This paper first appeared in the journal Energy Systems and Policy, Volume 15, pp. 181-188, 1991.
Energy and Environment: The Light Path
New York, New York 10021-6399
This paper is dedicated to Cesare Marchetti, who lit the path.
Abstract For 200 years, the world has progressively lightened its energy diet by favoring hydrogen atoms over carbon in our hydrocarbon stew. The successful decarbonization of the energy system, the key to the alleviation of numerous environmental problems, will ultimately depend on the use of pure hydrogen fuel produced from sources and processes that are carbon-free. The outlook for aggregate reductions in the materials that an individual consumes, dematerialization, is less certain. Rapid evolution of the energy system along its current trajectory, combined with cultural change, can avert the environmental danger.
Key words decarbonization, dematerialization, hydrogen.
Our environmental problem started long ago when the Judeo-Christian God instructed Adam and Eve to go forth and multiply. For 3 million years or so, we tried and failed this assignment and thus lived in balance, more or less, with the rest of creation. The balance was a painful, unsatisfying one for humans, with high mortality, a chancy diet, and life restricted to a narrow range of hospitable climates. When we harnessed fire half a million years ago, the first major step was taken toward solving the problems of the raw, the cold, and the dark; fire would vastly extend human range and food supply. With the invention of agriculture 10,000 years ago, our species finally obtained the means for steady increase.
In 1859 Charles Darwin published the scientific basis for the biblical maxim to multiply. Recall the full title of Darwin's classic, On the origin of species by means of natural selection or the preservation of favored races in the struggle for life. Darwin's research followed a century of engineering breakthroughs that made possible the transition from addition to multiplication.
The agricultural story is important for the environment in numerous ways, but one merits emphasis here. The high rates of productivity and labor efficiency, eventually achieved by the mechanization of agriculture, released people from the land and fed the growth of cities. In the nineteenth century, metropolitan London was the largest city with perhaps 10 million people. Today Japan's Shinkansen Corridor extending from Tokyo to Osaka houses some 80 million. Worldwide the human population is now 55 percent urban. By the time population reaches 10 billion, the urban share may be 70 or 80 percent. We will live in a world of many enormous urban agglomerations.
City size and density are probably the most important factors in determining social complexity and technological evolution. The size of a city, defined as a large group of people connected in daily routines, depends on both population and speed. Higher speed reduces density, keeping population constant, or increases population by extending area at constant density. The size and density enable specialization and bring together people to combine ideas. They provide filters and competition for selection and set the market niche for new ideas and products. The technological paradigms for the world emerge from the high-level metropolises. Their growth and the interactions they have with one another and the hinterland pose the most difficult technical problems of communication, transport, and other needs and focus the resources to address them.
By 1800 or so in England and other early loci of industry, high population density and the slow but steady increase in energy use per capita increased the density of energy consumption. As the British experience demonstrated, if energy consumption per unit of area rises, the energy sources with higher economies of scale gain an advantage (Marchetti, 1975). Wood and hay, the prevalent energy sources at the start of the nineteenth century, are bulky and awkward to transport and store. Consider if every high-rise resident needed to keep both a half cord of wood at hand for heat and a loft of hay for the Honda. Think of the problems of retail distribution of these goods in cities with land prices of Tokyo, Singapore, Frankfurt, or Paris. Sales of wood in cities today are, of course, limited to an occasional decorative log providing more emotional than physical warmth. Biomass gradually lost the competition with coal to fuel London, Manchester, and other multiplying and concentrating populations, even when wood was abundant.
Coal had a long run at the top of the energy heap. It ruled, notwithstanding its devastating effects on miners' lungs and lives, the urban air, and the land from which it came; but about 1900 the advantages of an energy system of fluids rather than solids began to be evident. On the privacy of its rails, a locomotive could pull a coal car of equal size to fuel it. Coal-powered automobiles never had much appeal. The weight and volume of the fuel were hard problems, especially for a highly distributed transport system. Every automobile filling station could not have a rail siding to deliver its coal supply nor the acreage to store its coal. Oil had a higher energy density than coal--plus the advantage of flowing through pipelines and into tanks. Systems of tubes and tins can deliver carefully regulated quantities of fuel from the scale of the engine of a motor car to that of the Alaska pipeline. It is easy to understand why oil defeated coal by 1950 as the lead energy source for the world.
Yet, despite many improvements from well-head to gasoline pump, distribution of oil is still clumsy. Fundamentally, oil is stored in a system of metal cans of all sizes. One of these cans was called the Exxon Valdez. Transfer between cans is imperfect. This brings out a fundamental point. The strongly preferred configuration for very dense spatial consumption of energy is a grid that can be fed and bled continuously at variable rates. There are two successful grids, namely, gas and electricity.
Natural gas is distributed through an inconspicuous, pervasive, and efficient system of pipes. Its capillaries reach right to the kitchen. It provides an excellent hierarchy of storage, remaining safe in geological formations until shortly before use. Natural gas can be easily and highly purified, permitting complete combustion.
Electricity, which must be made from primary energy sources such as coal and gas, is both a substitute for these (as in space heating) and a unique intermediary to a variety of devices that exist only because electricity became widely available (Starr, 1990). Electricity is an even cleaner energy carrier than gas and can be switched on and off with great effect. Electricity, however, continues to have the disadvantage that it cannot he stored efficiently, as today's meager batteries show. It also loses in transmission; with present infrastructure, a span of 1000 km is about the economic limit. Lacking reserves in time and space, the electric power system is largely shaped by maximum rather than mean demand. Because mean demand is typically one-half of peak, an adequate electrical system looks large. It also looks inefficient to an engineer or banker, who wants expensive capital stock to be hard at work 24 hours per day rather than merely poised for action that may rarely come. Moreover, because of its limited storage, electricity is not much good for dispersed uses, such as cars.
The share of primary energy used to make electricity has grown steadily in all countries over the past 75 years and in the United States approaches 40 percent. In absolute terms, U. S. electricity growth, though irregular, has averaged about 3 percent per year the past 20 years. Nonelectric demand remains considerably larger. Because of inertia of capital stock and imperfect substitutability, the ratio will not now change rapidly. Thus, the core energy game for the next 30-40 years is to make a gas-electric system work as well as possible.
The No. 1 political task is to give a hand to natural gas and to reduce the biases in favor of other fuels. Legislative activity and subsidies have superannuated coal in the United States, Germany, Britain, Spain, Poland, and numerous other nations. Billions of public dollars per year prop up coal through fuel use requirements, pricing provisions, programs in fossil energy research and development, and government "cost-sharing" for clean coal plants. These subsidies should stop. Clean coal is an oxymoron, and the technologies that seek it are costly to install and complicated to maintain. Even as a source of electricity, coal is inferior. Though small, experimental plants may do better, coal-fired power stations typically achieve an efficiency of only about 30 percent. Gas turbine steam power plants are at 50 percent, and for this and other reasons can operate at costs equal to or below coal (Lee, 1989). They produce less CO2 and NOX, no ash, and none of the gypsum that comes from scrubbing coal. The United States should replace coal power stations with natural gas facilities and encourage this elsewhere.
We must tighten the noose around coal. Its use should be restricted to plants meeting stringent requirements for environmental performance. Globally, perhaps 50 to 100 billion tons more coal may be used (about 20 to 40 years of current consumption) before coal largely disappears from the market (Ausubel et al., 1988). If recent illness and accident rates are sustained, as many as 100,000 men will die directly from bringing it to market. It would be a good use of money to retrain miners for other work or to subsidize them to keep digging tunnels, but for purposes such as water supply, waste water, and transportation infrastructures.
If it is dusk for coal, it is mid-afternoon for oil. Oil has already been losing out in energy markets other than transport. The environmental challenges for oil are well understood, and pressure should be maintained to meet them. Over the next 10 to 20 years the United States should press worldwide for a tighter distribution system to address leaks, spills, and damaging forms of disposal; complete desulfurization of gasoline, heating oil, and diesel; and the elimination of lead and the associated use of catalytic converters and other techniques, including reformulated gasoline, to reduce CO and NOX. The continuation of oil usage can be tolerable for many decades with appropriate norms and controls.
For gas, the next decades should be a time of relative and absolute growth (Linden 1987, MacDonald, 1990). With estimates of the gas resource base having more than doubled over the past 20 years to very large volumes, we should encourage its adoption in the transport sector as well as for electric power (Burnett and Ban, 1989). There are already upwards of 700,000 natural gas vehicles in the world. Italy's fleet leads the way, but numbers are growing from Brooklyn to New Zealand. Natural gas can do a great deal to clear the skies of Los Angeles, Denver, and Phoenix, not to mention Mexico City, Delhi, or Bangkok. It should be made easier to build and access gas pipelines.
Attention must, of course, be given to safety and environmental aspects of gas use. Pipelines and tanks can explode with tragic consequences. Natural gas is also a source of greenhouse gas emissions, though each unit of energy-produced oil on average yields about one-third more CO2 and coal two-thirds. Flaring and leakage of methane, itself a powerful greenhouse gas, should be reduced for environmental as well as economic reasons. Worldwide losses are probably about 2 percent of extraction but could and should be held below 0.5 percent.
So, energy history must not end with natural gas, and, in fact, it contains a simple, strong thread that suggests it will not: decarbonization. For 200 years the world has been progressively lightening its energy diet by favoring hydrogen atoms over carbon in our hydrocarbon stew (Marchetti, 1985). Coal has only one hydrogen for each carbon atom, oil two, and natural gas (methane), of course, is CH4. If we are concerned about greenhouse gas emissions, smog, and spills, decarbonization is the powerful, clear energy prescription. The global energy system has been moving in this direction but perhaps not fast enough, especially for those most anxious about climatic change. With business as usual, the decarbonization of the energy system will require another hundred years or so.
The success of decarbonization will ultimately depend on production and use of pure hydrogen fuel (H2) (Ausubel, 1990). Environmentally, hydrogen is the immaterial material; its combustion yields only water vapor beside energy. The hydrogen of course must come from splitting water--not cooking coal or another hydrocarbon source. The energy to make the hydrogen must also be carbonfree.
One of the advantages of shifting the energy system first to natural gas is that the hydrogen infrastructure will mimic and thus learn from that of gas. The transport technologies are basically similar. There are other steps that can be taken to hasten and deepen the penetration of hydrogen during the next decades (Dinga, 1989). Because hydrogen escapes and ignites easily, progress is needed on storage, especially at the smaller scale of end-use through such means as metal hydrides and light gas cylinders of fiber-reinforced resins with impervious liners. Leadership should come from the aerospace industry, which already uses liquid hydrogen as a rocket propellant. This is an industry that puts a great premium on safety precautions, leak detection, and lightweight strength and has access to capital and markets that allow it to use the best available techniques.
Naturally, one asks how the hydrogen will be made. Safe, efficient, cheap production of H2 should be one of the highest priorities of the government agencies for energy, transportation, and space as well as private industry. There are several alternatives, including solar and photovoltaic routes. I also believe this is the most promising niche for nuclear systems. I am just old (or young) enough to have been impressed by school books of the 1950s and 1960s that argued that splitting the atom was the greatest technological breakthrough since the harnessing of fire. We have been impatient. It seems quite reasonable that it will take 50 to 75 years to understand how to use atomic power. I agree, however, with critics of nuclear power that fission is a contrived way to boil water and extravagant if required only about half of each day to make electricity for our homes and businesses.
What seems special about nuclear energy is its potential as a source of electricity for electrolysis and high temperature process heat while the cities sleep. Nuclear electricity and heat could make H2 on the large scale needed to meet the demand of billions of consumers. If temperatures above approximately 800oC can be economically sustained, wider kinetic possibilities exist, and the job of making ample hydrogen through thermochemical reactions may be much eased.1 For this level of heat high temperature gascooled reactors (HTGRs) are an appealing line for development. Any design for a new generation of reactors must feature inherent safety, and HTGRs appear to do so (Brown, Boveri, and Cie, 1985). Excessive elevation of temperature stops the reactor. Fissionable material is in the form of particles less than 1 mm in diameter sealed in fuel elements the size of tennis balls, each of which provides its own containment and does not release radioactivity even if the reactor is abandoned. Reactors to produce hydrogen could be far from population concentrations and pipe their main product to consumers.
This quick survey of our evolving energy menu leaves open at least two important and related questions: What about efficiency and what about developing countries? With regard to efficiency, I take the engineer's perspective that increasing efficiency is embedded into the lines of development of any machine or process. Measured in terms of fundamental performance, systems of transport, communications, farming, energy, and so forth, have been getting more efficient, with very few exceptions. In spite of market failures and other obstacles, efficiency improvements are well documented for everything from aircraft and autos to air conditioners and ammonia production (Nakicenovic and Grübler, 1989). Motors, light bulbs, refrigerators, and building materials will become more efficient, as will overall systems. An important opportunity may involve superconducting materials for transport and storage of electricity. What is new is not efficiency gains but their recognition.
The harder question may be lifestyles and behavior. We live in more numerous and smaller families. We want more square feet per capita in our residences. We want personal vehicles. We want to travel further and therefore at higher speed. We rarely reuse or repair products, though some products are becoming smaller and lighter. In short, the outlook for decarbonization is good, but the outlook for aggregate reductions in the materials (or embedded energy) that an individual consumes, that is, dematerialization, is uncertain (Herman et al., 1989).
A corollary concern is that developing countries, especially China and India, may rapidly recapitulate the developing pattern of the rich countries of the North on a larger and even more environmentally destructive scale. For example, it is feared that China will massively expand its coal use. I do not believe this need or will happen.
Twenty years of studies show that there is only one global energy system. Connected by common technology, capital, and information, it is dynamic, and all nations are coupled to it. The same year that Darwin published his theory of evolution, Colonel Edwin Drake drilled the first oil well in Titusville, Pennsylvania, and Chinamen soon lit kerosene lamps. Naturally, some nations are early adopters of technologies and others hop late onto the bandwagon. Thus, if one looks at the changing use of boat, train, bus, and plane for intercity transport in China, the evolution of market shares resembles the rest of the world, with perhaps a 30-year lag. However, the diffusion of technologies in nations or regions that are late to adopt is not nearly as pervasive as for the early adopters.
In fact, China would need to increase its rail network twenty times to achieve a spatial density comparable to that obtained by the industrialized countries in the 1920s when they relied most on coal (Grübler, 1990). China's railroads, the infrastructure of the coal economy, are already declining. Instead, in China as elsewhere motor vehicles and aviation are ascending. The nineteenth century industrial paradigm is forever gone. Do not expect to find coal-fired buses or coal-fired 747s on a future visit to Beijing. The structure of end-use demand, including the density of population in China's coastal plain, strongly favors natural gas and electricity.
Some argue that a viable alternative is for China to build many advanced coal plants near coal resources and a system to transport the electricity rather than the coal. But why bother with coal if there is gas? A major natural gas discovery in one of the poorest areas of China was announced in 1991 (The New York Times, 25 June). If the North wishes to lessen concern about environment and development, technologies for exploration and drilling for natural gas and loans for gas infrastructure should be top priorities for development cooperation. Recall that 90 percent of all hydrocarbon drilling has been in the United States and Canada, so that low estimates of reserves in many areas may reflect scant searching rather than dry earth.
At the same time, the ecological modernization of the North may have worrisome short-term effects on the poor countries of the South. Nature, especially carbon, is by far the largest export of the South and the former Soviet Union as well. The commodity price flares of the 1970s were followed by lasting reductions in imports to the North of products such as copper and major economic problems in numerous developing countries. If the North becomes vastly more efficient and frugal in resource use and reliant on indigenous energy, the developing countries may be pinched again. Of course, the potential energy frugality of the rich also provides an environmentally attractive pool of power to meet the demands of growing economic sectors and populations.
Overall, the trend of technological evolution evokes optimism about the relation of energy and environment. We are seeing the light. Scientists and engineers can do much to clarify the evolution underway and pave the way for favorable developments. The next decades are the time to realize the vision of the hydrogen economy first outlined twenty years ago (Gregory, 1973).
The environmental danger remains more in the potential than in what has so far happened. In fact, only a few percent of the Earth's surface are needed for human settlements. Though much of the surface has been transformed by human action, less than one percent of the land is covered by human artifacts. Fifty five percent of the United States's population concentrate on 10 percent of its area. The Earth's woods still cover 80 percent of the territory that they covered 3,000 years ago. In Europe the stock of forests may have grown 25 percent between 1971-1990 (Kauppi et al., 1992). The amount of land used for farms globally has been unchanged for 40 years. Genetic engineering and dietary changes could further free land from food production as tractors liberated peasants from stoop labor. We can choose to leave much more of the land unturned as well as avert massive alteration of the composition of the atmosphere.
Though hydrogen in principle can cleanly power 10 billion people in a hundred megacities, the energy system depends on long-term social acceptance and, therefore, must be seen as part of a larger environmental solution that is cultural and technological. For some time, it has been evident that modern societies are well organized to research and develop specific actions to correct problems. To be effective, such actions must mesh with attitudes and behaviors, for example, about what is considered harmful and how time is allocated. A Great Renunciation of economic life and material goods does not seem near nor in the interest of many. Yet, some renewed concept of "peace with nature" is surely required in which to embed our engineering design and to set totems and taboos for production and consumption (Meyer-Abich, 1986).
In animism ancient religions incorporated powerful brakes to the destructive actions, which the technical means always available to humanity permit. At the siege of Massilia (modern day Marseilles), Julius Caesar was short of wood and ordered his soldiers to fell a sacred grove. The soldiers trembled at the idea of wounding the annointed oaks and refused. Angered, Caesar took an axe and chopped down a tree. Perhaps unfortunately for Western civilization he went on to triumph in a series of battles, in fact, killing or enslaving half the able-bodied men of Gaul and devastating its towns and agriculture (Holmes, 1911).
It is progress that George Washington, the father of his country, was filled with regret when he cut the cherry tree. Alas, his response stemmed from characteristically pragmatic American considerations, not from feelings for natural objects. We must check our overenthusiastic cutting and burning and more generally our arrogant view of nature in favor of a more democratic view of all creation (White, 1968). We must recognize that multiplication and materialization jeopardize our own success in the Darwinian struggle for life and that such success must be redefined. Markets, among the most sophisticated systems of information and feedback, can do much to foster and channel the evolution of energy systems. To balance the myopia of markets, ethical and aesthetic criteria must specify the energy system as well as budgets, costs, and economies of scale.
To review, I believe the leading influence on the national and world energy diet will be the daily routines of the great population concentrations. The cities must be fueled in a safe, healthy, and environmentally attractive way for their own sake and to preserve the rest of the planetary surface. The United States and other industrialized nations must favor natural gas more strongly, both domestically and elsewhere. Meanwhile, we must firmly endorse decarbonization, take further actions to keep it on course, and prepare the way for hydrogen. We must take care that the ecological modernization of the North does not worsen the position of the South. We should seek to encourage in our culture dematerialization and the reanimation of Nature.
1 Present thermochemical cycles require temperatures as high as 1800oC, but an aggressive search holds promise of success at lower temperatures in a decade or two.
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