3
Human Causes of Global Change

All the human causes of global environmental change happen through a subset of proximate causes, which directly alter aspects of the environment in ways that have global effects. We begin this chapter by outlining and illustrating an approach to accounting for the major proximate causes of global change, and then proceed to the more difficult issue of explaining them. Three case studies illustrate the various ways human actions can contribute to global change and provide concrete background for the more theoretical discussion that follows. We have identified specific research needs throughout that discussion. We conclude by stating some principles that follow from current knowledge and some implications for research.

IDENTIFYING THE MAJOR PROXIMATE CAUSES

The important proximate human causes of global change are those with enough impact to significantly alter properties of the global environment of potential concern to humanity. The global environmental properties now of greatest concern include the radiative balance of the earth, the number of living species, and the influx of ultraviolet (UV-B) radiation to the earth's surface (see also National Research Council, 1990b). In the future, however, the properties of concern to humanity are likely to change—ultra-violet radiation, after all, has been of global concern only since the 1960s. Consequently, researchers need a general system for



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Global Environmental Change: Understanding the Human Dimensions 3 Human Causes of Global Change All the human causes of global environmental change happen through a subset of proximate causes, which directly alter aspects of the environment in ways that have global effects. We begin this chapter by outlining and illustrating an approach to accounting for the major proximate causes of global change, and then proceed to the more difficult issue of explaining them. Three case studies illustrate the various ways human actions can contribute to global change and provide concrete background for the more theoretical discussion that follows. We have identified specific research needs throughout that discussion. We conclude by stating some principles that follow from current knowledge and some implications for research. IDENTIFYING THE MAJOR PROXIMATE CAUSES The important proximate human causes of global change are those with enough impact to significantly alter properties of the global environment of potential concern to humanity. The global environmental properties now of greatest concern include the radiative balance of the earth, the number of living species, and the influx of ultraviolet (UV-B) radiation to the earth's surface (see also National Research Council, 1990b). In the future, however, the properties of concern to humanity are likely to change—ultra-violet radiation, after all, has been of global concern only since the 1960s. Consequently, researchers need a general system for

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Global Environmental Change: Understanding the Human Dimensions moving from a concern with important changes in the environment to the identification of the human activities that most seriously affect those changes. This section describes an accounting system that can help to perform the task and illustrates it with a rough and partial accounting of the human causes of global climate change. A TREE-STRUCTURED ACCOUNTING SYSTEM A useful accounting system for the human causes of global change has a tree structure in which properties of the global environment are linked to the major human activities that alter them, and in which the activities are divided in turn into their constituent parts or influences. Such an accounting system is helpful for social science because, by beginning with variables known to be important to global environmental change, it anchors the study of human activities to the natural environment and imposes a criterion of impact on the consideration of research directions (see also Clark, 1988). This is important because it can direct the attention of social scientists to the study of the activities with strong impacts on global change. Because the connections between global environmental change and the concepts of social science are rarely obvious, social scientists who begin with important concepts in their fields have often directed their attention to low-impact human activities (see Stern and Oskamp, 1987, for elaboration). An analysis anchored in the critical physical or biological phenomena can identify research traditions whose relevance to the study of environmental change might otherwise be overlooked. For example, an examination of the actors and decisions with the greatest impact on energy use, air pollution, and solid waste generation showed that, by an impact criterion, studies of the determinants of daily behavior had much less potential to yield useful knowledge than studies of household and corporate investment decisions or of organizational routines in the context of energy use and waste management (Stem and Gardner, 1981a,b). Theories and methods existed for each subject matter in relevant disciplines such as psychology and sociology, but much of the research attention had been misdirected. The idea of tree-structured accounting can be illustrated by the following sketch of a tree describing the causes of global climate change. The chief environmental property of concern is the level of greenhouse gases in the atmosphere. The major anthropogenic

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Global Environmental Change: Understanding the Human Dimensions greenhouse gases, defined in terms of overall impact (amount in the atmosphere times impact per molecule integrated over time), are carbon dioxide (CO2), chlorofluorocarbons (CFCs), methane (CH4), and nitrous oxide (N2O). If the trunk of the tree represents the greenhouse gas-producing effect of all human activities, the limbs can represent the contributing greenhouse gases. Table 3-1 presents the limbs during two different time periods and a projection for a future period. Both natural processes and human activities result in emissions of greenhouse gases. For instance, carbon dioxide is emitted by respiration of animals and plants, burning of biomass, burning of fossil fuels, and so forth. If each limb of the tree represents human contributions to global emissions of a greenhouse gas, the branches off the limbs can represent the major anthropogenic sources of a gas, that is, the major categories of human activity that release it. These are proximate human causes of climate change, and their impact is equal to their contribution of each greenhouse gas times the gas's radiative effect, integrated over time. For the same emissions, the representation of impact will vary with the date to which the impact is projected. Tables 3-2 and 3-3 allocate emissions of the most important greenhouse gases during the late 1980s to human activities. Major human proximate causes, such as fossil fuel burning, are conducted by many actors and for many purposes: electricity generation, motorized transport, space conditioning, industrial process heat, and so forth. A tree branch, such as one representing fossil fuel burning, can be divided into twigs that represent these different actors or purposes, each of which acts as a subsidiary proximate cause, producing a proportion of the total emissions. It is possible to make such a division in numerous ways. Fossil fuel burning can be subdivided according to parts of the world (countries, developed and less-developed world regions, etc.), sectors of an economy (transportation, industrial, etc.), purposes (locomotion, space heating, etc.), types of actor (households, firms, governments), types of decisions determining the activity (design, purchase, utilization of equipment), or in other ways. Different methods may prove useful for different purposes. Table 3-4 illustrates one way to allocate the carbon dioxide emitted from fossil fuel consumption to the major purposes (end uses) of those fuels. The tree structure can be elaborated further by dividing the subsidiary proximate causes defined at the previous level into their components. Such analysis is important for high-impact activities.

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Global Environmental Change: Understanding the Human Dimensions TABLE 3-1 Estimated Human Contributions Per Decade to Global Warming of Major Greenhouse Gases During Three Time Periods, in Watts per square meter (percentage in parentheses) Gas 1765-1960a 1980sa 2025-2050 Projectionb CO2 0.059 (68) 0.30 (55) 0.51 (67) CH4 0.018 (21) 0.06 (11) 0.07 (9) CFCs, HCFCs 0.001 (1) 0.13 (25) 0.11 (15) N2O 0.003 (4) 0.03 (6) 0.04 (5) Stratospheric H2Oc 0.006 (7) 0.02 (4) 0.024 (3) Total 0.087 0.54 0.76 These estimates are of "radiative forcing" by greenhouse gases, that is, the change they produce in the earth's radiative balance that in turn changes global temperature and climate. Radiative forcing is calculated from current gas concentrations in the atmosphere, which include gases remaining in the atmosphere from all emissions since the beginning of the industrial era, set here at 1765. It is not identical to the "global warming potential" of gases emitted by human activity, a property that integrates the effects of gas emissions over future time. Global warming potential is affected by the different atmospheric lifetimes of greenhouse gases before breakdown, so that the relative importance of gases for global warming depends on the future date to which effects are estimated. In addition, chemical reactions in the atmosphere convert some radiationally inactive compounds into greenhouse gases over time. The estimation of the global warming potential of currently emitted gases is quite uncertain due to incomplete knowledge of the relevant atmospheric chemistry. An early estimate of the 100-year global warming potential of gas emissions in 1990 allocates it as follows: CO2, 61%; CH4, 15%; CFCs, 12%; N2O, 4%; other gases (NOx, nonmethane hydrocarbons, carbon monoxide), 8% (Shine et al., 1990). Although these estimates differ from the radiative forcing estimates in the table, the differences are not great in terms of the relative importance of the gases for the global warming phenomenon. Our analysis uses the estimates of radiative forcing because they are far less uncertain. a Source: Shine et al. (1990:Table 2.6). b Source: Shine et al. (1990:Table 2.7), assuming a "business-as-usual" scenario with a coal-intensive energy supply, continued deforestation and associated emissions, and partial control of CO and CFC emissions. Uncertainties for the future projections are very large. Total effects of greenhouse gases projected for 2025-2050 varied by a factor of 5 from the "accelerated policies" scenario, which projected the lowest level of emissions, to the "business-as-usual" scenario, which projected the highest. c Stratospheric water vapor is believed to increase as an indirect effect of CH4 emissions.

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Global Environmental Change: Understanding the Human Dimensions TABLE 3-2 Global Emissions of CO2, CH4, and N2O From Human Activities in the Late 1980s Activity Emissions (%) Range Notes CO2 emissions (Mt carbon per year)         Fossil fuel burning 5,400 (77) 4,900-5,900   Tropical deforestation 1,600 (23) 600-2,600   Total 7,000       CH4 emissions (Mt CH4 per year)         Rice paddies 110 (31) 25-170 Function of acreage and cropping intensity Digestion in ruminants 80 (23) 65-100 Primarily domestic Gas, coal production 80 (23) 44-100   Landfills 40 (11) 20-70 Decay of wastes Tropical deforestation 40 (11) 20-80 Biomass burning Total 350       N2O emissions (Mt N2O per year)a         Fertilizer use 1.5 (38)     Fossil fuel combustion 1 (25)     Tropical deforestation 0.5 (13)     Increased cultivation of land 0.4 (10)     Agricultural wastes 0.4 (10)     Fuel wood and industrial biomass 0.2 (5)     Total 4       Note: Mt = million metric tons a Estimates of N2O emissions are highly uncertain. For example, Watson et al. (1990) give a range of 0.01-2.2 for fertilization. In addition, N2O releases from unknown sources are probably larger than all anthropogenic releases. It is not clear how much of the unaccounted releases is anthropogenic. Sources: For CO2 and CH4, Watson et al. (1990); for N2O, National Academy of Sciences (1991a). For instance, automobile fuel consumption can be analyzed as the product of number of automobiles, average fuel efficiency of automobiles, and miles driven per automobile; the determinants of each of these factors can be studied separately. Researchers might then investigate the social factors that affect change in the number of automobiles and their typical life span, such as household income, household size, number employed per household, and availability of public transportation. More detailed analysis can be carried out until it no longer would provide information of high enough impact to meet some preset criterion. Again, there are many ways to ana-

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Global Environmental Change: Understanding the Human Dimensions lyze an activity such as automobile fuel consumption, and the most useful approach is not obvious a priori. The task of making such accounts, even for a single tree, is enormous. The work can be eased by using the impact criterion: analysts might reasonably choose to move from trunk to limb to branch to twig only until the contribution falls below a preset level of impact for the time period of concern. Data collection and substantive analysis of the thinnest twiglets can be deferred. Table 3-5 presents a composite of the accounts of individual green TABLE 3-3 Anthropogenic Sources of Atmospherically Important Halocarbons in the Late 1980s Halocarbon Production × 106 kg/yr Global Warming Potentiala Percent of Total Effectb Usesc CFC 11 (CCl3F) 350 3,500 17 Aerosols, refrigeration, foams CFC 12 (CCl2F2) 450 7,300 60 Aerosols, refrigeration, foams CFC 113 150 4,200 13 Cleaning electronic components HCFC 22. (CHCl2F) 140 1,500 3 Refrigeration, polymers CH3CCl3 545 100 2 Industrial degreasing Others     5   Note: Production estimates are from Watson et al. (1990), except for CH3CCl3, which comes from World Meteorological Organization (1985). Projections of future production are very sensitive to changes in economic growth, and relatively quick substitution is possible when alternative chemicals become available. CFC 22 production doubled between 1977 and 1984 (e.g., fast-food packaging), as did CFC 113 production (electronics industry). a Numbers represent the integrated effects over 100 years of release of one unit mass of the compound, relative to CO2. Integration over other time horizons would change the relative potentials because of differing atmospheric residence times. Source: Shine et al. (1990:Table 2.8). b Percentage of 100-year effects of all 1990 halocarbon emissions. Source: Shine et al. (1990:Table 2-9). c Projected atmospheric effects depend not only on total production but also on the balance between end uses. When CFC 11 and CFC 12 production shifted from aerosols to other applications after 1976, the result was a longer lag time from production to entry into the atmosphere.

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Global Environmental Change: Understanding the Human Dimensions TABLE 3-4 Disaggregation of Carbon Dioxide Emissions by Economic Sector and End Use (percentages, United States, 1987)   Economic Sector End Use Industrial Buildings Transportation Total Steam power, motors, appliances 19 7   26 Personal transportation (automobiles, light trucks)     20 20 Space heating 1a 16   17 Freight transport (heavy truck, rail, ship, other)     7 7 Heating for industrial processes 6     6 Lighting 1a 5   6 Cooling __a 5   5 Air transportation     5 5 Water heating   3   3 Other 5     5 Total 32 36 32 100 Note: U.S. data are unrepresenative of world energy use in various ways. However, the United States is responsible for approximately 20 percent of global CO2 emissions. a 2 percent in the single category of heating, ventilating, air conditioning, and lighting was allocated one percent each to heating and lighting. Source: U.S. Office of Technology Assessment, 1991. TABLE 3-5 Estimated Composite Relative Contributions of Human Activities to Greenhouse Warming   Gases (Relative Contribution in percent) Activity CO2 CH4 CFCs N2O Other Total Fossil fuel use 42 3   1.5   46.5 CFC use     25     25 Biomass burn 13 1   1   15 Paddy rice   3       3 Cattle   3       3 Nitrogen fertilization       2   2 Landfills   1       1 Other       1.5 4 5.5 Total 55 11 25 6 4 101   Source: Compiled from Tables 3-1, 3-2, and 3-3. For interpretation of the data, see the note at Table 3-1.

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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/2000/REC-xhtml1-20000126/DTD/xhtml1-transitional.dtd"><tit le>Global Environmental Change: Understanding the Human Dimensions <link rel="stylesheet" type="text/css" href="http://books.nap.edu/openbook/nap.css"/><p class="bodytextfp"> house gases that gives the approximate contribution of major classes of human activity to climate change. Figure 3-1, one of the possible tree diagrams incorporating this information, identifies the human activities that call for finer-grained analysis on the basis of their impact. The more detailed, U.S.-centered accounting in Table 3-4 shows why much more detailed analysis is warranted for explaining the purchase and use of automobiles and light trucks with different levels of energy efficiency (perFIGURE 3-1 A tree-structured representation of relative contributions of human activities in the late 1980s to greenhouse warming. Note: Thicknesses of limbs and branches are proportional, where numbers are provided, to the contribution of the activity named. Where numbers are not provided, worldwide data were not available for further disaggregation. Even where numbers are provided, they are subject to varying degrees of uncertainty, as noted in the text. Sources: <a href="50.html#p200064699960050002">Table 3-5, except for the disaggregation of fossil fuel use into economic sectors, which was calculated from U.S. Office of Technology Assessment, 1991, Table 9-1 and Figure 9-2.

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Global Environmental Change: Understanding the Human Dimensions sonal transportation) than for explaining the choice or operation of water heating systems for buildings. For a policy-oriented analysis based on such an approach, see National Academy of Sciences, 1991b. Accountings such as the one represented in Figure 3-1 can help guide the research agenda for the human causes of global change. They are critically dependent, however, on analyses from the natural sciences to sketch the trunk and major limbs, that is, to identify the most important environmental effects of human action and the technologies that produce those effects. Natural science can help social science by providing an improved picture of the trunk and limbs, and particularly by improving estimates of the uncertainties of their sizes. The uncertainties of some components are quite large (see, for instance, Table 3-2. estimating the relative contributions of different human activities to methane releases), and attention should be paid to whether, in the full account, these uncertainties compound or cancel each other. Research that estimates the relative impacts of proximate human causes of global change on particular environmental changes of concern, specifying the uncertainty of the estimates, is essential for understanding the human dimensions of global change. As tree diagrams move from the trunk out toward the branches and twigs, analysis depends more on social science. For each important environmental change, there are several possible accounting trees, each consistent with the data but highlighting different aspects of the human contribution. Social science knowledge is needed to choose accounting procedures to suit specific analytic purposes. Whatever accounting system is used, social scientists conducting research on the human causes of global change should focus their attention on factors that are significant contributors to an important global environmental change. LIMITATIONS OF TREE-STRUCTURED ACCOUNTING Because many different tree diagrams may be consistent with the same data, tree diagrams must be treated as having only heuristic, not explanatory, value. They are useful but not definitive accounts. A more serious limitation of tree-structured accounts is that they do not by themselves illuminate the driving forces behind the proximal causes of global change. Social forces that have only indirect effects on the global environment, and that may therefore be omitted from tree accounts, can have at least as

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Global Environmental Change: Understanding the Human Dimensions much impact as the direct effects. Consider, for instance, the rate of female labor force participation, which affects energy use in many different ways. With an increase in the proportion of women in the labor force, there tend to be more automobiles and miles driven per household, increased travel by plane, and, because of the associated decrease in household size, increased per capita demand for residential space conditioning and household appliances (see Schipper et al., 1989). Because these factors appear in different branches of Figure 3-1, the figure is not useful for representing the effect of female labor force participation on energy demand. The broader social process—the changing role of women in many societies—has even wider effects on energy use, but is still harder to capture in the figure. Despite these limitations, the accounting tree is useful as a preliminary check on the likely impact of a major social variable. When such a variable has a high impact, it is worth considering for inclusion in models of the relevant proximal causes of global change. Tree-structured accounting is also limited in that it can evaluate human activities against only some criteria of importance (such as high and widespread impact), but not others (such as irreversibility). Consideration of criteria of importance other than current impact may require detailed empirical analyses of factors that look small in an accounting of current human causes of environmental change. An example, elaborated in the next section, concerns future CO2 emissions from China. If per capita income grows rapidly there, Chinese emissions may increase enough to become tremendously important on a world scale. To make projections, it would be very useful to have detailed studies of the effects on emissions of increased income in other countries that have undergone recent spurts of economic growth, such as Taiwan and South Korea, even though these countries have no major impact on the global carbon dioxide balance. EXPLAINING THE PROXIMATE CAUSES: THREE CASES As we have shown, all human activity potentially contributes, directly or indirectly, to the proximate causes of global change. This section presents three rather detailed cases of human action with high impact on important global environmental changes to explore what lies behind the proximate causes. Taken together, the cases illustrate human causes that operate through both industrial and land-use activities and in both developing and devel-

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Global Environmental Change: Understanding the Human Dimensions oped countries. They illustrate how multiple driving forces interact to determine the proximate human causes of global change and why systematic social analysis is necessary for understanding how human actions cause it. In the section that follows, we discuss the interrelationships among the driving forces at a more theoretical level. THE AMERICAN REFRIGERATION INDUSTRY In 1985, the head of the British Antarctic Survey, Joseph Farman, reported that his team had discovered a heretofore unobserved atmospheric phenomenon: a sudden springtime thinning of the ozone layer over Antarctica, allowing ultraviolet radiation to reach the ground much more intensely than was ordinarily the case (Farman et al., 1985). Subsequent scientific investigations soon led to what is now the most widely accepted explanation of what was happening. Chlorine compounds derived mostly from chlorinated fluorocarbon gases (CFCs), mass-produced by industrial societies for a variety of purposes, reacted in the stratospheric clouds over Antarctica during the cold, dark, winter months to produce forms of chlorine that rapidly deplete stratospheric ozone when the first rays of the Antarctic spring sunlight arrive (Solomon, 1990). Massive destruction of ozone followed very quickly, until natural circulation patterns replenished the supply and closed what came to be known as ''the ozone hole.'' Human activities in distant areas of the planet had brought a sudden and potentially devastating change to the Antarctic and its ecosystems, a change that did not bode well for the ozone layer in other parts of the planet (Stolarski, 1988). To understand this event and the political controversies that followed in its wake, one has to reach back through almost a century's worth of history, long before CFCs existed. Until almost the end of the nineteenth century, refrigeration was a limited technology, based almost entirely on natural sources of supply. Urban Americans who could afford to drink chilled beverages relied on metropolitan ice markets, which cut ice from local ponds in the winter and stored it in warehouses for use during the warm months of the year. Breweries and restaurants were the heaviest users of this stored winter ice, which was sometimes shipped hundreds of miles to provide refrigeration. Boston ice merchants, for instance, were regularly delivering ice to consumers in Charleston, South Carolina, and even the Caribbean by the fourth decade of the nineteenth century (Hall, 1888; Cummings, 1949; Lawrence, 1965).

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Global Environmental Change: Understanding the Human Dimensions ermas, 1970; Offe, 1985). Bias toward growth and a hubristic disregard for physical limits, others have argued, are today the principal driving forces (e.g., Boulding, 1971, 1974; Daly, 1977). Some point to "humanistic" values, derived from the Enlightenment, that put human wants ahead of nature and presume that human activity (especially technology) can solve all problems that may arise (Ehrenfeld, 1978). Some assert that increased environmental pressures are associated with materialistic values of modern society (e.g., Brown, 1981), implying that materialism is amplified in the social atmosphere of the Western world. Sack (1990) argues that environmental degradation is intimately tied to social forms and mechanisms that have divorced the consumer from awareness of the realities of production, hence leading to irresponsible behavior that exacerbates global change. And some analysts have traced environmental problems to a set of values, rooted in patriarchal social systems, that identify woman and nature and define civilization and progress in terms of the domination of man over both (e.g., Merchant, 1980; Shiva, 1989). Some researchers argue that a secular change in basic values is occurring in many modern societies. Inglehart (1990) presents survey data to suggest that across advanced industrial societies, a value transition from materialist to postmaterialist values is occurring that has significant implications for the ability of societies to respond to global change with mitigation strategies that involve changes in life-style (see also Rohrschneider, 1990). Along a similar line, Dunlap and Catton have argued that a "dominant social paradigm" that sets human beings apart from nature encourages environmentally destructive behavior but that a "new environmental paradigm" that considers humanity as part of a delicate balance of nature is emerging (Dunlap and Van Liere, 1978, 1984; Catton, 1980; Catton and Dunlap, 1980). Other writers claim that a change in environmental ethics is necessary to prevent global environmental disaster (e.g., Stone, 1987; Sagoff, 1988). Short-sighted and self-interested ways of thinking can also act as underlying causes of environmental degradation. The inexorable destruction of an exhaustible resource that is openly available to all, what Hardin (1968) called the "tragedy of the commons," is, at a psychological level, a logical outcome of this sort of thinking. Individuals seeking their short-term self-interest exploit or degrade open-access resources much faster than they would if they acted in the longer-term or collective interest (Dawes, 1980; Edney, 1980; Fox, 1985).

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Global Environmental Change: Understanding the Human Dimensions Direct challenges to these analyses are few, in part because they are compatible with analyses that emphasize the role of other driving forces. Cultural values, short-sightedness, and self-interestedness can both cause and respond to other major social forces, such as political-economic institutions and technological change. For example, global expansion of capitalism is seen by some as inextricably linked to a transformation of attitudes toward material production (Cronon, 1983; Merchant, 1991; Worster, 1988). Economists treat market behavior as an expression of preferences, which are ultimately attitudes, so the treatment of the environment is an indirect result of attitudes, even in economic analysis. Where controversy tends to arise is over the relative primacy and hierarchical ordering of attitudes and beliefs relative to other causal factors, especially the degree to which beliefs and attitudes can be given causal force in their own right or are products of more fundamental forces. The empirical associations underlying some claims have also been called into question (e.g., Tuan, 1968, on White, 1967). On the side of human response, however, at least some sense of the autonomy of attitudes and beliefs is implicit in every analysis that offers explicit recommendations for action. Research Needs As with the other driving forces, the most interesting questions for research concern the ways in which the central variables—here, cultural and psychological ones—interact with other driving forces to produce the proximate causes of global change. Observational and experimental studies of these relationships have been done, although almost always with relatively small numbers of individuals in culturally and temporally restricted settings (see, e.g., Stern and Oskamp, 1987, for a review). They indicate that attitudes and beliefs sometimes have significant influence on resource-using behavior at the individual level, even when social-structural and economic variables are held constant, and that attitudinal, economic, and other variables sometimes have interactive effects as well. But these studies do not explain the sources of variation in individual attitudes. It seems likely that attitudes and beliefs have significant independent effects on the global environment mainly over the long-term—on the time scale of human generations or longer—and that within single lifetimes, attitudes function as intervening variables between aspects of an individual's past experience and that individual's resource use.

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Global Environmental Change: Understanding the Human Dimensions Testing this hypothesis would require research conducted over longer time scales than is common in psychological research. CONCLUSIONS This section distills some general conclusions or principles from the chapter and outlines their implications for setting research priorities. THE PROXIMATE CAUSES Research on the human causes of global environmental change should be directed at important proximate sources. It is critical to develop reasonably accurate assessments of the relative impact of different classes of human activity as proximate causes of global change. This chapter offers such an analysis—what we call a tree-structured account—for the human contribution to the earth's accumulation of greenhouse gases. Similar accounts should be made for the human contributions to other problems of global change. The task is relatively simple in the sense that the initial accounts need not have great precision. For social scientific work to begin, it will be sufficient to know whether a particular human activity contributes on the order of 20 percent, 2 percent, or 0.2 percent of humanity's total contribution to a global change. Such knowledge will allow social scientists to set worthwhile research priorities until more precision is available. Current impact is not the only criterion of importance. Estimating the relative contributions of different future human activities to global changes is a more difficult, but equally important, part of assessing the importance of proximal causes. The difficulty lies in predicting future human activities, particularly the invention and adoption of new technologies. Initially, projections of the future accounts based on simple models will suffice to guide the research plan for human dimensions. However, researchers should be aware of their limitations and should occasionally test their analyses against a variety of scenarios of future human contributions to global change. Although it is more difficult to quantify other aspects of importance, these can provide strong justifications for research. For example, human actions that may be proximate causes of irreversible environmental change must be considered important beyond the magnitude of the change they may cause. Researchers should be able to demonstrate the significance of

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Global Environmental Change: Understanding the Human Dimensions their chosen subjects not only in terms of the theoretical and empirical issues in their fields, but also in terms of importance to global environmental change. All the research needs identified in this chapter presume that the importance criterion is applied to particular efforts to meet the needs. SOCIAL DRIVING FORCES Understanding human causes of environmental change will require developing new interdisciplinary teams and will take lead time to build the necessary understanding. Listed below are some central considerations for guiding research. The driving forces of global change need to be conceptualized more clearly. Different kinds of technological change and of economic growth clearly have different implications for the global environment, but much still needs to be learned about which aspects of change in these and other variables drive environmental change. A better typology of development paths is needed, so that researchers can identify the ways different styles of development affect the environment and the conditions under which a country or region takes one path or another. The same is true for research on the ways nation-states organize the management of natural resources. Driving forces generally act in combination with each other. As the case studies demonstrate, the driving forces of global change are highly interactive. Brazilian deforestation is due to the combined effects of economic incentives, land tenure institutions, and government policy; Chinese coal use depends on the combined effects of economic development, the country's technological state, its political structure, and its economic policies; the development of CFCs was a function of population migration, economic incentives, and new technology. An additive model of these relationships is not viable, so the study of single causal factors in isolation is misleading. The various driving forces should be studied in combination, using multivariate research approaches. These include quantitative multivariate studies that treat particular proximate causes (e.g., emissions of carbon dioxide and other greenhouse gases) as a joint function of population, economic activity, technological change, and political structures and policies. Such studies may be conducted using both national-level data on demographic and economic variables and indicators of policy and social-structural vari-

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Global Environmental Change: Understanding the Human Dimensions ables, some of which might have to be constructed for the purpose. Detailed case studies using qualitative methods are also important, as the case summaries in this chapter illustrate. Qualitative methods can offer a depth of understanding not available from quantitative analyses, which by their nature are limited to those variables already quantified. Moreover, each method acts as a check on conclusions drawn from the other. Driving forces can cause each other. For example, new technologies can promote economic growth, which in turn allows for further technological development; materialistic ideologies contributed to the rise of capitalism, which promotes materialistic ideas. More complex mutual causal links also exist among several driving forces. Such relationships are difficult to disentangle and further complicate analyses of the human causes of global change. To understand the nature of these interactive relationships, it is important to compare different places and to follow the relationships over time. The forces that cause environmental change can also be affected by it. Population growth is a good example of feedbacks between human actions and the global environment. Population growth increases the demand for food, which creates pressure to make agriculture both more intensive and extensive. These changes eventually bring diminishing returns, reducing food production per capita and creating downward pressure on population. The diminishing returns can be postponed by improved technology, but technology also interacts with the environment. Humans can increase food production by using tractor power, chemical fertilizers, pesticides, and herbicides, but these technologies rely on fossil energy and therefore eventually reach limits imposed by scarcity, price, or environmental consequences. Relationships among the driving forces depend on place, time, and level of analysis. It is easy to illustrate the principle. For places: economic growth has been more dependent on fossil-fuel energy in China than in other countries, even other developing countries; the causes of deforestation in Brazil are distinct from its causes in other countries. For times: fossil-fuel energy use increased almost in lockstep with economic activity in industrialized countries for many years; since the 1970s, the correlation has been nearly zero (see Chapter 4). Also, the long-term effects on the global environment of a technology such as refrigeration with CFCs have been much different from the effects over a shorter time span—not only because of increasing use of the technology, but also because of the secondary effects of migrations made

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Global Environmental Change: Understanding the Human Dimensions possible by the technology. For levels of analysis at the local level, the inefficiency of Chinese energy use can be understood in terms of outmoded technology and lack of funds for replacing it; at the national level, low prices for coal and the system of production quotas appear as critical factors; at the world level, the entire system of command economies is implicated. All the relationships are equally real and important, yet answers derived at each level are incomplete. IMPLICATIONS FOR RESEARCH 1. The highest priority for research is to build understanding of the processes connecting human activity and environmental change. Better studies focused on the driving forces and their connections to the proximate causes are necessary for effective integrative modeling of the human causes of global change. Quantitative models will be of limited predictive value, especially for the decades-to-centuries time frame, without better knowledge of the processes. More is generally known about the causes of population growth, economic development, technological change, government policies, and attitudes and culture—the driving forces of global change—than about their interrelationships and environmental effects. This is so because study of the driving forces is supported by organized subdisciplines or interdisciplinary fields in social science, such as population studies, development studies, and policy analysis, whereas an interdisciplinary environmental social science—a field that examines the environmental effects of the driving forces—is not yet organized. There is a critical need for support of the research that would constitute that field. Research on the processes by which human actions cause environmental change should begin from the basic principle that the relationships are contingent: the effect of such variables as population on environmental quality depends on other human variables that change over time and place. This fact has three major implications for research strategy: understanding the human causes is an intrinsically interdisciplinary project; the important human causes of global change are not all global; and comparative studies to specify the contingencies are critically needed (see #2 and #3 below). Research at the global level is important but far from sufficient for understanding the human causes of global change. 2. Over the near term, research on the human causes of environmental change should emphasize comparative studies of glob-

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Global Environmental Change: Understanding the Human Dimensions al scale. We can distinguish three types of global-scale analysis: aggregate, systemic, and comparative. Aggregate analysis at the global level examines human-environmental relationships on the basis of measures of the entire planet. Such analysis uses a small number of time-series data points and considers the entire planet the unit of analysis. For example, total atmospheric carbon dioxide can be correlated with global fossil fuel combustion over a period of time. Systemic analysis of human-environmental relationships emphasizes facets of human activity that operate as a global system (i.e., a perturbation anywhere in the system has consequences throughout). For example, the world oil market is a global system in that changes in oil production anywhere reverberate through the system and may have global environmental impacts, for example, by changing the rate of consumption of oil or other fuels. Analyses of such relationships may use globally aggregate data or local and regional data linked to the phenomena of interest. Comparative analysis at the global scale can take various forms. It might employ a large number of local or regional data points, worldwide in coverage. For example, the relationships of population, economic development, and government policies to deforestation may be studied by comparing data with the nation-state as the unit of analysis (e.g., Rudel, 1989). This approach is limited by the availability and comparability of relevant data (see Chapter 6). In contrast, case-based comparative studies can be selected so that a sample of units represents the range of socioeconomic and environmental contexts of the world. The case-comparison approach allows for more contextual detail at the expense of complete coverage. For example, a set of cases could be used to explore the various pathways that lead to conversion of wetlands to other uses. Aggregate studies at the global level have limited value because the small number of data points make it impossible to identify the contingent relationships that shape the proximate human causes of global change. Systemic approaches have greater value in principle, but few human activities have the kind of systemic character that makes general circulation models of atmospheric processes valuable. Even the world oil market, one of the most globally systemic of environmentally relevant human systems, is affected by national policies such as trade restrictions and tax policies that interfere with world flows. Perhaps the most valuable research over the near-term will come from comparative studies that involve either a large number of representative data points or a smaller number of selected regional case studies from around

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Global Environmental Change: Understanding the Human Dimensions the world. The social sciences have a long tradition of comparative research and can usefully apply the conceptual and methodological tools they have developed to the problem of global environmental change. 3. Human dimensions research should prominently include comparisons of human systems that vary in their environmental impact. Comparisons between countries or localities or of the same place at different time periods can show why some social systems produce as much human welfare as others with less adverse impact on the global environment. A number of important issues lend themselves to comparative and longitudinal approaches, including: the causes of deforestation (studies can compare deforestation rates in countries that vary in their land tenure systems, development policies, and governmental structures); the effects of imperfect markets on release of greenhouse gases and air pollutants (studies can compare the emissions of countries or industries with different regulatory or pricing regimes); the sustainability of different agricultural management systems (studies might compare nearby localities in the same country); the effects of different industrial development paths on fossil fuel demand (studies might compare time-series data for different countries); the determinants of adoption of environmentally benign technologies or practices (for example, studies might compare industries or firms that do and do not recycle waste products); the relationship of attitudes about environmental quality and materialism to environmental policies in different countries. Such studies can ''unpack'' broad concepts, such as technological change, economic growth, and population growth, that are frequently offered as explanations of how human activities cause global change. Comparative studies offer the best way to get inside the broad concepts and identify more specifically the features of growth and change in human activity that drive environmental change. 4. Researchers should study the causes of major environmental changes both globally and at lower geographic levels. Global aggregate analysis may show a very different picture from analyses at lower levels of aggregation. It is important to have both pictures because aggregate data can obscure the variety of causal processes that can produce the same outcome. For example, the global relationship between economic growth and greenhouse gas

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Global Environmental Change: Understanding the Human Dimensions emissions may change considerably if centrally planned economies become extinct. To estimate the size of any such effect, it is necessary to have studies at the national level. In addition, policy responses, particularly mitigation responses, require understanding of the activities that drive global change at the level at which the responses will be made. Depending on the topic, it may be important to conduct studies at the level of the nation-state, the community, the industry, the firm, or the individual. For studies below the global level, priorities should be set on the basis of the potential to gain understanding of the global picture or to make significant responses to global change. Thus, a high-priority study might be one that focuses on a country or activity that by itself contributes significantly to global change; or one that is expected to generalize to a sufficient number of individuals, firms, or communities to matter on a global level; or one that illuminates variables that explain important differences between actors at the chosen level of analysis. At each level of analysis, projects that meet such criteria are worthy of support, independently of what is known at the global level. 5. Important questions should be studied at different time scales. The full effects of technological and social innovations—both on society and on the natural environment—are often unrecognized for decades or centuries. The CFC case shows how the effects of human activities can look very different depending on the time scale used for analysis: a technology developed to refrigerate food had much wider global implications several decades later, after it was applied to refrigerating buildings. Such cases need to be collected so they can be studied systematically and testable hypotheses derived about what kinds of innovations are likely to acquire the social momentum that produces long-lasting and increasing effects on the global environment, such as has resulted from CFC technology or from the Brazilian development strategy used in the Amazon Basin. Theory is particularly weak for this purpose. Historians can offer convincing accounts of the current effects of changes of the distant past, but social scientists have little ability to project the effects of current changes in human systems equally into the future. 6. Research should build understanding of the links between levels of analysis and between time scales. For example, social movements mediate between individual attitudes and national policies; the interactions of individuals and firms can result in the creation of national and global markets; and national policies can stand or fall depending on whether thousands of firms or millions of individuals willingly comply. Because of these linkages, hu-

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Global Environmental Change: Understanding the Human Dimensions man action at one level of aggregation may depend on events at another level. Theory about these relationships is relatively weak, but the problem is of active interest to social scientists in several disciplines. If excellent data sets are compiled, the problem of connecting levels of analysis may attract leading disciplinary researchers to the topic of global change to build theory that would aid in understanding it while advancing their own fields. Linking time scales is also critical to the global change agenda. The question is this: Which social changes, occurring on the time scale of months to years, are likely to persist or be amplified over time, to the extent that they will be significant to the global environment on a scale of decades to centuries? Obversely, which short-term changes are likely to disappear over time? Physical scientists know which halocarbons are long-lived catalysts for the destruction of stratospheric ozone and which ones are quickly destroyed; social scientists do not yet know much about which social changes catalyze other changes or about which ones are relatively irreversible. Historical cases, such as the CFC case, suggest some interesting hypotheses; over the near-term, efforts to catalogue and compare such hypotheses would be a useful first step toward a theory of the long-term effects of social change. The general problem has received very little attention from social scientists. Improved understanding of the human analogues of long-lived catalysts may contribute to increased interest in long-term phenomena in social science. NOTES 1   Some species, such as rosewood, are selectively eliminated from the forest for economic reasons. It is reasonable to expect that in an ecosystem characterized by many smaller species, such as insects dependent on a single species for food, that the selective cutting of one tree species will cause multiple extinctions. 2   The mechanism is rather complex. Evapotranspiration in the Amazon forest appears to cause a regional climatic increase in precipitation. In such a regime, large-scale clearing, which reduces evapotranspiration per land area even if trees are replaced by other vegetation, will decrease rainfall downwind. Because species diversity in Amazonia is directly related to levels of rainfall, lower rainfall in any region can be expected to reduce the number of species in that region. 3   Species with large area requirements are disproportionately affected when forest clearing is fragmented, as it typically is in Amazonia. Under those conditions, an individual or functional group of individuals with a large area requirement is less likely to find adequate forest resources

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Global Environmental Change: Understanding the Human Dimensions     within its area. Species with wide ranges are unlikely to be extinguished by habitat destruction within their range, but such destruction is likely to eliminate entirely the habitats of some of the species in the area with smaller ranges. Finally, although humans might be expected to husband populations of species with economic value, this has not typically been the case on frontiers, as the exploitation of Amazonian rosewood and the American bison illustrate.