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

Chapter 1: Introduction: Motivation, Major Goals and Program Objectives

 Introduction: Motivation, Major Goals and Program Objectives

The North American Carbon Program described in this document represents a major expansion of U.S. efforts to address gaps in scientific knowledge of climate change. The central goal is to provide the scientific information needed to inform policies designed to reduce contributions by the United States and neighboring countries to atmospheric carbon dioxide (CO2) and methane (CH4). The program will provide scientific data and analysis to determine the fate of CO2 emitted to the atmosphere by combustion of fossil fuels. It is also aimed at comprehensive understanding of the rates and mechanisms controlling carbon uptake and release from soils and vegetation in North America and the adjacent Atlantic and Pacific Oceans. Additionally, the program will develop reliable quantitative knowledge of the sources and underlying processes that release other important gases, including carbon monoxide (CO), to the atmosphere.

The broad goal is to reduce uncertainties about the carbon cycle component of the climate system, and to develop scientific and technical tools to forecast future increases in concentrations of atmospheric CO2 and CH4, the most important greenhouse gases. The intent is to provide the scientific information needed to design effective and economical policies for the United States and neighboring countries to manage carbon sources and sinks.

The program’s focus on North America is designed to deliver the detailed process-level understanding of CO2, CH4, and CO sources and sinks that will be required to design carbon management strategies for the United States, Canada, and Mexico. North America is a major part of the global carbon cycle, and its diverse climate and ecological zones provide analogues for many parts of the world. Thus, the NACP will help build the foundations for analysis of the carbon cycle worldwide.

 The Opportunity

A strong scientific consensus now exists that human emissions of greenhouse gases have important climatic consequences, and that these consequences, as well as the impacts on ecological balances from the direct physiological effects on vegetation, will grow in the future. A primary cause of these changes is the increase in atmospheric CO2, which is emitted to the atmosphere by burning of fossil fuels, cement production, and changes in land use such as deforestation. Carbon dioxide is inert in air, and thus is not removed by chemical breakdown in the atmosphere. Nevertheless, only about half of the CO2 released to the atmosphere since the beginning of the industrial revolution remains there. The portion removed has been taken up and stored in the oceans and on land, by processes that we refer to as “sinks.” Studies to identify and understand sinks have emerged as critical for assessing long-term changes in atmospheric concentrations in the past, and will dramatically enhance understanding of how the earth's climate will evolve in the future.

Atmospheric CH4 is second only to CO2 as an anthropogenic greenhouse gas. A molecule of CH4 may contribute more than 20 times as much as a molecule of CO2 to radiative forcing, and CH4 is also a key species in the chemistry of the atmosphere. Methane was, until recently, the most rapidly increasing greenhouse gas, rising 145% since the beginning of the industrial revolution. After years of near-steady growth averaging about 12 ppbv/yr, growth rates became unsteady in the 1990s, from 15 ppbv/yr (1991, 1998) to 0 ppbv (2000). The long-term increase and currently variable growth rates are not well understood, and we cannot presently predict future increases or decreases with confidence.

The study of the global carbon cycle has the potential for fundamental breakthroughs in the next few years. A number of recent developments bring us to this important threshold.

  • Atmospheric measurements and transport models enable increasingly accurate quantification of regional sources and sinks for CO2 and CH4.

  • High-resolution measurements of carbon isotopes and oxygen are establishing the relative size of carbon sinks on land and in the oceans.

  • New satellite sensors provide the foundation for more sophisticated and accurate estimates of land and ocean primary production, as well as changes in land use and land cover.

  • An increasingly comprehensive network of local-scale flux experiments is powering a new generation of process studies and interpretations.

  • Ocean measurements are able to discern human effects on ocean carbon, allowing quantification of exchange between air and sea on decadal time scales.

  • Inventories of forest, grassland, and agricultural regions are quantifying regional carbon sources and sinks, and the processes that contribute to them, with higher resolution and accuracy.

  • Experimental studies simulating past and future conditions are revealing new details about the mechanisms regulating the exchange of carbon between land vegetation and the atmosphere and between the ocean and the atmosphere.

  • A growing interdisciplinary community is documenting past and present patterns of land use and cover change.

  • Mathematical models to simulate carbon balance at local, regional, and global scales have the power and reliability to serve as integrators of diverse data streams.

The scientific agenda for crossing this threshold was outlined in the document A U.S. Carbon Cycle Science Plan (CCSP) (Sarmiento & Wofsy, 1999), developed by a broad community of scientists responding to a request from federal agencies participating in the U.S. Global Change Research Program. The CCSP addresses two fundamental scientific questions:

  • What has happened to the carbon dioxide that has already been emitted by human activities (past anthropogenic CO2)?

  • What will be the future atmospheric CO2 concentration trajectory resulting from both past and future emissions?

These questions, extended to include CH4, were articulated into long-term goals:

Goal 1. Quantify and understand the Northern Hemisphere terrestrial carbon sink.

Goal 2. Quantify and understand the uptake of anthropogenic CO2 in the ocean.

Goal 3. Quantify and understand the global distribution of carbon sources and sinks and their temporal dynamics.

Goal 4. Determine the impacts of past and current disturbance, both natural (e.g., boreal fires) and anthropogenic (e.g., land use) on the carbon budget.

Goal 5. Provide greatly improved projections of future atmospheric concentrations of CO2 and CH4.

Goal 6. Develop the scientific basis for societal decisions about management of CO2, CH4, and the carbon cycle.

Targeted investments in carbon cycle research can yield large dividends in advancing scientific research, assessment, and decision making, providing a direct response to the recent report from the National Academy of Sciences, Climate Change Science: An Analysis of Some Key Questions (NAS, 2001). This report (commissioned by the White House) attached the highest priority to scientific research on the carbon cycle.

The national dialogue on policy issues related to the carbon cycle will demand increasingly better data and predictive capabilities in the coming years. The North American Carbon Plan (NACP) described in this document provides a core element of an overall strategy for supporting that dialogue, providing science at a new level of relevance and credibility for North America and the Northern Hemisphere. The NACP should be viewed as a major component within the broader context of the U.S. Carbon Cycle Science Plan, and complements other planning efforts for the CCSP. For a summary of recommendations regarding global scale atmospheric and oceanic in situ monitoring, see the U.S. Large Scale CO2 Observation Plan (LSCOP) (Bender et al., 2001).

 A New Integrative Framework

The NACP is a set of multiagency, integrated research initiatives focused on the United States, Mexico, and Canada, and adjacent oceans, to quantify regionally resolved sources and sinks for CO2, CH4, CO, and to understand the underlying processes.

The program will provide comprehensive understanding of uptake and release of these gases. It will separate influences of combustion and biogenic sources, and determine the sensitivity of sources and sinks to environmental conditions (climatic variations, sunlight, temperature, soil moisture), ecological and historical factors, (phenology, vegetation cover, prior land use), and management (in forests, agricultural land, and wild lands). The NACP will assemble the knowledge required to assess future carbon content of the oceans, land, and atmosphere for future scenarios of emissions, and provide a basis for carbon management and carbon trading.

Recent research has led to the development of key techniques and the discovery of critical results about many aspects of the carbon cycle. The NACP envisions bold new steps in scientific integration and communication, building on past progress, to put these techniques and results to work in the interest of the public and decision makers. The new integrative framework will need to incorporate data from a wide range of sensors, locations, and processes and to connect measurements obtained at the “leaf level” with regional and continental scale data. The results of this integration need to be assessed, applied to the broad range of issues affected by the carbon cycle, and communicated to stakeholders in comprehensive scientific reports on the state of the carbon cycle. The specific needs can be described by means of the following three categories:

  1. Comprehensive long-term and intensive observations to quantify carbon stocks and fluxes for the atmosphere, plants, soils, and oceans.

    Presently, the major limitation on our ability to localize and quantify carbon sources and sinks is the sparseness of most data sets, and lack of integration of different types of data. Because no single set of measurements is definitive, we recommend strengthening the network of atmospheric, ocean, and land measurements, making each more complementary to the others. Specific tasks that contribute to this would include the following:

    • Strengthen the nation’s network for continental and global atmospheric sampling of CO2, CH4, and other greenhouse gases, including additional surface stations plus frequent, long-term, samples from a range of altitudes, using aircraft, tall towers, flux towers, and surface stations.

    • Develop the technology for measuring accurate concentrations of atmospheric CO2 and CH4 from satellites.

    • Deploy aircraft experiments designed to quantify the variability of atmospheric CO2, CH4, and CO over a range of spatial and temporal scales, to design efficient, long-term, monitoring strategies.

    • Enhance inventories for carbon accounting in North American rangelands, forests, wetlands, and agricultural lands to include the full range of locations, plants, and soils.

    • Synthesize data on past and present land use and land cover change.

    • Develop monitoring techniques and strategies to measure the efficacy and impacts of carbon management programs.

    • Develop instruments, including airborne instrumentation for routine measurements of CO2, CH4, and CO, for routine vertical profiling, and shipboard and moored autonomous devices to assess mechanisms controlling ocean CO2 fluxes.

    • Enable sustained observations to track the movement of carbon from the ocean surface to interior.

    • Utilize data collected during field studies to develop and improve algorithms for current and proposed satellite sensors that provide information about land and ocean fluxes of CO2, CH4, and CO.

    • Improve the accounting of emissions of CO2, CH4, and CO from human activities, and clarify the links between carbon emissions and economic activity, food security, and quality of life.

  2. Process studies to define key mechanisms responsible for carbon exchanges among the atmosphere, oceans, and land.

    A comprehensive understanding of the carbon cycle on land and in the oceans will require improved understanding of particular mechanisms and combinations of processes. Process studies are especially critical for isolating effects of individual mechanisms, facilitating their representation in models, and for projecting carbon cycle processes outside the range of current conditions. A number of specific goals warrant increased emphasis:

    • Expand and strengthen the nation’s network of studies to measure CO2 and CH4 exchange between land vegetation/soils and the atmosphere using flux towers (AmeriFlux) and ecological and edaphic measurements, emphasizing the understanding of year-to-year variation.

    • Quantify carbon storage and release due to land management practices, including those designed to enhance carbon sequestration in biomass and/or soils.

    • Perform manipulative experiments to understand the effects of enhanced nutrient availability on carbon uptake in the ocean and of simulated global changes on ecosystem carbon balance on land.

    • Conduct field studies to evaluate the effectiveness of deliberate management strategies to sequester carbon in the oceans and on land, as well as the impact of these strategies on natural and human systems.

    • Explore the interaction between carbon cycle management, including sources of CH4 and sources and sinks of CO2, and social systems, including economic, institutional, and sociological aspects.

  3. Quantitative frameworks to integrate the observations and process studies for scientific and decision-making objectives.

    Integrating the products of the observations and process studies will require targeted improvements in the models and in the infrastructure that supports integrative work. There are several specific needs:

    • Improve the representation of past human actions in carbon cycle models.

    • Integrate short-term responses to weather and long-term responses to ecosystem development and climate in carbon cycle models.

    • Strengthen the representation of ocean circulation in the ocean component.

    • Evaluate and validate the representation of underlying mechanisms, including social and economic processes.

    • Improve the infrastructure for developing and running integrated models with land, ocean, and atmospheric components.

    • Develop “nested” models, with the capability to provide information on a wide range of spatial scales, from a few meters to the entire globe.

    • Assemble sufficient computing resources to run fully coupled models that link a dynamic carbon cycle, including CO2 and CH4, to climate, biological processes, land use change, climate, and ocean circulation.

 Building a North American Partnership

The NACP aims to quantify and understand land biosphere-atmosphere carbon fluxes, emphasizing processes in North America for the following reasons: (1) there is intrinsic interest in the United States, Canada, and Mexico, with their strong sources of fossil fuel emissions of CO2, CH4, and CO; (2) the proposed research methods should be evaluated within a limited area before application to larger regions and eventually the globe; and (3) logistics and technology do not yet allow such an approach on a global scale. The long-range goal of the proposed program is to develop a system that ultimately will contribute to understanding the carbon cycle on a global scale. One of the challenges will be to develop partnerships with Canadian and Mexican researchers, ideally at scientist-to-scientist and agency-to-agency levels. NASA’s highly successful Boreal Ecosystem Study (BOREAS, 1993-1999) is a model of productive scientific cooperation with a neighboring country in carbon cycle studies.

 Parallel Efforts in Europe, Australia, and Japan

The EU and European nations are sponsoring an ambitious carbon program, including process studies, eddy flux, surface concentration and airborne profiling in Continental Europe and in Russia. A project (“COCO”) will assimilate radiances from the NASA AIRS instrument to retrieve global CO2 concentrations from space. The European Centre has an impressive program to develop high-resolution meteorological models and projects to enable assimilation of atmospheric CO2 data. Japan supports both flux and free-air measurements of CO2 at home and in Siberia. Australia has a vigorous program that emphasizes coupled development of observing systems and models. Several European countries as well as Japan are also mounting basin-scale ocean carbon observational campaigns.

The NACP is intended to be a major component of the emerging international framework for carbon studies, eventually leading to integration of these regional programs into global assimilation models to provide the strongest possible foundation for societal decisions pertaining to carbon and climate change. Linking with international efforts in the Northern Hemisphere is essential for resolving the North American contribution to global carbon sinks.

 Reporting to the Nations of North America and the World

The NACP will sponsor a regular series of reports on the state of the carbon cycle that will identify, characterize, and quantify major regional sources and sinks of CO2; project future changes; and enable analysis of the effects of different management practices. These reports will present scientific findings to inform the public and support decision making on a continuing basis. The reports will be an evolving product that provide governmental and private stakeholders a synthesis of current data resources and knowledge on the science of the carbon cycle, with implications for economic and policy decisions. For the first phase of the program, the reports will focus on five deliverables:

  • Explaining how the carbon cycle works.
  • Presenting emissions estimates and trends.
  • Producing regional-scale carbon inventories and flux estimates.
  • Assessing the potential of carbon management strategies.
  • Evaluating the stability of carbon storage.
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