Understanding of the Earth’s carbon cycle is an urgent societal need as well as a challenging intellectual problem. The impacts of human-caused changes on the global carbon cycle will be felt for hundreds to thousands of years. Direct observations of carbon stocks and flows, process-based understanding, data synthesis, and careful modeling are needed to determine how the carbon cycle is being modified, what the consequences are of these modifications, and how best to mitigate and adapt to changes in the carbon cycle and climate. The importance of the carbon cycle is accentuated by its complex interplay with other geochemical cycles (such as nitrogen and water), its critical role in economic and other human systems, and the global scale of its interactions.
The need for improved understanding of the global carbon cycle and better research coordination led to the development of the first U.S. Carbon Cycle Science Plan, published more than a decade ago. That document outlined a plan for land, atmosphere, and ocean observations; manipulative experiments; and Earth-system modeling to improve our understanding of the contemporary carbon cycle and our ability to predict its future.
The development of a new Plan was initiated by the U.S. Carbon Cycle Interagency Working Group (CCIWG) and the Carbon Cycle Science Steering Group (CCSSG), and outlines a strategy for refocusing U.S. carbon cycle research based on the current state of the science. The development of this Plan was led by a committee of 25 active members of the carbon cycle research community, and the result is intended to provide U.S. funding agencies with information on community-based research priorities for carbon cycle science over the next decade. The Plan emphasizes the long-lived, carbon-based greenhouse gases, carbon dioxide (CO2) and methane (CH4), and the major pools and fluxes of the global carbon cycle. The recommended research is global in scale, and there is therefore a strong need for international cooperation and collaboration.
While many of the research goals in the 1999 Science Plan remain important for the coming decade, new research thrusts are also needed. These thrusts include a more comprehensive look at the effects of humans on carbon cycling, including the consequences of carbon management activities; the direct impacts of CO2 on ecosystems and their vulnerability or resilience to changes in carbon and climate; a quantitative understanding of the uncertainties associated with the carbon cycle; and the need to coordinate researchers from the natural and social sciences to address societal concerns.
The Plan is organized around three overarching questions:
Question 1. How do natural processes and human actions affect the carbon cycle on land, in the atmosphere, and in the oceans?
Question 2. How do policy and management decisions affect the levels of the primary carbon-containing gases, carbon dioxide and methane, in the atmosphere?
Question 3. How are ecosystems, species, and natural resources impacted by increasing greenhouse gas concentrations, the associated changes in climate, and by carbon management decisions?
In addition, the Plan recognizes the central role of sustained observations that underlie all of the outlined science objectives. There is need for an optimally designed and integrated system for long-term observations, data collection, and data management.
Incomplete representations of the carbon cycle cause large uncertainties in estimates of future changes in the climate system. Conversely, uncertainties about future climate also make it more difficult to predict future changes in the carbon cycle. In balancing the global carbon cycle and gaining a process-level understanding of its components, it is important to evaluate, understand, and deal with the uncertainty that arises through measurements, models, analyses, and projections, and the complex interdependence of the carbon, climate, and socioeconomic systems.
The overriding science questions provide basic long-term direction for guiding carbon cycle research. To make progress toward answering the questions, and to provide guidance for continuing research, we have outlined six science goals that should be pursued over the next decade. These six goals (together with references to the overriding questions they are primarily designed to address), are:
Goal 1 (Q1, Q2): Provide clear and timely explanation of past and current variations observed in atmospheric CO2 and CH4 – and the uncertainties surrounding them.
The scientific community needs to be able to provide the broader public with a clear and timely explanation of past and current variations observed in atmospheric CO2 and CH4, as well as the uncertainties surrounding these explanations. We note that ‘timely’ is an important part of this goal. To serve public policy needs, atmospheric observations and clear analyses are needed in close to real time. To address this goal, we need to develop the capability to accurately estimate variability in carbon sources and sinks as well as the processes controlling that variability.
Goal 2 (Q1, Q2): Understand and quantify the socioeconomic drivers of carbon emissions, and develop transparent methods to monitor and verify those emissions.
This goal seeks to derive process-level understanding of the human processes and motivations that determine carbon emissions from energy use, industrial activity, and land use. Improved understanding will enable better evaluations of current emissions levels and better projections of future emissions, including the implications of alternative policy scenarios. Atmospherebased measurements, remotely-sensed observations, evaluation of socioeconomic parameters, and other tools need to be developed to provide confirmation and confidence in mitigation commitments. The institutions and infrastructure for monitoring and verification of international agreements must come from the national and international political processes, but the tools and methods need to be developed by science.
Goal 3 (Q1, Q2, Q3): Determine and evaluate the vulnerability of carbon stocks and flows to future climate change and human activities, emphasizing potential positive feedbacks to sources or sinks that make climate stabilization more critical or more difficult.
All carbon reservoirs and carbon processes are not equally vulnerable to change, resilient to stress, responsive to management, or susceptible to unintended side effects of management decisions. We need to be able to identify which carbon pools and flows are most vulnerable and to understand the physical, chemical, and biological processes important in determining the degree of vulnerability of these pools and flows. We also need to predict the consequences of carbon management and sequestration schemes on vulnerable pools and to support carbon management goals by prioritizing the resources that are needed to assure the stability of the most vulnerable stocks and flows.
Goal 4 (Q3): Predict how ecosystems, biodiversity, and natural resources will change under different CO2 and climate change scenarios.
The direct effects of elevated greenhouse gas levels, along with the accompanying changes in climate, are likely to alter ecosystems profoundly on land and in marine and freshwater environments. Beyond the interaction with climate change, there is a need to assess the direct impact of increasing atmospheric greenhouse gas concentrations on ecosystems, beyond their potential role as carbon reservoirs or sinks. Three examples of such impacts are altered marine ecosystem structure due to ocean acidification, biodiversity impacts on land and in the ocean, and the potential stimulation of net primary productivity due to additional CO2. The interacting effects of climate and biogeochemistry need to be understood.
Goal 5 (Q1, Q2, Q3): Determine the likelihood of success and the potential for side effects of carbon management pathways that might be undertaken to achieve a lowcarbon future. This goal is especially important as concerns increase over anthropogenic impacts on the atmospheric concentrations of greenhouse gases and their impacts on the global carbon cycle. There is a need to understand interlinked natural and managed systems sufficiently for individuals, corporations, and governments to make rational and well-informed decisions on how best to manage the global carbon cycle, and especially the anthropogenic impacts on this cycle.
Goal 6 (Q1, Q2, Q3): Address decision maker needs for current and future carbon cycle information and provide data and projections that are relevant, credible, and legitimate for their decisions.
The scientific community needs to provide carbon cycle information needed by decision makers and other stakeholders, understand how decision making affects the evolution of the carbon cycle, and determine how information about the carbon cycle can be relevant to policy decisions. Meeting the needs of decision makers requires an interactive process in order to understand those needs. This goal also recognizes the need to be anticipatory. The needs of decision makers a decade from now will not necessarily be the same as the needs they confront now and a goal of research is to anticipate and probe creatively so that we are prepared to confront tomorrow’s questions.
A number of key cross-cutting research components comprise the central core for advancing carbon cycle science over the next decade, and these have been grouped into four highpriority elements. These elements embody the action items of carbon cycle research, with each of them contributing to all six research goals. The first element encompasses sustained and focused observations, which include atmospheric, ocean/coastal/inland water, terrestrial ecosystem, demographic/social, and remote-sensing observations. The second element includes studies of system dynamics and function across scales, including intensive process studies and field campaigns, manipulative laboratory experiments, and manipulative field studies. This work should be designed as coordinated, integrative studies across traditional disciplinary boundaries where appropriate and possible. The third element focuses on modeling, prediction, and synthesis, including improving existing models, adding human dimensions to Earth system models, and augmenting synthesis activities. Finally, the fourth element centers on communication and dissemination, including improving dialogue among the decision-making community, general public, and scientific community, developing appropriate tools for communicating scientific knowledge to decision makers, and evaluating the impact of scientific uncertainty on decision making.
Interdisciplinary studies and improvements in both inclusion of, and collaboration with, the social and political sciences are essential to the success of this Plan. Visions of the future need to be strengthened through interactions with integrated assessment efforts and studies of carbon management. Similarly, the increasing importance of international collaboration is also apparent. U.S. scientists need to participate and take leadership roles in international assessments and syntheses, field campaigns, model intercomparisons, and observational networks. Such international participation offers opportunities to leverage investments in resources and to contribute the knowledge and creativity of U.S. scientists to coordinated research.
The conduct of science depends on the institutions and structures that support the research. Institutional structures and opportunities to improve coordination and to ensure the achievement of the Plan’s research goals include:
Providing more opportunities for sustained, long-term funding.
Enhancing carbon cycle data management.
Encouraging directed calls for integrated topics in carbon cycle research, including research in the social sciences.
Facilitating efforts to contribute to integrated, interdisciplinary efforts such as the assessments of the Intergovernmental Panel on Climate Change.
Establishing stronger links between the CCIWG of the U.S. Global Change Research Program and other U.S. interagency working groups focused on climate change and mitigation.
Developing a strong connection between carbon cycle research and the developing ocean acidification program.
Expanding the North American Carbon Program to a new Northern Hemisphere Carbon Program.
Improving international linkages.
Using the North American Carbon Program and Ocean Carbon and Biogeochemistry program as models to initiate similar, problem-oriented research communities, including the creation of a group with strong roots in both the social and natural sciences.
Implementing a process for periodic measurement and evaluation of progress in pursuing the goals of this Plan.
Continuing to provide broad support for education and training, with an increased emphasis on interdisciplinary education focusing on carbon/climate science and decision making in a global context.
The overriding priority detailed in this research Plan is to develop and maintain a broadly-focused, balanced, integrated research agenda. Along with our emphasis on CO2 and CH4, additional non-greenhouse gases, such as carbon monoxide (CO) and the ratio of oxygen to nitrogen (O2:N2), provide important constraints on the global carbon cycle and are part of the plan in that context. Consideration of the greenhouse gas nitrous oxide (N2O) and other non-carbon greenhouse gases is essential, but beyond the scope of this Plan. In general, connections between the global carbon cycle and the cycles of water, plant nutrients, and oxygen will need to be made to round out our understanding of the controls on the global carbon cycle, but these are not directly included under this Plan. Our intention is that complementary studies will be linked to the carbon cycle research proposed here to provide a broader understanding of the global carbon cycle and other biogeochemical cycles. Finally, throughout this document we emphasize the importance of an integrated system to collect and maintain the essential data that drive scientific understanding.
The Plan outlined here must be implemented efficiently and effectively. It is clear, however, that the breadth and intensity of the research agenda will depend on the resources available. We estimate that the total U.S. carbon cycle budget will need to be increased to approximately $500 million per year, not including platform costs (e.g., satellites, ship time, aircraft time), to achieve the goals outlined in this Plan. The interdependence of the many components of this research Plan is critical and the final approach needs to maintain balance among the various research foci, within the resources that are available. Greater commitment of resources will allow more complete understanding sooner, to the benefit of society as a whole. The importance of carbon cycle research within the pressures of confronting global change justifies this accelerated commitment of resources.