The series of processes by which carbon compounds are interconverted in the environment, chiefly involving the incorporation of carbon dioxide into living tissue by photosynthesis and its return to the atmosphere through respiration, the decay of dead organisms, and the burning of fossil fuels.
This carbon cycle diagram shows the storage and annual exchange of carbon between the atmosphere, hydrosphere and geosphere in gigatons - or billions of tons - of carbon (GtC). Burning fossil fuels adds about 5.5 GtC of carbon per year into the atmosphere. Carbon released by burning biofuels is partly balanced by carbon fixed during biofuel feedstock growth. - NASA