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Changing Climate: Report of the Carbon Dioxide Assessment Committee (1983)

Chapter: CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY

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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Suggested Citation:"CLIMATIC CHANGE: IMPLICATIONS FOR WELFARE AND POLICY." National Research Council. 1983. Changing Climate: Report of the Carbon Dioxide Assessment Committee. Washington, DC: The National Academies Press. doi: 10.17226/18714.
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Climatic Change: Implications for 9 Welfare and Policy Thomas C. Schelling 9.l INTRODUCTION The protagonist of this study has been carbon dioxide. The research has been motivated by concern that atmospheric carbon dioxide is increasing and may increase faster as the use of fossil fuels continues to grow and by the known potential for a "greenhouse effect" that could generate worldwide changes in climate. The group responsible for the report is the Carbon Dioxide Assessment Committee; the study was author- ized by an act of Congress concerned with carbon-intensive fuels; and the agency principally charged with managing the research is the Depart- ment of Energy. The topic is usually referred to as "the carbon dioxide problem," a global challenge to the management of energy resources. In a chapter on the welfare and policy implications, however, there are reasons for taking climate change itself as our theme, not carbon dioxide or energy. First, over the span of time this report has to cover there could be changes in climate not due to human activity. Changes due to carbon dioxide have to be assessed against some projected background of natural change. The consequences of an increment in global temperature, for example, would depend on whether it were super- imposed on a warming, a cooling, or no trend at all. Second, carbon dioxide is not the only climate-affecting substance that people inject into the atmosphere. Other gases have greenhouse effects; and dust from farming and industrial activity and the myriad changes made in the Earth's surface can alter climate. Not only must the impact of carbon dioxide be assessed together with other climate- changing activities, but any policy response needs a focus wider than carbon dioxide. Third, there is a natural tendency to define a problem by reference to the agent of change and to seek solutions in the domain suggested by the naming of the problem, "fossil fuels" or "CO2." There is a legitimate presumption that in matters of the Earth's biosphere any drastic change may produce mischief. There is also a widespread methodological preference for preventive over meliorative programs and for dealing with causes rather than symptoms. But it would be wrong to commit ourselves to the principle that if fossil fuels and carbon dioxide are where the problem arises, that must also be where the solution lies. 449

450 Finally, although a precautionary attitude toward any drastic changes in world climates is prudent, we do not know that there actually is a problem until we have completed the investigation of what changes in climates may occur and what damages or blessings they may bring. In assessing something as complex as global meteorological dynamics, it is wise to avoid any formulation that speaks of "a problem" in the singular or that attempts to evaluate changes absolutely, without regard to the pace of change over time. Until we reach the welfare and policy implications, research on atmo- spheric carbon dioxide generates its own agenda: sources of emissions, projected uses of fuels and patterns of land use, sources and sinks in the carbon cycle, radiative balance of the atmosphere and interchange of heat between oceans and air, changes in atmospheric temperature and induced changes in wind and precipitation, feedback through water vapor and reflecting ice, and the direct effect of carbon dioxide on photosyn- thesis. Which among the uncertainties are likely to yield to further research, on what time schedule, and how to deploy research resources are questions that have to be answered through a systems approach; but the main features of the system and its inputs are generated by a process that is mostly straightforward, even if not all of the relevant inputs can be anticipated before the research gets under way. But the agenda for policy implications demands an iterative process. To illustrate, at certain CO2 concentrations there are food-producing locations where reduced rainfall or snowfall is likely, and reduced food output, unless there are compensating improvements in water supply or water conservation or changes in crops or farming technology. To assess this change in climate requires projecting water resources and technologies and farming techniques; and to choose policies requires attending to whether it will be more economical to reduce production of C02 or to increase production of water. We have a choice between conserving fuel and conserving water. While conserving fuel is an obvious policy option at the outset, the parallel importance of conserving water emerges only at the end of the scenario, enlarging the domain of required research. Defining the problem as "the CO2 problem" can focus attention too exclusively on energy and fossil fuels, compared with calling it the water or the rainfall problem or, more evenhandedly, the issue of climate change. How the issue is named can affect its apparent character. If the solution to foreseeable problems has to be reduced C02 emissions, both the problem and the solution are global in a severe sense. A ton of CO2 produced anywhere in the world has the same effects as a ton produced anywhere else. Any nation that attempts to mitigate changes in climate through a unilateral program of energy conservation or fuel switching, or scrubbing of CO2 from smokestacks, in the absence of some international rationing or compensation arrangement, pays alone the cost of its program while sharing the consequences with the rest of the world. Worldwide agreements involving the main consumers or pro- ducers of fossil fuels might be essential to programs for reducing C02 emissions; in contrast, water development and conservation is usually a national responsibility or involves a few neighboring countries.

45l So the organizing framework for welfare and policy implications of atmospheric CO2 should be built around climate change not around the carbon dioxide. 9.l.l Uncertainties In approaching these welfare and policy implications there are two kinds of uncertainty. One is the subject of the preceding chapters: uncertainties about sources and uses of energy, which in turn embody uncertainties about population, per capita income, energy-using and energy-producing technologies, density and geographical distribution of populations, and the distribution of income; a multitude of uncertain- ties about the carbon cycle; and, finally, all the uncertainties in translating a growth curve for C02 in the atmosphere into appro- priately time-phased changes in climate in all the regions of the globe. The second is uncertainty about the kind of world the human race will be inhabiting as the decades go by, through the coming century and beyond. This overlaps the uncertainties just mentioned: per capita income, for example, both influences the use of fossil fuels and affects how readily the world's population can afford, or can adapt to, changes in climate. Similarly, the structures people inhabit, the ways people and goods are transported, the foods people eat, the ways countries defend themselves, and the geographical distributions of populations within and among countries all affect land use and the kinds and amounts of energy used and hence the production of CO2; but they also affect the ways that climate impinges in living and earning, even on what climates are preferred. The mobility of people, capital, and goods— the readiness with which people can migrate, goods can be traded, and capital for infrastructure and productive capacity can flow among regions and countries—will also determine how much difference the changes in climate can make. The location and significance of national boundaries, and various international and supranational institutions, would have much to do with whether adverse climatic effects in some places can be offset, in a welfare assessment, by improvements in other places. 9.l.2 The Time Dimension In addition to uncertainty, there is the problem of managing an indefinite succession of future times. There is a temptation to pick some arbitrary concentration of CO2, like double the current level, and to experiment with variables to get an idea of when in the next century that particular concentration might occur, using the median of some probability distribution that yields a single date. Alternatively, we pick a date, like the middle of the next century, and estimate the likely change in "climate" from now to then; to do this we have to pick some arbitrary conventional figure, like the mean expected increment in global atmospheric temperature, as index of the seriousness of climate change.

452 These simplifications can be helpful as long as it is kept continu- ously in mind that they are merely shorthand expressions for a dynamic process of many dimensions. The trick is keeping that continuously in mind. It is possible to do something more sophisticated. As in the approach to C02 emissions (this volume, Chapter 2, Section 2.l), we can make random selections of probabilistic values of key variables and generate time paths into the future for climate change. That generates more information than a person can keep in mind, especially if the sev- eral time paths are not roughly parallel; we then have the same problem of compressing all those results into a manageable number of dynamically descriptive parameters. Even then, what remains is a somewhat arbitrary intermediate variable with no direct climatic interpretation. Even if temperature change were all we really wanted to know in the different regions and localities, the global mean temperature is little help unless each of us knows how to extract from it the atmospheric tempera- tures at geographical locations of interest. But usually we are even more interested in winter and summer precipitation, humidity, cloud cover, fog, wind velocity, seasonal temperature variability, and the annual variations of temperature and rainfall around their local means. So even locally we have no single measure of what we might mean by climate change. Whatever the way we translate a CO2 concentration into some standard index like mean temperature (or temperature differential between pole and equator), and however we translate that locally into rain and snow and wind and sunshine and degree days, there is still no assurance that the changes that interest us in the things we call "climate" will vary proportionally with that numerical index (or even monotonically) in any given location. And finally, sports fans and farmers do not even agree on what is an improvement in climate and what is a worsening. For all these reasons it is difficult to keep in mind what it is that we want to be talking about as a "measure" of climate change in the future. 9.l.3 Discounting, Positive or Negative Then there is how we think about the future. The climate changes anticipated are at an unaccustomed planning distance in the future. The troubling changes are probably beyond the lifetimes of contemporary decision makers but not beyond intimate association; our grandchildren will live into the span of time we have in mind. There arises the issue of discounting costs and benefits that accrue in the future for comparison with costs incurred now. Should future populations count equally with present populations, or count more because there will be more of them, or count less because we feel less concern for people remote in any significant dimension like space, time, or nationality? Will future populations on average have vastly superior living standards, or somewhat better, or worse than today's generation? A century from now will large parts of the world's popula- tion be in extreme poverty, or will nearly everybody be better off, climate change notwithstanding, than most of the world's population is

453 now? If we were to undergo economic sacrifices to improve the well- being of future generations, is what we might do about climate change likely to be worth more than alternative legacies that we might leave them? These are not questions to be answered here—nor are there universal answers; they will be answered differently by different people and different governments—but they are unavoidable in an actual judg- ment on the welfare and policy implications of climate change in the lives of our grandchildren and their children. 9.l.4 Perspective on Change The most perplexing uncertainties are not in the train of events from the burning of coal to the changes in precipitation and temperature. Those at least have a certain structure. More open-ended and unre- stricted, and demanding imagination as much as estimation, are questions about what the world will look like. How will people be living and working and moving and raising families and entertaining themselves in Peking or New York or on the plains of Kansas or Patagonia, in the Nile Valley, southern England, or northern India? A mistake hard to avoid is superimposing a climate change that would occur gradually in the distant future on life as we know it today—today's habitations and transport, today's agriculture and construction and fishing, today's urban complexes, today's working hours and living standards, diet and warmth, indoor and outdoor activity. A useful exercise is to project ourselves 75 or l00 years into the past and imagine how different life is now, with its blessings and its problems, from what we might have expected had we been concerned, toward the end of the last century or the beginning of this one, with climate changes during the decades we are now experiencing. Anyone can amuse himself with a list of technologies, political events, and demographic and environmental phenomena that would be most startling to students of social policy around the turn of the last century. Electronics was not dreamed of. Electric light would have been new in our lifetime and unknown to most of our countrymen. There was telephone but no radio. Nuclear energy for electricity or propul- sion, let alone for weapons and medicine, was way over the horizon. (Transatlantic travel by zeppelin was a generation in the future.) Satellites in geosynchronous orbit would have been useless without today's electronics. Anesthesia was by ether, there were no anti- biotics, bedbugs were a scourge, and yellow fever had caused abandon- ment of the Panama Canal. Air-conditioning was by ice, and the New York World Trade Towers would have seemed like first steps toward enclosing cities. Electric street railways were transforming our cities. California had half the population of Massachusetts. Soybeans were not grown in Iowa nor rice in California. The greatest military advance to come in the next war was an unbelievably lethal defensive combination of machine guns, barbed wire, and mud. Russia was czarist. Africa belonged to Europe. Average weekly working hours in U.S. industry were 60, and there were no child labor laws. U.S. life expectancy at birth was 47 years (it is now 74). Only

454 a third of the U.S. population lived in places with more than 5,000 inhabitants, barely a fifth in places with 50,000. More than a quarter of the horsepower of all prime movers in the United States came from animals. Will there be changes in the way people live and work over the next hundred years that make as much difference as in the past hundred? Has our forecasting and assessing improved since the turn of the last cen- tury? If we had perfect climate forecasts for all the inhabited regions of the world for the century that begins, say, in the year 2025, there would undoubtedly be important parts of the world, and segments of populations in all parts of the world, where it would be difficult to put an algebraic sign on the apparent welfare impact, let alone assess the magnitude. For the world as a whole we might not be confident of the direction of change in some aggregate measure of welfare. Undoubtedly there will be places where some predicted change in climate could have no foreseeable benefit and where some potential damages could be foreseen with clarity. But unless we impute to our- selves foresight much superior to what we might willingly claim for ourselves were we doing our work in l900, it is likely that most of the identifiable changes in welfare due to climate change would be, for most parts of the world, swamped by other uncertainties. Even whether, on behalf of the world, we would prefer the mean global atmospheric temperature to rise by a couple of degrees over the next hundred years, or to fall by that amount, or to stay as it is, would depend on considerations other than assessments of what the specific changes in local and regional climate would do to life and welfare in the affected populations.* 9.l.5 Prudential Considerations What are those other considerations? One is that drastic change in the environment is costly to adapt to. Our technologies, our homes, our habits, our crops, and our travel patterns and recreational activities— but most of all the knowledge and custom that people bring to bear in earning their livings, the technologies embedded in structures and equipment, the genetics of plants and animals—arose in evolutionary processes. Any change in the environment that makes the work habits and the technologies and the crops unsuitable requires migration, adaptation, and replacement. All of these are costly and uncertain. To this it can be replied, inconclusively, that if the change is slow the adaptations and replacements, even the migrations, need not be traumatic or even especially noticeable against the ordinary trends of *A personal observation: Every expression of concern that I have read or heard about the effect of rising temperatures on human health and comfort has been about summer heat; I conjecture that in l900 the comments would have been about winter cold, autumn frost, and spring thaw, and the tone would have been positive.

455 obsolesence, movement, and change. The issue is suddenness and unexpectedness. Of course, where migration is politically impossible, or capital immobile, the movements and adaptations may not be forthcoming. A powerful argument is that we are good at recognizing precisely those impacts that we are good at accommodating. The reason we recog- nize them may be that we already know enough about them to anticipate and to adapt. It is consequences we have not thought of that may find us no better at adapting than we were at anticipating. They could be of greater magnitude than the consequences we can foresee. An example might have been the potential collapse of the West Antarctic ice sheet; that one has been thought of, but there could be something comparably different from ordinary climate that we have not thought of. It is wise to be concerned about any prospective change in some major index of climate, like the mean annual global atmospheric temperature, that goes beyond the boundary of values believed to have been experi- enced throughout the history of civilization. Certainly the temperate parts of Europe and North America would find bleak the prospect of a global cooling by two or three degrees, if the experience of the reported "Little Ice Age" of a few centuries ago is any guide. Still, it is not a cooling we are faced with but a warming, and there may be an asymmetry in our favor. Or we just look at things from the point of view of temperate climates that have more to lose from a cooling than from a warming. Or perhaps we just have not done the thought experi- ment of superimposing the colder winters on today's world and, by a series of approximations, thought of how we might adapt to such winters. A fair conclusion from the preceding chapters is that there could be, within the next l00 or 200 years, a systematic global change in climate exceeding anything that has occurred in the last l0,000 years. To be specific, the mean annual global atmospheric temperature would be higher, and the temperature differential between poles and equator would be smaller. And in specific locations the major components of climate, like temperature and rainfall, may move outside the limits experienced during the past l0,000 years. 9.l.6 Variation in Human Environments This prospect is sometimes described as a greater change in climate than people have undergone during recorded history. That is a dramatic way to describe the relative perturbation of some crucial global climate variables. But if we have in mind people and their climates, rather than climates in fixed localities, and especially if we think of mankind rather than individuals, that understates the climate changes to which people have been subjected individually and through which mankind has passed statistically. The members of this committee undergo greater changes in climate whenever they meet than most populations will undergo if they remain stationary while climate changes during the next hundred years. People who moved north in the United States during the l930s in search of jobs or west in the l940s, who migrated southwest in the postwar period in

456 search of pleasant environments, who left economically declining parts of New England, or who were recruited into the army, all experienced long-term or permanent changes of climate greater than any changes typically recorded over the past l0,000 years. People experience climate change mainly by moving. People have been moving on continental and intercontinental scales at least since the time of the Roman Empire. If changes in climate during the past several thousand years have been small in comparison with the changes we must consider possible during the coming hundred years, the latter are simi- larly small in comparison with the changes that large parts of the world's population have undergone in populating the western hemisphere. Even if people did not move, differential population growth in regions with different climate would have meant that "mankind" underwent large changes in average or statistical climate—the fractions of the popula- tion living in different climates. There is no indication that new kinds of climate will result from the rise in global average temperature. Climates will shift; some climates may become more and some less widespread. But the variation in climate is so great from desert to pine forest to rain forest, from the wide variation of summer and winter temperatures in the Dakotas to the narrow band of San Francisco, from permafrost on the North Slope to fog on the California coast, that the changes over time will still be unremarkable compared with variations across space. In l860, 98% of the U.S. population lived in humid continental or subtropical climates; barely 2% were scattered among the tropical, semiarid, or steppe climates, the marine and Mediterranean climates, or the mountain climates. In l980 the percentages in these latter zones had increased from 2% to 22%. There is continuous cross-migration among areas: in each of the two 5-year periods between l970 and l979, approximately l0 million people switched residence from one to another among the four large divisions—Northeast, North Central, South, and West. For the United States as a whole, slightly over half of the population has spent its life to date in the same state; the fraction who will spend, or have spent, an entire lifetime in the same state is much smaller. Climate variation even within the humid subtropical region, which had 32% of the population in l860 and again in l980 (but 29% in l920) is perhaps as great as the likely changes due to CO2, so movement within the climate "region" adds to the amount of relevant mobility. And this is still apart from the significant changes in micro- climate—local rather than regional—entailed in movement from countryside to Pittsburgh, Jersey City, or Milwaukee. The actual climates numbers of Americans have experienced since l800 are suggested by Table 9.l and the subsequent maps (Figures 9.l-9.5) that illustrate it. 9.2 A SCHEMA FOR ASSESSMENT AND CHOICE We now develop a framework for policy choices. The framework ought to be comprehensive. It should include theoretical possibilities that may

457 TABLE 9.l U.S. Population by Climatic Zone3-'^ (Figures in Parentheses are Percentage of Total Population in that Climate Zone) Climatic Population ZoneS Description 1800 1860 1920 1980 Aw Tropical wet and dry 0 2,996 129,741 2,793,140 (Savannah) (<l) (<l) (1) BSTotal Total semi a rid and steppe 0 64,018 4,291,664 21,000,465 (<1) (4) (9) BSi Southern California 0 15,657 1,138,802 11,801,232 BS2 Central Valley of California 0 17,426 276,820 1,262,423 BSk Middle-latitude steppe 0 30,935 1,4l5,622 7,936,810 BWh Tropical and subtropical 0 28,029 743,263 4,955,742 desert (<l) (<1) (2) Caf Humid subtropical 2,034 ,536 9,426,517 32,360,561 71,932,014 (warm summer) (42) (32) (29) (32) Cb Marine (cool summer) 0 39,246 1,795,406 4,447,811 (<D (2) (2) Cs Dry-summer subtropical 0 202,420 1,636,597 8,675,763 (Mediterranean) (<l) (2) (4) Daf Humid continental 2,348 ,030 16,074,866 59,811,474 90,882,262 (warm summer) (49) (54) (54) (40) Dbf Humid continental 435 ,665 3,586,555 9,394,792 13,7l0,636 (cool summer) (9) (l2) (8) (6) ^otal Total undifferentiated 0 184,896 l,559,963 9,147,733 highlands (<l1 (1) (4) Hl Northwestern Mountain 0 158,012 1,343,146 8,l50,762 Reg ion H2 Colorado Mountain Region 0 28,884 167,123 891,756 H3 Arizona Mountain Region 0 0 49,694 105,215 ^Source: U.S. Census Bureau, 1800, 1860, 1920, 1980; data compiled by Clark University Cartographic Service. ^Climatic zones shown in Index Map. be of no contemporary significance, because we have to think about choices as they evolve through the century. The framework should make room for imagination, not just for options that currently look cost-effective. The framework should lend itself to different levels of universality. While atmospheric C02 is a global condition, the consequences and many of the policy implications will be regional and local. Governments will assess consequences and choose policies according to the climatic impacts on their own populations and territory. At the same time, some national governments, including ours, need a framework for assessing consequences worldwide and policy options that are international in scope. Just as governments will assess differently the implications of climate change for their own countries, some perceiving gains and others losses, so will interests be divided within countries. Not only are some countries, like our own, large enough to have diverse climates subject to different kinds of change, but people in the same climate are affected differently according to how they live and earn their living, their age and their health, what they eat, and how they take

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463 their recreation. Our framework has to be susceptible of disaggregation. The framework should be construed as moving through time. The changes take time; the uncertainties unfold over time; policies and their effects have lead times, lag times, and growth rates. Governments and people will attach different discounts to events and conditions at different distances in the future. And a country that appears to be victim or beneficiary of a climate change forecast for the next 75 years would not be helped or hurt the same amount, or even in the same direction, by an additional 75 years of the same scenario. Uncertainties in the forecast CO2 effects on climate are not merely uncertainties in some average magnitude but also, especially in local or regional change, uncertainties about the algebraic sign of some measure of net welfare and in the distribution of gains and losses among sectors of a population. What we do not want, therefore, is a framework for assessing welfare and policy that is oriented toward some "bottom line." There will be as many bottom lines as there are users of the framework, according to their interests and responsibilities over space, time, and people. 9.2.l Five Categories The framework (Table 9.2) consists of a sequence of discrete cate- gories. They can be thought of as arrayed from left to right. The point of departure, Category l, contains the options for affecting the production of CO?. This is taken as starting point not to prejudice the question whether fuel and energy policies are the preferred policies for anticipating climate change but because this is the most familiar category, the one that occurs first and most naturally to people con- cerned with CO2 and climate change and the category least likely to be challenged as inappropriate, irrelevant, or improper. The framework itself entails no necessary presumption that the less CO2 the better. The last remark suggests a Category Zero preceding no. l, the back- ground, including any natural changes in climate, against which poten- tial changes are to be judged. The sequence of these categories is generated by the premise that, taking the background into account, future emissions of C02 would probably prove nonoptimal: reducing CO2 emissions is an obvious set of policies even if not the preferred set, and successive categories might be generated by following a sequence of "next steps." Thus Category 2, following production of CO2, is removal. If we cannot help producing too much, can we remove some? If too much is produced and not enough removed, so that the concen- tration is going to increase and climate is going to change in sys- tematic fashion, can we do something about climate? Category 3 consists of policies to modify climate and weather. Finally, Category 4 is all the policies or actions taken in conse- quence of anticipated or experienced climate change. It is important to include actions as well as policies because much adaptation will be by individuals and private bodies, and the term "policy" might exces-

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465 sively imply that the reactions to foreseen climate change, or to climate uncertainty, were solely the responsibility of governments. 9.2.2 Background Climate and Trends Absent a C02 effect, would global temperature rise or fall, or neither, or both, over the next hundred or two years, and by how much; and what uncertainty is there in our estimate? If the Earth were in for a cooling trend and prospects were universally gloomy, an off- setting greenhouse effect—the burning of fossil fuels—would offer some desired climate modification as an inadvertent but beneficial by-product. Indeed, as a by-product not easily controlled, it would be beyond diplomatic dispute and not dependent on agreement or cooperation. If the natural trend were toward a warmer atmosphere, added warming would aggravate concern. Part of this background is the emission, and residence in the atmo- sphere, of other gases or particulates that affect radiation in either direction. Several have been identified that could have a significant greenhouse effect. Over the coming century other emissions or environ- mental effects might have similarly significant inadvertent effects on global climate. Other background elements are the expected rise or fall in sea level, subsidence of land near sea level, and whether more land and more people, as in The Netherlands, will be below sea level already. An important background variable here is the fraction of the world's population and capital structures that would be expected over the coming century to populate low-lying areas that might have to be abandoned or protected. More generally, for climate rather than sea level, what are the regional demographic trends and the likely (continuously changing) distribution of populations among the changing climate zones? Migra- tion and relative growth expected in the normal course of events could aggravate or mitigate the damages due to climate changes and enhance or negate the benefits. If the main effects of climate change will be on agriculture, back- ground variables must include population and income, land use and agricultural productivity, dietary practices, and other determinants of whether decrements in food output due to climate change would be expen- sive to make up or to do without, at the income levels at that time. (The problems of assessing gains and losses to the people of a country, or to parts of the population of a country, are illustrated by the observation that for 50 years the government of the United States has had a policy of removing farmland from cultivation in the interest of higher farm incomes.) The prospects for water supply—sources, uses, transport, storage, and conservation—are evidently of importance. Rainfall, snowfall, and evaporation are among the key elements in climate change. Diminishing groundwater or growing needs for irrigation would be main determinants of whether increased rain and snow would be welcome and how costly reduced precipitation would be.

466 This list is incomplete in two respects. First, it consists only of highlights and does not contain everything that a priori we could recog- nize as relevant background, especially in judging the needs and problems of particular countries and regions. But it is necessarily incomplete also because when we come to the fourth category, policies to adapt, to mitigate, or to take advantage of climate change, we are bound to uncover significant parts of the background whose significance was not apparent the first time around. 9.2.3 Production of CO? There are two subdivisions, energy and land use. Energy breaks into three: reduced energy, reduced fossil fuels, and less carbon-intensive fossil fuels. The different sources of energy have different advantages and disad- vantages. Petroleum is the most versatile, gas the cleanest (except for pure hydrogen); nuclear power is limited to large-scale production of steam (or, indirectly, hydrogen); hydroelectric is fixed in location. Reducing energy thus has different effects on CO2 according to whether the savings are in transport, electric power, home heating, or indus- trial processes. And CO2 per unit of heat varies among countries because of the mix of energy sources. Among the fossil fuels gas produces the least and coal the most CO2 per unit of heat (oil about 0.8 and gas 0.6 times the carbon of coal). Because their production is itself energy-intensive, coal-based syn- thetics entail the greatest injection of C02 per unit of heat, count- ing the emissions of a synthetics plant. Currently interesting coal- based synthetics appear to require about 40 units of coal to convert l00 into synthetics and thus would put 40% more carbon into the atmo- sphere than plain coal, per unit of heat. (For petroleum refining the corresponding figure is about 5%.) Most of the known fossil resources are not gas and oil but coal and other currently uneconomical sources like shale, heavy oil, and tar sands. Shale is high in carbon per unit of heat because of the fuel used in retorting the shale. Land use is the other subdivision in this category, but it cuts across Categories l and 2 symmetrically. There is no way to "unuse" fuel that has been burned, but forests can be grown or cut and the net effect can go either way. Preserving a forest rather than permanently removing it can be thought of as producing less CO2 or removing it from the atmosphere. The relevant land use is more than living biomass. Dead matter on and in the soil amounts to two or three times the carbon of the living vegetation. What happens to forests affects the release of carbon from the exposed soil and so does what happens to unforested land through cultivation and erosion.

467 9.2.4 Removal of C(^ Removal shares with production the characteristic that it affects the global inventory. The incentives, therefore, are nonexistent for the individual, the firm, or the small nation, as long as removal is at any significant cost. The costs fall entirely on whoever undertakes removal; the benefits are shared indiscriminately. Removal can be subdivided into processes that take CO2 out of the atmosphere at large and those that "scrub" it from stack gases and other exhausts. The former are unrestricted by locale and operate on concentrations in the hundreds of parts per million (ppm); the latter operate at fixed sites and on much denser concentrations, in the tens or hundreds of thousands of ppm. A natural way to remove carbon at large is through photosynthesis. In growing, trees remove CO2. They release it on being consumed by fire, termites, bacteria, fungus, and in other forms of oxidation. Permanent removal requires that the global stand of forests increase in carbon content or that fallen and felled trees be preserved from oxidation. Three apparent possibilities for permanently increasing the carbon content of standing forests would be to increase the forested area, to increase the carbon density of forest by enhancement of growth or lon- gevity, and to enhance the density of carbon by cultivating alternative species. The first is "land management" and typically constitutes abstaining from deforestation or guarding against erosion. The second should occur to some extent as a consequence of CO2 enhancement; we have no reliable extrapolation from greenhouse experiments with enhanced CO2 to the long-term growth of natural forests. The third could provide a criterion for reforestation. There are some orders of magnitude to keep in mind. The carbon in existing vegetation is roughly equal to the carbon in the atmosphere. Worldwide, forests cover a quarter or a third of the continents, and this amount is about three times the area of land in cultivation or pasture. Reforested land takes a few decades to a century to reach, say, 75% of the carbon density of mature forest, depending on whether the climate is warm and humid, temperate, or subpolar. The preponder- ant fraction of carbon in living vegetation is trees, not shrubs, grasses, and crops. A one seventh decrement in forest worldwide of average carbon density thus adds—and promptly, because of disposal for clearing—on the order of l00 gigatons of carbon (Gt of C); a one seventh increment in forest removes, more slowly, the same l00 Gt of C. A doubling of atmospheric C02 (from current levels) is an addition of about 700 Gt of C; increasing mature forest by a seventh would thus offset a seventh of a doubling, or, what is approximately the same thing, might retard the growth of atmospheric CO2 by something like a decade during the second half of the next century. Biomass is an exceedingly land-intensive form of carbon storage; it requires a permanent inventory of living trees. An alternative would be to grow trees for harvest and preserve them from decay. If refor- estation is the reverse of deforestation, "refossilization" of har- vested forest would be the reverse of fossil fuel combustion. ("Fossil" is Greek for "dug up.")

468 A few pertinent considerations. Preserving trees on site (coating them in plastic?) utilizes land, as biomass does. Floating logs down- river and sinking them in the deep ocean has been thought of; getting them to the rivers and towing them to sea would be expensive and fuel- intensive. Randomly stacked, l00 Gt of C in the original lumber would occupy something like l000 km3 on the ocean bottom. One more technology might be increasing the transfer of carbon from ocean surface to deeper ocean. Pumping, perhaps by thermal gradient energy, has been proposed; the benefits with any currently conceived technology would be small compared with the cost. "Scrubbing" from stack gases requires disposal. Possibilities are pumping into deep ocean, where ocean is accessible, or piling up sludge somewhere, unless usable construction materials can be extracted or formed. One hundred gigatons of carbon might be associated with l00-200 km3 of sludge. One conclusion is inescapable, irrespective of a hundred years' tech- nological change: "sweeping" the atmosphere with trees can be no great part of any solution to a CO2 problem. That does not mean that a strategy for the use of lands and forests should ignore CC^, only that the role of trees, standing or fossilized, will be modest. "Scrubbing" from stacks and "washing" by the oceans offer the possibility of yielding to technological advance. 9.2.5 Modification of Climate and Weather The common distinction is between weather and climate. Both include the same descriptive components—temperature, humidity, rain and snow, clouds and fog, hours and intensity of sunlight, and other atmospheric details of special interest like visibility and ceiling for aircraft. Weather is what is experienced at a given time, where time is longer than instantaneous, as in "occasional showers" or "gusting winds," but no longer than the few days covered by short-range forecasts. The exact definition is not necessary to make the distinction with "climate." The latter is a probabilistic description of weather throughout the seasons of the year. Climate differs from weather in describing not a state but a pattern, including seasonal change; it includes averages and departures from average. And because variation from seasonal norms, if not permanent, is included in the definition of climate, it is inher- ently defined over decades, while weather, though not instantaneous, is defined over hours or days. The distinction, though useful, is inadequate for classifying some interventions. Seeding clouds is weather modification; there are no known or intended effects of more than short duration. Managing green- house gases that have long residence times, like carbon dioxide, is clearly climate modification, whether intended or not, and of course it could be intended. But two kinds of intervention are not so easily classified as weather or climate. One would be manipulating gases or particulates that affect incoming or outgoing radiation and have resi- dence times of months or years, not days or decades. The other would be a sustained program of cloud seeding, if it could be reliably and

469 predictably done, to affect permanently the probable rainfall or snowfall at certain times of year. Our classification of modification techniques can take the "warming" due to C02 as point of departure: one category is affecting the global radiation balance.* According to the preceding chapters, there is now little doubt that this can be done on a huge scale. It is exactly what we are doing with CO2. The fact that it is uninten- tional and that the consequences may not be welcome do not contradict that we know how, at some expense if necessary, to change the world's climate more than it has changed in the last l0,000 years. Warming the atmosphere currently is more economical than cooling it, because it happens as a by-product of energy consumption that would be costly to reduce or terminate. If we were faced with a "little ice age" over the next centuries, we might be glad to get some of that C02 in the atmosphere at no cost and without having to negotiate climate change diplomatically. But we know that in principle cooling could be arranged. Volcanic eruptions have done it. Considering the development of nuclear energy in both its explosive and its controlled uses and the feat of landing a team on the moon and returning it safely, and that we now know how to warm the Earth's atmosphere, we should not rule out that technologies for global cooling, perhaps by injecting the right particulates into the stratosphere, perhaps by subtler means, will become economical during coming decades. Next are nonradiative climate interventions. Possibilities include changing the courses of rivers (discussed in the Soviet Union), damming seas, and opening sea-level canals. Some would be within the juris- dictions of nations, some international. Weather modification should also be assessed with a long-term per- spective. Techniques for precipitating rain and snow, acquisitively because the precipitation is desired or pre-emptively to dump it else- where, could have a mitigating effect on undesired climate changes even if the time to develop them to the point of economic utilization were as long as the time that has elapsed since the first communication by electric spark. Some control of hurricanes may be achievable. Attention is usually on their destructiveness, but in many places hurricanes are a deter- minant of rainfall over large areas. Systematic suppression would create a significant change in regional climate. One more illustration that climate and weather modification are not an empty or uninteresting category is the possibility that the floating arctic ice cap could be made to disappear during part of the summer by depositing some substance, like soot, that would absorb the sun's *"Warming" is in quotation marks because the greenhouse effect is a global average temperature phenomenon but may result in colder as well as warmer temperatures in particular localities, or during particular seasons, and the "warming" is, furthermore, likely to be less important as a temperature change than as a determinant of winds, clouds, precipitation, sunshine, and other components of weather and climate.

470 heat. Whether an ice-free Arctic itself should be called "weather," the absence of ice would affect the climate of the surrounding areas. (The word "climate" is awkward here, as it is in connection with the prevalence of hurricanes; the result is a permanent part of the seasonal cycle only if the activity is sustained or repeated; and while an individual hurricane would count as "weather," the effect of 2 months' ice-free Arctic would not fit the short-range definition of weather.) Before going on to Category 4, it is important to recognize the distribution of incentives for climate or weather modification. It is characteristic of the "CO2 problem" that though it may be in the interest of the world economy to restrict, at some cost, the use of fossil fuels, it is probably not in the interest of any single nation to incur on its own the cost of any reduction in global CO2. Whether any of the climate and weather modifications that might be undertaken, aside from suppression of CQ^, would be unilaterally attractive to individual nations, is more problematic. If the capacity to affect the radiative balance at nonprohibitive cost were acquired by several nations that disagreed about the optimum balance, that technology could be a source of conflict. More obviously, countries that view hurricanes as disasters and countries that view them as water for their crops would have different preferences about which if any hurricanes to suppress or to modify, or to generate. (The possibility of unilateral action, especially if it could be surreptitious and unverifiable, could cause trouble.) This section can be summarized by three points. (l) We know that in principle weather and climate modification are feasible; the question is only what kinds of advances in weather and climate modification will emerge over the coming century. (2) Interest in C02 may generate or reinforce a lasting interest in national and international means of climate and weather modification; once generated, that interest may flourish independently of whatever is done about C02. (3) Weather and climate modification may be more a source of international tension than a relief; and CO2 may not in the future dominate discussion of anthropogenic climate change as it does now. 9.2.6 Adaptation Adapting to a change in climate is often thought of as an alternative to preventing it. For reasons that are often implicit, but not neces- sarily illegitimate or unpersuasive on that account, prevention is usually the preferred alternative. Prevention will certainly not, however, be absolute. Such deliberate reduction in emissions as may be achieved will be costly—and increasingly costly as lower emission levels are approached. So there is an inescapable question of how much, if any, restriction or removal will appear worthwhile to those who have to take the decisions—or to pay for them. Deciding how much CO2 suppression makes sense requires an assessment of adaptation in the aggregate.

471 Most adaptation will be undertaken by units the size of a nation or smaller—families, firms, ministries and departments, cities, counties, and states or provinces. Even participation in an international pro- gram of CO2 suppression would be a national decision. The costs and benefits of adapting rather than preventing would thus be most mean- ingful at the level of each nation. Thus, except for a comparison with CO2 suppression or climate modification, adapting to change is not an aggregate process. It is largely a multitude of decentralized, unconnected actions. And most of the adaptation to change that will take place in most societies over the next hundred years will not be adaptation to climate change. Migra- tion, for example, can be motivated by changing climate; but migration within and between countries may still be responding a hundred years from now, as it is now, to political conditions and economic oppor- tunities, and changing climate would be only one element in the politics or the economics. If we think how life has changed in our own country in 75 years during which the population changed from rural and small town to urban—real income per capita doubled three times, the popula- tion 65 and older increased from 4 to l2%, and life expectancy at birth grew from 50 to 75 years—and suppose that comparably dramatic changes may occur at the same rate in the future (although not necessarily along the same dimensions), it is evident that in the way they live and earn their livings people will be making multitudinous adaptations. Furthermore, the microclimates of many urban areas (Los Angeles, Mexico City, Tokyo) have changed drastically in the last 50 or 75 years. And changing technology and changing incomes always entail continual adapta- tion to one's local climate, even when that climate is not changing. Adaptation can be subdivided into governmental policies and private actions. Government policies can be further subdivided into those taken at a national or subnational level and those that are necessarily or preferably international. And there are two aspects of a CO2-based climate change that are so different that they need to be kept separate, especially as they may not seem to be what is usually meant by "climate." One is changing gaseous composition of the air we breathe. The other is changing sea level. 9.2.7 Breathing C0? Little attention is paid, by those who study carbon dioxide and climate change, to any possible direct effects of C02 in the air we breathe on human health or on the animal population. Any natural anxiety about the health effects of a doubling or quadrupling of an important gas in the air we breathe—the substance that actually regulates our breathing rate—is relieved by the observation that for as long as people have been living indoors, especially burning fuel to heat themselves, people have been spending large parts of their lives—virtually all of their lives for people who work indoors and travel in enclosed vehicles—in an atmosphere of elevated C02. Doubling or even quadrupling CO2 would still present a school child with a lesser concentration during outdoor recess than in today's classroom.

472 There is, furthermore, no documented evidence that CO2 concentra- tions of 5 or l0 times the normal outdoor concentration damage human or animal tissue, affect metabolism, or interfere with the nervous system. (Industrial safety limits for chronic exposure are currently 5000 ppm— about l5 times the atmospheric concentration.) Nor is there theoretical basis for expecting direct effects on health from the kinds of C02 concentrations anticipated. But even though the answer is easy and reassuring, the question has to be faced. It will occur to people who hear about changes in the atmosphere that their grandchildren are going to breathe. And there have not been experiments with either people or large animals that spent their whole lives, including prenatal life, in an environment that never contained less than, say, 700 parts per million of carbon dioxide. So the question deserves attention, even though there is no known cause for alarm. 9.2.8 Change in Sea Level A dramatic possible consequence of CO2-induced climate change is a significant rise in sea level. The three phenomena related to climate that may raise the sea level are thermal expansion of the water, reduced land ice and snow due to melting and wind erosion, and enhanced flow of glacial ice. The West Antarctic ice sheet is grounded below sea level and possibly susceptible to a rise in ocean temperature, which might cause faster glacial flow or "collapse." The estimated volume suscep- tible to such a process is equivalent to a rise in ocean levels of 5 or 6 m. (Floating ice, of course, does not affect the water level.) Large portions of the Earth's population, territory, and capital structures are within 5 or 6 vertical meters of today's high-water mark. Thermal expansion of the water and melting of land ice have possible effects, as explained in Chapter 8, of 60-70 cm if CO2 should double over the coming century. Many serious shoreline problems are sensitive to sea-level changes on the order of tens of centimeters, and 65 cm, though modest sounding on a calm day at the seashore, could produce a variety of profound environmental changes. It is the West Antarctic ice sheet, however, that ranks as the major potential threat. Obviously speed and warning time are crucial to any assessment of costs and damages. It is concluded in Chapter 8 that any disappearance of the West Antarctic ice sheet would take centuries rather than decades and would be progressive rather than sudden. There are three principal ways that human populations can adapt to a rising sea level. One is retreat and abandonment. A second is to build dams and dikes. A third is to build on piers and landfill. The basic division is between abandonment and defense. 9.2.9 Defenses against Rising Sea Level Defense against a sea-level rise of several meters has received little attention in the United States. The threat is unfamiliar and only

473 recently recognized. (Actual defenses against high seawater are extremely localized in the United States.) Most people recall, when reminded, that parts of Holland have been below sea level for centuries. (More than half of the l4 million Dutch live below sea level.) People recall, when reminded, that large areas of many cities, including familiar airports, are built on landfill. The professions that defend against river and tidal floods, storm surges, and land subsidence have only very recently been drawn into the CO2 discussion. It is therefore worth emphasizing that there are ways to defend against rising sea levels. For many built-up and densely populated areas they could probably be cost-effective for a rise of 5 or 6m. Even where defending against 5 m were not cost-effective, defending against a meter or two could make sense for a century or two. Defense is not an empty hypothetical or purely speculative option. The economics of dikes and levees depends on the availability of materials (sand, clay, rock); on the configuration of the area to be protected; on the differential elevation of sea level and internal water table; on the depth of the dike where it encloses a harbor or estuary; on the tide, currents, storm surges, and wave action that it must with- stand; and on the level of security demanded for contingencies like extreme ocean storms, extreme internal flooding, earthquakes, military action, sabotage, and uncertainties in the construction itself. The Dutch build their seaward dikes with sand from the nearby ocean bottom; other structural materials are used for the base of the dike (under the sand), to cover and enclose the sand, and to provide facing against waves and currents. The dikes are not impermeable; there is permanent seepage requiring some pumping. It is noteworthy that with current technology the Dutch have found that 5 or 6 m is about the mean-sea- level difference that they can safely and economically build against with the plentiful and nearby sea sand as the primary material. Much of the coastal diking does enclose land 5 or 6 m below sea level. (The dikes are actually built to ll or l2 m to guard against heavy seas during an extreme spring tide augmented by a storm surge—the piling up of water by the force of storm winds acting on the funnel-shaped North Sea.) Besides keeping the ocean out, there have to be dikes—we call them levees—for conducting rivers to the sea. If a river runs through a city and the final 50 km of the river is no more than 5 m above sea level, the surface of the river must rise by 5 m if the sea level does, and 50 km of levee are required. The dikes in Rotterdam hold back not the ocean but the waters of the Rhine and other rivers, the surfaces of which cannot be below sea level. On the economics of diking it can be kept in mind that the Dutch for centuries have found it economical to reclaim the bottom of the sea, at depths of several meters, for agricultural, industrial, and residential purposes. This is true not only of inland seas of which only the mouth needs to be diked but of extensions directly into the ocean where half or more of the perimeter of the newly acquired land needs to be diked against the full fury of North Sea storms. A rudimentary illustration of the economics can be based on the Boston area. A full 5 m would cover most of downtown Boston. Beacon

474 Hill, containing the State House, would be an island separated by about 3 km from the nearest mainland. Most of adjacent Cambridge would be awash. But it would take only 4 km of dikes, mostly built on land that is currently above sea level, to defend the entire area. Perhaps even more economical, because it would avoid the political costs of choosing what to save and what to give up and of condemning land for right-of- way, would be a dike 8 or l0 km in length to enclose all of Boston Harbor. If that were done, new deep-water port facilities would have to be constructed outside the enclosed harbor; locks would permit small boats in and out. The Charles and Mystic Rivers would have to be accom- modated. Whether in a couple of hundred years there would be any significant flow in those rivers would depend on changing climate and increasing demand for water. Levees, a diversion canal, or pumping could be compared for costs and ecological impacts. We have no professional estimate of what such a system would cost. Some professional guesswork suggests that at today's values the cost of defending against even the full 5-m rise is less, perhaps by an order of magnitude, than the value preserved. Actually, to judge by the Dutch experience, reclaiming tidelands and harbor bottoms and even land in the open sea could become irresistably attractive during the coming centuries, either by landfill or by dikes. The situation is totally different for an area like the coast of Bangladesh. If we imagine the sea level rising by a meter or two per century for enough centuries to reach 5 or 6 m, Bangladesh differs from Boston in having a huge coastal area subject to inundation, rather than a concentration of capital assets that can be enclosed by a few miles of dikes, and in being so susceptible to internal flooding with fresh- water that the levees required to protect the country would be many times greater than the length of the shoreline. Thus the example of Boston cannot demonstrate that protection would be the preferred course everywhere and that it would reduce damage everywhere by an order of magnitude. The example only demonstrates that defense may compete favorably with slow retreat from the sea for densely populated urban areas. Where defense is not practicable, retreat is inevitable, at least selectively. In urban concentrations, where buildings may last a century, good hundred-year predictions of sea-level change (including likely erosion and storm damage) should permit orderly evacuation and demolition of buildings. Urban renewal and interstate highways have already had such effects. (In the United States, the law and the politics of real-estate development would determine whether recently evacuated areas could selectively be rebuilt using landfill or piers.) The most severe dangers appear to be in areas, like Bangladesh, where dense populations dependent on agriculture occupy low coastal plains already subject to freshwater or seawater flooding. 9.2.l0 Food and Agriculture The only readily identified potential impact of significant magnitude on future living standards is on agriculture. Virtually all agricul-

475 ture everywhere is outdoors. It is dependent on sun and rain or irrigation from remote rain and snow; it is sensitive to temperature, especially frost; it is subject to beneficial and harmful activities of insects, worms, and microorganisms, and to weeds, all of which in turn are affected by weather and climate. Rainfall affects leaching and salinity and erosion. Animals are dependent on weather and climate indirectly through the crops they feed on and the pests that afflict them and directly through their sensitivity to temperature, humidity, or wind and snow. Most farm labor is applied outdoors, in unconditioned climate. Much the same can be said for fishing. Poultry has moved indoors in many parts of the world; not only is the climate conditioned but the length of the artificial day is controlled. Plastic has helped greenhouses to multiply. If genetic engineering can increase the efficiency of photosynthesis or facilitate the nonagricul- tural manufacture of protein, food production may become much less dependent on natural climate during the coming century. Still, in most of the world, a land-intensive agriculture, outdoors, seems almost sure to be the dominant form for at least most of the coming century. Despite agriculture's almost certain substantial dependence on climate throughout the future, it is nevertheless not yet possible, with today's crops and today's technologies and today's distribution of agricultural activity over the Earth, to assess the aggregate impact accurately enough even to be sure of its algebraic sign. As mentioned earlier, there is a presumption that climate change, independent of what the change is, being costly or difficult to adapt to, has a disadvantageous expectation. There is a presumption that the direct effect of CO2 on photosynthesis, though it could affect weeds, too, might increase yields somewhat. A warming in northern latitudes could bring additional land under cultivation, although the quality of such land for crops is not promising. The effects of rainfall and snowfall are too mixed and uncertain to allow a prediction of their net effect. It is prudent, however, to expect that if climate change occurs rapidly, the costs in the aggregate will be positive and for some countries severe. A fair guess seems to be that any likely rate of change of climate due to C02 over the coming century would reduce per capita global Gross National Product by a few percentage points below what it would otherwise be. If global economic production were to stagnate and popu- lation to grow, so that food production became an even greater portion of world output, and so that large parts of the world's population continued poor and largely dependent on the production of food for their own livelihoods, the projected climate changes could be exceed- ingly bad news. If world productivity improves at a reasonable rate and population growth dampens over the coming century, food production should be a diminishing component of world income. A rise of l0% or even 20% in the cost of producing food would be a few percent of world income at the outside. That lost income should occur in a world of appreciably higher living standards than those that prevail today. A curve of world per capita income plotted over time would be set back probably less than half a decade. That is, the living standards that might have been achieved by 2083 in the absence of climate change would be achieved instead in the late 2080s.

476 Adaptation to changing climate would take several forms. The devel- opment of water resources, typically an enterprise with lead times of several decades, becomes more urgent. Novel sources of freshwater, like large-scale desalinization or the mining of icebergs, becomes relevant to accessible coastal areas. Crops resistant to saline soil, or irrigable with brackish water, could be at a premium in plant genetics. Cultivation technologies that do not turn or disturb the soil should be increasingly improved. Water storage and transport, and inhibition of evaporation, would receive continued attention. A development that is difficult to assess is change in dietary habits. Besides reflecting changed levels of income, working arrange- ments, and climates themselves, these may be affected by food- preparation technologies that are now even beyond speculation. 9.2.ll Global Warming and Energy Consumption The pure temperature feedback on the use of energy, both as a cost- saving (heating) and an additional cost (cooling) and as a consequent damper or booster to fuel consumption, is of obvious relevance. Such estimates as there are do not indicate that any overall reduction or increase in energy use, due solely to temperature change, would be of major significance, whichever way the net effect goes. It is curious that the most immediate consequence to come to mind in connection with a global warming is not a major element in the overall energy assessment. In understanding such an estimate, it can be noted that there is little one can do except to imagine the difference it would make in present society, living as it does and where it does now, to have temperatures of the kind projected in relation to CO2 to which we were already adapted. There have been no efforts to imagine the distribution of the population by climates a hundred years from now, the structures in which people would live and work, the technologies for heating or cooling air or human skin, the energy sources for heating and cooling, the effects of local population densities, or any of the other elements that would go into a cost comparison. Estimates also have had no basis in wind or humidity. This estimate, that temperature itself will matter little in overall energy use, is therefore a first approximation that can be straightforwardly arrived at by imagining summer and winter thermostat changes equivalent to the forecast change in ground-level atmospheric temperature in different regions or lati- tudes. Degree days of heating and cooling yield a result that is not an impressive fraction of the current cost of heating and cooling. What this estimate does is to remind us that the most important effects of increases in global average atmospheric temperature, or even regional temperatures at different latitudes, are not temperatures per se but changes in the other dimensions of climate, especially precipita- tion, driven both by the average warming and by the changing temperature gradients between equator and pole.

477 9.2.l2 Distributional Impact The most likely possibility to emerge from the work done so far in relation to CO2 is that the impact of climate change on global income and production, and specifically the agricultural component of it, would not be of alarming magnitude. Particular regions or countries, especially those dependent on agriculture for a large part of their earnings, could be severely affected. The result would look more like a redistribution of global income than a large subtraction from it. The absolute amount of such redistribution need not be large for it to affect some areas very adversely. Poorer countries would be especially at risk, if the global distribution of income bears close resemblance to that currently prevailing, mainly because it is in the poorer coun- tries that food production is a large part of total income and the capacity to adapt would be the smallest. An important international means of adaptation would therefore be compensatory transfers of income, capital, and technical assistance. Saying so does not make it politically feasible, but after 35 years of bilateral and multilateral foreign aid programs the compensatory approach to global imbalances and maldistributions appears to be a permanent part of the institutional landscape. In any event, in considering the disaggregated gross changes in production and income rather than the global net changes, we need not be committed to letting the chips lie where they fall. Certainly if global income were pre- dicted to rise substantially in the aggregate at some level of CO2, but particular areas were to be disastrously affected, some system of compensation would be optimal in a purely income-maximizing sense. A distinction should be made between compensation arrangements oriented toward CO2 or climate and transfers from richer to poorer countries not tied to the particular alleged origins of poverty or hardship. If CO2 becomes the focus of concerted international action over a prolonged period, the predictions and measures of climate change and their attributions to CO2 and other causes, together with national "contributions" to CO2 through combustion of fossil fuels, will become articles in diplomatic commerce. In that case, claims for compensation as a matter of right may emerge as a redistributive basis, along with judicial-like procedures for assessing claims and obligations. If instead the CO2 accumulation gradually changes climates but there is no internationally organized regime of fossil fuel restriction, compen- sation would be less like "categorical aid" and more like general welfare or income support—always subject, of course, to international political divisions and disputes. Table 9.3 summarizes possible background changes and societal response strategies to climate change. 9.3 SUMMING UP When the work leading to the current report was begun, the energy crisis that began in the winter of l973-l974 was barely 5 years old and reactions to the rising energy prices of the l970s were barely

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480 visible. Projecting a continued worldwide increase in the use of fossil fuels of 4% per year, reflecting historical experience, gave estimates of several thousand gigatons of additional carbon in the atmosphere by the end of the twenty-first century, something between two and three doublings over current levels. Such a projection was both alarming and unreasonable—alarming not only because of climate change but of sheer atmospheric contamination, and unreasonable in implying that coal consumption might actually increase fiftyfold or l00-fold. That was not an estimate, merely an illustrative projection of historical trend. In the interim, the impact of rising fuel prices on fuel consumption has become more visible, and fuel prices have doubled again; current projections for fossil fuels are commonly closer to 2% growth. At that more moderate rate the accumulated atmospheric carbon at the end of another l00 years would still be at least double the current quantity, but far less than the several thousand gigatons of the earlier projec- tion. The depressed rate of increase compared with the first three quarters of this century reflects higher fuel prices and national energy policies. The prospects are therefore much less alarming than some of those earlier calculations made them appear. And if successive increments in C02 were going to be increasingly harmful to climate, the lowered estimates of C(^ correspond to even more significant reductions in the impact of climate change. Nevertheless, there is still the prospect of climate change within the coming century that takes us outside the boundaries experienced within the past l0,000 years. There is no reason for believing that that development is to be welcome, and there are many reasons for the contrary. The first policy question that usually suggests itself is what can be done through national and international efforts to reduce the combustion of fossil fuel. Next there comes a complex of questions about how to respond and adapt, internationally, nationally, locally, and individually, to the varieties of climate changes that are to be expected in the different places around the globe where people live. For many reasons it is unlikely in the foreseeable future that national governments will embark on serious programs to reduce further their dependence on fossil fuels to protect the Earth's climate against change. One reason is that governments are already saturated with reasons to reduce their dependence on fossil fuels, having made what many of them believe are heroic adaptations to high and uncertain fuel prices during most of the decade that began l0 years ago. If the rate of increase of carbon emissions can be held to 2% instead of the 4% that might have been projected from earlier experience, the doubling time for atmospheric CO2 is increased from about two thirds of a century to a full century. Had a universal tax on fossil fuels been proposed a decade ago to discourage the burning of fuel and to mitigate the coming climate changes, it is inconceivable that anyone would have proposed raising fuel prices as much as they have been raised. (Of course, no one would have proposed that the proceeds accrue as profits to the producers of fuels.) While some supply response to the current high price of fuels can be expected, the prospects are for continued

48l high and even rising fuel prices despite some current softness in the market for crude oil. The appetite for still higher prices, or still further restrictions on fuel consumption, as a means of further stretching out future additions to atmospheric carbon dioxide will not be forthcoming. As emphasized earlier, any single nation that imposes on its consumers the cost of further fuel restrictions shares the benefits globally and bears the costs internally. For only the very largest fuel-consuming nations, probably for only the Soviet Union and the United States, might it be in the national interest unilaterally to suppress further the use of fossil fuels in the interest of mitigating climate change. And even that trade-off is certain to look unpersuasive to consumers paying current fuel prices. Some global rationing scheme that enjoyed the participation of the major producers and consumers of fossil fuels would be required if there were to be severe action at the national level. In the current state of affairs the likelihood is negligible that the three great possessors of the world's known coal reserves—the Soviet Union, the People's Republic of China, and the United States of America—will consort on an equitable and durable program for restrict- ing the use of fossil fuels through the coming century and successfully negotiate it with the world's producers of petroleum and with the fuel- importing countries, developed and developing. It makes sense therefore to anticipate changing climates. In any event, no regime for further restricting fossil fuels would hold emissions constant, so climate change is what we should expect. Evidently, the value of developing the nonfossil sources of energy is at least as great as it would have been under a regime of fossil- fuel restriction and, if anything, more valuable. Are there long lead-time projects or policies that need now to be adapted to the prospects of changing climates? Water resources and related technology may have lead times of half a century; water is therefore a candidate for planning in a context of potential climate change. As forecasts for climate change become clearer, there may be strong indications for research and development related to agriculture, fisheries, and pests. Military planning will probably be alert to changes on land and sea. Certainly coastal planning should be affected by forecasts of rising sea levels. But nothing urgent is foreseeable yet. The foreseeable consequences of climate change are no cause for alarm on a global scale but could prove to be exceedingly bad news for particular parts of the world. Generally, the more well-to-do coun- tries can take in stride what may prove to be a reduction (probably not noticeable as such) by a few percent in living standards that will likely be greater per capita by more than l00% over today's. But one has to question whether this relatively calm assessment can be applied to a country, say Bangladesh, where food production is already at the margin of subsistence and coastal flooding is already serious. Is it an especial hardship for the people of Bangladesh that the nations on whom would depend any permanent regime for globally rationing the use of fossil fuels in the interest of stable climate are unable to take a long economic view and to reconcile intense political differences?

482 Those concerned with the future welfare of Bangladesh have more reason to be concerned with population growth than the growth of CO2. They have to be more concerned about the floods that will occur during the next 20 or 30 years than the floods that may occur during the 20 or 30 years after the middle of the next century. If the developed coun- tries were prepared to make substantial economic sacrifices now to help to provide a more benign climate for Bangladesh a hundred years from now, anyone responsible for Bangladesh would probably prefer to have those economic sacrifices take the form of more immediate economic contributions to the country's standard of living and economic growth. Specifically, if a global tax on carbon fuels were used to depress the trajectory of future carbon in the atmosphere, a country like Bangladesh would be far more interested in an immediate and continuing claim on some of the proceeds of such a tax than on the future climatic effects of the tax. It is unlikely that countries currently as poor as Bangla- desh would elect to join the rest of the world in paying higher fuel prices just to suppress carbon dioxide. I earlier referred to this "calm" assessment of the "foreseeable" consequences of climate change. As remarked earlier, there is probably some positive association between what we can predict and what we can accommodate. To predict requires some understanding, and that same understanding may help us to overcome the problem. What we have not predicted, what we have overlooked, may be what we least understand. And when it finally forces itself on our attention, it may appear harder to adapt to, precisely because it is not familiar and well understood. There may yet be surprises. Anticipating climate change is a new art. In our calm assessment we may be overlooking things that should alarm us. But it is difficult to know what will still look alarming 75 years from now. It will be a while before the subject settles down.

Annex 1 Report of Informal Meeting on C02 and the Arctic Ocean Roger R. Revelle On June l-2, l982, a group of experts was informally convened by the Carbon Dioxide Assessment Committee to discuss the implications of C02-induced climatic changes for the floating sea-ice coverage of the Arctic Ocean. The meeting was held at the Philadelphia Centre Hotel, Philadelphia, Pennsylvania, in conjunction with a meeting of the American Geophysical Union (AGU). The assistance of the AGU is gratefully acknowledged. A list of participants is appended to the following notes that summarize the views expressed at the meeting. MAJOR POINTS OF DISCUSSION l. The Arctic ice has been a stable climate feature. There is quite good evidence for persistence of the ice cover all year round for the last 700,000 years and perhaps for the past 3,000,000 years, although there is debate about whether the Arctic may have been open in summer from 700,000 to 3,000,000 years ago. The existence of glacial marine sediments in the Arctic basin shows that ice rafting occurred during the past 5,000,000 years. Longer ago than 5,000,000-l5,000,000 years, the Arctic may have been open year round. Global cooling patterns are such that an initial freeze-up of the Arctic may have occurred l5,000,000 years before present, although there is no direct evidence. The physical reasons for the persistence of the Arctic ice are not well understood but may reflect both dynamic and thermodynamic processes such that when little (excess) ice exists, correspondingly more (less) ice is produced the next winter. 2. Studies on whether the Arctic sea ice will completely melt in summer, and if so, whether the ice will remain melted in winter, as suggested by Flohn (l982), have produced ambiguous results. Ewing and Donn (l956) proposed an explanation for-ice sheet cycling (i.e., ice ages) based on an intermittently open Arctic. Quantitative analyses have not confirmed this hypothesis. MacCracken (l968) devel- oped a simulation model, which indicated that an open Arctic is not stable; under present climatic and geographic conditions, there is such strong cooling in winter that a year-round open Arctic could not persist. MacCracken's result does not preclude an Arctic open only in summer. Energy balances worked out by Fletcher (l965, l973) and Rakipova (l966) indicate that an open Arctic would be stable. Fletcher 483

484 finds that during summer (April to August) atmospheric heat loss over an ice-free Arctic would be greater than at present. This implies more vigorous circulation and cooler lower latitudes than when the ice is present in summer. Maykut and Untersteiner (l969) applied one-dimensional sea-ice models with prescribed atmosphere conditions. They suggest it would require an additional 6 kcal cm"2 yr"l (~8 W m-2) oceanic flux to melt the Arctic ice in summer. This amount is equivalent to a warming of the atmosphere of roughly 8°C during the summer only or a year- round warming of a few degrees greater than the Arctic surface warming that is projected by Manabe and Wetherald (l975) for a doubling of atmospheric C02 concentrations. Parkinson and Kellogg (l979) developed and applied a regional ocean sea-ice model. They claimed quite good verification, although Hibler (l979) disputes whether verification was adequate. When the Parkinson- Kellogg model is run with either an annual average 5°C warmer Arctic atmosphere (Manabe and Wetherald, l975, 2 x C02 result) or a 6°C summer, 9°C winter warmer atmosphere (Budyko, l974, seasonal pattern), the result is that Arctic ice melts in summer and returns in winter. One caveat should be noted in the Parkinson-Kellogg analysis, namely, that their temperature change was applied uniformly in the vertical (instead of being assumed to occur primarily in the subinversion layer) to calculate the change in downward flux, which may overestimate the change in the flux in regions without clouds. Hibler has not yet run his model on a CO2 study but doubts that the ice will melt with only a 5°C warming of air temperatures. 3. Oceanographic studies are still quite limited for the case of an open Arctic. There is now a very strong, salinity-induced, density stratification, the causes of which are not fully understood. If this stratification can be broken and does not reform, then the Arctic might be able to remain open through the winter. This possibility is not considered likely. Parkinson and Kellogg (l979) found that even an upward heat flux from the ocean ten times greater than the present flux would not prevent return of ice in winter. The stratification could be reduced in several ways, for example, by changes in wind mixing or by limiting sources of freshwater, which include sea-ice melt and river runoff. The latter, in turn, depends on precipitation in the upper mid-latitude watersheds of the major Arctic rivers and, potentially, on water-management policies. 4. There have been few studies of the effect of less ice or no ice in summer (independent of a CO2 change) on atmospheric circulation. One modeling study (Herman and Johnson, l978) indicates that with less ice, winter storm tracks shift poleward, presumably because the inten- sity of the winter polar high is reduced. Since the surface temperature (and the temperature at the top of the intensified Arctic stratus layer) are not projected to change signifi- cantly in summer, there is little reason to expect significant changes in the 300-700-mbar temperature, the gradient of which is probably a major factor in determining meridional eddy fluxes of heat and water vapor. Thus, with an open Arctic in summer, there could be little hemispheric effect, despite the implications of Fletcher's (l965) energy-balance analysis.

485 With respect to the local meteorology around the basin, there are suggestions that the warmer land would induce a stronger sea-breeze regime. It is not agreed whether the open ice condition would lead to a minimonsoonal-induced increase in precipitation on surrounding lands or just to an intensification of the existing stratus regime (in the style of the U.S. West Coast) in which the clouds move inland and evapo- rate rather than precipitate. It is agreed, however, that the present summerlike Arctic conditions would last longer each year, winter being shorter. During the winter, the delayed and less-extensive freezing that would result if the Arctic were open in summer probably implies a reduction in the intensity of the polar high and a poleward shift of 5-l0° lati- tude of wintertime storm tracks. That the mid-latitude effect in the winter would be greater than the summertime effect is rather a new suggestion. It may well be, however, that as the duration of winter- time climate is shortened and the summertime lengthened by the warming, the most significant climatic effects will instead be during the transition seasons. If storm tracks are shifted 5-l0°, a significant precipitation pattern change is likely to occur in mid-latitudes. TENTATIVE CONCLUSIONS l. Given the apparent long-term stability of Arctic ice, one must be cautious in projecting a melting due to prospective warming from increasing CO2 concentrations. A number of climate and ice models suggest that the Arctic ice may melt in summer with a warming of about the magnitude that may be induced by a doubling of C02 and increase of other greenhouse gases, but this conclusion must be viewed as still tentative. The representations of the Arctic in energy balance and most climate models that have melted Arctic ice with a O>2 warming usually do not include changes in cloud cover, ice dynamics, or the effects of open leads and salinity stratification. Owing to dynamic and thermodynamic processes, ice thickness may respond more readily to temperature increases than ice extent. How- ever, verification of ice extent and thickness estimates from climate models is not yet adequate. 2. While atmospheric effects of reduction in Arctic ice remain highly speculative, some poleward shift of storm tracks seems likely, and most significant climatic effects may occur during transition seasons. PROSPECTS FOR PROGRESS There are a number of research efforts that should bring progress in understanding effects of a greenhouse warming on the Arctic. Specifi- cally, efforts should be made to l. Improve general circulation models and other models (e.g., sea ice, Arctic stratus, ocean dynamics, and radiation balance) and use

486 them in studies focused on Arctic response. Proper handling of cloud cover in the Arctic merits special attention, as do sensitivity studies using improved sea-ice models. 2. Study stability of the Arctic Ocean density stratification and the potential for its destruction. 3. Obtain long central Arctic sediment cores that could improve the record of the Arctic Ocean for the period l0,000-l5,000,000 years ago. REFERENCES Budyko, M. I. (l974). Climate and Life. English edition, D. H. Miller, ed. International Geophysical Series, Vol. l8. Academic, New York. Ewing, M., and W. L. Donn (l956). A theory of ice ages. Science l23:l06l-l066. Fletcher, J. O. (l965). The Heat Budget of the Arctic Basin and Its Relation to Climate. The RAND Corp., R-444-PR, Santa Monica, Calif. Fletcher, J. 0. (l973). Numerical simulation of the influence of Arctic sea ice on climate. Energy Fluxes over Polar Surfaces. WMO Publication No. 36l, Geneva. Flohn, H. (l982). Climate change and an ice-free Arctic Ocean. In Carbon Dioxide Review: l982, W. C. Clark, ed. Oxford U. Press, New York, pp. l45-l79. Herman, G. F., and W. T. Johnson (l978). The sensitivity of the general circulation to Arctic sea ice boundaries: a numerical experiment. Mon. Wea. Rev. l06:l649-l664. Hibler, W. D., Ill (l979). A dynamic thermodynamic sea ice model. J_. Phys. Oceanog. MacCracken, M. C. (l968). Ice age theory by computer model simulation. Ph.D. Dissertation. University of California, Davis/Livermore. Maykut, G. A., and N. Untersteiner (l969). Numerical Prediction of the Thermodynamic Response of Arctic Sea Ice to Environmental Changes. The RAND Corp., RM-6093-PR, Santa Monica, Calif. Manabe, S., and R. J. Wetherald (l975). The effects of doubling the C02 concentration on the climate of a general circulation model. J. Atmos. Sci. 32:3-l5. Parkinson, C. L., and W. W. Kellogg (l979). Arctic sea ice decay simulated for a C02-induced temperature rise. Glim. Change 2.:l49-l62. Rakipova, L. (l966). The Influence of the Arctic Ice Cover on the Zonal Distribution of Atmospheric Temperature. The Rand Corp, RM-5233-NSF, Santa Monica, Calif.

487 Informal Meeting on CO2 and the Arctic Ocean June l-2, l982 Philadelphia, Pennsylvania Invited Participants Roger R. Revelle, Chairman University of California at San Diego Kirk Bryan, Jr. Geophysical Fluid Dynamics Laboratory/NOAA David L. Clark University of Wisconsin Joseph O. Fletcher National Oceanic and Atmospheric Administration William Hibler Geophysical Fluid Dynamics Laboratory/NOAA William W. Kellogg National Center for Atmospheric Research Michael C. MacCracken Lawrence Livermore National Laboratory William Ruddiman National Science Foundation (OCE) John Walsh University of Illinois John S. Perry National Research Council David A. Katcher, Consultant Chevy Chase, Maryland

Annex 2 Historical Note Jesse H. Ausubel The issue of carbon dioxide and climatic change has now been on the research agenda for more than a century. Indeed, by the l980s it has acquired quite a distinguished scientific provenance. In the l860s J. Tyndall began suggesting that slight changes in atmospheric composition could bring about climatic variations. The first precise numerical calculations about how much increased carbon dioxide concentrations would influence the Earth's surface temperature were made by Svante Arrhenius (l896, l908). He estimated that a doubling of atmospheric CO2 concentrations would produce a global warming of about 4-6°C. At the same time, T. C. Chamberlin (l899) was developing theories that the large variations in the Earth's climate, including periodic glaciation, could be attributable to changing carbon dioxide concentrations. C. F. Tolman (l899) provided the first major insights into the critical role of the oceans in the global distribution of carbon dioxide. By the early decades of this century, there was a lively debate among scientists on the direction of future CO2 concentrations. Some, like Arrhenius (l908), built their conception of future develop- ment on the expectation that the atmosphere is gaining in C02 under the present regime of "evaporating" our coal mines into the air. Others, like C. Schuchert (l9l9), stressed the volcanic origin of much C02 and worried that the ultimate extinction of the Earth's "plutonic fires" would bring in train the depletion of atmospheric CO2 and the extinction of life. "Life and its abundance at any time are conditioned by the amount of this gas (CO2) present in the atmosphere." In his classic work, Elements of Physical Biology, A. J. Lotka (l924), stimulated by a general interest in the history of systems in the course of irreversible transformations, also explored the carbon cycle. Lotka offered one of the first eloquent formulations of the CO2 issue: ...to us, the human race in the twentieth century [this phenomenon of slow formation of fossil fuels] is of altogether transcendent importance: The great industrial era is founded upon, and at the present day inexorably dependent upon, the exploitation of the fossil fuel accumulated in past geological ages. 488

489 We have every reason to be optimistic; to believe that we shall be found, ultimately, to have taken at the flood this great tide in the affairs of men; and that we shall presently be carried on the crest of the wave into a safer harbor. There we shall view with even mind the exhaustion of the fuel that took us into port, knowing that practically imperishable resources have in the meanwhile been unlocked, abundantly sufficient for all our journeys to the end of time. But whatever may be the ultimate course of events, the present is an eminently atypical epoch. Economically we are living on our capital; biologically we are changing radically the complexion of our share in the carbon cycle by throwing into the atmosphere, from coal fires and metallurgical furnaces, ten times as much carbon dioxide as in the natural biological process of breathing. . .[TJhese human agencies alone would. . .double the amount of carbon dioxide in the entire atmosphere. . . . Lotka estimated a doubling time of 500 years, based on continued usage of coal at l920s levels. If he had used the logistic ("Lotka-Volterra") equations for which he was to become famous to calculate future emissions as a result of human activities, Lotka would have given a doubling time in the middle of the twenty-first century. V. I. Vernadski (l926) was among the first to show the extent to which the Earth, its atmosphere as well as its hydrosphere and land- scapes, is indebted to living processes, to the biota. The theoretical ecologist V. A. Kostitzin (l935) dealt extensively with the circulation of carbon in his monograph "Evolution de l'atmosphere, circulation organique, epoques glaciares." Kostitzin provides a general review of available information and some of the theories concerning the circula- tion of oxygen, carbon, and nitrogen and discusses the long-term changes in their abundance in the atmosphere and soil. He reviews the theories in light of a simple model, incorporating a system of linear and quad- ratic differential equations, one of the early formal attempts to model the cycles. In his concluding remarks Kostitzin warns against confus- ing the relative short-term stability of nature with the absolute, but misleading, long-term stability of mechanical systems "which does not, in fact, exist, either in mechanics or in biology." By l938 G. S. Callendar was focusing directly on the industrial production of carbon dioxide and its influence on temperature. He went on (l940, l949) to speculate that a l0% increase in atmospheric CO2 between l850 and l940 could account for the observed warming of northern Europe and northern America that had begun in the l880s. G. Plass, of the Aeronutronic Division of the Ford Motor Company, was responsible during the l950s for the development of surface energy balance approaches to climate sensitivity that yielded the first "modern" estimates of global surface temperature response to increased CO2. R. Revelle and H. E. Suess, in the opening of their often-cited l957 paper, dramatically emphasized the significance of the rise in atmospheric CO2: "Human beings are now carrying out a large-scale geophysical experiment...." They also pointed out for the first time that most of the CO2 produced by the combustion of fossil fuels would

490 stay in the atmosphere and would not be rapidly absorbed by the ocean. Revelle was instrumental in incorporating accurate and regular measure- ments of the concentration of CO2 into the program of the Inter- national Geophysical Year (IGY). Meanwhile, the potential societal significance of climatic change had not gone unrecognized. J. von Neumann (l955), noting the effects of increasing atmospheric CO2, anticipated that deliberate human modification of climate would become a major issue in world affairs. The most constructive schemes of climate control would have to be based on insights and techniques that would also lend themselves to forms of climatic warfare as yet unimagined... [UJseful and harmful techniques lie everywhere so close together that it is never possible to separate the lions from the lambs. This is known to all who have so laboriously tried to separate secret, "classified" science or technology (military) from the open kind; success is never more—nor intended to be more—than transient, lasting perhaps half a decade. Similarly, a separa- tion into useful and harmful subjects in any technological sphere would probably diffuse into nothing in a decade. . .After global climate control becomes possible, perhaps all our present involvements will seem simple. We should not deceive ourselves: once such possibilities become actual, they will be exploited. It will, therefore, be necessary to develop suitable new political forms and procedures. Broader public concern with the implications of rising CO2 content of the atmosphere probably dates to a conference on the topic sponsored by The Conservation Foundation in March l963. Conference participants included Plass and C. D. Keeling, who was responsible for the continuous monitoring program of atmospheric C02 begun at Mauna Loa in Hawaii and at the South Pole in l957 during the IGY. The report of the conference states in part: It is known that the carbon dioxide situation, as it has been observed within the last century, is one which might have considerable biological, geographical and economic consequences within the not too distant future. . .It is estimated that a doubling of the carbon dioxide content of the atmosphere would produce an average atmospheric temperature rise of 3.8 degrees (Celsius). This could be enough to bring about an immense flooding of the lower portions of the world's land surface, resulting from increased melting of glaciers. . . . The report goes on to recommend special emphasis on continuation of the C02 monitoring program and more exact quantitative knowledge of the biosphere, themes that have been maintained over the past two decades. The Conservation Foundation report also concluded: There is a need for a watchdog. The effects of the continuing rise in atmospheric C02 while not now alarming are likely to

491 become so if the rise continues. A committee of the National Academy of Sciences, National Research Council, might be charged with exploring the problem.... The CO2 issue was subsequently raised as a national concern in Restoring the Quality of Our Environment, the Report of the Environmental Pollution Panel of the President's Science Advisory Committee, in l965. Since that time, the CO2 issue has been included in most lists of potentially serious environmental problems. REFERENCES Arrhenius, S. (l896). On the influence of carbonic acid in the air upon the temperature of the ground. Phil. Mag. 4l:237. Arrhenius, S. (l908). Worlds in the Making. Harper, New York. Callendar, G. S. (l938). The artificial production of carbon dioxide and its influence on temperature. Q. J. Roy. Meteorol. Soc. 64:223. Callendar, G. S. (l940). Variations in the amount of carbon dioxide in different air currents. Q. J. Roy. Meteorol. Soc. 66:395. Callendar, G. S. (l949) . Can carbon dioxide influence climate? Weather 4:3l0. Chamberlin, T. C. (l899). An attempt to frame a working hypothesis of the cause of glacial periods on an atmospheric basis. J. Geol. 1:545. Kostitzin, V. A. (l935). Evolution de l'atmosphere, circulation organique, epoques glaciares. Hermann, Paris. Lotka, A. J. (l924). Elements of Physical Biology. Williams & Wilkins, Baltimore, Md. Reprinted l956, Dover, New York. Plass, G. (l956). Effect of carbon dioxide variations on climate. Tellus 8:l40. President's Science Advisory Committee (l965). Restoring the Quality of our Environment. Report of the Environmental Pollution Panel. The White House, Washington, D.C., November l965. Revelle, R., and H. E. Suess (l957). Carbon dioxide exchange between atmosphere and ocean and the question of an increase of atmospheric CO2 during the past decades. Tellus 9: l8. Schuchert, C. (l9l9). In The Evolution of the Earth and Its Inhabitants, J. Barrell, C. Schuchert, C. Woodruff, R. Lull, and E. Huntington, eds. Yale U. Press, New Haven, Conn. The Conservation Foundation (l963). Implications of rising carbon dioxide content of the atmosphere. The Conservation Foundation, New York. Tolman, C. F., Jr. (l899). The carbon dioxide of the ocean and its relations to the carbon dioxide of the atmosphere. J. Geol. 7:585. Tyndall, J. (l863). On radiation through the Earth's atmosphere. Phil. Mag. 4:200. Vernadski, V. I. (l926). Biosphere, articles—first and second. Nautchtechizdat, Moscow (in Russian). von Neumann, J. (l955). Can we survive technology. Fortune, June l955.

Annex 3 Energy Security Act of 1980 94 STAT. 774 42 USC 8911. Report to Congress. Results, report to Congress. Recommenda- tions. PUBLIC LAW 96-294—JUNE 30, 1980 SUBTITLE B—CARBON DIOXIDE STUDY SEC. 711. (aXD The Director of the Office of Science and Technology Policy shall enter into an agreement with the National Academy of Sciences to carry out a comprehensive study of the projected impact, on the level of carbon dioxide in the atmosphere, of fossil fuel combustion, coal-conversion and related synthetic fuels activities authorized in this Act, and other sources. Such study should also include an assessment of the economic, physical, climatic, and social effects of such impacts. In conducting such study the Office and the Academy are encouraged to work with domestic and foreign govern- mental and non-governmental entities, and international entities, so as to develop an international, worldwide assessment of the problems involved and to suggest such original research on any aspect of such problems as the Academy deems necessary. (2) The President shall report to the Congress within six months after the date of the enactment of this Act regarding the status of the Office's negotiations to implement the study required under this section. (b) A report including the major findings and recommendations resulting from the study required under this section shall be submit- ted to the Congress by the Office and the Academy not later than three years after the date of the enactment of this Act. The Academy contribution to such report shall not be subject to any prior clearance or review, nor shall any prior clearance or conditions be imposed on the Academy as part of the agreement made by the Office with the Academy under this section. Such report shall in any event include recommendations regarding— (1) how a long-term program of domestic and international research, monitoring, modeling, and assessment of the causes and effects of varying levels of atmospheric carbon dioxide Public Law 96-294, June 30, l980; Title VII—Acid Precipitation Program and Carbon Dioxide Study; Subtitle B—Carbon Dioxide 492

493 should be structured, including comments by the Office on the interagency requirements of such a program and comments by the Secretary of State on the international agreements required to carry out such a program; (2) how the United States can best play a role in the develop- ment of such a long-term program on an international basis; (3) what domestic resources should be made available to such a program; (4) how the ongoing United States Government carbon dioxide assessment program should be modified so as to be of increased utility in providing information and recommendations of the highest possible value to government policy makers; and (5) the need for periodic reports to the Congress in conjunction with any long-term program the Office and the Academy may recommend under this section. (c) The Secretary of Energy, the Secretary of Commerce, the Administrator of the Environmental Protection Agency, and the Director of the National Science Foundation shall furnish to the Office or the Academy upon request any information which the Office or the Academy determines to be necessary for purposes of conduct- ing the study required by this section. (d) The Office shall provide a separate assessment of the inter- agency requirements to implement a comprehensive program of the type described in the third sentence of subsection (b).

Annex 4 Background Information on Committee Members WILLIAM A. NIERENBERG, Chairman, is the Director of the Scripps Institution of Oceanography of the University of California at San Diego. Dr. Nierenberg was trained in physics and has performed and directed research extensively in nuclear physics and in physical oceanography. He is a Member of the National Academy of Sciences and the National Academy of Engineering and has served in numerous capacities as an advisor on national and international scientific affairs. He is a former Chairman of the National Advisory Committee on Oceans and Atmosphere and is currently a Member of the National Science Board as well as Chairman of the Peer Review Panel on Acid Rain of the President's Office of Science and Technology Policy. PETER G. BREWER is a Senior Scientist at the Woods Hole Oceanographic Institution. For the past 2 years, Dr. Brewer has been on leave directing the Marine Chemistry program of the National Science Foundation. Dr. Brewer's research interests include measurement of CO2 in the oceans and the use of tracers for ocean circulation studies. LESTER MACHTA is Director of the Air Resources Laboratory of the National Oceanic and Atmospheric Administration. Dr. Machta's research interests focus on the measurement and analysis of secular and anthropogenic trends in atmospheric conditions. He has participated in several major studies of critical environmental problems and has recently served as Chairman of the Atmospheric Sciences Work Groups of the Joint U.S.-Canadian Task Force on Acid Rain. WILLIAM D. NORDHAUS is Professor of Economics at Yale University and a staff member of the Cowles Foundation. Professor Nordhaus's research interests include energy economics, innovation and technological change, and a growing number of aspects of the carbon dioxide issue. During l977-l979 Professor Nordhaus was a Member of the President's Council of Economic Advisers. 494

495 ROGER R. REVELLE is Professor of Science and Public Policy at the University of California, San Diego. Professor Revelle's research interests include physical and chemical oceanography, marine geology, water and energy resources, and population studies. He is one of the founders of the field of modern CO2 studies, having begun his continuing work on the subject in the l950s, established the monitoring of CO2 at Mauna Loa during the International Geophysical Year (1957), and brought the subject to national attention while serving on the Panel on Environmental Pollution of the President's Science Advisory Committee in l965. Professor Revelle is a Member of the National Academy of Sciences, a Past President of the American Association for the Advancement of Science, and the recipient of numerous awards and honors for his research and leadership in oceanography and resource analysis. Dr. Revelle chaired the NRC Committee that authored the l977 report Energy and Climate. THOMAS C. SCHELLING is Professor of Political Economy at the Kennedy School of Government of Harvard University. Professor Schelling has written extensively about conflicts between individual and collective behavior. His current interests include addictive behavior, energy policy, environmental policy, and arms control and national security. Professor Schelling is a Member of the Institute of Medicine and currently serves on the NRC Commission on Behavioral and Social Sciences and Education. Professor Schelling chaired the NRC Panel on Economic and Social Aspects of CO2 Increase, the predecessor group of the Carbon Dioxide Assessment Committee. JOSEPH SMAGORINSKY is a Visiting Senior Fellow in the Department of Geological and Geophysical Sciences at Princeton University and former Director of the Geophysical Fluid Dynamics Laboratory. Dr. Smagorinsky's interests include atmospheric general circulation, theory of climate, and atmospheric predictability. He has served on many NRC committees in atmospheric sciences and is Past Chairman of the Joint Organizing Committee for the Global Atmospheric Research Program and the Joint Scientific Committee for the World Climate Research Program. PAUL E. WAGGONER is Director of the Connecticut Agricultural Experiment Station. Dr. Waggoner is trained in both meteorology and agricul- tural sciences. His research includes physiology of crop yield, pest management, and relationships between air quality and plant growth. Dr. Waggoner is a Member of the National Academy of Sciences and participated in the l976 NRC study on Climate and Food. GEORGE M. WOODWELL is Director of the Ecosystems Center at the Marine Biological Laboratory in Woods Hole. Dr. Woodwell's research has centered on the structure and function of natural communities and their role as segments of the biosphere. He has worked and written extensively on the ecological effects of toxic substances, especially ionizing radiation and persistent pesticides. He is a Past President

496 of the Ecological Society of America, Fellow of the American Academy of Arts and Sciences, one of the founders of the Environmental Defense Fund, the Natural Resources Defense Council, and the World Resources Institute, and is currently Chairman of the World Wildlife Fund and the International Conference on the World after Nuclear War.

QC 879.8 .N37 1983 c.l National Research Council (U.S.). Carbon Dioxide Changing climate ID//00003198

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