Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. 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. 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, b. 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 s. Consequently, researchers need a general system for. 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 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, 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, , 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, a,b.
Theories and methods existed for each subject matter in relevant disciplines such as psychology and sociology, but much of the research attention had been misdirected. The idea of tree-structured accounting can be illustrated by the following sketch of a tree describing the causes of global climate change. The chief environmental property of concern is the level of greenhouse gases in the atmosphere. The major anthropogenic.
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 presents the limbs during two different time periods and a projection for a future period. Both natural processes and human activities result in emissions of greenhouse gases.
For instance, carbon dioxide is emitted by respiration of animals and plants, burning of biomass, burning of fossil fuels, and so forth. If each limb of the tree represents human contributions to global emissions of a greenhouse gas, the branches off the limbs can represent the major anthropogenic sources of a gas, that is, the major categories of human activity that release it. These are proximate human causes of climate change, and their impact is equal to their contribution of each greenhouse gas times the gas's radiative effect, integrated over time. For the same emissions, the representation of impact will vary with the date to which the impact is projected.
Tables and allocate emissions of the most important greenhouse gases during the late s to human activities. Major human proximate causes, such as fossil fuel burning, are conducted by many actors and for many purposes: electricity generation, motorized transport, space conditioning, industrial process heat, and so forth.
A tree branch, such as one representing fossil fuel burning, can be divided into twigs that represent these different actors or purposes, each of which acts as a subsidiary proximate cause, producing a proportion of the total emissions. It is possible to make such a division in numerous ways. Fossil fuel burning can be subdivided according to parts of the world countries, developed and less-developed world regions, etc.
Different methods may prove useful for different purposes. Table illustrates one way to allocate the carbon dioxide emitted from fossil fuel consumption to the major purposes end uses of those fuels. The tree structure can be elaborated further by dividing the subsidiary proximate causes defined at the previous level into their components. Such analysis is important for high-impact activities. 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 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.
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The estimation of the global warming potential of currently emitted gases is quite uncertain due to incomplete knowledge of the relevant atmospheric chemistry. 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. Uncertainties for the future projections are very large. Total effects of greenhouse gases projected for 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.
N 2 O emissions Mt N 2 O per year a. For example, Watson et al. In addition, N 2 O releases from unknown sources are probably larger than all anthropogenic releases. It is not clear how much of the unaccounted releases is anthropogenic. 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-. 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 presents a composite of the accounts of individual green. Note: Production estimates are from Watson et al. 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 and e.
Integration over other time horizons would change the relative potentials because of differing atmospheric residence times. Source: Shine et al. When CFC 11 and CFC 12 production shifted from aerosols to other applications after , the result was a longer lag time from production to entry into the atmosphere. Note: U. However, the United States is responsible for approximately 20 percent of global CO 2 emissions.
Source: Compiled from Tables , , and For interpretation of the data, see the note at Table For a policy-oriented analysis based on such an approach, see National Academy of Sciences, b. Accountings such as the one represented in Figure 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 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. 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. 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.
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