Background

The carbon cycle has recently become interesting to policy makers. It has been of scientific interest for a long time because life on earth depends on it. Carbon dioxide released by the respiration of all living organisms is taken up by plants, which use it in the process of photosynthesis, in which the carbon is fixed as organic matter and the oxygen is released back into the atmosphere, thus providing food for other organisms and replenishing the oxygen needed to support metabolism. What has made the carbon cycle interesting to policy makers is its relationship to global climate change: increased releases of carbon-containing “greenhouse gases” account for the great majority of “radiative forcing” or increased net retention of solar radiation, which is the primary source of the threats of floods, droughts, intense storms, and the other potential disasters that might result from global warming (see Figure 1).

This increased radiative forcing is quite clearly the result of human interactions with the carbon cycle. Figure 2 illustrates the point for carbon dioxide: for over 400,000 years, the atmospheric concentration of carbon dioxide fluctuated between about 180 and 280 parts per million; in the past 100 years, it has shot up to almost 350 and it is expected to continue rising rapidly. Nothing but human activity can explain this unprecedented change. The same is true for changes in the atmospheric concentrations of methane and the chlorofluorocarbons. The main human activities that contribute to climate change are shown in Figure 3. It is easy to see the predominant importance of carbon-related activities, including fossil fuel



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Human Interactions with the Carbon Cycle: Summary of a Workshop Background The carbon cycle has recently become interesting to policy makers. It has been of scientific interest for a long time because life on earth depends on it. Carbon dioxide released by the respiration of all living organisms is taken up by plants, which use it in the process of photosynthesis, in which the carbon is fixed as organic matter and the oxygen is released back into the atmosphere, thus providing food for other organisms and replenishing the oxygen needed to support metabolism. What has made the carbon cycle interesting to policy makers is its relationship to global climate change: increased releases of carbon-containing “greenhouse gases” account for the great majority of “radiative forcing” or increased net retention of solar radiation, which is the primary source of the threats of floods, droughts, intense storms, and the other potential disasters that might result from global warming (see Figure 1). This increased radiative forcing is quite clearly the result of human interactions with the carbon cycle. Figure 2 illustrates the point for carbon dioxide: for over 400,000 years, the atmospheric concentration of carbon dioxide fluctuated between about 180 and 280 parts per million; in the past 100 years, it has shot up to almost 350 and it is expected to continue rising rapidly. Nothing but human activity can explain this unprecedented change. The same is true for changes in the atmospheric concentrations of methane and the chlorofluorocarbons. The main human activities that contribute to climate change are shown in Figure 3. It is easy to see the predominant importance of carbon-related activities, including fossil fuel

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Human Interactions with the Carbon Cycle: Summary of a Workshop FIGURE 1 Global mean radiative forcing of the climate system for the year 2000, relative to 1750. Source: Working Group I, Intergovernmental Panel on Climate Change (2001). and chlorofluorocarbon use, biomass burning, and paddy rice and cattle production, in this picture. The U.S. Global Change Research Program (USGCRP) has identified the global carbon cycle as a major program element, allocating $221 million of its $1.6 billion budget for 2002 to it (Subcommittee on Global Change Research, 2001). An interagency Carbon Cycle Working Group, advised by an outside scientific steering committee and guided by a Carbon Cycle Science Plan (CCSP, Sarmiento and Wofsy, 1999) sets research directions for this effort. The CCSP and the scientific steering committee strongly reflect the intellectual concerns of fields of natural science that study the cycling of carbon through the atmosphere and the biosphere. Although the CCSP notes the critical role of human activities in perturbing the carbon cycle, it does not include any research on these activities. The U.S. government’s carbon cycle research activity has not yet integrated the relevant fields of the social and behavioral sciences. It is in this context that the USGCRP’s Carbon Cycle Working Group asked the National Research Council’s Committee on the Human Dimensions of Global Change to hold a workshop on Human Interactions with

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Human Interactions with the Carbon Cycle: Summary of a Workshop FIGURE 2 Atmospheric carbon dioxide concentration over the past 400,000 years. Past data from Vostok ice-core record; future projections from IPCC Third Assessment “business as usual” scenario. Sources: Hibbard et al. (2001). Vostok ice core data from Petit et al. (1999); projection from Prentice et al. (2001). the Carbon Cycle. The basic purpose of the workshop was to help build bridges between the research communities in the social sciences and the natural sciences that might eventually work together to produce the needed understanding of the carbon cycle—an understanding that can inform public decisions that could, among other things, prevent disasters from resulting from the ways humanity has been altering the carbon cycle. Members of the working group hoped that a successful workshop would improve communication between the relevant research communities in the natural and social sciences, leading eventually to an expansion of the carbon cycle program element in directions that would better integrate the two domains.

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Human Interactions with the Carbon Cycle: Summary of a Workshop FIGURE 3 Relative contributions of human activities to greenhouse warming, late 1980s. Source: National Research Council (1992). In planning the workshop, the committee and the working group considered organizing it around carbon cycle issues as they might be seen by social and behavioral scientists. A workshop organized in this way might have helped increase interest in carbon cycle research among social scientists by showing the relevance to the carbon cycle of existing bodies of research on (a) human activities that affect the carbon cycle (e.g., on energy modeling; on the underlying causes of fossil fuel consumption, agricultural intensification, and other major carbon-related human activities; and on the diffusion of technology in agriculture and energy production) and on (b) human activities that respond to the carbon cycle (e.g., on the creation and maintenance of environmental management regimes; on integrated

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Human Interactions with the Carbon Cycle: Summary of a Workshop assessment modeling; and on disaster preparedness). It was finally decided, however, that it would be more useful at present to treat the USGCRP’s carbon cycle researchers as the primary audience. The workshop was therefore organized to focus on a small number of issues that are already recognized as important by this group and for which the relevance of the social sciences is readily apparent. A possible outcome was that the carbon cycle research effort would move in directions that would encompass such issues. The workshop did not attempt to develop or even outline a comprehensive research agenda on human interactions with the carbon cycle. Thus, the workshop, which was held in Washington on November 5, 2001, addressed the following three substantive topics (see the Appendix for the agenda and a list of the participants): The future of fossil fuel consumption Carbon implications of future land use/land cover transformation Modeling human interactions with the carbon cycle.