Carbon cycle. Diagram illustrating the processes that cycle carbon (white arrows) through different regions of the Earth. These reservoirs, forming the global carbon budget, are termed the biosphere, geosphere, hydrosphere, and atmosphere. Sunlight is used by plants such as trees to incorporate atmospheric carbon dioxide into plant sugars and tissues during photosynthesis (green arrow at left). Carbon dioxide is released during plant and animal respiration (blue arrows at left), and the decay of organic matter in the soil (orange arrows at left), and from volcanoes during eruptions. Some carbon dioxide is absorbed by the oceans (green arrow at right), and is also removed from the atmosphere by rain and chemical weathering (orange arrow at centre). Fossil fuel emissions (blue arrow at right) add carbon dioxide to the atmosphere.