Rising atmospheric carbon dioxide concentration and its potential impact on future climate is an issue of global economic and political significance. The need to understand how carbon cycles through the Earth system is therefore critically important to our ability to predict any future climate change. Recent policy debates have demonstrated the need for a comprehensive, unbiased scientific understanding of sources and sinks of carbon dioxide on continental and regional scales, and how sinks might change naturally over time or be enhanced by human activities. The National Research Council’s report, Global Environmental Change: Research Pathways for the Next Decade, specifically emphasizes the need for a comprehensive carbon cycle research strategy.

    The USGCRP is answering this call by establishing the Carbon Cycle Science Initiative. USDA, DOE, DOI, NASA, NSF, DOC/NOAA, and the Smithsonian will take part in this initiative. The new program is poised to provide critical unbiased scientific information on the fate of carbon dioxide in the environment to contribute to the ongoing public dialogue. The program will:

Carbon dioxide is exchanged naturally between three active reservoirs: the atmosphere, the ocean, and land ecosystems. Human activity has increased the amount of carbon dioxide now being exchanged between these reservoirs. Carbon dioxide is initially added to the atmosphere as a product of combustion of fossil fuel and as emissions from conversion of forested land to agriculture. About half of what is added remains in the atmosphere, and the rest is taken up by the other two reservoirs — the ocean and land and freshwater ecosystems. Uptake of carbon dioxide by these reservoirs is commonly referred to as a "sink." While we can measure the concentration of carbon dioxide in the atmosphere quite accurately, measurements of storage of carbon in the ocean and land ecosystems are still considerably uncertain.

    For the past decade or more, independent approaches and innovative tools have greatly increased our understanding of how carbon dioxide is transported and stored in the Earth system. Most past research has tended to focus, appropriately, on each component of the carbon cycle separately. However, the carbon system is fundamentally integrated, and understanding of each component is now reaching the point where answers are available for how the carbon cycle operates as an integrated whole. This information is essential for use in designing and optimizing any potential carbon mitigation strategies envisioned in the next two decades.

    The storage reservoir, or sink, for carbon that we know the least about is the land ecosystem. Estimates from atmospheric and oceanic data and models have predicted that the terrestrial sink is larger in the Northern Hemisphere than in the Southern Hemisphere. Recent studies have attempted to refine the location of the Northern Hemisphere sink to a continental-scale region. While there is considerable debate about the magnitude and location of the terrestrial sink, there is strong evidence that it may be very significant.

    However, humans may have inadvertently both created and destroyed terrestrial carbon sinks in the past from their manipulation of the land surface for settlement, food and energy production, and water management, for example. Climate also likely influences the magnitude of both the terrestrial and the oceanic sink. We have now reached a state of knowledge in the carbon cycle research arena where we can begin to tackle these questions and provide unbiased, scientific information to society about the location, magnitude, and cause of carbon sinks.

    Figure 7. Soil organic carbon in the United States
    (See Appendix E for additional information)
Program Goal
The overarching goal of the Carbon Cycle Science Program (CCS) is to answer the following fundamental questions:
  1. What has happened to the carbon dioxide that has already been emitted by human activities (anthropogenic carbon dioxide)?
  2. What will be the future atmospheric carbon dioxide concentration resulting from past and future emissions?

FY 2000 Program Highlights
The major focus of the initiative in FY 2000 will be on determining the location, magnitude, and cause of carbon sinks in North America, and how North America compares to other key regions, such as South America. Estimates of the Northern Hemisphere sink range widely; a program of integrated observations, process research, and modeling will narrow this range and provide a more accurate estimate of the North American terrestrial sink and its variability. The strategy will be to combine appropriate research approaches from the atmosphere, oceanic, terrestrial, and human dimensions aspects of the carbon cycle, providing information on various temporal and spatial scales, necessary to providing an accurate picture of the current state of the terrestrial carbon sink over North America.

    To accomplish these objectives, carbon cycle science research activities will include:

Understanding from each of these areas will be synthesized to represent our current state of knowledge of the carbon system, as well as incorporated into carbon system models, to provide a best estimate of how carbon sources and sinks may change in the future. This integrated approach will be the most efficient and effective way to understand the carbon sink and to provide the most accurate information on the current state of the sink over North America.

Carbon Cycle Science Initiative
FY 2000 Budget by Agency
(Dollars in Millions)

  7.0       DOC/NOAA
 14.8      DOE
  3.4       DOI
 81.1      NASA Space-Based Observations
 37.5      NASA Scientific Research
 13.1      NSF
  0.3       Smithsonian
 31.5      USDA
____    _______________
188.7       Total

    Achieving this task will require new technologies for measuring the atmosphere-land-ocean carbon system. In addition, the existing observational networks and monitoring programs will be maintained and enhanced, especially observations of undersampled aspects of the global CO2 cycle, such as spatial distributions in the atmosphere, ocean temporal variations, changes of net ecosystem production (e.g., carbon gain), soil carbon transformations, and land use/vegetation changes in the tropics. Large-scale observations will be tested with locally-derived process models and hypotheses about spatial and temporal variability of CO2 exchange among the major Earth system reservoirs. Models to predict carbon sources and sinks and their interannual/decadal variability (ocean and land) will be refined, incorporating the most important mechanisms and providing predictions with enhanced credibility.

    Carbon cycle science has a unique opportunity. Exciting techniques and a new threshold of understanding have paved the way for the next stage of carbon cycle science in the United States: developing an integrated, whole system predictive capability for the carbon system. The ultimate goal is to provide integrated estimates of carbon sources and sinks, with a focus in FY 2000 on implementing activities to determine the magnitude, location, and cause of the North American terrestrial sink. The knowledge base will then be available to provide input on how sinks might be enhanced and how they might change in the future — information of critical importance to potential decisions to manage the carbon system.

    In FY 2000, activities in the Carbon Cycle Science program will provide the following results:

  • A state-of-the-science report assessing the magnitude, location, and cause of the North American terrestrial sink from available data, and a research strategy for addressing uncertainties in the terrestrial sink estimates that are not reconcilable with current data;
  • Implementation of integrated observation, research, and modeling activities to provide more accurate information on the location, magnitude, and cause of the North American terrestrial sink based on these identified uncertainties;
  • A synthesis of global ocean carbon dioxide data, enabling the design of a research strategy for monitoring changes and identifying variability in the oceanic sink;
  • Improved parameterization of key processes controlling carbon storage, such as air-sea gas exchange, a major uncertainty in ocean sink estimates;
  • An improved, long-term, integrated monitoring strategy for carbon measurements in the atmosphere, ocean, and land ecosystems.

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