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Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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losses included $2 billion to $5 billion by international airline and hotel chains from lost tourism.

Extreme weather events compounding local vulnerabilities (multiple stresses) can disrupt predator/prey relationships (functional biological diversity) and can generate biological surprises, such as population explosions of pests and pathogens that can affect human, plant, and animal health. The impacts of extreme events and epidemics can ripple through economies, affecting agriculture, productivity, trade, and tourism, in addition to their direct effects on regional human health and well-being.

There is, of course, much uncertainty about the role of climatic change in causing ecological changes that have costly effects on humans. A major recent example that highlights the difficulty in assigning causation is the collapse of the commercially important northern cod populations off the coast of eastern Newfoundland and Labrador, Canada, in the late 1980s and early 1990s. This collapse led to a costly program to compensate the over 30,000 people who could no longer work as fishers or fish processors. Debates continue about the roles of the North Atlantic Oscillation and other, more specific, climatic and oceanographic changes relative to the role of overfishing.18 There is also uncertainty about the links from ecological consequences to human consequences because of gaps in knowledge about the ability of human communities to respond effectively to anticipated ecological changes.

In those regions where climatic variability is associated with El Niño-Southern Oscillation (ENSO) events, there is hope that improved understanding of sea surface temperatures and associated changes in atmospheric circulation will result in advance warnings of droughts, floods, and epidemics and reduced losses.19 This type of human dimensions research highlights the importance of improved understanding of climate change and variability, the need to consider social vulnerability and adaptive capacity when forecasting the consequences of global change, the potential benefits of predicting climatic extremes, and the need to evaluate carefully options for reducing greenhouse gas emissions.

Key Scientific Questions

Key scientific questions for research on the human dimensions of global change can be grouped into four broad interrelated interdisciplinary categories:

  • What are the major human causes of changes in the global environment and how do they vary over time, across space, and between economic sectors and social groups?
  • What are the human consequences of global environmental change for key life support systems, such as water, health, and agriculture, and for economies and political systems?
  • What are the potential human responses to global change? How effective
Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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  • are they and at what cost? How do we value and decide among the range of options?
  • What are the underlying social processes or driving forces behind the human relationship to the global environment, such as human attitudes and behavior, population dynamics, and economic transformation? How do they function to alter the global environment?

Research on the human dimensions of global change has value both as basic science and for informing environmental decisions. It increases basic understanding of how past human activities have created present environmental conditions, how past environmental changes and variations have affected human well-being, and how people have responded to these variations and changes. By developing understanding of human-environment dynamics, human dimensions research improves the knowledge base for anticipating future environmental changes and for informing policies aimed at reshaping the environmental future. Studies of the human consequences of and responses to global change help inform judgments about what kinds of responses would be most desirable (e.g., mitigation, adaptation options) and about how to organize those responses to achieve the desired effects. Below we describe the major science issues, review progress that has been made in understanding them, and identify some lessons that have been learned from previous research.

What Are the Major Causes of Changes in the Global Environment

What has been learned in recent years about human causes of global environmental change? One major focus of research has been the explanation of changes in the composition of the Earth's atmosphere. Looking at the atmosphere through human history, one finds that the concentrations of several gases (carbon dioxide, methane, nitrous oxide) changed only a little for more than a thousand years and then started to increase rapidly around 1800. The obvious hypothesis to explain these data is that prior to industrialization in the nineteenth century the related basic cycles of the Earth's environment were in approximate equilibrium and aggregate human activity was too small to be detectable in globally averaged data; then, increasingly since the Industrial Revolution, aggregate human activity has changed the composition of the atmosphere, in particular adding measurably to the concentrations of certain gases. Similarly, looking at the history of land use and land cover, one finds significant changes occurring, although over longer time periods. The obvious hypothesis to explain these observations again is that human beings altered the land and used resources to meet the needs of a rapidly growing population and an expanding industrial economy. Research into the direct human causes of global change has thus focused on changes in land and

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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energy use. But there is also a growing body of work on the fundamental social processes that drive human use of the environment.

Human Activity and Land Use Change

Interest in the causes of local and regional land use changes is long standing in the social sciences.20 Significant steps have been made in documenting the long history of human transformation of land cover and in explaining the major forces that drive land use. These studies are of interest to a wide range of social and environmental scientists because land is a key factor in social relationships and resource use. But these studies also provide specific contributions to scientific understanding of biogeochemical cycles (especially the carbon cycle), regional climate modification, and alterations in natural ecosystems and are a critical basis for policies to mitigate and adapt to climate change, conserve biodiversity, and reduce land degradation.21 Land use studies provide a powerful rationale for maintaining land and marine remote sensing satellite systems and suggest ways in which these technologies can be made more germane to decision making.

The global change research community has made considerable progress in recent years on several important questions, such as the social causes of deforestation in regions like the Amazon River basin and Southeast Asia; the role of social, political, and economic institutions in land use decisions; and the relationships between population and land use (and land cover) change.22 There have also been tremendous improvements in the ability to combine social, physical, and remote sensing data within geographic information systems, often with the explicit purpose of understanding how processes at local scales are nested in regional, national, and global scales.23

Additionally, human dimensions research has highlighted the important distinction between land use and land cover. Whereas land cover refers to the land's physical attributes (e.g., forest, grassland), land use expresses the way such attributes have been transformed by human action (e.g., ranching, crop production, logging); that is, land use measures provide a socioeconomic portrait of a landscape.24 Land cover is directly represented in global climate models. Land use links land cover to the human activities that transform the land.

The emerging field of environmental history has provided important data on the trajectories and causes of land use changes in the past. For example, historical studies of the U.S. Great Plains have shown how changes in the use and management of grazing and croplands relate to government policy and economics and in turn influence the cycling of carbon and nutrients.25 Historians and geographers have also reconstructed the history of human use of such regions as the Mediterranean, Caribbean, and Latin America.26

Historical studies of land use have altered scientific thinking on the past and the present in a variety of ways. For instance, many observers have presumed that much of the humid tropical forests is pristine or that human impacts on the

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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global environment mainly occurred in recent decades. However, research has shown that many forests were cleared in the distant past or have been managed for centuries and that their current rich biodiversity may be a product of past human manipulation, resulting in higher frequencies of species with economic, medicinal, and other human uses than might be expected to result from natural processes of secondary succession.27

Although human population growth is commonly seen as the major cause of land cover change and destruction of habitats for biota, particularly because of land clearing to grow food, the role of population is in fact far more complex. Numerous cases do suggest that population growth and/or migration are correlated with increasing rates of tropical deforestation, but just as many suggest that population growth need not lead to increasing deforestation—when alternative employment, settlement concentration, and other processes are available as alternatives to land clearing, to provide a population with an acceptable standard of living.28 In fact, there is considerable evidence that only at higher population densities does one find more intensive and efficient use of land.29

Research on land management practices has demonstrated that overexploitation of common-pool natural resources—the so-called tragedy of the commons30—is not an inevitable consequence of human nature and the spatial distribution of resources but is contingent on the structure of human communities and the condition of social institutions that effectively govern access to a resource, monitor its condition, and establish sanctions for overexploitation.31 Both cultural traditions and contemporary legal rules, such as land tenure rules, are critical in influencing how land can be used and by whom.

The emergence of integrated and interdisciplinary approaches to understanding land use and environmental issues has resulted in a series of studies that show how political and economic structures constrain individual choices about management of land and resources.32 For example, colonial legacies of unequal land tenure and export-oriented production, combined with current unfavorable terms of trade and debt, have driven many peasants to overuse their land, adopt polluting technologies, or cut their forests.33

Social scientists have begun to make greater use of orbital Earth-observing satellites in recent years. The interest in understanding the social dimensions of land use change has challenged some of the inferences about land use drawn by natural scientists by showing, for example, the importance of secondary growth and the likely miscalculations of biomass and carbon pools resulting from overly aggregated analyses that fail to quantify the differences between mature and 10-year-old regrowth vegetation.34 Social scientists have explained the processes underlying various patterns of forest change seen on satellite images in terms of the development of transportation networks, land tenure, and export agriculture. Social scientists have also made important contributions to explaining satellite observations of vegetation dynamics in Africa and to understanding land use change in areas undergoing urbanization.35

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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Field studies of land use have provided information of great relevance to global and regional atmosphere-biosphere modeling. For example, coarse-resolution satellite data tend to represent the predominant soil type or vegetation in each grid cell, even if a minor soil or vegetation type is of major economic or ecological significance. Such a representation of the data can seriously misrepresent land use and productivity potential as well as biogeochemical cycles. Another important development is the focus on explaining trends and patterns in land use intensification, in which crop yields are increased through the use of agricultural chemicals and irrigation, resulting in alterations in regional and global biogeochemical cycles and ecosystems.

Progress in the past decade is evident in the rise of an International Human Dimensions Programme/International Geosphere-Biosphere Programme (IHDP/IGBP) core project on land use/land cover change, with a coordinated, comparative, multilevel strategy for understanding, monitoring, and modeling land use.36 In developing frameworks, case studies, and models of how social forces drive changes in land use and land cover, this type of comparative research program has the potential to explain and predict land use change but also to assist in identifying strategies for managing land use and protecting ecosystems.

Recent important U.S. initiatives include the expansion of the population program at the National Institute of Child Health and Human Development (NICHD) into population and environmental research in 1995, the creation in 1996 of an NSF-funded research center that works on land use—the Center for the Study of Institutions, Population and Environmental Change at Indiana University—and the National Aeronautics and Space Administration's (NASA) Land Use Cover Change request for proposals. In summary, there has been considerable progress in understanding the human causes of land use change, including the following insights:

  • Humans have been altering land cover and use for centuries.
  • Some regions that now appear pristine have been subject to human management since prehistoric times.
  • There is no simple relationship between population and deforestation or between common property rights and resource degradation.
  • The analysis of institutions—in their broadest sense, including political, legal, economic, and traditional institutions—and their interactions with individual decision making is critical in explaining land use.
  • Satellite images can provide important insights for social science, and social science can help guide satellite programs to useful applications.
  • The age and gender structure of landholding households affects how much forest is cut for farming.
  • Tax incentives affect Amazonian deforestation.37
  • Secure land tenure is important to long-term resource conservation.38
Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
×
  • Road construction in forests leads to increased deforestation not only by farmers claiming land but also by logging companies.

However, there is still inadequate knowledge on such key issues as these:

  • How to develop land management institutions that both respond to local needs and mitigate global environmental change.
  • How to aggregate in-depth studies of land cover and land use to provide global projections of use in large-scale modeling and international management of global change.
  • The role of population mobility in land use change.
  • How to best use the expanding range of satellite data in land use/land cover change research.

Human Impacts on Coastal and Marine Ecosystems

Global change research encompasses the study of changes in coastal and marine ecosystems insofar as they are affected by physical and socioeconomic processes that are global in scale and effect. Social and applied scientists have investigated the importance of coastal and marine ecosystems for many communities, regions, and nations. They have also addressed the ways in which resource use and pollution have altered the condition and biodiversity of coastal ecosystems in many regions of the world, including the destruction of protective and productive mangrove ecosystems, the degradation of coastal lagoons and estuaries and species that live or reproduce in them, and the minor contamination of even the deep and remote oceans.

Steady increases in demand, technological capacity, and effort have led to a long-term trend of increasing fish catches, which is believed to have leveled off during the 1990s, indicating limits to sustainable harvests.39 Heavy fish mortality means that environmental fluctuations as well as other human impacts, such as pollution and degradation of habitat, make fisheries even more vulnerable.40 Social scientists and others have documented the roles of technological change, population growth, institutional structures, and social attitudes in driving demand for fish and other marine resources, as well as in shaping the nature and effectiveness of fisheries management, and they have sought ways to use these resources more sustainably.41 They have also contributed to understanding the ecological and social concerns associated with mariculture, which is increasing throughout the world as a way to compensate for declining natural resources.42 This research also contributes to several related themes identified in this chapter, including the links between economic globalization (e.g., of industrial shrimp farming), conflicts over common property resources and loss of forest lands (mangroves); the emergence of new social institutions (social movements in resistance to industrial aquaculture); and the use of new information technologies (communications and

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
×

spatial) in resource management.43 Research on common property management, discussed in a later section of this chapter, has drawn many important examples from marine ecosystem use.44

Some important insights of this research include the following:

  • People have responded to problems in coastal marine systems primarily by intensifying, diversifying, and expanding the areal extent of their uses of those systems, tending to extend such problems to the global level.
  • Globalized systems of production and marketing, combined with increases in population and consumer demand and patterns of subsidization, increase competition between countries and communities for scarce marine resources.
  • Rules of free and open access, combined with the weaknesses of international management regimes, make it difficult to control harvesting in deep ocean and other multinational fisheries.
  • Restricting access is a necessary but not sufficient approach to reducing incentives to overharvest and pollute marine ecosystems.
  • The technical and institutional tools of marine resource management have not adequately incorporated the effects of coastal development, wetlands drainage, dams, and pollution of rivers and oceans in diminishing breeding habitat and degrading marine resources.
  • The success of fisheries and coastal management depends on functional interdependence between local institutions and regional, national, and international institutions.

Current knowledge is not adequate to achieve several essential goals:

  • Provide complete geographic coverage of the status of human use of marine and coastal resources.
  • Analyze and model changes in the abundance of fish and marine mammal populations as a function of multiple social and environmental stresses, including interannual, decadal, and longer-term climatic change.
  • Evaluate the full range of institutions, including traditional systems, to understand how they increase or reduce human impacts on coasts and oceans.

Changes in Energy and Materials Use

Fossil fuel use is the most prominent human activity that alters the composition of the global atmosphere. Since the 1970s, a burst of human dimensions research seeking to understand the consumption of fossil fuels has been proceeding simultaneously at several levels. The methods developed for studying energy use have more recently been applied to human transformations of the global

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
×

nitrogen cycle and to human consumption of other environmentally significant materials. The results are useful as inputs to climate models, for anticipating future rates of environmental change, and for identifying effective ways to mobilize social and economic forces to alter trajectories of environmental change.

First, fossil fuel use has been disaggregated by fuel type, geographic region, mediating technology, and social purpose (lighting, water heating, transportation, steel making, etc.). It has been shown that patterns and environmental impacts vary greatly by country and that national-level consumption varies with technology, population, and other factors, such as industrialization and degree of central planning of economies.45

Second, progress has been made in understanding patterns and changes in energy and materials use across countries and over time.46 Energy use and its environmental impacts, for example, generally increase as a function of economic prosperity, but there are exceptions. Countries beyond a certain level of affluence experience declines in per capita environmental impact, although considerable dispute remains about where the turning point lies.47 Also, the energy-affluence link breaks down in certain periods, including those characterized by rapidly increasing relative energy prices and significant policy interventions.48 Thus, changes in prices and policies allowed economic growth to continue in the United States without increases in energy use or carbon emissions between the mid-1970s and the mid-1980s, but energy use has been increasing since then, driven by increasing travel demand, shifts in the vehicle fleet, and other factors, and similar trends have been occurring in other developed countries.49 Long-term trends show decreasing carbon emissions per unit of energy use due to fuel switching and electrification, decreasing materials use per unit of economic output, and replacement of dense materials such as steel with lighter-weight materials such as plastics.50 These rates of change have an autonomous dynamic and respond to the prices of inputs, but little is known about how public policy might alter the trends to enhance environmental quality.

Third, patterns of energy and materials use have been studied in relation to particular variables that may account for changes and variations in use, and some of these variables can be affected by public policy. At the household level, for example, energy use is affected by income and fuel prices, household structure and social group membership, and by individual knowledge, beliefs, and habits, as well as by the energy-using technologies that households possess.51 Research on the determinants of consumer decisions to take advantage of technical and economic possibilities to improve energy efficiency indicates that more is required than favorable attitudes and accurate information. There is significant potential to improve residential energy efficiency with appropriately designed interventions. The research strongly suggests that the most effective interventions are specific to consumers' situations and that they use combinations of information, incentives, and social influence. Participation of affected consumers in program design can greatly increase effectiveness.52

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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Research has focused on identifying how the energy consumption patterns of firms and individuals change as a function of changes in information, incentives, technology, and social organization, thus illuminating the potential for reducing society's reliance on fossil fuels by promoting the adoption of new technologies or changing behaviors and preferences. Specific areas of extensive research include technology-focused research on energy consumption, energy efficiency, renewable energy, and nuclear power; research on price elasticities and response to incentives; and research on behavioral and informational factors affecting change in consumer choice.53 Consumer energy choices are also shaped by political and economic structures that influence regulations and incentives for different types of energy, transportation, and housing policy, as well as the reach of advertising to different regions and social groups.

Research on energy conservation has blended behavioral and technological analyses to compare the technical potential for reducing the energy use required to provide an energy service, such as indoor climate control, with actual reductions in energy consumption. It has examined ways to achieve more of this potential reduction by identifying and removing barriers to energy conservation, such as subsidies and other market distortions, principal-agent problems, incomplete consumer knowledge and misinformation, and problems related to the early stages of the introduction of new technology. This research provides a basis for selecting promising policy options to achieve national commitments to stabilize greenhouse gas emissions.

Materials balance analysis provides the basis of an accounting system that tracks the stocks and flows of certain materials, particularly the chemical elements, through the human economy. Analysis of material flows in this fashion has been called industrial metabolism and industrial ecology.54 As in energy research, the analysis begins with descriptive work that clarifies the principal human activities dominating each materials flow; proceeds to explorations of behavioral, economic, technological, and policy-related determinants of these activities; and expands to include prospects for changes in consumption patterns over time, including changes related to economic development.55 One element that has been productively studied is nitrogen, which in the form of nitrous oxide acts as a greenhouse gas and affects the chemistry of stratospheric ozone and in several chemical forms plays a role in nitrogen fertilization of the biosphere. The predominant role of fertilizer production in human-induced changes to the global nitrogen cycle was only recently recognized.56

Our understanding of energy use is far more sophisticated than it was two decades ago. It has led to the broader concept of environmentally significant consumption and to the idea of applying analyses like those used for energy to various nonelemental materials of environmental importance, such as wood, steel, cement, glass, and plastics.57

An important part of research on energy use is scenario making, which seeks to extrapolate current energy use patterns into the future.58 Time horizons of

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
×

prominent scenarios range from a decade to a century. Two important goals of scenario making are transparency (explicit reviewable assumptions) and self-consistency. For global change studies, most scenarios are built on the basis of models of the evolution of national economies, often assuming a similar evolution for large groups of countries at a similar stage of economic development and structure. Typically, population growth is exogenous to the models, and per capita energy consumption is the subject of investigation. The most significant uncertainties relate to the determinants of the rate of introduction of new technologies.59 Rarely addressed to date but presenting major sources of uncertainty are changes in preferences over time, such as those that might accompany new environmental information.60

Scenario making is a conservative activity in that it assumes only slow changes from established trends; it is not well suited to exploring the significance of surprises and catastrophes. Nonetheless, over the past two decades, scenario making to elucidate energy consumption has become a highly developed art, featuring dialogues among modelers to ensure quality control and intercomparisons and to highlight debatable assumptions. Scenario building has been an essential basis for IPCC assessment models of future climate and analyses of mitigation options, the latter employing models used for scenario building in policy analysis of greenhouse gas emission control strategies.61

Important insights of such activities include the following:

  • Estimates of future emissions of greenhouse gases are highly sensitive to assumptions about future economic, technological, and social changes, particularly about the autonomous rates of decarbonization and improvement in the energy efficiency of technology, about the likelihood of further large-scale economic transformations, and about the stability of preferences.
  • Energy and materials uses are determined by multiple factors: they are not simple functions of population or economic activity but depend on complex interactions of these factors and others.

Future emissions of greenhouse gases will be driven by pressures from increasing affluence and population, with countervailing trends that reduce the amount of energy and materials used per unit of economic activity and the rate of emissions per unit of energy and materials used.

Current knowledge is inadequate to accomplish some tasks critical to understanding consumption trends, their potential environmental consequences, and the possibilities for altering them. These tasks include:

  • Clarifying the determinants of ''autonomous'' change in energy and materials efficiency and thus improving the accuracy of projections of change in greenhouse gas emissions and in the pressure on depletable resources.
Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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  • Specifying the ways in which population, technology, affluence, preferences, policies, and other forces interact to change the rates of environmentally significant consumption in high-consuming developed economies and particularly in developing economies, where large increases in consumption are anticipated.
  • Identifying and quantifying important sources of variation in the adoption of environmentally beneficial technology among firms within industries.

What Are the Human Consequences of Global Environmental Change?

Human dimensions research has made important progress in understanding the consequences of global change for people and ecosystems. Drawing on earlier research in applied climatology and natural hazards, the past 10 years have seen a major effort to understand the potential impacts of climate change on human activity, as well as studies of the impacts of past and present climate variability, the impacts of ozone depletion on human health, and the effects of land degradation and biodiversity loss on society. Credible climate impact assessments are a basis for developing policy responses to global climate change and for successful application of information on current climate variability to resource management.

Consequences of Future Climate Changes

The first studies of potential global warming impacts analyzed how crop yields and water resources would change in developed countries in response to climate scenarios of monthly changes in temperature and precipitation, based on coarse and uncertain output from climate models simulating the equilibrium response to a doubling of carbon dioxide levels in the atmosphere.62 Later crop modeling efforts have incorporated the direct physiological effects of higher carbon dioxide levels, employed transient climate scenarios and daily data, covered developing countries, and replaced the concept of the unresponsive farmer with that of people capable of flexible adaptation to climate change.63

It appears that many U.S. farmers will be able to adapt to the climate changes expected from a doubling of atmospheric carbon dioxide levels by shifts in technology and crop mix but that others, especially in developing countries, will experience lower yields because they cannot afford technology and may be farming more biophysically vulnerable land.64 Some studies of economy-wide impacts arrive at similar conclusions;65 however, these conclusions may be sensitive to some of the assumptions underlying the analyses, as discussed in more detail in the section below on integrated assessment.

A major conceptual advance occurred in moving from impact assessments based on climate model scenarios to analyses based on an understanding of vulnerability.66 The lack of consensus about how climate may change at the

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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regional level, and the recognition that changes in social systems may be more important than changes in natural systems in determining the impacts of drought and other climatic shifts, reoriented the Working Group 2 of the second IPCC assessment to pay more attention to vulnerability assessment. For example, rapid increases in water demand have increased drought vulnerability, and the spread of urban settlements into coastal and flood-prone regions has increased vulnerability to sea level rise and severe storms.

Another innovation is the development of multisectoral regional assessments of the consequences of climate change. The Missouri-Illinois-Nebraska-Kansas (MINK) and Mackenzie River basin studies are good examples of a regional and cross-sectoral approach to climate impact assessment. The MINK study examined what would happen if the drought conditions of the 1930s were imposed on the economy and resources of the MINK region of the future. Taking into account adaptation, the study showed that, on the whole, agriculture would be able to cope with climate change better than forests or water resources and that impacts on the regional economy would be minor.67 The Mackenzie River basin study examined the impacts of climate change in the Canadian Arctic using several climate and socioeconomic scenarios and including local stakeholders in defining policy questions and potential responses. The study found significant effects on northern ecosystems and hydrology.68

These new approaches to climate impact assessment have relevance far beyond the study of global warming. Many of the methods can be used to understand the impacts of seasonal to interannual climate variability, thus increasing the usefulness of forecasts on that timescale based on improved understanding and modeling of El Niño. The new approaches can also be used in analyzing the impacts of decadal shifts in atmospheric circulation and climate variability. For example, statistical crop models were used69 to correlate ENSO with maize yields in Zimbabwe, and several early warning systems for famine also drive crop models with climate information to manage food security.

One of the most significant emerging areas of research is the effects of climate change and variability on human health. Several studies have shown that climate change may result in changes in the incidence and prevalence of such diseases as cholera and malaria, which debilitate human populations,70 as well as changes in the geography of crop and livestock pests and diseases. For example, as plants have migrated upslope in the highland tropics in response to warmer climate, and tropical summit glaciers have generally retreated, and freezing levels in the mountains have moved up 150 m since 1970, mosquito-borne diseases have increasingly infested highlands and high-elevation cities such as San José, Costa Rica, and Nairobi, Kenya. Extreme events such as high temperatures have been linked to increased mortality, especially of older people and the infirm, in major cities.71

Important developments and insights in this general area of research include the following:

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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  • The consequences of environmental change depend as much on the social systems that produce vulnerability as on the biophysical systems that cause environmental change.
  • The consequences of environmental change are strongly dependent on the ability of people and social systems to adapt; consequently, access to economic resources is a key mediator between environmental changes and their impacts.
  • Climate models can be linked to crop models to provide early warnings of famine.
  • Human health may be an important area affected by climate change.

Knowledge is not yet adequate to achieve several goals critical to anticipating the likely consequences of future environmental changes, such as:

  • Developing indicators of vulnerability that are sensitive to regional and social variations.
  • Projecting vulnerability estimates into the future.
  • Linking mesoscale outputs of climate models to regional impacts, taking into account vulnerability and the ability of vulnerable individuals and social systems to adapt.

Impacts of Past and Present Climate Variability

The most noticeable and perhaps most serious effects of long-term climate change may not be slow changes in average temperature or precipitation but rather such extreme events as storms, droughts, heat waves, floods, and wildfires; in some climate change scenarios, epidemics may be the most serious of all the dangers. Because of the importance of such episodes to society, environmental scientists are increasingly attempting to predict changes in the frequency of extreme weather events and to identify the boundary conditions for the spread of disease. Social scientists have explored the impacts of climate variability in historical and archeological studies and in research on the human impacts of climatic natural disasters. These studies have highlighted the importance of understanding vulnerability and adaptation.

Several recent studies suggest links between drought and the collapse of civilizations in Asia and Latin America. For example, the abandonment of settlements in the Andean altiplano and Amazon River basin has been shown to correlate with paleoenvironmental evidence of severe El Niño events.72 A large body of work examines the influence of climatic variations on European and North Atlantic history,73 showing the effects of the Little Ice Age and cooler periods associated with volcanic eruptions and the vulnerabilities of different social systems to those changes. As scientists gain new insights into paleoclimatic variability, rapid climate change, and shifts in decadal circulation patterns, social

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
×

scientists can apply archeological and historical techniques to examine the human dimensions of these events.

Insights from natural hazards research also have great relevance to understanding the consequences of climate variability.74 In the immediate aftermath of floods, hurricanes, and fires, social cohesion increases, and buildings and services tend to be restored with much greater speed than they were originally developed. Anticipatory responses, however, are more uneven, even under normal regimes of climate variability. For example, many vulnerable households and businesses fail to insure adequately against floods, even when warned of an increased near-term likelihood of flooding, and vulnerable communities often resist planning and zoning changes that would render them less vulnerable. If global climate change increases the frequency of so-called 100-year floods and other natural disasters or brings about disasters outside the range of previous experience, weaknesses in anticipatory responses will become more costly.

Researchers have begun to think about hazard response in terms of systems, recognizing that societies have always had systems for responding to the range of climatic variations, including extreme weather events, that they normally experience. For example, seasonal migration in drought-prone areas, crop diversification, hazard insurance systems, social norms of helping, flood control, fire management policies, zoning regulations, river monitoring, and other social and technological systems can alter the frequency, severity, extent, and distribution of economic losses associated with hazards. Such social systems can make as much difference in human outcomes as the distribution of weather events themselves, largely because of the effects of these systems on vulnerability.75

Global environmental change challenges human hazard management systems with potential major environmental surprises resulting from the nonlinear behavior of global environmental systems. Societies may be faced with rapid climate change events, ecological collapse, or epidemics that may be different in kind, faster in rate of onset, or greater in severity than the changes for which existing hazard management systems are prepared. We do not know how societies may alter their hazard management systems to face the prospect of such environmental surprises. However, studies of environmental risk management and decision making show that changing practices in anticipation of high-consequence/low-probability events poses a major challenge: democratic societies typically have great difficulty reaching consensus on policies to manage these sorts of environmental risks and even in arriving at widely shared understanding of them.76

Hazards research has also shown the potential value of understanding the consequences of El Niño and other potentially predictable aspects of seasonal to interannual climate. Several studies have linked El Niño events to major disaster losses in such regions as Northeast Brazil, Australia, and Southern Africa, and insights from these studies can contribute to applications of improved predictions of climatic conditions. For example, the correlations between crop yields and

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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droughts associated with El Niño indicate the potential value of forecasts to food security.77

Important insights and findings from this area of research thus include the following: the vulnerability of a society and of its hazard management systems is often more important than the magnitude of a climatic event in determining impacts on people, and past climatic variations may have been associated with large-scale abandonment of human settlements and major migrations. More information is needed about the following issues: the consequences of newly identified rapid climate changes of the past and the ability of hazard and resource management institutions to respond to surprising shifts in climate and to seasonal forecasts.

Ozone Depletion

The main reason for widespread concern about low Antarctic ozone levels, and an important stimulus for policies to eliminate ozone-depleting chemicals, has been the concern that declines in stratospheric ozone could affect human health by increasing skin cancer, causing eye problems, and stressing immune systems. Considerable research has been directed to better understanding the links between ozone depletion and human health, as well as possible impacts on ecosystems. Most of the research to date consists of epidemiological and medical studies on the effects of increased ultraviolet (UV) radiation.

Considerable progress has been made in understanding the links between UV exposure and skin cancer, and investigating the still-controversial link of UV exposure to cataracts.78 Additional research is needed to accomplish several critical goals: to examine the effects of ozone depletion on animal populations and ecosystems of economic or other societal value, to understand behavioral and demographic aspects of UV exposure, and to link trends in industrial use of ozone-depleting chemicals to risks for human health and ecosystems.

Environmental Change and Security

Another set of studies has examined the ways in which global change may lead to conflict, mass migration, or threats to national security. This research tends to build on studies of deforestation and climate impacts that suggest that environmental change may cause competition over resources, refugee migration, or political unrest. For example, it has been suggested that environmental degradation in developing countries has resulted and may again result in violent conflicts.79 It has also been discussed how climate change may create conflict over international water resources and may destabilize food security.80 A new IHDP project sets out to examine the relationship between global change and security from global to local scales.

This research focus has achieved one important end: highlighting the plausibility of several types of potential impacts of global environmental change on

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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conflict and security. More research is needed to accomplish a related goal: providing careful empirical analysis of the relative roles of environmental change and other factors affecting conflict and migration.

What Are the Potential Human Responses to Global Change?

It is difficult to separate conceptually the causes and impacts of global change from responses to it because in many cases responses to environmental change immediately modify the causes and the impacts. For example, the adaptive responses of farmers to drought have shown how hazard warning systems moderate disaster losses. Studies have examined human responses to global change at the individual, community, national, and international levels. This section reviews progress in several pertinent areas of research, including international environmental policy, local and regional institutions, decision making and risk analysis, and valuation. We also examine progress in "integrated assessment" of global environmental changes.

International Environmental Policy

Much of the work on global-level international policy and institutions has focused on the development and implementation of regulatory "regimes" established through transnational, regional, and international agreements, such as the Montreal Protocol, the Climate Change Treaty, and the Biodiversity Treaty. These studies draw on work on the theory of international regimes, bargaining, and the structural and institutional conditions supporting international cooperation.81 They have built the beginnings of a useful body of data and identified suggestive empirical regularities, although they have not yet supported rigorous testing of hypotheses. More specifically, these studies have focused on regime formation, the modes of influence of international environmental institutions, the use of financial transfers for international environmental protection, long-term comparative national and international policy development, the implementation of international environmental agreements, the analogy between international environmental protection and local management of common-property resources, and the systems for monitoring and enforcing compliance.82

A significant body of research on policy instruments at the national and subnational levels is highly relevant to implementing international environmental agreements. This research has led to improved understanding of the strengths and limitations of strategies such as regulation, various classes of financial incentives and penalties, liability law, provision of information, inducements for technological development, disaster prevention and preparedness, and alterations in the structure of markets for mitigating and responding to global change.83

The following are some important findings and insights of this research domain:

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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  • Several systematic difficulties exist in changing the behavior of specific targeted nation states, even when policies are backed up with financial resources.84
  • Policy is often strongly path dependent in that early decisions may constrain or determine later ones, thus making discussion of alternative policies extremely difficult at later stages.85
  • Transnational networks of scientists can play a strong role in early definition and framing of an issue, although they have only limited ability to motivate international agreement or to influence the interpretation of scientific knowledge by political decision makers.86
  • Assessment of risks and response options tends to follow, rather than lead, political target setting, and the range of options tends to contract over time.87
  • Coercive sanctions have limited effectiveness in enforcing compliance, compared with carefully designed, linked systems involving rule design, information provision, granting of capacity and legal authority to selected actors, and transparent processes of implementation distributed among multiple formal and informal institutions.88

Knowledge is not yet adequate to achieve the following:

  • Identify specific combinations of policy instruments and monitoring strategies that will induce a broad range of actors to behave in ways that lead to achieving internationally agreed-upon goals.
  • Identify specific international and national institutions that can effectively link the international, national, and local levels and make it possible to design effective and acceptable policies.

National and Local Institutions

Human responses to global environmental change are shaped by institutions, defined broadly as the norms, regulations, interpretations or understandings, and social organizations that bear on a particular activity. The past decade has seen a renaissance of research on the structure and dynamics of social institutions and a change in thinking about how these institutions shape human activity.89 This work is being applied increasingly to problems of institutional design for managing environmental change.90 It is developing a knowledge base on how social institutions have succeeded and failed at long-term management of environmental resources that will be useful for informing future environmental policy choices.

The fundamental issue for environmental management is that of designing incentive-compatible institutions.91 Such institutions are capable of internalizing, within individual households, private firms, and public organizations, the costs of the negative effects of human activities, effects such as pollution, when they are

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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not otherwise penalized by the market. These so-called externalities are a major source of environmental stress. Even if accurate measurement is developed of the costs of externalities, the question remains of how to design institutions to avoid generating these negative effects. At present we are better at dealing with emissions and other externalities after the fact than at preventive institutional design.

An important focus of recent research on national and local institutions is property rights institutions, as they bear on the management of environmental resources.92 One advance has been to demonstrate the ambiguity of such terms as "the commons" and "common property" and hence the need to specify property rights arrangements in more detail.93 The term "common property" has been used to signify, at one extreme, unregulated open-access situations, as in many high-seas fisheries, frontier agricultural or mining development, and air and water pollution. At the other extreme, it has referred to highly regulated and tightly circumscribed systems governing the use of land or natural resources as found in some communities, where ''commons" signifies a viable institution of collective rights and responsibilities.94 Most ''common property" institutional arrangements are somewhere in between.

Research has increasingly focused on alternatives to top-down government control over commons situations, alternatives such as collective action on the part of resource users, and market-based systems of allocation. Attention has been redirected to questions about external and internal conditions under which collective action can prevent or mitigate environmental problems. This line of research has produced significant insights, showing, for example, that common-pool resources are not inevitably destroyed by human overexploitation as presumed in the model of the tragedy of the commons. Rather, the fate of these resource pools depends on the formal and informal institutions that monitor their condition and control their use.

Comparative case studies and game theory experiments show the importance of time, scale, and socioeconomic structure to the success of collective action, and they show the need for local institutions to establish good systems of monitoring, communication, and normative control of behavior.95 They also show the importance of appropriately structured linkages between local organizations, which tend to have more detailed knowledge about resources, and higher-level organizations, which can enforce access rules and address externalities beyond the locality.96 These findings bear on questions of institutional reform and innovation, suggesting as they do some advantages of more decentralized management regimes.

Important advances in the knowledge of institutions include the following:

  • The discovery that common-pool resources have sometimes been managed sustainably by societies for periods of several centuries.
  • The development of a typology of institutions for managing common-pool resources (particularly property rights institutions).
Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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  • The development of the beginnings of a body of knowledge about how particular institutional types can effectively sustain resources.
  • Recognition of the importance of locally based and self-organized institutions for monitoring and controlling resource use.
  • Recognition of the ways that higher-level institutions can constrain and enable local ones.

Knowledge is not yet adequate to match particular institutional types appropriately to resource types and social settings or to identify effective ways of linking institutions across levels to maintain particular resource types.

Market Mechanisms

Property rights research also has led to research on market-based policies. Recognizing that in many situations neither local-level management nor command-and-control solutions may be effective or feasible, researchers have focused on the use of exclusive tradeable property rights or privileges in environmental management.97 In marine fisheries, long plagued with open-access problems, individual transferable quotas have become increasingly popular. Research shows some economic benefits but mixed results with regard to creating incentives for conservation.98 Emissions trading has been shown to reduce the costs of regulation.99 Experiments have been under way to apply this idea internationally, for example, by using international carbon emissions offsets to help developing countries finance environmental regulation.100 Distributional effects of trading are major issues for both fisheries and emissions regulation.

Research on modifying the ways in which markets allocate environmental resources has significant insights to offer in responding to global change. Some of this work is based on estimating the full social value of an environmental resource and instituting taxes or other financial incentives to bring the resource's price into line with its social costs. Important advances in the area of market mechanisms include indications that market-based policies (e.g., transferable quotas, emissions trading) have significant cost advantages in theory and in some applications and recognition that the effects of these policies are situation dependent. Knowledge is not yet adequate to meet several critical needs for understanding how market mechanisms would work in practice, such as estimating distributional effects of particular market-based policies and matching market-based policies to resources and social and political conditions for optimal effectiveness.

Valuation of Responses to Global Change

Responses to global change require that decision makers face important questions of resource allocation: How can decisions appropriately take into

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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account the value of resources that have no market price? How do and how should societies allocate resources between present and future generations? How do and how should societies decide equity issues within the present generation?

Many studies use forms of cost-benefit analysis to compare the costs and benefits of various responses to global change. In these studies the economic costs of impacts as well as responses are usually included. The results of cost-benefit analyses tend to be highly sensitive to assumptions about nonmarket values, such as those of ecological services like water purification and crop pollination, human health and life, and prevention of species extinctions. Considerable effort has recently been devoted to approaches for evaluating nonmarket values by various "indirect market" methods, such as measuring the cost of activities engaged in to compensate for the effects of pollution and "hedonic pricing" (e.g., estimating the amount of increased compensation offered workers for more hazardous jobs). Each of these methods has been applied to a restricted class of nonmarket values, and each has certain clear limitations.101 Partly to overcome the limitations of indirect market approaches, economists have increasingly turned to contingent valuation methods, in which individuals are asked directly to express their willingness to pay for particular environmental improvements. This technique has found some acceptance in policy circles, but methodological and conceptual questions about the approach are still being hotly debated.102 Some progress has also been made in estimating the nonmarket value of environmental resources for inclusion in national income accounts.103

Researchers have also examined the use of novel methods for integrating disparate kinds of values without converting them to monetary units. Techniques of multiattribute utility analysis allow values to be integrated in various ways to reflect users' value priorities.104 Simulations and policy-exercise studies clarify key uncertainties, values, and interactions, and deliberative methods involve both experts and nonexperts in interpreting analyses.105 Such experiments promise to yield methods that complement economic techniques of valuation, where the latter give incomplete or inconclusive results.

There also have been efforts to deal analytically with the obligation of the present generation to future generations. For example, a choice not to mitigate climate change benefits the current generation but imposes unknown adaptation costs on future generations. These analyses are highly sensitive to the discount rate used to represent tradeoffs between present and future resources. Critics of conventional cost-benefit analysis often insist that the discount rate approach results in a dictatorship of the present over the future. The issue of how to take into account obligations of the present toward the future and the problem of intergenerational income distribution both remain unresolved. Ethical analyses and discussions of these issues remain more unsatisfactory than economic analyses; however, scientific debate remains contentious.106 Analytical techniques are also being developed to address equity issues in the present generation.107

This field of investigation is in a highly vigorous state. For its results to have

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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satisfactory practical value, analysis must develop to the point at which it can give confidence in the validity of particular analytical techniques for estimating nonmarket values and provide a satisfactory way of analyzing equity issues, particularly those relating to intergenerational equity.

Understanding Risk, Uncertainty, and Complex Choices

Responding to the prospect of global change requires interventions in complex systems that are not fully understood. Decision makers can benefit from recent advances in understanding human judgment and decision processes regarding complex environmental choices. Over the past decade this research has increasingly clarified why scientific efforts to analyze and assess global environmental threats do not easily lead to social consensus on policy responses to those threats. This research shows that, while analyses normally focus on a few critical outcomes, such as sea level rise or species extinction, nonexperts commonly consider multiple dimensions of environmental conditions and decisions, such as risks to human health, economic costs and benefits, the extent of scientific uncertainty and ignorance, catastrophic potential, and threats to aspects of the environment with intrinsic value. Moreover, even single dimensions such as human health are multifaceted; people assess risks partly depending on whether they believe they can control personal exposure and their own emotional responses to the specific hazard.108 The factors that matter most to people can vary with the situation and with their social position, and these differences then influence their policy preferences.109

These findings have implications for scientific choices and the policy process. Chief among them is the idea that the information that results from science-driven research agendas is not necessarily considered useful or relevant by those whose decisions the scientific analysis is intended to inform. For scientists to know what information will be considered useful and relevant, they must have input from those who participate in environmental decisions. Each technique used to assess environmental risks inevitably makes judgments about what the problem is that needs scientific input, which dimensions of the problem should be investigated, and their relative importance.110 Consequently, decisions that rely on any particular analytical technique are often rejected by people who do not accept its underlying judgments. Moreover, decisions made without the participation of some of the interested and affected parties tend to be rejected by those parties. Consequently, decision processes that are too narrowly based, either in terms of analysis or participation, often fail to meet decision makers' needs for information and involvement.111

The ability to reach an implementable decision depends on the process that combines analysis and deliberation to frame scientific questions, gather and interpret information, and present it to participants in the decision in ways that address their needs for information and understanding. The critical elements of this

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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decision process and some important related research questions have been identified.112 The decision process is also a major concern of the new National Center for Environmental Decision Making Research, established by NSF. Additionally, research has begun to illuminate how scientific and technical information is incorporated into environmental decision making at local, national, and international levels.113

A number of important findings have been made in this research area:

  • Whereas many risk assessments consider only a few dimensions of risk (e.g., mortality risk, economic loss), nonspecialists' judgments about risk typically consider multiple dimensions.
  • Objections to the results of risk assessments often arise from disagreement about judgments underlying the assessments or from restricted participation in making those judgments.
  • The adequacy and acceptability of a judgment about risk depend on both the underlying analysis and the deliberative process that judged which analysis to do, how to collect information, and how to interpret it.

Knowledge is not yet adequate in this field to accomplish several essential tasks, such as:

  • Adequately characterizing uncertainties and scientific disagreements about the nature and extent of risks.
  • Designing processes that combine analysis and deliberation to ensure that information is developed and organized to meet the needs of the range of decision participants.
  • Structuring procedures that inform scientists' work and decision makers' understanding with a combination of formal analysis and the information, perspectives, and judgments of others involved in risk decision making.

Integrated Assessment

One approach used to understand the implications of policy responses to global change is known as "integrated assessment." In integrated assessment, methods or processes are applied to combine knowledge from multiple domains, such as socioeconomic and biophysical fields, within a consistent framework to inform policy and decision making. Integrated assessments of environmental issues have been conducted since the 1970s,114 but the past 10 years have seen a flood of interest and activity, particularly to address global climate change. Since 1990 the number of integrated assessment projects relating to climate change has grown from only a few to more than 40.115

Although the concept of integration has been very broadly applied with

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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regard to what is integrated and how, recent practice in the area of climate change has been rather narrow. Integration can mean "end-to-end" connection of a causal chain from fossil fuel emissions and land use to their impacts, with weighing of climate change impacts against measures to reduce them or to adapt. (Some amount of such "vertical" integration is often taken as a requirement for integrated assessment.) Integration can also denote expanding each link of this chain to consider more diverse source activities and emissions, more atmospheric and biotic processes, more forms and sectors of impacts, or more spatial detail or heterogeneity of agents. Integrated assessments may also examine social and biophysical linkages between climate change and other issues (e.g., ozone depletion, tropospheric air pollution) or include linkages to other social or policy issues such as public health or economic development. In addition to formal modeling, methods for integration can also include structured cross-disciplinary discourse; judgmental integration of data, theory, and formal models from separate domains; and structured heuristic processes such as simulations, scenario exercises, and policy exercises.

A major purpose of integrated assessment is to provide a consistent framework for the representation, propagation, analysis, and communication of uncertainties. A striking result of the few attempts to integrate uncertainty quantitatively across biophysical and socioeconomic domains has been that, among the various kinds of uncertainties, socioeconomic uncertainties appear to predominate in assessing aggregate impacts and net benefits of policies and decisions. Key socioeconomic uncertainties include future population growth and migration, social and political determinants of environmentally relevant consumption, rate and character of technological change, adaptation-mediated regional impacts of climate and environmental change, effects of policies, and variation in preferences.

For example, in an early assessment that integrated energy-economic and carbon cycle models, it was found that the largest contribution to uncertainty in atmospheric CO2 concentrations at the end of the next century came from estimates of the ease of substitution of fossil and nonfossil energy inputs in the economy and general productivity growth;116 uncertainty in the airborne CO2 fraction and in total fossil fuel resources ranked near the bottom of all contributions to uncertainty. In 1993 and 1996, studies using a stochastic integrated-assessment model found that differences in preferences dominated climate uncertainty in determining preferred policy choice.117

Recent integrated climate assessment, however, has stressed vertical, or end-to-end, integration, primarily by building single integrating computer models. These models typically combine and modify preexisting models of energy and the economy, atmospheric chemistry and dynamics, oceans, the terrestrial biosphere, and/or agriculture and other forms of land use. In each project some domains are represented richly, others very schematically. Most integrated as-

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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sessment projects have a national to global scale, rather coarse spatial and sectoral resolution, and weak representation of policies and political processes.

Early work on integrated assessment of climate change combined energy-economic models with either accounting or input-output systems to develop comprehensive emissions scenarios or with simple highly parameterized atmospheric models to project the effect of specific economic and control scenarios on atmospheric trace gas concentrations.118 More recent projects have added climate and impacts modules.

Projects differ in their conceptual emphasis and the potential insights they can offer. Some concentrate on the dynamics of emissions, atmospheric accumulation, impacts, and responses. These projects postulate a single global optimizing producer-consumer and require a common metric for abatement costs and climate damages, so they normally represent regional or global climate damages by simple aggregate functions of temperature change. These models allow the investigation of dynamically optimal abatement strategies that balance, over time, the costs of emissions abatement and damages from climate change or that meet a specified environmental target at minimum cost. They also permit study of how preferred policies depend on alternative specifications of damage functions, discount rates, the dynamics of impacts and technological change, or the structure of world regions and of bargaining.119

Other integrated assessment projects concentrate on the specification and propagation of uncertainty, allowing identification and ranking of key policy-relevant uncertainties or the elaboration of adaptive and learning strategies for responding to progressively resolved uncertainty over time.120 Still other projects concentrate on the elaboration of spatial and sectoral detail for climate impacts, human adaptation and responses, and human-mediated feedbacks through land use change to the climate system.121

Integrated assessment practitioners have claimed insights such as the following: that a large near-term abatement effort for climate change is not justified; that the market impacts of climate change in high-income countries (but not low-income ones) will be small; that optimal abatement paths would reduce gross domestic product by only a few percent, compared with unconstrained paths, and can be accomplished with carbon taxes of a few dollars per ton; and that delays of a few decades in controlling emissions are preferable to immediate action, even if stringent reductions are subsequently determined to be needed.122 These conclusions, however, depend on several particular characteristics of most assessment models: they offer very limited representation of the possibility of extreme events; they only reference doubled CO2 scenarios and so fail to include the concentrations likely by the end of the next century under aggressive fossil fuel growth, which drives atmospheric, ecosystem, and impacts models all far out of their validated ranges; they include weak or no representation of multiple interacting environmental stresses; and they assume limited learning in technological change or policy.

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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Important advances in knowledge from integrated assessment modeling include the following:

  • The finding that socioeconomic uncertainties dominate biophysical uncertainties in contributing to aggregate uncertainty about future climate impacts and preferable response strategies.123
  • Initial quantitative estimates of the benefits available from various levels of international cooperation to manage climate change.
  • An evaluation of the implications of sulfate aerosols in climate change for alternative abatement strategies.
  • A preliminary characterization of the effects of linked demographic, economic, and climatic pressures on land cover and atmosphere.124

Knowledge is not yet adequate in this field to achieve the following:

  • Reduce major socioeconomic uncertainties in integrated assessment models.
  • Estimate impacts and preferable policies from models that relax some of the most important restrictive assumptions of existing models (e.g., doubling of CO2 concentrations).
  • Provide acceptable techniques for choosing among model simplifications, so that outputs best meet users' needs.

What Are the Underlying Social Processes, or Driving Forces, Behind the Human Relationship to the Global Environment?

Human dimensions research has also examined fundamental questions about the broader political, social, technological, and economic forces that shape the human activities that cause environmental change and influence its consequences. The number of such forces that may directly or indirectly alter the global environment has no limit. This section focuses on several driving forces about which important scientific progress has been made and which are often mentioned as arenas for policies to mitigate environmental change. There are many other important social forces and phenomena whose direct or indirect environmental effects may also be large and that may also have policy significance. These include national taxation policies, economic inequality within and between countries, war and the international arms trade, and societies' treatment of women. Important scientific progress has been made in understanding how humans perceive global change; the ways that individuals and institutions cope with environmental changes; and the dynamics of human populations, technological change, and economic transformations.

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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Public Attitudes and Values

Public support is necessary for any collective response to global environmental threats, whether through policy decisions or the aggregated actions of large numbers of individuals and organizations. A series of studies shows strong and persistent concern and support for environmental quality and protection in a variety of countries, rich.and poor;125 in the United States and other countries where relevant data are available, this support cuts across socioeconomic lines. In some developed countries, concern is strongly correlated with education; in some it is strongest in younger age cohorts. Concern about global environmental problems relative to local and national ones is strongest in developed countries, whereas in countries with highly visible pollution problems, environmental issues closer to home are seen as relatively more serious.126 Environmental concern is strongest in countries with serious objective pollution problems and in countries with strong environmentalist values.127

Research on the factors underlying environmental concern finds that it is partly rooted in basic psychological values, particularly concerns with the welfare of others and of future generations and a widespread belief in the sacredness of nature.128 This work draws on extensive basic research that has developed a comprehensive typology of human values.129 Additionally, environmental concern reflects beliefs about how environmental conditions may affect those things that an individual values, suggesting that public response to newly identified environmental conditions may depend on the kinds of consequences projected for those conditions.130 Despite some widely held misconceptions about the causes of climate change,131 such variation from accepted scientific accounts does not seem to diminish levels of public concern with the environmental problems that also concern scientists.

The other side of the coin of environmental concern is an apparent unconcern by individuals about the environment, as reflected in increasing levels of materials and energy consumption associated with increased income. Critics of "consumer society" point to advertising and the mass media as drivers of materialist attitudes and desires and argue that these forces and others are driving the emerging middle classes in many developing countries to emulate North American styles of consumption. These plausible arguments have not yet been supported by careful quantitative studies of the relevant social forces, attitudes, and behaviors.132

Important advances in knowledge in this area are documentation of widespread support for environmental protection across countries and socioeconomic groups and initial identification of the ways that values, beliefs, and attitudes affect political support for environmental policy. Knowledge is not yet adequate to relate the development of public attitudes to mass media coverage of environmental issues and the roles of elites, interest groups, advertising, and social movement organizations and to model the development of public support for

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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action on emerging global environmental issues as a function of new scientific knowledge.

Individual and Household Behavior

Household consumption of energy and certain materials is important both in causing and in responding to global change. Consumer behavior is determined partly by values, attitudes, and beliefs but is strongly mediated by nonattitudinal factors, including the cost and inconvenience of making environmentally significant behavioral changes, the availability of relevant technologies, institutional barriers, knowledge about which behaviors are effective, and the presence or absence of supporting public policies and social pressures. Consequently, the determinants of consumption are highly situation specific, and efforts to change the environmentally relevant consumption of households require multifaceted approaches that identify and address the barriers to change that are most important for the specific behavioral change and target actor.133 Considerable progress has been made in understanding certain key classes of consumption, such as residential energy use in some high-income countries. A major research challenge, only now beginning to be addressed, is to understand how the factors that drive such consumption vary with national and cultural context.

Political behavior is also important to responses to global change. As in the case of consumption, the connections between individual concerns and political influence are complex and imperfect. Political action reflects opportunities for effective political participation individually and through environmental organizations, changing value priorities, the framing of issues in the mass media and by interested parties, and the actions of scientific experts individually and through epistemic communities.134 Research linking environmental attitudes to political participation and influence is helping build understanding of the political feasibility of policies to meet international commitments.

Important advances in knowledge of individual and household behavior include the following:

  • Improved understanding of the many factors affecting specific types of environmentally significant consumption at the household level (especially energy use) in high-income countries and recognition of the situation specificity of these effects.
  • Recognition of the various factors affecting individuals' political behavior on environmental issues.
  • Appreciation of the need for multifaceted approaches in policies aimed at altering consumption patterns.

Knowledge is not yet adequate to achieve several ends:

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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  • Project environmentally significant consumption in developing countries as a function of economic, demographic, and other changes.
  • Model the causes and trajectories of environmentally significant household consumption other than energy.
  • Develop more realistic assessments of likely environmental policy outcomes that take behavioral responses into account.

Economic Transformations

Various large-scale economic transformations around the world may have major implications for the generation of environmental change and for human vulnerability to it. These transformations include the dependence of an increasing proportion of the world's population on global markets for necessities such as food and fuel that were previously produced locally, much of them outside the money economy; increasing liberalization of international trade;135 the emergence of service economies in place of manufacturing-based ones in most high-income countries; and the transformation of formerly socialist economies from a central command model to a more decentralized market-based one.

One of the most important themes in the past 10 years of social science research has been the ''globalization'' of economies and cultures.136 The increasing mobility of capital and labor has facilitated the expansion of transnational corporations and massively restructured the geography of industry, agriculture, human settlements, and all of their associated environmental impacts.137

The environmental effects of trade liberalization are more complex than sometimes realized. Despite claims that trade liberalization has predictably negative environmental impacts, the limited existing evidence suggests that environmental impacts are sometimes positive (e.g., better allocation of soil and water resources in agriculture) and sometimes negative (e.g., foreign investment in countries with lax environmental regulations). Analyses of overall impacts must consider the effects on resource allocation, the scale of overall economic activity, the composition of output (e.g., manufacturing vs. services), effects on developing "green" technologies, and the interactions of trade with policy.138

The North American Free Trade Agreement (NAFTA) stimulated some important work on the environmental implications of changing trading regimes. Although some scholars claimed that NAFTA would result in improved environmental conditions, especially in Mexico, others suggested that free trade would result in environmental degradation as communities relaxed regulations to attract industry or as polluting industries moved to Mexico to take advantage of lower wage rates.139 NAFTA was also predicted to alter agricultural production patterns in ways that would increase Mexico's vulnerability to U.S. droughts.140

Perhaps the most important and dramatic change in the global political economy in the past 10 years is the collapse of the Soviet bloc and the transfor-

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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mation of Eastern European economies. These economies had previously been among the most energy and pollution intensive in the world. Studies showed that in the immediate aftermath of political changes in such countries as Russia and Poland, greenhouse gas emissions decreased as industrial production and consumption fell in the ensuing economic crisis.141 Now, as foreign investment and privatization transform these economies, the implications for the global environment in terms of emissions, land use, and resource management are unclear.

Important advances have been made in understanding the effects of economic transformations:

  • Most of the world's food is now produced within a global system, in which most of the basic grain on the world market is produced in very few countries. The fact that many countries depend on food imports greatly enhances the regional and global impacts of climatic change and variation in those grain-producing regions on which much of the world depends.
  • Industrial production is shifting from core industrial countries to the developing world.
  • The service sector has grown dramatically, especially in urban areas, contributing to increased vulnerability of human settlements, as poor people move into cities for work and must often live in hazard-prone environments.

Knowledge is still inadequate for several needs:

  • Establishing the theoretical and empirical links among economic globalization, global environmental change, and the consequences of global change.
  • Estimating the net overall and regional environmental effects of trade liberalization.
  • Estimating the likely long-term environmental effects of ongoing economic transformation in the former socialist bloc.

Human Population Dynamics

The past decade has seen substantial progress in understanding fundamental population processes: fertility, mortality, and migration as well as the relationships among them that determine population growth, age structure, and geographic distribution. This research is important to global change because population dynamics are some of the most important driving forces behind land use change and energy use and a factor in increasing demands for food, water, and living space that increase vulnerability. Efforts to reduce fertility (i.e., the num-

Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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ber of births per woman) have received the most research and policy attention, with Asia, the Middle East, Africa, and Latin America being the areas of interest.

Based on evidence from censuses, the World Fertility Survey, the Demographic and Health Surveys, and other surveys, it is now conclusive that fertility rates have dropped in a sufficient number of formerly high-fertility countries to produce substantial reductions in the world's fertility. The world's total fertility rate has dropped to approximately 3.0 today—thus having achieved most of the reductions needed to reach replacement-level fertility. The Middle East and sub-Saharan Africa are still the regions with the highest levels of fertility, but even there evidence is emerging that fertility reductions have begun.

Considerable research has examined the causes of this fertility decline. Almost all countries that have achieved substantial fertility declines in the past 25 years have had concerted family planning programs. The effectiveness of these programs in reducing fertility levels, as opposed to other factors, such as rising education levels, has been rigorously debated.142 Most agree that family planning programs have been one of many factors leading to fertility decline; the disagreement revolves around the size of the family planning program's effect.

With respect to mortality, most reductions in the past were attributable to declines in infant and child mortality. That trend is now shifting, and attention has been turning to questions of how long people might live. The debate on the limits has not been resolved,143 but the research fueling the debate has helped to increase our focus on morbidity associated with increasing longevity and the need to have global change research include the effects of increased longevity.

Human migration is an issue of emerging importance for global change because of the possible environmental impacts of concentrated populations and the vulnerability of these populations to extreme events, especially when people are concentrated in coastal zones or floodplains.144 Research progress in understanding migration has been hampered because accurate data are hard to acquire, and when they can be collected, they tend to be aggregated.

Finally, household size has been declining in a number of countries as affluence increases. For example, in the United States the proportion of all households with just one or two members increased from 46 percent in 1970 to 57 percent in 1995. Since households have effects on the environment from production and consumption that are somewhat independent of the number of household members, models should consider both population growth and growth in the number of households. Important findings in human population dynamics include the following two fundamental ones:

  • Total fertility rates are declining worldwide, particularly in countries that have had concerted family planning programs.
  • Human migration, particularly urbanization and movement to vulnerable environments, has been identified as a major potential influence on future environmental change.
Suggested Citation:"Key Scientific Questions." National Research Council. 1999. Human Dimensions of Global Environmental Change: Research Pathways for the Next Decade. Washington, DC: The National Academies Press. doi: 10.17226/9641.
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Knowledge is not yet adequate to estimate the environmental effects of particular types of migration or to model environmental impacts as a function of household size and composition as distinct from population effects.

Technological Change

A major source of uncertainty in projecting future human contributions to global change and analyzing response costs is the rate at which improved technology will lead to the substitution of abundant natural resources for scarce ones and of reproducible capital for depletable resources. Economists and technologists have typically viewed technical change as widening the possibility of substitution among resources. This has frequently led to a bias in favor of assuming adaptation strategies for response rather than mitigation strategies. Ecologists and other biologists have typically regarded substitutability as being narrowly restricted. The argument about biodiversity is, in part, a reflection of these alternative views. The problem has not yet been modeled satisfactorily, nor has sufficient empirical research been conducted to test the alternative perspectives. However, dialogue between the two theoretical camps is increasing and signs of a conceptual synthesis are beginning to appear, in which the questions are formulated in terms of the relationship between rates of substitution and rates of resource consumption.145

Past research has documented some regularities in the time path of change in environmentally significant technologies, including rates of technology diffusion and secular trends toward so-called dematerialization and decarbonization; it has also documented variations around general time trends.146 There has been a lively empirically based debate about the extent to which scarcity may induce innovations that reduce costs and find substitutes, a debate that may be heading toward synthesis.147 Extensive studies have also been conducted of the conditions favoring adoption of technological innovations. This research is starting to make it possible for modelers of global change effects and builders of integrated assessment models to replace ad hoc coefficients of technological change with numbers based on empirical analysis and sound theory.

Important advances in this field include the following: identification of secular trends toward dematerialization and decarbonization of economies, along with variations around these trends; identification of factors influencing the rates of adoption of technological innovations; and identification of the substitution rate of inexhaustible resources for depletable ones as a key parameter for studies of sustainability.

Knowledge is not yet adequate to model the factors influencing variations in average rates of decline in national energy intensity and related indicators and variations around the average among industries and firms or to model the effects of environmental policies on rates of innovation in environmentally benign technologies.

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This publication is extracted from a much larger report, Global Environmental Change: Research Pathways for the Next Decade, which addresses the full range of the scientific issues concerning global environmental change and offers guidance to the scientific effort on these issues in the United States. This volume consists of Chapter 7 of that report, ''Human Dimensions of Global Environmental Change,'' which was written for the report by the Committee on the Human Dimensions of Global Change of the National Research Council (NRC). It provides findings and conclusions on the key scientific questions in human dimensions research, the lessons that have been learned over the past decade, and the research imperatives for global change research funded from the United States.

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