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Carbon Cycle

Definition

The path through which carbon is exchanged between the Earth's spheres (hydrosphere, cryosphere, lithosphere, biosphere, atmosphere).

Summary

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% and CH4 concentrations in the atmosphere have increased by 150%.

Research Questions

1. What are the magnitudes and distributions of North American carbon sources and sinks on seasonal to centennial time scales, and what are the processes controlling their dynamics?

2. What are the magnitudes and distributions of ocean carbon sources and sinks on seasonal to centennial time scales, and what are the processes controlling their dynamics?

3. What are the effects on carbon sources and sinks of past, present, and future landuse change and resource management practices at local, regional, and global scales?

4. How do global terrestrial, oceanic, and atmospheric carbon sources and sinks change on seasonal to centennial time scales, and how can this knowledge be integrated to quantify and explain annual global carbon budgets?

5. What will be the future atmospheric concentrations of carbon dioxide, methane, and other carbon-containing greenhouse gases, and how will terrestrial and marine carbon sources and sinks change in the future?

6. How will the Earth system, and its different components, respond to various options for managing carbon in the environment, and what scientific information is needed for evaluating these options?

Source: Climate Change Science Program, and The Subcommittee Global Change Research. "Our Changing Planet: The U.S. Climate Change Science Program for Fiscal Year 2006." Washington: Climate Change Science Program Office, 2006.

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