It is essentially certain that as CO2 levels in the atmosphere increase the Earth will become warmer. The results of climate model studies indicate that a CO2 doubling would raise temperatures globally by 1.5-4.5 oC, and evidence that the Earth is already warming appears to be firm. Although climate models disagree in the details of their predictions, they nearly all predict more summer dryness in continental interiors (Houghton, 1996). It will in all likelihood be at least a decade and possibly much longer before models are able to predict details of regional climate change. In the meantime the skeptics will no doubt remain skeptical.
Yet the evidence that global warming is already occurring is strong, and it seems reasonable that we should act to prevent it from becoming extreme. But this is certainly no time to abandon our trust in technology. Abundant energy is necessary for modern society. It will be necessary in the developing world if the populations there are to achieve some amount of prosperity. There are ways to reduce CO2 emissions by increasing end use efficiency (Rosenfeld et al., 1997). However, the real key to supplying carbon free energy more likely lies in development of affordable and safe nuclear (fission and fusion) and renewable energy. In a very real sense global warming has become an engineering problem. Given the rather daunting challenge of supplying the world with 10 to 30 TWt of carbon free energy within the next 50 to 100 years, and even more if atmospheric CO2 is to be stabilized, as implied by the various scenarios, it appears inevitable that we should explore a wide range of possibilities without preconceived notions. The range of options under serious consideration by most researchers is perhaps too limited.
Policy choices are often based on "optimal" responses to what is likely to happen in the future: to forecasts. In the next chapter Lempert and Schlesinger remind us that "the one thing that we know for sure about forecasts is that most of them are wrong". This is consistent with our general philosophy that we need to keep open a wide range of policy options and possible energy sources.
This is not to say that forecasts themselves are not useful. The real goal of the Framework Convention on Climate Change is to stabilize the atmospheric concentration of CO2 at a level that is safe in some, currently unspecified and (really unknown), sense. There are, of course, an infinity of possible paths for accomplishing this. Climate change presents a problem of decision making under conditions of great uncertainty. Lempert and Schlesinger argue that robust strategies can result from adaptive-decision processes that change over time in response to observations of changes in climate and as economic conditions evolve. Robust strategies are those that will work reasonably well over a broad range of plausible future scenarios. As an example they examine the impacts of climate variability on the choices of near-term policies, and find that under many circumstances a combined strategy involving direct technology incentives designed to encourage early adoptions of new emission-reducing technologies in addition to price-based incentives such as carbon taxes and emission trading is more robust than strategies involving either of these policies alone. The various technologies examined in later chapters of this volume can be useful, along with the tool described in this chapter, in shaping future policy actions that strike a balance between these two types of incentives and appeal to many stakeholders.
In Chapter 4 Hassol, Strachan and Dowlatabadi argue that although improving energy efficiency will play an essential part in reducing CO2 emissions, it cannot by itself reduce emissions to a reasonable target during this century while meeting global energy demands at a reasonable cost. Energy efficiency (or the lack of it) is intricately tied to structural changes in the economy and also to sector-specific technological change. Many modelers treat technological learning as exogenous, and fixed by model assumptions, while it is more realistic to consider it endogenous, and to allow it to be affected by other parameters in the model, responding to interacting factors such as policies, prices, and research and development. This parallels the discussion in Chapter 3 in the sense that it evolves and is affected by feedback processes over time.
In the next several decades greenhouse emissions from developing countries will surpass those from developed countries. Therefore, energy intensity trends (E'IGDP) in those countries will be crucial in determining the amount of carbon free energy needed to stabilize the atmospheric loading of CO2. However, lack of data and modeling experience along with dynamically changing economies make prediction of future E'IGDP difficult. Some question even its relevance. Although E'IGDP seems to be falling in China, purchasing power parity might be more nearly relevant than GDP, and when this is used as a measure of economic gains energy intensity gains (based on E'/PPP) disappear.
The authors go on to discuss the path dependence of shaping the future availability of various energy efficient technologies and their relations to policy instruments, including case studies of transportation, buildings, industrial production and electricity generation.
Chapter 5 focuses on terrestrially based renewable energy options. Short and Keegan discuss costs and benefits of renewable energy technologies along with the anticipated cost reductions over the next 20 years. Hydroelectricity and biomass have been cost competitive for many years, and already provide substantial energy globally. Their discussions of market opportunities and barriers, including the problem of "lock in", are particularly helpful.
Renewable energy resources, of course, exist in enormous quantities, but are generally dispersed. Places where a given renewable resource (e.g. solar, wind, geothermal) is most concentrated are generally not places where many people live. The problem of intermittency must also be addressed. In this regard the authors discuss briefly the problem of energy carriers in the form of hydrogen, superconductivity and electric vehicles. Short and Keegan conclude that the potential for terrestrially based renewable energy is huge, pointing to IPCC figures that show a potential some 21 times global energy use today.
Berry and Lamont further address the problems of transport and storage in Chapter 6. The transportation sector will be a particularly difficult one, and the authors provide an extensive and useful discussion of hydrogen powered vehicles. Gasoline and diesel fuel are used almost exclusively as transportation fuel, and as various countries develop the demand for personal transportation vehicles will grow. They conclude that the key technology is the one that links electricity and transportation fuel, efficient hydrogen production through electrolysis.
2.3.5 Nuclear fission
In Chapter 7 Krakowski and Wilson discuss the possible contribution of nuclear fission reactors to the future fossil free energy mix. Following World
War II there was a rapid growth in the commercial application of nuclear energy. Since that time, however, there has been little growth, although a few industrialized countries (notably France) have continued to sustain a meager growth. The costs of building nuclear power plants have increased, while those for fossil fueled plants have decreased. In addition, the idea of environmentally clean, safe and inexpensive nuclear energy has given way to the prospects of accidental releases of dangerous radioactive materials, the generation as byproducts of breeder reactors materials of military interest, and dangers and difficulties associated with radioactive waste. Krakowski and Wilson thus identify the four cardinal issues that need to be addressed before nuclear energy can become acceptable as an energy source: radioactive waste, proliferation of materials of military interest (plutonium), cost and safety.
It is clear from this (as well as other) chapters that there is sufficient economically recoverable 235U for nuclear fission reactors to contribute as much energy as that postulated in the various scenarios until at least 2100, that is, ramping up to 5 TWe within 100 years. Depending on assumptions about 235U resource availability, breeder reactors will have to be employed after 2050 if they are to continue to contribute to CO2 stabilization unless some inexpensive method is found to extract uranium from seawater. Nevertheless, any viable future for nuclear energy will depend largely on the rate at which barriers to public acceptance are lowered. Even so, substantial increases in renewable energy resources will be required if atmospheric CO2 is to be stabilized, absent very large improvements in E'IGDP.
The other arm of nuclear energy is nuclear fusion. Fusion occurs when the positively charged nuclei of two low atomic number elements approach closely enough for the attractive short-range nuclear forces to overcome the repulsive Coulomb force. The mass of the fused nuclei is smaller than the combined masses of the separate nuclei, and the mass deficit is released as energy. Getting the two nuclei close enough requires that they have very high energy. Temperatures must be at least ten million Kelvins and the density must be very high. The density-time-temperature combination must be at least 1021 keVm~3 s_1. The basic problem with the fusion option is that we have not yet been able to reach this level. Nevertheless, Molvik and Perkins believe that we are near enough that fusion has a chance to become the energy source of choice early in this millennium. Unlike fission, fusion reactors are in some sense inherently safe because the fuel in the core at any time is sufficient for at most only a few seconds of operation. Molvik and Perkins discuss several different fusion fuels and reactor configurations in Chapter 8. They conclude that "An innovative fusion energy research program, focused on the critical issues, will maximize the probability of achieving the full potential of fusion energy. The development of a virtually limitless energy source will provide a profound benefit to future humanity."
In Chapter 9 Criswell summarizes the problems and prospects of energy efficiency and of the energy sources discussed in earlier chapters, often coming to somewhat different conclusions. The potential for a variety of possible future energy sources is given in his Tables 9.2 to 9.6. These include many of those considered in other chapters: wind, bio-resources, peat, gas hydrates, hydroelectric, tides, waves, ocean thermal and geothermal energy. He concludes that most renewable sources discussed in Chapter 5 cannot by themselves, and perhaps even in combination, supply all of the energy needs of the world in the 21st century. Chapters 5 and 9 will no doubt provide plenty of opportunity for a spirited discussion between proponents of Earth-based renewables and those who doubt that they can supply our future energy needs. Close examination of the details and comparing numbers from Chapter 5 with those in Tables 9.2, however, reveals that the differences between the two chapters lie mostly in the fact that Criswell is basing his conclusions on a world which consumes energy at a rate of 60 TWt, a level that will probably not be reached for 100 years. Criswell addresses the question of which power sources have the potential for supplying 20 TWe by 2050, this being a level consistent with many of the future scenarios that is necessary to provide the global economic growth implied in the scenarios. His major emphasis, however, is on the possibility of supplying renewable (solar) energy from space by locating solar collectors outside the Earth's atmosphere and beaming power down by microwaves. This will certainly be the most controversial chapter in this book. Criswell argues (convincingly, in my opinion) that lunar solar power (LSP), in which solar energy is collected by large solar panels located on the Moon can become feasible and relatively inexpensive if we have the will to invest in it.
Geoengineering is defined in various ways by different scientists. Many scientists define it as large-scale intentional engineering of the environment for the primary purpose of controlling or counteracting changes in the chemistry of the atmosphere. This definition is consistent with the idea that it is used to remove the CO2 from the atmosphere as rapidly as fossil fuels or other sources emit it, so that the atmospheric loading does not increase (at least beyond "safe" levels). However, other forms of geoengineering involve controlling the climate itself by, for example, reflecting away sunlight to cool the climate and counteract the greenhouse effects of increasing CO2 (Flannery et al., 1997). It is also not explicitly a "what if nothing else works" idea. Sequestering carbon, for example, can certainly be imagined as one more way, along with increasing energy efficiency, of limiting the buildup of atmospheric CO2.
In Chapter 10 Keith examines many possible geoengineering options. Most of them involve huge engineering enterprises, from radiation shields to sequestering carbon by fertilization of the ocean to aforestation. In many of these schemes one must ask the obvious question "and what else happens?" Keith discusses the risk of side effects and unintended consequences as well as political and ethical considerations.
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