In all four spheres of the environment, the element carbon occurs in the form of various compounds.
Refers to the flow of carbon (in various forms, e.g. as carbon dioxide) through the atmosphere, ocean, terrestrial biosphere and lithosphere. The atmosphere, as the smallest reservoir, only contains ca. 0.001% of total carbon. Accordingly, it is the most sensitive to changes. The vast majority (ca. 99.8%) is in the lithosphere. The chemical transformation of compounds containing carbon and exchanges of these compounds among the four spheres of the environment are collectively referred to as the global carbon cycle. Exchanges of carbon between the spheres primarily involve carbon dioxide. The carbon cycle consists of several sub-cycles.