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The Global Carbon CycleOverview
Carbon Cycle Science Home Page
The Carbon Cycle. Basic background information from NASA's Earth Observatory Reference section.
Human Interactions with the Carbon
Cycle. Summary of a Workshop. |
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Carbon is important as the basis for the food and fiber that sustain and shelter human populations, as the primary energy source that fuels economies, and as a major contributor to the planetary greenhouse effect and potential climate change. Carbon dioxide (CO2) is the largest single forcing agent of climate change, and methane (CH4) is also a significant contributor. Atmospheric concentrations of CO2 and CH4 have been increasing for about two centuries as a result of human activities and are now higher than they have been for over 400,000 years. Since 1750, CO2 concentrations in the atmosphere have increased by 30 percent and CH4 concentrations in the atmosphere have increased by 150 percent.
Approximately three-quarters of present-day anthropogenic CO2 emissions are due to fossil fuel combustion (plus a small amount from cement production). Land-use change accounts for the rest. The strengths of CH4 emission sources are uncertain due to the high variability in space and time of biospheric sources. Future atmospheric concentrations of these greenhouse gases will depend on trends and variability in natural and human-caused emissions and the capacity of terrestrial and marine sinks to absorb and retain carbon. Decisionmakers searching for options to stabilize or mitigate concentrations of greenhouse gases in the atmosphere are faced with two broad approaches for controlling atmospheric carbon concentrations: 1) reduction of carbon emissions at their source—such as through reducing fossil fuel use and cement production or changing land use and management (e.g., reducing deforestation); and/or 2) enhanced sequestration of carbon—either through enhancement of biospheric carbon storage or through engineering solutions to capture carbon and store it in repositories such as the deep ocean or geologic formations. Enhancing carbon sequestration is of current interest as a near-term policy option to slow the rise in atmospheric CO2 and provide more time to develop a wider range of viable mitigation and adaptation options. However, uncertainties remain about how much additional carbon storage can be achieved, the efficacy and longevity of carbon sequestration approaches, whether they will lead to unintended environmental consequences, and just how vulnerable or resilient the global carbon cycle is to such manipulations. Successful carbon management strategies will require solid scientific information about the basic processes of the carbon cycle and an understanding of its long-term interactions with other components of the Earth system, such as climate and the water and nitrogen cycles. Such strategies also will require an ability to account for all carbon stocks, fluxes, and changes and to distinguish the effects of human actions from those of natural system variability. Because CO2 is an essential ingredient for plant growth, it will be essential to address the direct effects of increasing atmospheric concentrations of CO2 on terrestrial and marine ecosystem productivity. Breakthrough advances in techniques to observe and model the atmospheric, terrestrial, and oceanic components of the carbon cycle have readied the scientific community for a concerted research effort to identify, characterize, quantify, and project the major regional carbon sources and sinks—with North America as a near-term priority. The agencies responsible for CCSP carbon cycle research (DOE, NASA, NIST, NOAA, NSF, USDA, and USGS) have planned a coordinated, interagency, and multidisciplinary research strategy to bring together the broad range of needed infrastructure, resources, and expertise essential for providing this information. A continuing dialogue with stakeholders, including resource managers, policymakers, and other decisionmakers, will be established and maintained to ensure that desired information is provided in a useful form.
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CCSP-supported
research on the global carbon cycle focuses on identifying the
size, variability, and potential future changes to reservoirs
and fluxes of carbon within the Earth system; and providing the
scientific underpinning for evaluating options to manage carbon
sources and sinks. Specific programs and projects focus on North
American and oceanic carbon sources and sinks; the impact of
land-use change and resource management practices on carbon sources
and sinks; projecting future atmospheric carbon dioxide and methane
concentrations and changes in land-based and marine carbon sinks;
and the global distribution of carbon sources and sinks and how
they are changing 
