systems, have energy costs of roughly $1 and $3/GJ, respectively. Either feedstock can be used to generate electricity with ICM at a producer cost of $15 to $25/GJ (5-7 cents/kWh). As noted above, the cost of electricity produced from wind (absent all subsidies) arguably lies in the same range. In contrast, the price of H₂ produced from wind via electrolysis would be $20 to $30/GJ, while the price of H₂ produced from fossil fuels via ICM would be $4 to $7/GJ; a relative cost advantage of roughly 1:3 for ICM-hydrogen over wind-hydrogen despite the assumed equality of electricity costs. Similar disadvantages apply to the production of hydrogen from nuclear or solar power, though not from biomass. Moreover, large-scale production of hydrogen from fossil fuel and its long-range transport are already mature technologies in the petrochemical industry.

The relative ease of producing hydrogen via ICM implies that wherever hydrogen could replace oil or natural gas, the potential exists for comparatively inexpensive mitigation of CO₂ emissions. Realizing this potential, however, will not be easy. Substantial technical and economic barriers will hinder the diffusion of hydrogen fuel technologies across the energy system. Technical barriers range from the comparatively straightforward problems of constructing hydrogen-capable gas distribution systems to the serious engineering challenges that stand in the way of hydrogen-powered transportation systems. The economic barriers—including both economies of scale and network effects—are no less daunting. Consider the introduction of hydrogen-capable distribution systems; even if costs were low for both the distribution system and the end-user technology, the introduction of new distribution systems will likely be slow because distribution and end-user equipment must evolve together against the economy-of-scale advantages of existing systems.

Global Models

Although we have a limited understanding of the role of ICM technologies in bringing down the cost of CO₂ mitigation in the electric sector, very little is known about the influence of ICM on the overall cost of mitigating climate change. The uncertainty arises from the need to combine global economic models with models of technological change in time scales of the order of a century. Looking back 30 years at previous attempts to model the evolution of energy systems does not inspire confidence. Forecasting technological change would be difficult enough if one wanted to predict the evolution of a single technology, such as large-scale electric power generation. Predicting technological change over century time scales is still harder, however, because clusters of technologies evolve as tightly coupled systems and the evolution of the full system is highly path dependent.

Two extreme scenarios for the future of centralized electric generation serve to illustrate this path dependence. First suppose that electric power generation is rapidly decentralized, driven by the diffusion of small natural gas-fired combined heat-and-power generators—the technology that offers the most cost- effective near-term CO₂ mitigation. This would initially prevent diffusion of ICM because CO₂ cannot be effectively collected from distributed sources, but it would enable a later wave of decarbonization as ICM hydrogen (produced from cheap coal) competed against expensive natural gas. Alternatively, the economies of scale in large ICM electric generation might lower the relative cost of electricity—under a system-wide carbon tax—and cause acceleration of the fraction of primary energy converted to electricity at centralized facilities.

Despite the daunting challenges, several groups have used integrated assessment models (see Parson and Fisher Vanden, 1997, for a review of such models) to study the effect of ICM on the overall costs of stabilizing CO₂ concentrations. These models allow one to compute the reduction in CO₂ emissions resulting from imposing a price on emissions that approximates the effect of a carbon tax or similar regulatory mechanism. The models may be used to find a trajectory of carbon price over time that most efficiently stabilizes CO₂ concentrations at a given level. Conventional economic models suggest that peak marginal carbon prices of order $500 to $1,000/tC will be necessary to stabilize CO₂ concentrations at around 450 parts per million (ppm).⁴ As we have seen above, simple technology cost estimates suggest that ICM could be used to mitigate a substantial fraction of total CO₂ emissions at much lower costs. The global model results in Figure 8.5 show decreases in mitigation cost of roughly a factor of two when ICM is included.

FIGURE 8.5

The effect of ICM on the global cost of stabilizing CO₂ concentrations. The y-axis shows the carbon price (set by a tax or equivalent regulatory mechanism) required to keep atmospheric CO₂ concentrations below about 550 ppm (twice preanthropogenic levels). (more...)

IMPLICATIONS

The oil crisis of the early 1970s intensified concerns that the world would soon run short of fossil fuels. Energy experts theorized that a global transition to nonfossil energy would be necessary within decades. Three decades later, although new discoveries and new recovery technologies have increased estimated fossil reserves and put to rest fears of their rapid exhaustion, concern about climate change has again led many experts to conclude that a rapid transition to nonfossil energy is required.

Part of the reason fears of oil scarcity proved exaggerated was that analysts failed to anticipate the potential for technical and managerial innovation to drive down the cost of petroleum exploration and extraction. We may have made a similar error in considering the link between fossil fuel use and climate. It has been assumed that the transfer of carbon from geologically isolated fossil reservoirs to the biosphere was a fundamental geophysical consequence of fossil energy use. Geological sequestration of CO₂ negates this assumption and raises the prospect that the long history of technical mitigation of the environmental impacts of fossil fuels can be extended to the climate problem.

By weakening the link between fossil energy and CO₂ emissions, carbon management makes it feasible to consider a fossil-based global economy through the next century, even in a greenhouse-constrained world. By reducing the severity of the threat that emission reduction poses to fossil industries and fossil-rich nations, carbon management may ease current political deadlocks. Stated bluntly, if carbon management is widely adopted and if existing fossil energy industries can extend their dominance into the new markets for carbon sequestration, then the increase in total energy costs will benefit industries that would otherwise lose by actions to abate emissions.

It is likely that carbon management will be a profoundly divisive issue for environmentalists. It may be opposed for at least two reasons. First, carbon management is only as good as the reservoirs in which the carbon is sequestered. If CO₂ leaks out much more quickly than we expect, then we leave our descendants with the double problem of uncontrollably rising CO₂ emissions and an economy still dependent on fossil energy. The history of toxic and nuclear waste disposal gives reason to be skeptical of expert claims about the longevity of underground disposal. Second, carbon management is a technical fix on a grand scale. It was first proposed as “geoengineering,” a term now shared by proposals to engineer the global climate, for example, by cooling the planet by the injection of aerosols into the stratosphere to reflect solar radiation (Keith, 2001). In addition to a reasonable distaste for technical fixes, carbon management collides with the deeply rooted assumption among many environmentalists that fossil fuels are the “problem” and that renewable energy is the “solution.” Yet, the rationale for support of carbon management is also strong. It may be that large-scale adoption of carbon management will allow the world to make aggressive CO₂ emissions cuts at a politically acceptable cost.⁵

ACKNOWLEDGMENTS

This research was supported by the Center for Integrated Study of the Human Dimensions of Global Change, a joint creation of the National Science Foundation (SBR-9521914) and Carnegie Mellon University with additional support from the Department of Energy, Environmental Protection Agency, National Oceanic Atmospheric Association, Electric Power Research Institute, Exxon, and Applied Precision Inc.

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DISCUSSION

Dave Cole, Oak Ridge National Laboratory: I wonder if you might elaborate on two points regarding the environmental aspect. First, elaborate a little bit on this issue of ocean sequestration and then on geologic storage of CO₂. Where do the environmentalists stand on these issues?

David Keith: With a few exceptions, CO₂ capture and sequestration is just are not on the radar screens of the environmental groups. But that is beginning to change. Several of the large environmental nongovernmental organizations NGOs know they need to grapple with CO₂ sequestration.

Concerning ocean sequestration, Norway is now separating out the roughly 10% of CO₂ that is in the gas on an off-shore platform from its largest gas field and shoving it down into a sandstone aquifer, whereas otherwise they would have been venting it. I have heard rumors that Greenpeace is going to try and get some other country to bring suit in the World Court to stop it because they believe it breaks the London Dumping Convention. I think, from my cursory reading, that Greenpeace is correct, that it does break the London Dumping Convention, because the Convention prohibits dumping industrial waste, not just in the ocean, but under the seafloor. If it's correct that Greenpeace would like to block Norwegian project, which in my view is an obvious environmental benefit, then that gives you a sense of how strongly people feel about the ocean.

I should add that not only has there been a huge Japanese research investment in oceanic sequestration, but there is a project that will run next year, funded by (I think) the Canadians, the Americans, and Japanese that will actually attempt to inject CO₂ at a rate of a kilogram per second. The project will run off Hawaii and will be used to model plume formation and so on. This experiment has got environmental groups to think about, and critique the idea of ocean sequestration.

Dave Cole: Just one quick comment to follow on that. The federal government is spending a fair bit of money examining the issue of ocean sequestration in terms of the geoenvironment.

David Keith: The overall budget for CO₂ mitigation is still small. As Bob Frosch said at a meeting we had at Harvard two years ago, we need to add a couple of zeros.

Dave Cole: Yes, I understand, but nonetheless, on these issues of policy and issues of environmental concern, I am concerned about the feedback between community interest or lack thereof and what really guides the research that we perform or the research that the federal government supports. There seems to be somewhat of a disconnect here.

David Keith: I couldn't agree more. I don't have any magic answer. There are more than a few disconnects both on the climate science side and on mitigation technology.

Dave Cole: The last part of my question concerns terrestrial sequestration. Are we going to encounter the same kinds of Greenpeace environmental concerns there—where people are actually within walking distance of where this stuff is being dumped?

David Keith: We just don't know because it is so early, but I think the answer is yes, but not as much for terrestrial as for oceanic CO₂ sequestration. At Carnegie Mellon, we had done a preliminary open-ended elicitation of knowledge and opinions about sequestration, with about 10 non-technical members of the community. While it is not representative, we found divergent views on geological sequestration where we found strong resistance to ocean sequestration.

Several folks I have talked to in the environmental community are willing to talk seriously about geological sequestration. But it is still in its early days. There are still no attempts at systematic risk assessment, and there is little sense of how, where, under what regulatory framework, and with what incentive sequestration would actually occur. All of these factors will likely influence people's reaction to geological sequestration.

Dan DuBois, National Renewable Energy Laboratory: I am a little more supportive of renewable energy than you are, but on the issue of how much CO₂ you could use, I think you are saying 0.1% or something like this. I think you misunderstand what people who worked with CO₂ would really like to do. They want to use CO₂ as an energy vector, much as you would use water splitting. When the CO₂ community talks about making a fuel from CO₂, we want to do much the same thing, only we want to make a liquid fuel. So if you have a nuclear source or a renewable energy source of electricity in the future, then you could provide not only hydrogen, which is a gaseous fuel, but also methanol a liquid—high-energy-density liquid fuels as well.

David Keith: I am quite skeptical that synthesis of fuels from CO₂ with energy provided by nuclear or carbon-free renewables can ever compete. But it is clear that we need systematic analysis that would come from some of you in the chemical sciences community. You can't arbitrarily start with nuclear or solar PV energy, which costs a lot, and only think about the subsequent analysis. You have to do a real analysis, which starts with fossil-free energy at a certain price or fossil energy at a certain price.

Dan DuBois: The question is, What price are you going to use and what assumptions are you going to make? This is a problem for 50 years in the future. You are saying that economic analyses 50 years in the future are very difficult. If you say that, on what basis are you going to make this economic analysis?

David Keith: All I am saying is that we should produce some robust analyses with transparent assumptions that address both sides of the problem. You clearly see the choice between either offsetting emissions, that is, using nonfossil energy to simply displace CO₂, or going to the CO₂ route to make fuels. A nice study like that could realistically be done with several assumptions, and if they are clearly laid out, would be a big help to DOE managers.

Footnotes

1

This essay is loosely based on a presentation at the National Academy of Sciences' Chemical Sciences Roundtable. In transforming it to published form, I have attempted to preserve some of the informality of a verbal presentation while (I hope) improving its organization and content. There was considerable skepticism expressed during the meeting about the scientific basis for concern about climate. I tried to answer this skepticism with brief opening comments; I have included them here, although they differ in style and content from the rest of this essay.

2

The process is often called CO₂ capture rather than separation, but I prefer separation because not all processes end with CO₂. It is also possible to produce carbonates or even pure carbon.

3

Oceanic sequestration is possible, and perhaps important, but I omit discussion of it here.

4

Including other radiative forcings, 450 ppm CO₂ is approximately equivalent to a doubling of CO₂ over preanthropogenic levels.

5

Several review articles cover much of the material presented here (Herzog et al., 1997, 2000, Socolow, 1997; Parson and Keith, 1998; Freund, 2000).