Carbon Cycle Science: An FY 2000 Initiative

Rising atmospheric carbon dioxide concentration and its potential impact on future cli-
mate 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 abili-
ty to predict any future climate change. Recent policy debates have demonstrated the
need for a comprehensive, unbiased scientific understanding of sources and sinks of car-
bon 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:

⚫ take advantage of ongoing breakthrough advances in innovative scientific techniques to measure, monitor, observe, and model the carbon cycle, making it possible to examine the carbon cycle comprehensively as an integrated system;

provide the scientific foundation for estimating the capacity of land ecosystems and the ocean to sequester and store carbon dioxide released as a result of human activities;

integrate modeling, observational, and process research to identify and quantify regional- to global-scale sources and sinks for carbon dioxide and other greenhouse gases;

⚫ seek to understand how these sources and sinks will function in the future and provide this essential information for future climate predictions; and

⚫ evaluate potential management strategies for enhancing carbon sequestration in the environment and in capture and disposal strategies.

Achieving these objectives will provide information to policymakers and assist with the
planning of future climate research activities. It will also provide valuable information
to land and forest managers in the public and private sectors, and contribute to the nat-
ural resource management missions of agencies such as USDA and DOI.

Full implementation of the new program will require a significant investment of
resources and a new level of interagency coordination to ensure integration.
Implementation of this program will be closely coordinated with international programs
(e.g., the International Geosphere-Biosphere Programme and the World Climate
Research Programme) to ensure a comprehensive international research strategy.

Background

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

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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 compo-
nent of the carbon cycle separately. However, the carbon system is fundamentally inte-
grated, 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 strate-
gies 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.

The ocean provides a long-term sink for carbon dioxide as a result of physical and biological processes that are largely independent of human control. 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.

Program Goal

The overarching goal of the Carbon Cycle Science Program (CCS) is to answer the fol-
lowing 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 Implementation of the USGCRP in FY 2000

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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:

Atmospheric and oceanographic sampling field campaigns over the continent and adjacent ocean basins, combined with atmospheric transport models to develop more robust estimates of the continental and subcontinental-scale magnitude and location of the sink (includes DOE, NOAA, and NSF).

Local-scale experiments conducted in various regions that will begin to identify the mechanisms involved in the operation of carbon sinks on land, the quantities of carbon assimilated by ecosystems, and how quantities might change or be enhanced in the future (includes DOE, NSF, Smithsonian, and USDA).

Evaluation of information from past and current land-use changes, both from remotely-sensed and historical records, to assess how human activity has affected carbon storage on land (includes NSF, NASA, USDA, NOAA, DOI, and DOE). Enhanced long-term monitoring of the atmosphere, ocean, forests, agricultural lands, and rangelands, using improved inventory techniques and new remote sensing, to determine long-term changes in carbon stocks (includes USDA, NASA, NOAA, DOE, and DOI).

Evaluation of potential management strategies for maximizing carbon storage, including evaluation of the variability, sustainability, lifetime, and related uncertainties of different managed sequestration approaches (includes USDA and DOE). Integration of new observations and understanding of carbon cycle processes in regional and global carbon system models to improve projections of future atmospheric concentrations of carbon dioxide and other greenhouse gases (includes DOE, NOAA, NSF, NASA, DOI, USDA, and Smithsonian).

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.

Achieving this task will require new technologies for measuring the atmosphereland-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.

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Implementation of the USGCRP in FY 2000

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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