Supplementary material to “Investigators Share Improved Understanding of the North American Carbon Cycle”

Richard A. Birdsey, USDA Forest Service, Newtown Square, Pennsylvania; Robert Cook, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Scott Denning, Department of Atmospheric Science, Colorado State University, Fort Collins; Peter Griffith, Science Systems and Applications, Inc., Carbon Cycle and Ecosystems Office, NASA Goddard Space Flight Center, Greenbelt, Maryland; Beverly Law, College of Forestry, Oregon State University, Corvallis; Jeffrey Masek, NASA Goddard Space Flight Center, Greenbelt, Maryland; Anna Michalak, Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor; Stephen Ogle, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins; Dennis Ojima, Natural Resources Ecology Laboratory, Colorado State University, Fort Collins; Yude Pan, USDA Forest Service, Newtown Square, Pennsylvania; Christopher Sabine, NOAA Pacific Marine Environmental Laboratory, Seattle, Washington; Edwin Sheffner, Earth Science Division, NASA Science Mission Directorate, Washington, D. C.; Eric Sundquist, U.S. Geological Survey, Woods Hole, Massachusetts

Citation:
Birdsey, R. A., et al. (2007), Investigators share improved understanding of the North American carbon cycle, Eos Trans. AGU, 88(24), 255. [Full Article (pdf)]

The U.S. North American Carbon Program (NACP) sponsored an “all-scientist” meeting, 22–24 January 2007, in Colorado Springs, Colorado, to review progress in understanding the dynamics of the carbon cycle of North America and adjacent oceans, and to chart a course for improved integration across scientific disciplines, scales, and earth system boundaries. The meeting participants also addressed the need for better decision support tools for managing the carbon cycle of North America, so that strong science capability can better inform policy as interest in taking action increases across the nation.

Herein we report on major themes that will help integrate the diversity of NACP science and fill significant knowledge gaps for understanding and managing the North American carbon cycle: integration among disciplines involving land, atmosphere, and ocean research; strengthening data management infrastructure to support modeling and analysis; identification of study regions that are critical for reducing uncertainties in the North American carbon balance; and integrating biophysical science with the human dimensions of carbon management and decision support.

The North American Carbon Program

The NACP Science Plan (Wofsy and Harris, 2002) and Science Implementation Strategy (Denning et al. 2005) lay the foundation for a program of interagency research to address several globally-important questions about the carbon cycle. The NACP is organized around the following questions: What is the carbon balance of North America and adjacent oceans? What are the geographic patterns of carbon fluxes and how is the balance changing over time? What processes control the sources and sinks, and how are they changing over 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, and provide resources to support decision makers? Participating agencies and scientists have initiated an integrated program of research to answer these questions, involving atmospheric, terrestrial, and marine studies with activities ranging from intensive field campaigns to long-term monitoring and modeling over a range of time and space domains. NACP goals, planning documents, and project profiles, as well as the abstracts and posters from this science meeting, may be found at http://www.nacarbon.org/.

NACP is a large and complex program supported by eight federal agencies and conducted by hundreds of scientists at federal, academic and other research institutions. The Carbon Cycle Interagency Working Group (CCIWG), made up of representatives from each of the participating federal agencies, provides overall programmatic direction and direct oversight of the NACP Coordinator. Scientific leadership is provided by a Science Steering Group (SSG) of NACP investigators appointed by the CCIWG. Additionally, U.S. leadership is working with counterparts in Canada and Mexico to develop a joint program that will take advantage of each country’s independent carbon research programs.

Need for Cross-Disciplinary Integration

The NACP, a multi-disciplinary program involving land, atmosphere, and ocean research, requires cross-disciplinary integration to evaluate the range of carbon sources and sinks contributing to the carbon balance of North America and adjacent oceans. For example, carbon dynamics in coastal margins are poorly understood, in part because few studies have integrated across terrestrial, atmospheric and ocean reservoirs and disciplinary boundaries. Opportunities exist within disciplines for investigators from a variety of projects to collaborate in integrative activities, by coordinating efforts that might have otherwise been conducted independently. Such within-discipline coordination is improving with guidance from the CCIWG and SSG, making it more likely that critical integration needs are met. For example, it is likely that NACP can couple diagnostic and prognostic modeling capabilities, and integrate these models with greenhouse gas reporting systems currently relying mostly on inventories (see the first State of the Carbon Cycle Report, SOCCR, 2007). Such integration would reduce gaps in knowledge of the carbon cycle, how it is changing, and why. Another opportunity is integration of data collected by various investigators across spatial and temporal scales. These activities would benefit U.S. reporting of greenhouse gas inventories by improving our fully-integrated estimates of the interannual variability in land-atmosphere-ocean carbon exchange, and attributing changes to major driving factors such as climate variability, wildfires, insect outbreaks, and land-use change.

Community Effort Needed for Integrated Observations, Modeling and Data Management

Integrated long-term observation systems are the backbone of the NACP. Some critical observations are “contributed” to the NACP from well-established programs such as land inventories conducted by USDA. The AmeriFlux network of temporally intensive observations has demonstrated relevance in quantifying the effects of climate variability on the carbon cycle at seasonal to interannual time scales (Law, 2005). Continuous high-precision CO2 concentration measurements are made at various locations across the continent for use in inverse modeling and investigation of large-scale patterns of atmospheric transport of CO2. These observation networks are of great value for understanding and verifying regional and cross-boundary sources and sinks, but face challenges to continuing operations. The open ocean observing system is being developed as a part of the Global Earth Observing System of Systems (GEOSS), but there currently is no established long-term program for the coastal margin component of that effort (http://www.oco.noaa.gov/). Remote sensing data and analyses have proven critical to supporting biophysical modeling activities within NACP. Hence, there is a need to insure that the satellite data required by NACP scientists are readily available and have consistent technical specifications.

The need for coupling different types of models is based on achieving better understanding of feedbacks between earth systems and eliminating boundary problems. There is an emerging effort to fully couple carbon (land and ocean) and climate models; this could be expanded to include emissions models that consider the full range of human drivers in diagnostic and prognostic analyses. Equally important is the need to support integrated modeling with robust data management. The meeting participants noted that large investments in individual projects were not matched by data system infrastructure to enable storage, search and access of data. Data archives do exist for the carbon flux, precision CO2 concentration data, and biological data collected by the AmeriFlux network (CDIAC; http://public.ornl.gov/ameriflux/), Fluxnet-Canada (http://www.fluxnet-canada.ca/), tree data of the USDA Forest Inventory & Analysis (http://fia.fs.fed.us/), and ocean carbon data (CDIAC: http://cdiac.esd.ornl.gov/oceans/home.html). These databases will serve a critical role in facilitating modeling studies and syntheses, but it will be a challenge to coordinate these diverse data sets into a meaningful synthesis. NASA is supporting a Modeling and Synthesis Thematic Data Center (MAST-DC; (http://nacp.ornl.gov/mast-dc/)) that will provide some data products and data management services. Furthermore, the NACP Office is hosting a searchable database of NACP project profiles that allows investigators to register their data requirements and planned data deliverables. This database is available online to the scientific community at the NACP web site: http://www.nacarbon.org/.

Resource constraints have delayed the implementation of some elements of the NACP infrastructure as originally planned (Wofsy and Harris, 2002). For example, the NACP has not yet fully implemented intermediate-tier field sampling needed to link intensive sites, such as AmeriFlux observations, to extensive inventories. Adjustments to the implementation plan that match program needs with resource availability are a major activity of the CCIWG and SSG.

Identifying Critical Regions for Understanding the Changing Carbon Cycle

The NACP has made some very good progress in a few areas. Assimilation of remote sensing data and atmospheric observations in a geostatistical framework is revealing some of the key uncertainties in understanding and managing the North American carbon budget (Michalak et al., 2006, Law et al. 2004, Chen et al. 2003). An intensive field campaign in the Mid-continental region is a test-bed of methods with goals of reconciling carbon flux estimates from “top-down” and “bottom-up” approaches to integrating models and data, in addition to revealing changes in sources and sinks within this largely agricultural region ( http://www.nacarbon.org/nacp/mci.html). This campaign is an example of integrative activities occurring within the NACP that will eventually lead to improved diagnosis, prediction and attribution of carbon sources and sinks at the continental scale.

Meeting participants identified a number of other regions where intensive studies can fruitfully address NACP goals. The coastal margins (ranging from head-of-tide in rivers to the edge of the continental shelf) are a “hotspot” of carbon cycle activity. Carbon flows between the land, ocean, and atmosphere in these regions are complex and dynamic, especially during events such as hurricanes, El Niño, and floods. Likewise, the Interior West region of mixed grasslands and woodlands has been poorly inventoried and sparsely monitored by intensive study sites, so that SOCCR identifies this area as having the most uncertain estimate of periodic change in carbon flux. Finally, the fate of “heritage carbon” under changing climate, particularly carbon stored in permafrost, bogs, and soil carbon in the Boreal/Arctic region, remains poorly understood. Lack of systematic monitoring and comprehensive modeling of carbon dynamics in these regions represents a critical shortcoming of carbon cycle science in North America.

Integrating Human Dimensions

Most of the NACP focus has been on the natural sciences, but to achieve its objectives, the NACP must integrate human dimensions with the biologic, atmospheric, and oceanic sciences. Human decisions influence the carbon cycle in North America through interactions between social and economic systems with the biological, chemical and physical processes leading to carbon transfers between lands, oceans and atmosphere. Two broad categories of human dimensions are in need of consideration. The first is to expand research on social processes that drive land use and fossil fuel emissions, quantitatively integrating them into diagnostic and prognostic land use/cover and emissions modeling. This will allow for the emergence of the carbon/climate/human modeling urgently needed to provide the science and analytical support tools for climate action programs at various levels of government.

This leads to the second area of human dimensions research, decision support for national, state, and local stakeholders in the public and private sectors. While there are emerging tools to support strategies for land management, there needs to be more attention to decision support for managing fossil fuel emissions, including independent monitoring and verification from atmospheric measurements, and a consideration of carbon consequences in coastal management decisions. Decision support should be more fully integrated with basic research to ensure that outcomes are as intended. It is critical to understand interactions between the industrial and biological aspects of the carbon cycle. An emerging decision-support need is to understand and quantify the combined effects of management actions on net radiative forcing rather than solely on atmospheric chemistry. This coupling of biogeochemical and biophysical knowledge is required to improve the understanding of, and accounting for, the effects of management and policy on warming potential.

Next Steps

The NACP Office and SSG are summarizing the specific recommendations that emerged from the meeting, and will present that summary to the CCIWG for consideration. We expect that, within the constraints of very tight budgets, NACP sponsoring agencies will take some of the recommended steps to more fully integrate the organization, infrastructure, and science. Immediately following the NACP meeting was a companion meeting of the Joint NACP involving Canada, Mexico, and the United States. The Joint NACP offers the intriguing possibility of much better understanding and management of the carbon cycle by considering a broader array of data sources, models, and management opportunities in the context of diverse national goals, policies, and land-use histories within North America.

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