The Carbon Cycle

The Earth’s Carbon Cycle is the biogeochemical exchange of carbon between the earth’s five main physical “spheres”—atmosphere, biosphere, pedosphere, hydrosphere and lithosphere. Human activity—including burning of fossil fuels, but also the “mining” of our soils—has radically altered carbon’s movement between these spheres, resulting in large net increases in carbon in both the atmosphere and hydrosphere, with consequent negative impacts on global climate and biological systems. CCI is dedicated to halting and reversing these imbalances through identification of human practices that restore natural cycles and that, if taken to scale, can increase carbon sequestration and reduce GHG emissions.

The figure at left depicts the different components of the carbon cycle, with values in parentheses shown as estimates of the major global carbon reservoirs (Houghton, 2007) in gigatons (GT) (Source: U.S. Department of Energy Office of Science).

For a more detailed explanation of the diagram, visit the United States Carbon Cycle Science Program.

Frequently Asked Questions

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