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Global Environmental Change: Understanding the Human Dimensions (1992)

Chapter: 3 Human Causes of Global Change

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Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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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

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

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.

  1. The chief environmental property of concern is the level of greenhouse gases in the atmosphere. The major anthropogenic

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

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.

  1. 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.

  2. 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.

  3. 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.

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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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.

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

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-

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

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.

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

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.

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

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Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

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

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

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-

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

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).

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

Given the expense and difficulty of obtaining this stored winter ice, food preservation was accomplished largely with chemical additives, the most common being ordinary table salt: sodium chloride. In the United States, pork was the most popular form of preserved meat because of the ease with which its decay could be arrested by salt. Beef was much less popular in preserved form, so those who ate it preferred to purchase it freshly slaughtered from local butchers. Then, in the 1870s, meatpackers began experimenting with ice-refrigerated railroad cars that could deliver dressed beef, slaughtered and chilled in Chicago, to consumers hundreds of miles away. Dressed beef, which was cheaper than fresh beef for a variety of reasons, soon took the country by storm, driving many wholesale butchers out of business and giving the Chicago packing companies immense economic power. The packers initially relied on complicated ice storage and delivery networks, cutting and storing millions of tons of winter ice along the railroad routes that delivered beef from Chicago to urban customers throughout the East. Their investment in ice storage technology contributed to dramatic shifts in the American food supply and was soon affecting foods other than meat. Fruits and vegetables from California and Florida and dairy products from metropolitan hinterlands throughout the East, were among the most important to benefit from the new ice delivery system (Cronon, 1991; Yeager, 1981; Kujovich, 1970; Giedion, 1948; Clemen, 1923; Swift and Van Vlissingen, 1927; Neyhart, 1952; Unfer, 1951; Fowler, 1952).

But natural ice was unreliable: two warm winters in 1888-1889 and 1889-1890 brought partial failures of the ice crop that encouraged the packers to turn to a more reliable form of refrigeration. Although the principle of mechanical refrigeration, in which compressed gas was made to expand rapidly and so lower temperatures, had been known since the middle of the eighteenth century, its first application on a large commercial scale was not found until the second half of the nineteenth century (Anderson, 1953). Urban brewers, especially in the warm climates of the South, were the first to make wide use of it. As the meatpackers sought to solve their problems with erratic winter ice supply, they too adopted mechanical refrigeration on a large scale after 1890. By the first quarter of the twentieth century, the delivery of perishable foods throughout the United States—and international food shipments as well—had come to depend on mechanical refrigeration. By drastically lowering the rate at which food decayed and hence making perishable crops available to consum-

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

ers through much of the year, refrigeration changed the whole nature of the American diet.

The most widespread early refrigeration technology depended on compressed ammonia gas, which easily produced desired drops in temperature for effective food storage. But ammonia (like other refrigerant gases such as sulfur dioxide and methyl chloride) had serious problems. For maximum efficiency, it had to attain high pressures before being released, which increased the likelihood that the compression equipment might fail. Accidental explosions were frequent, and the toxic nature of the gas caused a number of fatalities. Toxicity and the need for large expensive compressors kept mechanical refrigeration from making headway with retail customers, who represented an immense potential demand. That is why Thomas Midgely Jr.'s 1931 invention of Freon 12 represented a revolution for the refrigeration industry. Midgely, working at the request of the General Motors Frigidaire division, developed the new chlorinated fluorocarbon as the perfect alternative to all other refrigerant gases then on the market.

Nonflammable, nonexplosive, noncorrosive, and nontoxic, the various forms of Freon gas seemed the perfect technical solution to a host of environmental and safety problems. They also required less pressure to produce the desired cooling effect, so compressors could be smaller and less expensive. Freon soon came to dominate the market for refrigeration and opened up new retail markets because of its diminished capital requirements. Previously, consumers had bought their refrigerated food at the store just before eating it, since efficient and reliable household refrigeration was not generally available. Now American households could own their own refrigerators, making it possible for the food industry to shift much of its marketing apparatus toward selling chilled food in retail-sized packages. Frozen foods burst onto the American marketplace in the 1950s, as did fresh vegetables, dairy products, and other foods that are today accepted as ordinary parts of the national diet. Although European countries were slower to adopt these technologies, they too eventually followed suit.

No less importantly, the nontoxicity of Freon made it possible for refrigeration technology to be applied to the ambient cooling of buildings, so that air conditioning came to be an ever more important market for the gas. Air conditioning had been used in specialized industrial applications ever since Willis H. Carrier's use of the technique for a climate-controlled lithography plant in 1902. The introduction of Freon meant that air conditioning suddenly became much cheaper and safer in a way that allowed it to

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

be applied to office buildings and finally to residences as well. Air conditioning played a key role in the years following World War II in promoting urban growth in the region known as the Sun Belt, as well as in tropical areas around the globe. From Florida to Texas to southern California, the massive influx of new residents depended in no small measure on the ability of buildings to protect their occupants from summer heat. Air conditioning became a fact of life in such places, so much so that it is hard to imagine urban life in the Sun Belt without it. Its significance can be captured by two phenomena of striking environmental significance: the shift in the seasonal consumption of electricity from peak load during the winter months (when energy consumption for lighting and space heating had always traditionally been at its highest) to peak load during the summer; and the steeply upward slope in the production and consumption of chlorinated fluorocarbons. The upward trend in CFC production was also aided by the development of still other uses for CFCs: as nontoxic propellants in aerosol sprays and later, in the 1960s and 1970s, as solvents in the manufacture of integrated circuits.

CFCs are very stable gases: that is in fact one of the properties that made them seem so benign when measured by their toxicity and immediate environmental effects. But the very stability that made CFCs so attractive for so many applications proved finally to be their greatest hazard. Once released into the environment—and the proliferation of refrigerators, freezers, and air conditioners meant that Freon escaped at an ever increasing rate—CFCs began to permeate the atmosphere, eventually reaching its upper regions. There they encountered the ozone layer, the thin belt of unstable tripartite oxygen molecules that filters out much of the sun's ultraviolet radiation and protects living organisms on the surface of the planet from the effects of that radiation. In the presence of sunlight, CFC molecules became chemical agents capable of destroying many times their number of ozone molecules. This effect was first hypothesized in 1974 by the chemists Mario Molina and Sherwood Rowland of the University of California at Irvine, writing in the wake of the controversy over supersonic transport aircraft and with recent knowledge, developed through new detection technology, that CFCs were present in the atmosphere (Molina and Rowland, 1974). Their hypothesis was controversial but convincing enough to produce action by the United States and eight other countries to ban the use of CFCs in aerosol sprays in the late 1970s (unquestionably the most marginal of their uses). Significantly, the suggestion that CFCs might possibly be damaging

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
×

to the ozone layer did not have much effect on uses that were much more central to the industrial economy: food refrigeration, ambient air conditioning, and electronic manufacturing solvents. (The knowledge that CFCs account for a significant proportion of the human contribution to the greenhouse effect—about 25 percent by the mid-1980s—also did not have much effect.)

Not much effect, that is, until 1985 and the discovery of the ozone hole over Antarctica. Within two years' time, the scientific community agreed that CFCs were the most likely culprit; officials at DuPont, which produced 25 percent of the world's CFCs, declared the company's intent to phase out CFC production over the next decade and a half; and an international protocol was signed at Montreal, in which signatory countries declared their intention to cut CFC production and consumption in half by the end of the century (Benedick, 1989a, b; U.S. Office of Technology Assessment, 1988; Haas, 1989).

The lessons of this story about CFCs and the ozone hole are several. On the positive side, the rapid response of the scientific, industrial, and policy-making communities to the discovery of the ozone hole over Antarctica is reassuring proof that international agreements in response to global change are in fact possible. That the Montreal Protocol and the later, even stronger London amendments to it could be signed even in the absence of environmentally benign alternatives to the CFCs suggests people's perception of how serious and urgent the problem had become, but also their faith—encouraged by DuPont's actions—that alternatives would in fact be available by the time the agreement's deadline fell due. Indeed, the Montreal Protocol is a paradigmatic case of a quick technical fix, in which people respond to the environmental problems of a particular substance by finding (or hoping to find) a technology that can be used for exactly the same purposes without requiring any fundamental change in human economies or societies.

And that suggests some of the less reassuring lessons of this story. Refrigeration and air conditioning have today become so embedded in the American way of life, and in the ways of life of many people the world over, that it is hard to imagine modern food supplies and urban life styles without them. The very form of the post-World War II city, with its tall office buildings, fixed windows, and energy-intensive controlled climate systems, presumes a significant commitment to refrigeration and cooling. Almost no one has responded to the ozone hole by suggesting a retreat from these fundamental technologies of modern life: al-

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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most everyone assumes that existing technologies can be sustained more or less unaltered by introducing some other gas as an alternative to Thomas Midgley's 1931 invention. A quick technical fix may well be all that is needed, in which case the refrigeration-intensive (and energy-intensive and greenhouse gas-intensive) food and architectural systems of the twentieth century First World will continue to proliferate around the planet, with countries of the tropics presumably adopting them with even greater reason and greater intensity than those living in temperate regions.

Of course, such a chain of events might well accelerate global climate change. The invention of CFCs started a process that led to building practices and patterns of human settlement with two unexpected and long-term effects on the global environment: a built-in demand for CFCs and a built-in demand for energy, not only for space cooling but also for transportation to and between the new dispersed, warm-climate population centers. A quick fix for the effects of CFCs on the ozone layer might encourage the spread of the American pattern of energy-intensive settlement. A possible result is more rapid growth of greenhouse gas emissions than would otherwise be the case.

The encouraging policy success at Montreal in 1987 was dramatic, but may have depended on special circumstances: there were only about two dozen CFC producers worldwide, and reductions threatened few of the existing infrastructures that had developed over the previous century and a half. For that reason, the signing of the Montreal Protocol is a risky predictor of how other international negotiations may turn out when the response to global change seems to require greater alterations in historical practice, when there are many millions of responsible actors, or when the costs and benefits of change are less evenly distributed around the planet.

There is one final lesson of the CFC story that is most ironic of all. We would do well to remember that chlorinated fluorocarbons were themselves a response to serious environmental problems. They reduced the occupational hazard of compressor explosions, they all But ended toxic pollution (and deaths) from refrigerant gases, and they dramatically increased the variety and safety of the human food supply. For 50 years, they seemed a perfect example of a benign technical solution to environmental and engineering problems, with no negative side effects of any kind. We now understand that the very quality that made them seem so safe—their stability—means that they will continue to destroy ozone molecules far into the future even if we were to end their production and use at this instant.

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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The history of CFCs demonstrates, above all else, that human activities can have quite unexpected long-term effects on the environment. CFCs, initially developed to support a limited set of end uses in the refrigeration industry, have changed not only that industry but also significant aspects of human civilization. As a result, they have made major contributions both to stratospheric ozone depletion and to global climate change. Moreover, because CFCs have contributed to social changes that are built into national building stocks, transportation systems, and even political structures (congressional representation from the Sun Belt, for example), the indirect effects of CFCs on climate change may be very difficult to reverse, even if substitutes are found that do not harm the ozone layer. Dependence on refrigeration has created social pressures to resolve the ozone problem by technical means, a strategy that could have paradoxical results: the solution to the ozone problem could accelerate social processes that cause climate change. The CFC story demonstrates the tremendous difficulty of understanding the environmental effects of technological change. It suggests that connections need to be traced through a greater variety of technological and social systems and over longer periods of time than usually covered in social scientific studies. We return to these difficult long-term scientific challenges in Chapter 5. The CFC story also drives home the point that we cannot anticipate all the environmental or social effects of our own activities, suggesting that the best policies are those designed with considerable robustness to unintended consequences.

COAL COMBUSTION IN CHINA

Fossil fuel consumption accounts for over half the human contribution to the greenhouse effect, chiefly through the emission of carbon dioxide. Although the People's Republic of China is only the world's third-largest producer of carbon dioxide (after the United States and the Soviet Union), it is increasing its rate of production faster than any other country (750 million metric tons more in 1988 than in 1980—National Academy of Sciences, 1991a). Three-quarters of the Chinese emissions come from burning coal. The rapid increase in Chinese coal consumption—from 62 million tons (Mt) in 1952 to 812 Mt in 1985—can be traced to industrialization, electrification, and population growth (Xi et al., 1989). The trend seems likely to continue over the next several decades because China is in an energy-dependent phase of development and has few alternatives to coal. China has the world's third largest

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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coal reserves, after the Soviet Union and the United States, but is very limited in reserves of other fossil fuels (Xi et al., 1989) and lacks the capital for major investments in nuclear power or development of its large, but inconveniently located, hydroelectric potential.

Causes of Present Coal Burning

A simple way to analyze energy use in China is to use the accounting equation:

where E is energy consumption, P is population, and GNP is gross national product. Thus, energy use is the product of population, per capita economic output, and energy intensity—that is, energy use per unit of output. Chinese energy use in 1987 was 435 percent of what it was in 1965, while population was 147 percent, GNP per capita 305 percent, and GNP 97 percent of 1965 levels:

(data from World Bank, 1989:Tables 1 and 5). This analysis suggests that roughly two-thirds of the rapid increase in Chinese energy use was a result of economic development, and the rest was due to population increase. But a closer look at the relationship of energy use and GNP gives a different picture—one that puts much more emphasis on technology and its social control.

China's energy use is a story not only of economic development, but also of persistently intensive energy use. China's economy is far more energy-intensive than that of most other countries or, put another way, China gets much less economic output from each unit of energy. Tables 3-6 and 3-7 show that China's economy may be the most energy-intensive in the world. In terms of CO2 emissions per unit of economic output, China is by far the world leader (National Academy of Sciences, 1991a).

The few available analyses of energy use in China suggest that its energy intensity has two main sources: industrialization and inefficiency. Industry is more energy-intensive than other productive sectors, and China devotes a greater proportion of its recorded energy consumption to industry and is more dependent on coal in that sector, than most other countries (see Table 3-8). This pattern may be traceable to a Stalinist development policy that

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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favors heavy industry on ideological grounds. The government, which determines production by directive rather than allowing it to respond to demand, is said to continue to command steel production, despite huge surpluses (Smil, 1988, and personal communication).

TABLE 3-6 Energy Intensities in Selected Countries and Groups of Countries, 1987

Country

Energy Intensitya

Productivityb

China

1.81

76

India

0.69

199

40 other low-income countries

0.41

335

53 middle-income countries

0.60

229

25 high-income countries

0.34

404

a Kilograms of oil equivalent per U.S. dollar of GNP.

b U.S. dollars of GNP per barrel of oil equivalent (1 barrel = 137.2 kg).

Source: Calculated from data in World Bank (1989).

TABLE 3-7 The Most Energy-intensive Economies in the World, 1987

Country

Energy Intensitya

Productivityb

China

1.81

$ 76

Poland

1.75

78

Yemen, People's Democ. Republic

1.68

82

Zambia

1.52

90

Hungary

1.37

100

South Africa

1.30

106

Trinidad and Tobago

1.23

112

Jamaica

0.91

151

Note: Complete data not available for Afghanistan, Albania, Angola, Bhutan, Bulgaria, Burkina Faso, Burma, Chad, Cuba, Czechoslovakia, German Democratic Republic, Guinea, Iran, Iraq, Ivory Coast, Kampuchea, Korea (Democratic People's Republic), Mongolia, Namibia, Romania, U.S.S.R., Vietnam, and countries with less than 1 million population.

a Kilograms of oil equivalent per U.S. dollar of GNP.

b U.S. dollars of GNP per barrel of oil equivalent (1 barrel = 137.2 kg).

Source: Calculated from data in World Bank (1989).

Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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The main reason for energy intensity, however, appears to be an inefficiency that has several contributing causes:

  1. Inefficient End Uses Coal burning in China is typically done in small, old units owned by households or small enterprises—characteristics that spell inefficiency. In the United States, 85 percent of coal is burned to generate electric power, at an average efficiency of 36 percent. By contrast, 22 percent of Chinese coal is converted to electric power, with an overall efficiency of only 29-31 percent (Kinzelbach, 1989; Xi et al., 1989). The bulk of Chinese coal is burned at still lower efficiencies, in industry (46 percent of 1985 coal use) and for commercial and residential heating (26 percent). Residential coal stoves often have only 10-18 percent efficiency (Xi et al., 1989). Adoption of more efficient furnaces and replacement of coal-fired space heating with combined heat and power installations proceed slowly for lack of capital.

  2. Price Structure Policy sets coal prices for the state-owned mines artificially low, below the cost of production. Although the industry operates at a loss (Xi et al., 1989), the government is said to be reluctant to raise prices for fear of inflation and urban unrest. Many analysts see price as the key source of continuing

TABLE 3-8 Percentage of Commercial Energy Used for Industrial Purposes and Percentage of Industrial Energy Supplied by Coal in Selected Countries and Groups of Countries

Country/Group (Date)

Industrial Energy Use (%)

Direct Coal Use (% of Industrial Energy)

China (1980)

63

67

India (1984)

53

72

Brazil (1983)

45

35

Indonesia (1984)

44

1

Korea (south) (1985)

41

34

U.S.S.R. (1987)

33

28

Eastern Europe (1983)a

52

19

OECD members (1985)

36

26

a Bulgaria, Czechoslovakia, German Democratic Republic, Hungary, Poland, and Romania.

Source: Calculated from World Resources Institute and International Institute for Environment and Development (1988:Table 7.4).

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    inefficiency, in that efforts to improve efficiency in either mining or consumption look uneconomic with current prices.

    1. The Command Economy The practice of government-dictated production, combined with the price structure, allows highly inefficient enterprises to continue operating despite financial losses. Enterprises that could compete by using energy more efficiently do not have incentives to do so. Moreover, the system of production quotas encourages the shipment of uncleaned, unsorted coal with an energy value of 30 percent less than actual tonnage (Smil, 1988). Such coal fulfills quotas easily, inflating production statistics by over 100 Mt per year, but it strains the Chinese railroads, 40 percent of whose cars are devoted to moving coal; wastes fuel in transport; and results in substantial emissions of unburned particulates when the coal is used.

    Table 3-7 offers a rough guide to the amount of inefficiency a command economy can produce. Although data are available only for a few such economies, among these are four of the five least energy-productive economies in the world. The other large-population, low-income countries of the world, India, Indonesia, Nigeria, Bangladesh, and Pakistan, get 2.5 to 6 times as much production as China out of each unit of energy they use (data from World Bank, 1989). Although China cannot be expected to increase its energy productivity 2.5 times to India's level—the ample availability of low-cost coal in China gives it less incentive to economize on energy—it seems to have room for huge improvements in efficiency.

    Determinants of Future Coal Burning

    The future of global climate change depends very much on how energy-intensive future Chinese development will be. Between 1965 and 1987, Chinese coal use—and CO2 emissions—increased at the same rate as total economic output. If both continue to increase at the recent historic rate of 4 percent per year, the Chinese contribution to global CO2 emissions will quadruple in less than 40 years and surpass that of the United States, presuming that the latter also follows recent trends. However, if future economic growth can be less energy-dependent than past growth has been, the picture would be quite different (data from World Bank, 1989; Fulkerson et al., 1989).

    What determines whether economic growth will or will not increase CO2 emissions? Historical data show that successful

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    economic development in Western countries has been marked by a period of rapid industrialization and consumption highly dependent on increased use of energy from fossil fuels, followed by a period in which economic growth becomes less energy intensive. Economic growth can proceed with decreasing energy intensity because of shifts of production from industrial to service sectors and adoption of more energy-efficient processes and technologies (World Resources Institute and International Institute for Environment and Development, 1988:114); energy use per capita, however, has continued to increase in these countries (World Bank, 1989:173).

    The future of China's energy use can be analyzed in the terms of the accounting equation: population growth, economic development, and changes in energy intensity or productivity. A fourth factor—shifts from fossil fuels to other energy sources—is unlikely to have much influence in China for several decades unless there is a major international effort to promote such shifts.

    Population growth, barring wars, epidemics, and the like, is easier than the other variables to forecast, because it is driven mainly by the current age distribution and slowly changing fertility trends. Beyond a few decades, though, uncertainties increase: desired family size may change, as may population policy, which has recently been holding family sizes below the levels parents seem to prefer. Forecasts for the year 2025 give a range of 1.4 to 1.6 billion for China's population (29 to 51 percent above the 1985 level) (United Nations, 1989).

    Economic growth and energy intensity are closely interrelated and very difficult to forecast. The Chinese national growth plan calls for quadrupling GNP from 1980 to 2000, but for coal use to increase only 2.3 times (Smil, 1988; Xi et al., 1989). These forecasts call for the elasticity of energy/GNP to decrease from the 0.97 of the 1965-1987 period to about 0.6, a change that would save more fossil fuel in 2000 than China used in 1985, if the quadrupling of GNP is achieved.

    There are tremendous uncertainties in predicting whether these goals can be met, even though Chinese energy use is certainly inefficient enough to allow this much technological improvement. Some observers believe the goals can be met only after continued economic liberalization, including price reform and market incentives, and political reforms that would overhaul wasteful management practices and attract needed foreign technology, expertise, and capital (e.g., Smil, 1988). The probability of such policy changes is notoriously uncertain, as the political events of 1989 in China

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    and Eastern Europe attest. And given the current level of knowledge about the functioning of command economies, even if policy changes were known in advance, the success of their implementation, and therefore their precise effects on energy productivity, would be hard to predict.

    No one knows how the Chinese will use the fruits of future economic development. If they make major investments in energy productivity—for instance, modernizing the coal industry, using electricity to replace inefficient coal burning, and developing the service sector of the economy—much can be done to mitigate CO2 emissions. But other directions of investment, focusing on new manufacturing and expanded energy services such as refrigeration and personal transportation, would be much more energy intensive. If China makes a major shift toward market incentives, the decentralization of choice will promote efficiency in production, but it might also encourage energy-intensive consumption, as individuals gain disposable income. The net effect on energy intensity is still unknown.

    Another important unknown is whether government policies will emphasize energy efficiency and the global environment. China already has policies to reduce coal use, but not in order to improve energy efficiency. The priorities are urban air pollution, freeing rail cars for noncoal cargo, and reduction of sulfur oxide emissions. These priorities encourage some energy-productive investments, such as combined heat and power plants that capture waste heat to warm buildings. But other important energy-productive investments do not fit these priorities. The future thrust of Chinese environmental policy depends, of course, on politics. Current environmental policies have been set from the top down, influenced by the exposure of traveling Chinese officials to the environmental concerns of foreign scientists, international organizations, and investors (Ross, 1987). If China turns inward to resist democratization, global concerns about energy efficiency may not influence Chinese policy for a long time. If environmental politics in China decentralizes and democratizes, an opening will appear for local environmental movements, which have been prevented from forming horizontal linkages in the past (Ross, 1987). Freedom for Chinese environmentalists, however, might lead to pressure for local changes, rather than for policies that improve energy efficiency nationally.

    In sum, the Chinese contribution to global climate change depends on the interactions of technology with social factors, including population growth, economic development, policy, and

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    ideology. Scientists know much about the technical changes that could mitigate China's greenhouse gas emissions, but they have relatively little quantitative understanding of the social factors that make possible, and interact with, technological change. Enough is known to identify some of the critical determinants of Chinese energy intensity, but not to quantify their effects or specify their interactions. That will require further research. For example, critical changes in policy, such as increased emphasis on market incentives and decentralized decision making, might greatly improve energy productivity. Studies of transitions to increased market control in other command economies might provide valuable knowledge for projecting the likely effects of such policy changes on energy efficiency in China. The future of Chinese energy demand also depends on changes in the structure of the Chinese economy and of consumer demand. Careful comparative studies of the social determinants of energy intensity and changes in energy intensity at the level of nation-states are critical for understanding and projecting China's future contribution to the greenhouse effect.

    FOREST CLEARING IN THE AMAZON BASIN

    Clearing of tropical forests is generally considered to be the most important single cause of recent losses in the earth's biological diversity. It also accounts for about 15 percent of the effect of human greenhouse gas emissions. Clearing has been very extensive in recent years, and the disturbances are not readily reversible, as deforestation by indigenous slash-and-burn techniques had previously been (Conklin, 1954; Nye and Greenland, 1966; Sanchez et al., 1982). The damage is now so extensive and severe as to preclude regeneration to original cover without special measures that are only now being developed (Uhl et al., 1989).

    The most widely used definition of biological diversity includes three levels: genetic, species, and ecosystem diversity (Norse et al., 1986; U.S. Office of Technology Assessment, 1987). Deforestation reduces diversity at all three levels. Genetic diversity, or the diversity of genes within a species, provides the raw material for evolution, as it allows some individuals of a species to survive environmental changes that prevent other individuals from living or reproducing. Species diversity, which refers to the many million species now estimated to exist on earth, is richest in the tropical forests, particularly in the Amazon Basin (Erwin, 1988). Many of the Amazonian species are closely tied to particular forest ecosystems and tree species, so that they are very narrowly

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    distributed and especially vulnerable to extinction by regional or even local forest clearing. Ecosystem diversity, that is, the existence of distinctive communities of species in different physical situations based on factors such as soil types or height above the river channel (Prance, 1979), is also great in the Amazon Basin, even between physical situations that look identical to the untrained eye.

    Amazonian deforestation threatens these forms of biological diversity in many ways. Elimination of forests destroys the habitat of many species that are closely tied to particular trees or ecosystem types. Species whose habitats are not totally destroyed may become extinct when an insufficient number are left in the remaining habitat, or remaining patches do not contain the resources they need (such as nest sites or food from a particular tree necessary to sustain the species). Species may be eliminated because of ecosystem simplification, as when removal of a single species eliminates the many species dependent for their existence on the local population of that species,1 or when cutting eliminates the cool, moist, windless microclimates of the forest interior that many species require. Diversity is vulnerable to drying of the regional climate, because evapotranspiration from the forest generates about half the rainfall in the Amazon Basin (Salati and Vose, 1984).2 Deforestation can damage biological diversity by contributing to both global and regional climate change, especially if the result is a drier climate in the Amazon Basin. Road building, in addition to destroying the forest, increases access to it and facilitates further deforestation. Deforestation favors species that occur only in highly disturbed areas, such as weeds, mosquitoes, and cattle, and that spread disease, compete with native organisms, and change the soil structure (Denevan, 1981). Finally, much deforestation is a by-product of industries such as mining, which not only destroys the forest at the industrial site, but may also use large numbers of trees for fuel.

    Deforestation reduces biological diversity in several ways. In general, the species hardest hit are likely to be the ones with large area requirements, narrow ranges, or value to humans for food, medicine, or timber, yet the entire taxonomic spectrum may suffer major losses.3 Some threatened species may be important to the region's economy and culture, some are used far beyond the Amazon Basin, and some have potential value to humans that is not yet known. The threatened ecosystems provide regionally important services, such as creating soils, moderating temperatures, reducing soil erosion, cleaning the air and water, and preventing flood and drought (Smith, 1982). The net effect on hu-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    mans is impossible to estimate in advance but, whatever its size, it is likely to be irreversible.

    Causes of Deforestation

    Amazonian forest land is cleared for many purposes. Logging is a major industry, with four of the six states in the Brazilian Amazon Basin depending on wood products for more than 25 percent of their industrial output (Browder, 1988). Other industries destroy forest both as an integral part of the manufacturing process and as a by-product. For example, 610,000 hectares (ha) of forest per year are used to produce charcoal for iron smelting in the Gran Carajas region of Brazil (Treece, 1989). Damming rivers to generate electricity for aluminum refining and for urban power inundates huge areas because of the low relief of the land. But the largest single source of Amazonian deforestation and the focus of this discussion is cattle raising, which now covers an estimated 72 percent of the cleared area (Browder, 1988).

    The transformation of forest into inferior, rapidly degrading pasture was not inevitable. It was strongly influenced by national policies and supported by international development agencies, which encouraged migration and land clearing through land-titling arrangements, provided a publicly financed infrastructure of roads, and established credit and tax incentives to benefit ranching. Given these institutional conditions and the presence of abundant, accessible, and relatively cheap land in the Amazon, individual actors made rational economic choices that furthered their own best interests and helped create a system with its own economic and social momentum that continues deforestation even after state incentives have been removed.

    Road Building With support from the World Bank, the Interamerican Development Bank, and other international lending institutions, the Brazilian government improved and paved major north-south (Belem-Brasilia) and east-west (Cuiaba-Porto Velho) highways, hoping to tap the wealth of the Amazon, make minerals and timber accessible, and promote agricultural enterprises (Fearnside, 1989). If, as the planners intended, settlers had migrated from the poor, drought-stricken northeast to settle along the trans-Amazon highway, they might have developed the area intensively, with permanent, smallholder farming and agroforestry, and limited deforestation. But mass migration did not occur in the northeast, and much of the area was abandoned to pasture

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    (Browder, 1988; Moran, 1976, 1990). The opening of new lands and the relative absence of people favored extensive development, such as ranching, over intensive development.

    Land Tenure Rights For centuries, it has been the legal practice to grant rights of possession to whoever deforests a piece of Brazilian land. Rights of ownership soon follow (Fearnside, 1989). Squatters on public land can gain the rights to 100 ha by living on it and using it, but 100 ha is not sufficient for ranching. Ranchers often buy up the lots of failed farmers, and in 1974 it became possible for a company to acquire a tract of up to 66,000 ha (Smith, 1982). Large individual and corporate ranchers can build their own access roads and lay claim to extensive plots far from major highways. By the time roads are constructed, most state land in the Amazon is already claimed (Binswanger, 1989). Brazilian land laws encourage both extensive holdings and extensive use. For instance, the 1988 constitution provides that land ''in effective use,'' that is, cleared, cannot be expropriated for the purpose of agrarian reform (Hecht, 1989b).

    Speculation Land holding has been a useful hedge against Brazil's galloping inflation and an excellent speculative investment. Mahar reports that a farm laborer can "net the equivalent of $9,000 from clearing 14 ha of forest, planting pasture, and a few crops for a few years, and selling the 'improvements' to a new settler" (1988:38). This is four times what the laborer could hope to earn from ordinary farm work. The largest speculative gains accrue to large investors with good connections in government and the courts because the value of land is greatly influenced by "institutional factors such as validity of title, [and] access to credits" (Hecht, 1989b:229).

    Financial Incentives from Government To encourage development in the Amazon, the Brazilian government made rural credit available to those with a land title or a certificate of occupancy at low, indeed at negative, interest rates. The credits were so attractive that money flowed from the nonagricultural sector into extensive ranching (Binswanger, 1989). Small farms were not taxed on land, large ones could reduce their already low taxes by converting forest to pasture or crops (Binswanger, 1989), and corporations could deduct up to 75 percent of the cost of approved development projects in the Amazon from their federal tax liability (Browder, 1988). Corporations could also write off losses on Area-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    zon projects against taxable income earned elsewhere (Browder, 1988). These incentives favored extensive enterprises and encourage livestock production even when returns from beef alone did not pay the cost of production. Fiscal incentives for livestock raising have largely dried up since 1985, but the cattle population has continued to grow at an annual rate of 8 percent (Schneider, 1990), suggesting that profit can now be made without subsidies, partly from the appreciation of land values (Binswanger, 1989).

    Livestock and Crop Economics The strategy that is generally most immediately profitable when land is plentiful and labor scarce is one of extensive and often transitory use. An example is shifting cultivation, the predominant indigenous strategy of land use. Fire removes cut brush and trees, and there is no need to turn the soil, weed frequently, irrigate, drain, or terrace. Beef production demands even less work per unit output and, with the help of modern technology and fossil-fuel energy for clearing forests, can be much more extensive than shifting cultivation. Fattening cattle on grass requires little labor or expenditure on fencing and corrals, and no weeding. Ranchers can take advantage of the highly productive first years after forest clearance to overstock the range and increase short-term profit. Cattle projects supported by the Brazilian development agency, SUDAM, operated with as few as one employee per 400 ha (Denevan, 1981). Such ranches, established with government subsidies, are now able to survive without them by marketing more timber from the land, selling beef to recent migrants to the new urban centers in the region, walking their cattle to market, and using new and better-adapted grass species and selectively bred cattle (Schneider, 1990).

    Ideology, Politics, and Economics of Development Throughout much of the 1960s and 1970s, the Brazilian government with support from international financial institutions pursued a strategy of large-scale, capital-intensive development projects. These often meant monocropping, relatively low labor inputs, mechanization, and the maximization of short-term financial returns. The strategy, elaborated in textbooks on development (e.g., Rostow, 1960), was based on shared premises about the essential goodness of economic growth and made deforestation for lumbering and extensive cattle raising the most profitable activity on the Brazilian frontier (Partridge, 1984). The international debt incurred in part to promote such development increased demands for rapid returns, high profits, and the production of exports to pay the interest

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    charges (Hildyard, 1990). Recently, disappointing economic returns, declining international aid, and an awareness of rapid ecological deterioration are becoming associated with changing priorities, and analysts in the World Bank and elsewhere are becoming critical of the old development philosophy (Binswanger, 1989; Mahar, 1988; Schneider, 1990).

    The Role of Population Growth It is easy to see Brazil's average population growth of 2.8 percent in the 1970s as the source of land hunger and migration, raising the Amazon population by 6.3 percent annually (Browder, 1988). However, the period witnessed stronger movements of population from the already settled hinterland to cities, combined with considerable natural increase in urban areas. The decline in rural population density is reflected in the phrase, "Quando chega o boi, o homen sai," (When the cattle arrive, the men leave) (Browder, 1988:254). The extensive clearing of forest on the frontier reflects population pressure and food needs outside the local region, combined with a lack of population pressure locally (Denevan, 1981).

    Alternative Futures for Amazonia

    The Amazonian case illustrates the difference between intensive and extensive patterns of land use in tropical forests. Table 3-9 provides a summary representation of the extremes of these patterns, presented as ideal types (actual land use almost always has features of both types). The Amazonian forest has long been inhabited by peoples that used a mixture of these strategies to support their economies. Indigenous groups combined relatively extensive strategies, such as temporary or shifting cultivation followed by natural forest regeneration and hunting and gathering of dispersed game, fish, and wild food plants, with more intensive farming of alluvial riverine and other soils of high, renewable fertility. More recently, both native American (Posey, 1989; Prance, 1989) and immigrant populations such as the rubber tappers have maintained the forest by a mixed-management strategy that mimics rather than replaces the biologically diverse natural environment (Browder, 1989).

    The modern forms of land use most implicated in deforestation—cattle ranching, crop agriculture, and logging and other industrial uses—are extensive and rapidly expansive, market and capital dependent, specialized in one or a few commodities, and mechanized or labor saving. Some observers point to modern strat-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    TABLE 3-9 Land Use Type

     

    Extensive/Expanding

    Intensive/Stable

    Population

    Low density, growing migratory

    High density, permanent settlement

    Agricultural Production

    Low average yields, high variability, low crop diversity

    High average yields, low variability, high diversity (cereals, tubers, vegetables, trees, livestock)

    Size of Economic Units

    Large, tendency to increase land area

    Small, balanced fragmentation anti accretion

    Labor

    Low total inputs, seasonally variable, unskilled, high returns per hour, often hired

    High total inputs, steady inputs throughout year, skilled, low returns per hour, often household

    Technology

    Mechanical, energy imported, nonrenewable, capital intensive

    Simple, often manual, energy local, renewable, labor intensive

    Market Integration

    High, output sold, inputs largely purchased, national and international commodity markets

    Subsistence combined with cash production, not totally dependent on market prices, some purchased inputs

    Land Tenure

    Private, land values speculative but initially low, legal access politically determined

    Private and common property rights, land values high, inheritance important, legal protections

    Social Inequality

    High, growing polarization, landlord elite and landless wage laborers

    Moderate, stratified, smallholders significant, social mobility

    Resource Dynamics

    Extraction

    Recycling

    Response to Environmental Change

    Vulnerability, boom/bust cycles

    Resilience, buffering, flexibility

    Environmental Impact

    Degradation, decline in biodiversity, nutrient loss

    Sustainability, fertility renewed, conservation

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    egies of mixed development as an alternative way of using the forest for human needs. They claim that intensive, stable agricultural land use with a mixture of crops and livestock can be combined with labor-intensive efforts to maintain soil quality by careful, thorough tillage, agroforestry, manuring, terracing, irrigation, and drainage. Thus they can provide high, reliable, sustainable production from smallholdings with high inputs of household labor and little capital or fossil fuel energy. These systems may also help preserve mature forest ecosystems from destruction by reducing development pressure on them (Anderson, 1990).

    The potential for a future of less-extensive forest use in the Amazon Basin relates in part to land distribution. Inequality of land holdings in Brazil has increased greatly over the last few decades, with 70 percent of Brazilian farmers now landless and 81 percent of the farmland held by just 4.5 percent of the population (Hildyard, 1990). This pattern of increasing inequality also holds in the Amazon, making access to resources more difficult for subsistence farmers and hunters and gatherers and threatening indigenous land tenure systems based on communal rights (Chernela, n.d.; Poole, 1989). Larger landholdings bring more extensive use. In Pará state, for instance, small farms cultivate an average of 50 percent of their area, while farms of over 1,000 ha cultivate only 26 percent (Hecht, 1981). More intensive cultivation means that less forest must be displaced to meet human needs. Moreover, stable smallholders have an incentive to economize on land and keep it productive, so that land degradation can be slower with more intensive use. Thus, the current pattern of extensive development, by displacing indigenous peoples and small-scale extractors, has removed a brake on deforestation and threatens a store of valuable knowledge about the intensive management of forest species for human consumption.

    There are barriers to a transition to a mixed-development strategy in the Amazon. One is the social change resulting from the current extensive strategy. Another is the politics of change. With rural poverty increasing and a political choice between dividing up large landholdings and encouraging the landless to colonize unclaimed or "unused" frontier lands, migration and resettlement policies are much the more palatable alternative (Macdonald, 1981). And finally, there are intrinsic social limits. Although portions of the local environment could support intensive land use like that of the wet rice/garden systems of south China and Java, the necessary local density of population with plentiful labor and nearby markets are not present (Moran 1987:75). Extensive, extractive

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    land use with deforestation is likely to remain the most economically feasible and politically viable development strategy in the Amazon region because vast areas of cheap land are accessible and markets are distant.

    In sum, the causes of Amazon deforestation lie partly in the same frontier conditions that have led to extensive land use in nineteenth century North America and elsewhere. In addition, development policy around the world has supported capital-intensive development of export monocultures. The unique institutional and political history of Brazil has helped determine the particular development pattern there, a pattern significantly different from that of tropical forest development in Zaire or Indonesia (Allen and Barnes, 1985; Brookfield et al., 1991; Lal et al., 1986). A key to the future of the forests lies in policy changes that could limit deforestation and extensive land use while increasing food production from existing agricultural areas. However, the social and economic changes brought about by Amazonian development have created barriers to making and implementing such policies.

    EXPLAINING THE PROXIMATE CAUSES: SOCIAL DRIVING FORCES

    The examples above illustrate how the proximate causes of global environmental change result from a complex of social, political, economic, technological, and cultural variables, sometimes referred to as driving forces. They also show that studies of driving forces and their relationships have been and can be done (National Research Council, 1990b; Turner, 1989). However, little of this research has been conducted on a global scale, for at least three important reasons: demand for such studies is a very recent phenomenon; relevant data at the global level are scarce; and social driving forces may vary greatly with time and place. Consequently, much additional work is needed to support valid global generalizations.

    We distinguish five types of social variables known to affect the environmental systems implicated in global change: (1) population change, (2) economic growth, (3) technological change, (4) political-economic institutions, and (5) attitudes and beliefs.

    Vocal arguments have been made for each of these as the exclusive, or the primary, human influence on global environmental change. In each instance, supportive evidence exists below the global level. Evidence at the global level, however, is generally insufficient either to demonstrate or dismiss claims that a par-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    ticular variable causes global environmental change or is more important than some other variable.

    We briefly outline the evidence supporting and qualifying claims that each class of variable is an independent influence on global environmental change. Our citations are not meant to be exhaustive, but rather to refer the reader to typical sources and critiques of claims about the importance of particular variables. For many of the authors cited, links between key explanatory variables and global environmental change are only implicit; in such instances, we draw out the implications for global environmental change. We also outline some of the key unanswered but researchable questions regarding these driving forces.

    POPULATION GROWTH

    Of all the possible driving forces of environmental change, none has such a rich history in Western thinking as population growth. Starting with Malthus, scholars have attempted to understand the effects of population growth on resource use, social and economic welfare, and most recently the environment. Few debates in the social sciences have been so heated or protracted as that around the impacts of population growth. Clearly, each person in a population makes some demand on the environment and the social system for the essentials of life—food, water, clothing, shelter, and so on. If all else is equal, the greater the number of people, the greater the demands placed on the environment for the provision of resources and the absorption of waste and pollutants. Stated thus, the matter is a truism. The source of controversy centers around more complex questions. Does all else remain equal in the face of population growth? Do simple increases in numbers account for most of the increase in environmental degradation in the modern world? Can population growth occur without major environmental damage? If not, is population growth a root cause of the degradation that follows, or merely an effect of more deeply underlying causes, such as changes in technology and social organization?

    Ehrlich and others (Ehrlich, 1968; Ehrlich and Holdren, 1971, 1988; Ehrlich et al., 1977; Ehrlich and Ehrlich, 1990) hold that population growth is the primary force precipitating environmental degradation. They argue that the doubling of the world's population in about one generation accounts for a greater proportion of the stress placed on the global environment than has increased per capita consumption or inefficiencies in the production-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    consumption process. They do not hold that other factors are unimportant in placing stress on the earth's resources and on the biosphere, only that population growth must be considered primary, because if all other factors could be made environmentally neutral, population growth of this magnitude would still spur resource stress and environmental degradation. Indeed, it is argued that once population has reached a level in excess of the earth's long-term capacity to sustain it, even stability and zero growth at that level will lead to future environmental degradation (Ehrlich and Ehrlich, 1990).

    The critiques of this position are many. One strand of criticism argues that technological and socioeconomic factors are primary (e.g., Coale, 1970; Commoner, 1972; Harvey, 1974; Ridker, 1972a; Schnaiberg, 1980). Another criticism comes from those who argue that population, though it may be a driving force of change, is not necessarily a driving force of degradation (Boserup, 1981; Simon, 1981; Simon and Kahn, 1984). Rather, they view population growth as a driving force of improvement, which increases the capacity of society to transform the environment for the better, or as a reflection of society's success in improving the environment so as to support greater numbers. These critics offer evidence from long sweeps of history, such as the relationships between major sociotechnical changes in society and global increases in population (Deevey, 1960; Boserup, 1965). Others have suggested that these population increases are also associated with increasing global environmental change (Whitmore et al., 1991).

    Since World War II, concern with rapid population growth has motivated the U.S. government, private foundations, and multilateral aid agencies to fund a substantial body of research on the causes of population growth. In addition to supporting individual studies, these bodies have devoted substantial resources to institutional development by subsidizing education, professional journals, and centers of excellence. The result has been impressive in building demography as a respected, interdisciplinary field within the social sciences, and in gaining knowledge of the causes of population growth. As we note in Chapter 7, this experience provides a useful model for advancing interdisciplinary social science research on global change.

    Research on the causes of population growth provides some useful insight into the causes of global change and strategies to deal with them. For example, current fertility and mortality patterns suggest that world population will continue to increase well into the next century. But if fertility declines as fast throughout

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    the developing world as it has in a few developing countries, this growth might be reduced by almost 2 billion people by the time that the population of the developing world would otherwise have reached 8 billion (World Bank, 1984). This research helps clarify how much growth is more or less inevitable because of the momentum built into the age structure of the world population.

    Compared with research on the causes of population growth, very little research has been devoted to understanding its consequences for environmental quality. This is ironic, because it is concern with the consequences that motivates much support for research on the causes of growth. There is some research on the effects of population growth on economic growth and social welfare, though the topic is still subject to some controversy (much of this literature is summarized in National Research Council, 1986). Only a handful of empirical studies have examined the effects of population growth on the environment, and many of these are quite dated [e.g., Ridker, 1972b; Fisher and Potter, 1971). As a result, it is difficult to assess just how important population may be as a driving force. For example, in 1986 a National Research Council study committee composed of economists and demographers concluded that slower population growth might assist less-developed countries in developing policies and institutions to protect the environment, but could find little empirical work on the link between population growth and environmental degradation (National Research Council, 1986).

    Research Needs

    We believe an extensive research program is needed to explicate the environmental consequences of population growth and provide a sounder basis for deciding what actions may be appropriate in response. Such research should begin by acknowledging that the environmental consequences of population growth depend on other variables. For instance, a population increase of people with the standard of living and technological base of average North Americans in 1987 would use 35 times as much energy as an increase of the same number of people living at India's standards—and their respective effects on the global climate would be in roughly the same proportion. The critical questions for research, then, are about the conditions determining the environmental effect of a projected population increase at a particular place and time. What are the multipliers that represent the environmental impacts of a new person in a particular year and coun-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    try? To what extent are multipliers such as annual income or annual distance traveled constant for a country, and to what extent are they contingent on other factors that may change over time, such as the manufacturing intensiveness or energy supply mix of the country's economy or the country's policies on income distribution or energy development?

    ECONOMIC GROWTH

    Global economic growth, defined as increases in the measured production of the world's goods and services, is likely to continue at a rapid rate well into the future. The human impulse to want more of the material things of life appears to be deep-seated, and the areas of the world in which people are most lacking in material goods are those with the greatest—and most rapidly increasing—population. Assuming United Nations and World Bank projections for world population to double to about 10 billion in about 50 years, with 90 percent or more of that growth occurring in the developing countries of Africa, Asia, and Latin America, and assuming that per capita income grows 2.5 percent and 1.5 percent annually in the developing and developed countries, respectively (a low projection, in both cases, by standards of the last several decades), global economic output would quadruple between 1990 and 2040.

    Under these conditions the relative gap between per capita income in developing and developed countries would narrow, but the absolute gap would increase substantially. To the extent that per capita income aspirations in the developing countries are driven by comparison of their incomes with those in developed countries, aspirations for additional income growth in the developing countries may be even stronger in 50 years than they are now.

    Increased income or economic activity as measured by such indicators as gross national product is not, of course, equivalent to increased well-being. There is considerable debate in the economic literature on how to measure welfare, focused on such questions as how to count things people value that are not traded in markets and whether expenditures for pollution control should be considered an addition or a subtraction from net welfare (e.g., Daly, 1986; Repetto et al., 1989). Although these questions are very important for analyzing human-environment interactions, most current analyses of the effects of economic growth and environmental quality are based on conventional definitions of economic activity.

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    Economic activity has long been a major source of environmental change and, for the first time in human history, economic activity is so extensive that it produces environmental change at the global level. The key issues concern the extent to which current and future economic activity will shape the proximate causes of global change.

    The production and consumption of goods and services is bound by a fundamental natural law—the conservation of matter. Whatever goes into production and consumption must come out, either as useful goods and services or as residual waste materials. Since the conversion of inputs to useful outputs is never entire, it is fair to say economic activity inevitably stresses the environment by generating residual wastes.

    Wastes must be disposed of somewhere in the environment. Economists note that disposal presents no important social problem if it is managed to reflect its true social costs and to be equitable in the sense that the costs are borne by those who generate the residuals. However, true social costs can be very difficult to determine, especially when wastes alter biogeochemical processes that are poorly understood. And when the wastes are released to the atmosphere, rivers, and oceans, it is difficult to ensure that those who generate the waste pay the costs. The problem of defining social cost and the separation of those who generate the costs of waste disposal from those who bear them are the keys to the waste-induced environmental problem (Kneese and Bower, 1979).

    Economic growth also depletes the stock of nonrenewable natural resources such as coal, oil, natural gas, and metallic minerals and, in some cases, the stock of renewable resources as well, as when the rate of soil erosion exceeds the rate of restoration of soil and nutrients. Environmental degradation follows when extraction disturbs land or biota and when resource use generates wastes. Economic growth may also destroy aspects of the natural landscape, for example, pristine wilderness areas or vast geological features such as the Grand Canyon. Continued use of depletable resources will create economic pressure to develop renewable energy resources, expanded recycling, and substitute materials (see, e.g., Barnett and Morse, 1963; Smith, 1979; Simon and Kahn, 1984), but a quadrupling of the global economy over 50 years would result in continued resource depletion.

    Depletion of nonrenewable resources need not threaten long-run economic growth if management of the resources takes adequate account of their future value and the likelihood of finding substitutes. This condition may be easier to meet than the condi-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    tions for managing wastes because it is much easier to establish clear, enforceable property rights in nonrenewable resources and because such property rights permit creation of markets that provide price signals of changing resource scarcity and incentives to take future as well as current resource values into account. Property rights are relatively easy to establish because, unlike in the atmosphere and the oceans, nonrenewable resources are localized, spatially well defined, and fixed in place.

    But markets in nonrenewable resources are no panacea for the environmental effects of minerals extraction or fossil energy use. Current markets have no sure way to anticipate, and therefore reflect, the value future generations will put on the depleted resources. This is the issue of intergenerational equity in resource management, and there are strong arguments that markets cannot deal adequately with the issue (Sen, 1982; Weiss, 1988; MacLean, 1990). The values future generations will hold can only be guessed at, drawing on human experience so far. Given this uncertainty, most analysts advocate more cautious resource management than what current market signals indicate.

    So economic growth necessarily stresses the environment directly by increasing quantities of wastes and indirectly by depleting resources. However, the relationship between economic growth and environmental stress is not fixed. The key analytic questions concern the conditions under which a given amount of present or future economic growth produces larger or smaller impacts on the environment.

    Several conditions apply. It matters which pattern of goods and services is produced. An economy heavily weighted toward services appears to generate fewer wastes and less resource depletion per unit of output than one weighted toward manufactured goods. Experience so far indicates that consumption patterns shift toward services as per capita income rises, suggesting that the process of growth itself may induce less than proportional increases in environmental stress. It seems that past some point, consumers use their economic resources to purchase well-being that is decreasingly dependent on material goods (see Inglehart, 1990). If the historic pattern holds, future economic growth in the low-income developing countries will be materials and energy intensive for quite some time before a transition to a service economy sets in. But this projection is uncertain because of incomplete knowledge about the causes of that transition and the ways it might be altered by deliberate action.

    Other shifts in economies can also change the relationship between economic growth and environmental quality. Per capita

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    use of many materials has been declining in North America and western Europe for some time (Herman et al., 1989). Waste management based on recycling, redesign of production processes, and the treatment of the wastes of one process as raw materials for another can reduce the environmental impact of economic activity (e.g., Ayres, 1978; National Research Council, 1985; Haefele et al., 1986; U.S. Office of Technology Assessment, 1986; Friedlander, 1989). And an observed trend in the United States, in which the main source of pollution has shifted from production activities to consumption activities, has effects on the overall economy-environment relationship that are not yet clear (Ayres and Rod, 1986; Ayres, 1978).

    The environmental effect of economic growth may also depend on forms of political organization. The comparison of emissions of CO2 and pollutants in Eastern and Western Europe suggests that democratic countries may be able to deal more effectively with the effects of wastes than nondemocratic countries. When people who feel the effects, or become concerned about the effects on others, have ready access to political power, their concerns may possibly have more influence on policy. If this hypothesis is correct, then political trends toward democracy, such as in Eastern Europe, will tend to reduce the amount of degradation resulting from economic growth there.

    National policies also help determine the environmental costs of economic growth. In many developing countries, policies have favored extensive use of ''unused'' resources and "underpopulated" land to increase national power and improve the welfare of their citizens. Countries such as the United States, Canada, Argentina, and Australia had such policies during rapid development phases, and other countries have followed the example. This model of development through frontier occupation and rapid creation of wealth required cheap food and raw materials from rural areas, an infrastructure of roads and transport to open up these areas, and huge infusions of capital for enterprises and settlement. An alternative development model generates increased production per unit of land by agricultural intensification rather than by extensive land uses such as shifting agriculture or ranching (Boserup, 1990; Turner et al., n.d.). Development of this kind can be carried out in a sustainable manner (Conway and Barbier, 1990; Sublet and Uhl, 1990).

    Research Needs

    The effects of economic development on the proximate causes of global change appear to be contingent, among other things, on

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    the structure of consumer demand, the population and resource base for agricultural development, forms of national political organization, and development policies. However, the nature of these contingent relationships, particularly the relationships between policy and the other variables, is not understood in detail. Research is critically needed on the ways consumer demand changes as income increases, the effects of national policies on patterns of production and consumer demand, the effects of agricultural intensity on economic growth and the environment, and the causes of shifts from more to less energy-and materials-intensive economies. These questions call for research both within and across the boundaries of disciplines and academic specialties.

    TECHNOLOGICAL CHANGE

    Technological change affects the global environment in three ways. First, it leads to new ways to discover and exploit natural resources. Second, it changes the efficiency of production and consumption processes, altering the volume of resources required per unit of output produced, the effluents and wastes produced, and the relative costs and hence the supply of different goods and services. Third, different kinds of technology produce different environmental impacts from the same process (e.g., fossil-fuel and nuclear energy production have different effluents). Some technologies have surprising and serious secondary impacts, as the history of refrigeration illustrates (see also Brooks, 1986).

    In one view, technological development tends to hasten resource depletion and increase pollutant emissions. In this view, technology as currently developed is a Faustian bargain, trading current gain against future survival (e.g., Commoner, 1970, 1972, 1977). Modern technology is seen as a much more significant contributor to environmental degradation than either population or economic growth. One reason is that modern technological innovation progresses much faster than knowledge about its damaging effects, both because the effects are intrinsically difficult to understand and because the powerful economic interests that benefit from new technologies influence research agendas to favor knowledge about the benefits over knowledge about the costs (Schnaiberg, 1980).

    Three arguments are advanced to oppose or qualify the Faustian theme. In the first, technology's contribution to environmental change is deemed relatively unimportant (Ehrlich and Holdren, 1972). In the second, technological innovation and adoption are

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    seen as induced by other forces, particularly demand from population (Boserup, 1981) or market forces (Ruttan, 1971) and therefore not a driving force. The third argument is that technological change is a net benefit to the environment because it can ameliorate environmental damage through more efficient resource use and the lessening of waste emissions (e.g., Simon and Kahn, 1984; also Ausubel et al., 1989; Gray, 1989; Ruttan, 1971).

    These contradictory arguments, all plausible, can be weighed only by research that is specific (e.g., which technology, in which society, at what time) and that takes into account the other major social forces that cause or are affected by technological progress. For instance, technological progress is affected by the relative prices of energy, materials, and labor, with inventors and entrepreneurs having a built-in incentive to develop technologies that economize on the more expensive factors of production. As a result, technological development starting in countries with low-cost energy will be more energy intensive than technologies developed in countries in which energy is expensive and therefore more likely to have negative environmental effects. The effects of technology on the environments of poor countries may reflect the fact that much of the technological innovation adopted in poor countries originated in rich countries, which face different economic and environmental problems. National economic policies, as well as environmental and energy policies, can favor particular kinds of technological innovation and thus hasten or forestall environmental degradation. In the United States, debates about apportioning government energy research funds between nuclear, fossil, conservation, and renewable energy development have always been, in part, debates about the effect of these technologies on the environment. And the environmental effects of technology look quite different depending on the time scale being considered or the state of environmental knowledge when the analysis is done. For example, the environmental effects of refrigeration technology look much different now than they would have looked in an analysis done in the 1950s.

    Research Needs

    As with other human influences on the global environment, the effects of technology are likely to be contingent on the other driving forces. Consequently, research on the effects of technology on global change will need to consider the social context. Several critical topics for research are obvious: one involves com-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    parisons of the environmental impacts of different technologies for energy production and consumption, food production, and other human activities that can have major impacts on the global environment, a topic that has received some attention in the past (e.g., Inhaber, 1978; Holdren et al., 1979, on energy production). Such studies should be specific at first, focusing on the alternatives available in a particular place and time, and should examine the technologies as they are implemented in actual social systems rather than under idealized conditions. Another involves diffusion of production technologies across national boundaries, particularly from more-developed to less-developed countries: How do the environmental impacts differ between the innovating countries and the adopting countries, and how do the differences depend on the social organizations using the technologies (e.g., Covello and Frey, 1989)? A third concerns the effect of government policies on the development, adoption, and use of technologies with different kinds of environmental effects: What policy choices influence technology and its use in environmentally destructive or beneficial ways, and how do the effects of policy depend on the political, economic, and social context where they are adopted (e.g., Zinberg, 1983; Clarke, 1988; Jasper, 1990)?

    POLITICAL-ECONOMIC INSTITUTIONS

    It seems reasonable that the social institutions that control the exchange of goods and services and that structure the decisions of large human groups should have a strong influence on the effects of human activity on the global environment. These institutions include economic and governmental institutions at all levels of aggregation.

    A key institution is the market. Neoclassical economic theory argues that free markets efficiently allocate goods and services to the most valued ends. Thus, environmental problems can be analyzed in terms of market failures, that is, conditions that prevent markets from operating freely. Several types of market failure are relevant to environmental problems. First, the costs of the transactions necessary to resolve environmental problems in an optimal fashion may be prohibitively high because of the costs of collecting information, for example on the net present value to all affected of the future effects of resource use (e.g., Coase, 1960; Baumol and Oates, 1988). Second is the problem of "externalities." Individuals not involved in buying or selling a good or service may nevertheless be affected by the transaction, for ex-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    ample, if it alters the earth's ozone layer. But because they do not know what the effect will be, they may not engage in transactions to maximize their preferences. Third, government action may supersede the market (e.g., Burton, 1978; Coase, 1960), leading to inefficiencies, for instance, excessive and uneconomic cutting in U.S. national forests, or profligate use of coal in China due to artificially low prices and a production quota system that gives no premium for quality. Fourth, a lack of clearly defined private property rights may leave no one with the incentive to pay to prevent degradation. This situation can arise because of traditional social arrangements that allow free access to all (Hardin, 1968) or because of the indivisible, common-pool nature of resources such as open-access marine fisheries (Gordon, 1954) and the world atmosphere.

    The analysis that traces environmental degradation to the absence of free markets is criticized on several grounds. First, even smoothly working markets are likely to produce undesirable outcomes. Questions have been raised regarding the theoretical assumption that a dollar has the same value regardless of a party's wealth and the morality of treating polluters and pollution recipients as symmetric and reciprocal sources of harm to one another (Kelman, 1987; Mishan, 1971). Second, the tendency of markets to place a higher value on possible impacts in the near future than on those in the distant future conflicts with the goal of long-term sustainability and reduces the rights of future generations effectively to zero (Weiss, 1988; Pearce and Turner, 1990). Third, goods that have no price, whose production is highly uncertain, or that are valued by nonparticipants in markets, for instance, the survival of nonhuman species, tend to be systematically undervalued in markets (e.g., Krutilla and Fisher, 1975). Fourth, the theory of market failures does not compare the environmental effects of different kinds of imperfect markets. Knowledge does not support the easy inference that the more a market resembles theoretical perfection, the more of the benefits of free markets it provides (Lipsey and Lancaster, 1956; Dasgupta and Heal, 1979). This is a serious limitation because, for environmental resources such as the stratospheric ozone layer, the only markets are imperfect.

    Some analysts trace the roots of environmental problems to the system of free-enterprise competition that underlies markets (e.g., Schnaiberg, 1980). They argue that the capitalist, cash-based market system rewards those who exploit the environment for maximum short-term gain, an incentive structure fundamentally at

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    odds with conservation and long-term sustainability and, moreover, that the capitalist class exacerbates the process through its strong influence on public policy. The argument is sometimes illustrated with the case of development in the Amazon.

    The critique of capitalism can be criticized for relying on a global, highly generalizing contrast between capitalist market economies and precapitalist, subsistence, socially undifferentiated groups that presumably maintain a delicate balance with the natural environment. It does not account for the fact that noncapitalist societies without private property may perpetuate large-scale environmental abuses, as in the case of the drying of the Aral Sea for irrigation purposes in the Soviet Union (Medvedev, 1990) or the reliance on inefficient coal burning technology in China. It does not account for labor resistance to environmental protection when it seems to threaten loss of jobs, such as opposition to restrictions on mining and burning Appalachian coal. And it does not acknowledge the existence within fully integrated market economies of stable, intensively producing family farmers and smallholder land-use regimes that modify but do not permanently degrade their habitat.

    Some analysts trace environmental deterioration, particularly in developing countries, to an international division between rich Western industrial and poor Third World raw material-producing nations that fosters political-economic dependence. Unequal terms of trade drain capital from peripheral or satellite regions to core areas. Underdevelopment and poverty are "developed" and perpetuated by market mechanisms (Wallerstein, 1976; Frank, 1967). This analysis emphasizes the effects of foreign investment, loans, the operations of large corporations, and quantifiable movements of capital, labor, imports, and exports on particular changes in the environment. Again, the Amazon case is sometimes offered as an example.

    This dependency model highlights the important role of foreign capital and extractive industries, but because it pits a monolithic global capitalism against a similarly undifferentiated and largely passive Third World, it cannot account for the historical specificity of particular cases or the variability in internal dynamics as systems adapt (Wolf, 1982). Dependency theorists often overlook the role and complicity of national elites (Hecht and Cockburn, 1989). The model has been criticized as imprecise in that the notion of unequal terms of trade is inadequately defined. And contrary to the simple view of dependency, pressures from international lending institutions are now beginning to influence Area-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    zonian land use in a positive way (Schmink and Wood, 1987:50; but see Price, 1989). Some Latin American countries, such as Costa Rica, have taken leadership in setting aside tracts of tropical forests as parks and conservation areas, despite high debt levels and dependence on exports to the United States [Gamez and Ugalde, 1988]. A range of other factors in addition to dependency must be considered to account for the variety of resource use patterns in the Third World.

    The state is a major institution affecting global environmental change because state actions modify economic institutions and affect a wide range of human actions, including those with global environmental impacts. As already noted, democratic states may be more responsive to popular pressures to take action on environmental problems than nondemocratic states. It may be more difficult in the latter for nonelite groups to get environmental issues on national policy agendas and then to influence the legislative process through the expression of public opinion. Another critical dimension may be the degree of centralization of the political system. One perspective argues that systems in which decisions are decentralized, primarily through markets, are apt to respond more readily to resource constraints. However, under certain circumstances, a more centralized, state-controlled form of decision making might be better able to take a long-term and broader perspective.

    Specific public policies can also have significant environmental consequences, both intentionally and inadvertently. Many governments have pursued policies aimed at maximum exploitation of natural resources in pursuit of economic growth that give environmental concerns a low priority. However, many governments, primarily in the West, have also enacted policies to ameliorate the effects of industrial growth on the environment. State action can also have large unintended effects on the environment. For example, emissions of greenhouse gases and air pollutants in the United States have been greatly affected by the many policy choices of the U.S. government that have encouraged the use of the automobile as a form of personal transportation. Similarly, policies pursued by such federal agencies as the Army Corps of Engineers, the Department of the Interior, and the Atomic Energy Commission have affected environmental quality, even though—or perhaps because—environmental quality was not an issue in their policy deliberations. Knowledge about why different governments develop different environmental policies is discussed in more detail in Chapter 4.

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    Research Needs

    Clearly, political-economic institutions can affect the global environment along many causal pathways. We have identified some of the important areas in which more knowledge could add greatly to understanding of the causes of global change. One is the comparative study of the effects of different imperfect-market methods of environmental management—including the various pricing systems and regulatory approaches in operation around the world, market-like approaches not in use but potentially usable, and various mixtures—to determine their effects on global environmental variables as a function of where and when they are used, and on which human activities. Theoretical work classifying and analyzing the varieties of market imperfection could also make great contributions to understanding if directed toward the kinds of market imperfection characteristic of global environmental resources. A second important research area concerns the comparison of national policies in terms of their origins and their environmental effects. A third concerns the commonly alleged short-sightedness of corporate decisions about the environment. Under what conditions do capitalist actors adopt practices of natural resource use or waste management that preserve environmental values? What national policies affect the likelihood that they will adopt such practices? A fourth concerns the variation in development policies adopted by countries that are similar to each other in terms of level of development and dependency. To what extent is such variation dependent on the political structure of the state, national political culture, level of centralization of decision-making power, and other variables at the national level?

    ATTITUDES AND BELIEFS

    Widely shared cultural beliefs and attitudes can also function as root causes of global environmental change. Many analysts focus on broad systems of beliefs, attitudes, and values related to the valuation of material goods. An early argument in this vein attributed the modern environmental crisis to the separation of spirit and nature in the Judeo-Christian tradition (White, 1967); another traces the rise of capitalism with its materialist values and social and economic structures back to Protestant theology (Weber, 1958). The Frankfurt school of critical theory accorded a similar role to the spread of purely instrumental rationality (Hab-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    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).

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    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.

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    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

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    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-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    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

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    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-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    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

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    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

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    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-

    Suggested Citation:"3 Human Causes of Global Change." National Research Council. 1992. Global Environmental Change: Understanding the Human Dimensions. Washington, DC: The National Academies Press. doi: 10.17226/1792.
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    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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    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.

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    Global environmental change often seems to be the most carefully examined issue of our time. Yet understanding the human side--human causes of and responses to environmental change--has not yet received sustained attention. Global Environmental Change offers a strategy for combining the efforts of natural and social scientists to better understand how our actions influence global change and how global change influences us.

    The volume is accessible to the nonscientist and provides a wide range of examples and case studies. It explores how the attitudes and actions of individuals, governments, and organizations intertwine to leave their mark on the health of the planet.

    The book focuses on establishing a framework for this new field of study, identifying problems that must be overcome if we are to deepen our understanding of the human dimensions of global change, presenting conclusions and recommendations.

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