The North American Carbon Program Plan (NACP)
A Report of the Committee of the
U.S. Carbon Cycle Science Steering Group

Executive Summary

 Motivation for the North American Carbon Program (NACP)

In a recent report, the National Academy of Sciences (NAS, 2001) concluded that “progress in reducing the large uncertainties in projections of future climate will require addressing a number of fundamental scientific questions relating to the buildup of greenhouse gases in the atmosphere and the behavior of the climate system.” The NAS report identified research on sources and sinks of carbon dioxide (CO2) and other greenhouse gases as critical to reducing this uncertainty:

  • “How land contributes, by location and processes, to exchanges of carbon with the atmosphere is still highly uncertain.”

  • “How much of the carbon from future use of fossil fuels will be seen as increases in carbon dioxide in the atmosphere will depend on what fractions are taken up by land and by the oceans. The exchanges with land occur on various time scales, out to centuries for soil decomposition in high latitudes, and they are sensitive to climate change. Their projection into the future is highly problematic.”

The North American Carbon Program presented in this report describes related issues and a coordinated research effort to address them, focusing on North America and adjacent ocean basins. The plan outlines how to implement a principal recommendation of the U.S. Carbon Cycle Science Plan (Sarmiento and Wofsy, 1999). It is developed as a component of the U.S. Interagency Carbon Cycle Science Progrm and as a contribution to US climate change research planning.

Atmospheric CO2 has increased dramatically since the Industrial Revolution, principally owing to the combustion of fossil fuels, and has affected climate and plant metabolism worldwide. But less than half of the CO2 emitted has remained in the atmosphere. The remaining part has been taken up and stored as organic matter in vegetation, soils, and river basins on land, or as organic sediments or dissolved bicarbonate in the sea. Roughly 40% of fossil fuel input was removed in these ways in the 1980s, increasing to 50% in the 1990s (Battle et al., 2000). Measurements suggest that much of the non-atmospheric global uptake of CO2 may be in North America, although the conclusion is controversial because the data are grossly inadequate. Understanding why, and where, CO2 uptake has occurred is critical for knowing how the Earth's atmosphere and climate will evolve in the future, and what can be done about it.

Atmospheric methane (CH4) is second to CO2 as an anthropogenic greenhouse gas. Concentrations of CH4 have nearly tripled since 1700, but the rate of change has varied over time. Basic questions remain unanswered about why global changes in atmospheric CH4 have occurred.

Carbon monoxide (CO) is a key air pollutant and can be used as a tracer to distinguish combustion from biogenic sources of CO2.

Carbon stocks, the aggregate sums of carbon stored on land (organic matter in vegetation and soils) and in the oceans (e.g., organic or inorganic carbon in the water column or sediments), include economic resources such as timber. Changes in stocks can also either moderate or amplify atmospheric CO2 increases. Any possible efforts to manage carbon through sequestration of atmospheric CO2 in terrestrial or marine systems require observations and models to verify changes in stocks. International agreements to manage carbon also need reliable data on changes in carbon stocks, but current inventories lack sufficient scientific underpinnings for accurate, verifiable determinations.

The NACP focuses on the carbon-containing gases CO2, CH4, and CO, and on carbon stocks in North America and adjacent ocean basins. The program responds to the NAS report by seeking scientific understanding of sources and sinks for CO2, CH4, and CO, and of changes in carbon stocks needed to meet societal concerns and to provide tools to policy makers. The NACP addresses several basic questions:

  • What is the carbon balance of North America and adjacent ocean basins, and how is the balance changing over time? What are the sources and sinks, and the geographic patterns of carbon fluxes?
  • What factors control the sources and sinks, and how do they change with time?
  • Are there potential “surprises,” where sources could increase or sinks disappear?
  • How can we enhance and manage long-lived carbon sinks to sequester carbon?

The NACP will ultimately enable sustainable carbon management by developing proven scientific tools to diagnose past and current sources and sinks of greenhouse gases, and to predict future contributions from North America and adjacent ocean basins. The program will inform future decisions on policies to reduce net emissions of CO2 and CH4, and to enhance sequestration of carbon through land management or by other means.

The program is optimally designed to advance science for other critical problems: (1) the large-scale emissions, transformations, and long-range transport of air pollutants; (2) changes in species composition, health, and productivity, and the vulnerability to fire and drought of forests, croplands, and wild lands; and (3) forecasts of weather and climate.

 Goals of the NACP

The NACP has three overarching goals:

  • Develop quantitative scientific knowledge, robust observations, and models to determine the emissions and uptake of CO2, CH4, and CO, the changes in carbon stocks, and the factors regulating these processes for North America and adjacent ocean basins.
  • Develop the scientific basis to implement full carbon accounting on regional and continental scales. This is the knowledge base needed to design monitoring programs for natural and managed CO2 sinks and emissions of CH4.
  • Support long-term quantitative measurements of sources and sinks of atmospheric CO2 and CH4, and develop forecasts for future trends.
 Major Program Elements of the NACP

Major NACP program elements consist of atmospheric measurements, which show how land and oceanic systems influence atmospheric CO2 concentrations, and which provide crucial information for inferring carbon sources and sinks; models that assimilate and synthesize observational data; and measurements of carbon inventories and fluxes on land and in adjacent ocean basins, which allow assessing those mechanisms that ultimately determine atmospheric concentrations.

Atmospheric Measurements and Field Programs

Long-Term Atmospheric Measurements of the Carbon Budget. Ground-based, aircraft, and satellite measurement networks will provide spatially and temporally resolved, three-dimensional atmospheric data for the major carbon gases CO2 CH4, and CO, to enable reliable estimates for U.S./North American sources and sinks of these gases. These observations are required to obtain regional and continental sources and sinks for atmospheric CO2, CH4, and CO.

Intensive Field Programs. Large-scale airborne and field campaigns will provide data sets to evaluate and improve the design of atmospheric and surface measurement networks, to develop and test models that interpret observations, and to provide atmospheric “snapshots” to constrain fluxes. This effort will provide continual feedback on uncertainties in modeling and assessment tools for carbon accounting.

Inventories and Land and Ocean Surface Processes and Fluxes

Terrestrial Measurements and Modeling: Understanding the Land Biosphere. The NACP will combine enhanced carbon inventories, remote sensing, and models to provide a complete carbon accounting for the land sector, and comprehensive analysis of the mechanisms driving the fluxes. Full carbon accounting and attribution among causes will address fluxes of CO2 and CH4 in all major ecosystems, including forests, wetlands, and agricultural, urban, and suburban lands. New emphasis on carbon accounting, on lands (peatlands, scrub land, suburban landscapes) and carbon pools (roots, coarse woody debris, shrubs) not currently inventoried, and on scaling with remote sensing and models will all greatly improve the carbon budget for North America.

A hierarchical approach will support a multi-scale interpretation, with intensive studies providing access to details and mechanisms that are extended using remote sensing, extensive inventories, and mechanistic models. This multi-scale approach to land data will join the atmospheric and ocean studies as components in a unified analysis framework. Constraints from the atmosphere and oceans will increase the sophistication and accuracy of the estimates based on land data.

Marine Measurements and Modeling: Understanding Physical and Biological Processes in Ocean Basins Adjacent to North America. High-resolution measurements of air-sea fluxes of CO2, and process studies in coastal waters and adjacent ocean basins will define contributions of the ocean margins and adjacent ocean basins to the North American carbon budget. Large-scale ocean basin studies will help place North America in a global context and enable inverse model estimates of the North American carbon cycle. Establishing the oceanic boundary conditions for the continent is essential for accurate carbon accounting.

 Integrating Models and Model-Data Assimilation

NACP data sets will be quantitatively and qualitatively different from current data. We will know the atmospheric concentrations of CO2, CH4, and CO over the entire continent and adjacent waters at frequent intervals, requiring development of advanced database management, diagnostic models, and data assimilation. The flow of information and the integration to obtain regional carbon accounting are shown in Figure 1.

Figure 1. Data flow and integration in the NACP

Figure 1. Data flow and integration in the NACP

Figure 1 illustrates data flow and integration in the NACP. Complexity and level of synthesis increase down the figure. Valuable data products are delivered at each level. Note the central role played by the model-data fusion systems that combine observations from diverse sources, using data-driven models and advanced data assimilation and optimization methods.

A critical step will be to develop new classes of models to determine sources and sinks of CO2, CH4, CO, and other gases. The new diagnostic systems will build on, and complement, more conventional top-down (“inverse models”) and bottom-up (“ecosystem models”) analyses applied in the new, data-rich environment. Data-driven models of carbon dynamics in vegetation and soils will be combined with high-resolution meteorological information, surface flux data, and atmospheric concentrations to derive fluxes. Using advanced techniques, a quantitative representation of the state of the atmosphere and of the carbon cycle will be obtained consistent with atmospheric, oceanic, and land data in real time. Through the NACP, these new models will provide potent diagnostic and predictive capability for surface-atmosphere fluxes of CO2, CO, and CH4.

 Implementing the NACP

The NACP introduces many new elements into climate research, elements that must be tested and refined as the program proceeds. Thus, new long-term measurements, models, and analyses will be implemented in phases, closely coordinated from the start, with major initiatives in four key areas: (1) atmospheric measurements; (2) measurements, process studies, and modeling of land ecosystems (plants and soils) and adjacent ocean basins; (3) models that integrate atmospheric, land, and ocean data; and (4) regular state-of-the-art assessments of carbon cycle science and carbon inventories for North America. The new science to diagnose exchange fluxes between the Earth's surface and the atmosphere is coupled from the start with communication of results to the public.

Implementation of the NACP is envisioned in the form of three phases:

Phase 1. In the initiation phase (2002 - 2005), the program will include development of new instrumentation and initial model development for model-data fusion. Current agency programs will be realigned and refocused to strengthen existing measurement networks and inventories. Data sets for land disturbance history will be developed from satellite (e.g., LandSat) and land use inventory archives. Workshops will assess current uncertainties in CO2 and CH4 emission and sink inventories. Costs in the near term are modest as summarized immediately below (under “Highest Priority Enabling Developments”). Intensive field campaigns will test and refine the conceptual framework, starting in 2004, with a joint NACP-tropospheric chemistry study, the Intercontinental Transport Experiment-North America (INTEX).

Phase 2. During the testing and implementation phase (2005-2008), the program will undertake stepwise installation of the new observational network, including atmospheric, terrestrial, and marine elements, and further develop model-data fusion systems. New field measurements and procedures to integrate data from the NACP elements will be tested and refined by intensive field experiments. Space-borne data for biomass are expected to enhance regional terrestrial and marine carbon accounting capabilities. Phase 2 costs are estimated to be $50-$100 million per year above fiscal year 2002 expenditures.

Phase 3. In the operational phase (2008-), the networks and model-data fusion system will deliver reliable estimates of net sources and sinks for CO2, CO, and CH4, and of changes in carbon stocks over North America, along with a full suite of observations and associated analytical enhancements for a range of other science and operational objectives. Spacecraft that accurately measure atmospheric concentrations of CO2 and CH4 are envisioned for this time. Costs for this operational phase of the program are estimated to be $50-$100 million per year above fiscal year 2005 expenditures.

 Highest Priority Enabling Developments for the NACP

The following are critical needs in the near term to enable initiation and development of the NACP, and are recommended for immediate action. Estimated additional costs represent the latter part of Phase 1 (i.e., entry to Phase 2).

  1. Develop in situ sensors and sampling protocols for aircraft, ocean, tower, and soil and vegetation flux measurements of CO2, CO, and CH4. These should be robust, accurate, and operable by minimally trained personnel. The instruments represent near-term deliverables of the program. Cost estimates broken down by area are $1 million over two years for atmospheric CO2, $1 million over two years for atmospheric CO and CH4, $1-$2 million per year for two years for ocean CO2 buoy development, $1 million per year for two years for soil fluxes, and $2 million per year starting in two years for initial testing and deployments. The total cost estimate is thus approximately $5-$7 million per year.

  2. Perform model studies of network design and model-data fusion. This work requires a summer study institute, then sustained efforts to develop data assimilation/fusion systems by intensive evaluation of models against new data, such as flux and isotopic measurements. Components envisioned are a science team of about five groups outside operational centers ($1.5 million/year) and funding for NASA’s Data Assimilation Office (DAO), GFDL, and/or NWS’s National Centers for Environmental Prediction (NCEP) (with 10-20 full-time equivalents, $1.5-$3 million/year), plus computer hardware ($1-$2 million).

    A 20-year reanalysis of global meteorology, with a 10-km nested grid over North America, should be initiated in Phase 1 at one or more operational centers. This activity will deliver a critical product, with data tailored for mass budget analyses, for hindcasting and for refining network concepts using preexisting data. The estimated additional cost is $1-$2 million/year for one to two years to do this rapidly and enable the studies noted. The reanalysis is a near-term deliverable. The total cost estimate is $5-$8 million/year.

  3. Optimize national inventories for carbon accounting. Strategic enhancements are needed in current network designs for complete carbon accounting. Historical data on land cover, management, and disturbance need to be compiled and made available, and gaps must be filled by statistical estimation ($1-$2 million/year). Benefits will include more consistent and comprehensive historical data on land ecosystems, past human impacts, and natural disturbances. Gaps in geographic and biome coverage should be filled, especially for rangelands, mountainous areas, and developed lands. The USDA’s Forest Inventory Analysis and National Resources Inventory is a high priority for a strategic enhancement. The cost of additional sampling is $16-$32 million per year, but this sampling has many further benefits and should not be attributed entirely to the NACP. Total cost estimates attributable to the NACP, $10 million per year.

  4. Strengthen current observation networks.

    (a) Fill gaps and weaknesses in the current long-term measurements of greenhouse gases in the United States. The NOAA-CMDL greenhouse gas programs require sustained long-term (“baseline”) funding at $2-$4 million per year above current levels. These steps are extremely urgent to allow an expanded NACP program over the following five years, or even to maintain the status quo. Time-series ocean moorings are needed for atmospheric CO2 and marine pCO2 ($2 million/year). Better tracking of atmospheric trends are a near-term deliverable. Total cost estimate is $4-$8 million per year.

    (b) Begin the transformation of the AmeriFlux network into an integrated, near-real time network, and add representative long-term sites. Each new site will cost $300,000 plus $400,000/year to run and analyze data. The core AmeriFlux program needs strengthening, with enhanced quality controls, oversight, and improved information management systems. New sites in critical undersampled ecosystems, and projects to understand fluxes in complex terrain are needed. Costs for three to five new sites per year represent a ramp-up of $1 million per year for three years. Data on climate and pollution effects on ecosystems and agriculture are short-term deliverables. Total cost estimate is $8-$10 million per year for these items.

  5. Improve databases for fossil fuel use and land use/land cover. A State of the Carbon Cycle for North America report will be prepared that addresses current knowledge and new advances in understanding of all components of the natural and managed carbon cycle. This assessment will be updated as significant new findings are produced. Initially, the focus will be on establishing a consistent inventory of sources and sinks of CO2 and CH4 with associated uncertainties for each source and sink category. Methods to better integrate historical land use and inventory information with contemporary satellite estimates of land cover and use will be a crucial aspect of improving the quality of source and sink estimates. The improved databases and report will provide regularly updated information relevant to informing policy. Estimated costs are $1-$2 million per year.

  6. Develop remote-sensing technology. Better remote-sensing technology is needed for atmospheric CO2, CH4 and CO, and for above-ground biomass and soil moisture. Satellite data will be the key to long-term, accurate NACP data in the 5- to 10-year time frame. Near-term efforts should focus on airborne simulators of future spacecraft instruments, and on critical assessment of early products for atmospheric CO2 from existing satellites. The airborne simulators will be used to measure in situ profiles/columns of the gases. Airborne simulators are also essential to technology development for biomass and soil moisture satellite sensors, and will be extremely useful for intensive studies before spacecraft are deployed. Technology development is the near-term deliverable. Estimated new near-term costs for concept and technology development are $20-$25 million per year.

Total costs for Phase 1 ramp-up over five years from current expenditures are estimated at approximately $45-70 million above current levels. Much could be accomplished in the first and second years by focusing and coordinating current agency budgets.


An unprecedented level of integration among NACP elements is needed to resolve and attribute mechanisms for sources and sinks of CO2 and other greenhouse gases for North America. Previous carbon cycle research largely focused on studies of single components, such as the atmosphere or ocean, or employed small-scale process studies. But carbon is exchanged continuously through the atmosphere, land biosphere, soils, and oceans, and simultaneous study of these systems is required to obtain a coherent view of where and how carbon is stored in the North American region. The temporal and spatial scales of the program must be appropriately large for addressing climatic issues, and data and models from all components must be brought together to develop information on global carbon balances.

Integrating NACP elements is also essential to obtain quantitative understanding of the mechanisms regulating uptake of carbon. Mechanistic information on carbon uptake is gained at a local level, through process studies and inventories. But results must be scaled up and compared to information gained at regional and continental scales to determine the importance of mechanisms regulating carbon balances, and to project future operation or potential for management.

The NACP therefore emphasizes coordination and integration. A major element for this is provided by innovative new assimilation and data fusion systems that bring together diverse data and models, linking information at various scales to provide a consistent North American carbon balance. This coordination of science activities requires similar coordination among agencies involved in implementation, including inter-agency scientific and management committees, to ensure delivery on NACP goals.


The NACP requires extraordinary management arrangements because of the need for integration. The program’s elements will be implemented by several federal agencies, which should obtain scientific guidance from a unified science advisory committee to ensure that program elements are working together as necessary. There is already notable coordination among agencies at the level of scientific research programs, through the Carbon Cycle Interagency Working Group. The CCIWG commissioned the current plan to help implement a major element recommended in the Carbon Cycle Science Plan (Sarmiento and Wofsy, 1999). The NACP will also require a comparable degree of integration and coordination at higher, policy-making levels of the responsible federal agencies.

 Synergy with Other Scientific Problems of Social Interest

Atmospheric Chemistry. Carbon gases (CO2, CH4, and CO) are intimately associated with the principal sources of air pollution. The NACP will provide spatially and temporally resolved surface-atmosphere fluxes and long-range transport fluxes, helping to determine how much pollution is transported across the oceans to and from North America, and how redistribution of pollution occurs within North America. The framework of observations and data assimilation can be readily adapted to provide regional and continental sources and to define import and export fluxes of pollutants.

Resource Management and Ecological Sciences. The carbon budget of a region is an emergent property defining the health and productivity of ecosystems. NACP data will define processes related to carbon sequestration by major crops, fuel accumulation on fire-prone lands, and responses of major land and ocean ecosystems to environmental stresses (e.g., ENSO).

Weather Forecasting and Climate Modeling. Tracer distributions from the NACP will give direct measures of transport processes in the planetary boundary layer, long a bane of forecast models. Data for CO2 concentrations and fluxes directly benefit temperature retrievals. Climate feedback involving CO2 and CH4, the principal focus of the NACP, are major issues for climate prediction.

Formulation of Economic Methods for Carbon Management. The carbon accounting information produced by the NACP will support the development of robust, market-based tools and methods for national and international programs on carbon management.

 Summary of Overall NACP Deliverables
  • Measurements of sources and sinks for CO2, CH4, and CO for North America and adjacent ocean basins, at scales from continental (5,000 km) to local (10 km), with seasonal resolution.

  • Attribution of sources and sinks to contributing mechanisms, including climate change, changes in atmospheric CO2, nutrients, pollutants, and land use history.

  • Documentation of North America's contribution to the Northern Hemisphere carbon budget, placed in the global context.

  • Optimized sampling networks (both ground-based and remote) to determine past, current, and future sources and sinks of CO2, CH4, CO, and major pollutants.

  • Data assimilation models to compute carbon balances.

  • State of the Carbon Cycle for North America and Adjacent Ocean Basins, a periodic report communicating results to the public.

  • Data and observations to enable major advances in atmospheric chemistry, such as better determination of sources and transformations of pollutants; in resource management, as through improved knowledge of ecosystem function and response to global changes; and in weather forecasting and climate models, through real-time tracer concentration and flux data, and coupled models with improved representations of atmosphere-biosphere coupling, surface energy, and mass fluxes.

 Near-Term Deliverables of the NACP (2004-2007)
  • The first comprehensive North American State of the Carbon Cycle report, based on NACP results, synthesizing historical estimates and current measurements of carbon sources and sinks (2004).

  • Comprehensive inventories and databases on fossil fuel use, vegetation, soils, and land use and management in North America (2005).

  • Improved networks, sampling protocols, and data to track global and regional trends in atmospheric CO2, CO, CH4, ozone-depleting gases, and air pollutants, and carbon stocks (2005).

  • Improved data on the responses of terrestrial and coastal marine ecosystems (both managed and natural) to climate variations and pollution (2003-2005).

  • A new generation of prototype in situ and remote-sensing instruments essential for monitoring the status and trends of carbon sources and sinks at regional, national, and continental scales (2005).

  • High-resolution analysis of global weather from 1980 to the present. Carbon accounting models will combine these data with inventories of fossil fuel use, vegetation, soils, land cover and land management to significantly reduce uncertainties in the recent status and trends of North American sources and sinks of carbon (2006).

  • A second comprehensive North American State of the Carbon Cycle report, characterizing uncertainties in both historical estimates and current measurements on carbon sources and sinks. This assessment will be a major resource for the design of market-based methods for carbon management (e.g., carbon trading), and for policy formulation (2007).

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