Carbon dioxide is naturally produced and consumed by elements in the earth′s atmosphere, biosphere, and oceans. This is known as the carbon cycle.
Atmosphere
Carbon is captured from the atmosphere by plants during photosynthesis, oceanic chemistry, and other biological processes such as the weathering of silicate rock. After its use as a solid, carbon returns to the atmosphere as carbon dioxide during respiration, bacterial decay, combustion, and other natural phenomena including volcanic eruptions. In addition to animal and chemical contributions to the carbon cycle, humans return carbon dioxide and other greenhouse gases to the atmosphere through the use of fossil fuel energy during transportation, electricity consumption, as well as industrial processes such as cement production.
Biosphere
Carbon is an important component of life and plays a significant role in the structure, biochemistry, and nutrition of all living organisms. In the biosphere, carbon is used by many different types of organisms. Organisms known as autotrophs, produce their own organic compounds using carbon dioxide from the air or water around them. They do this by using energy from the sun to convert carbon dioxide and water into oxygen and glucose, a sugar and major energy source for living organisms. Heterotrophs, or organisms unable to perform photosynthesis, consume autotrophs using their glucose for energy. Carbon leaves the biosphere primarily through a process known as respiration where living organisms convert oxygen and glucose into carbon dioxide and water, reversing the photosynthetic reaction used to capture carbon dioxide from the atmosphere. The burning of biomass such as wood also releases carbon dioxide back into the environment.
Oceans
Around 36 trillion tonnes of carbon dioxide are contained in the ocean at any given time. While most of this carbon takes the form of bicarbonate ions, a chemical structure responsible for regulating the ocean′s acidity, carbon is also contained in oceanic organisms and mineral structures such as limestone.
