Carbon Dioxide 101


The carbon cycle is the process through which carbon is cycled through the air, ground, plants, animals, and fossil fuels. People and animals inhale oxygen from the air and exhale carbon dioxide (CO2) while plants absorb CO2 for photosynthesis and emit oxygen back into the atmosphere. Carbon dioxide is also exchanged between the atmosphere and the oceans. This natural system of processes keeps CO2 levels in the atmosphere stable over time. The figure below depicts the carbon cycle by showing how carbon moves between land, the atmosphere, and the ocean through various natural- and human-initiated processes. On land, carbon is contained within rocks, the soil, plants, and animals. When these decompose, the carbon can be emitted to the atmosphere as CO2. Once in the atmosphere, the carbon can then be absorbed by the oceans or by a land/ocean-based plant or animal. It is important to note that only a small amount of the Earth’s carbon moves through the carbon cycle each year.

Natural and Anthropogenic Carbon Fluxes
Natural and Anthropogenic Carbon Fluxes

Nature's carbon cycle normally keeps CO2 levels in balance, but human activity, mostly the burning of fossil fuels for energy production and transportation, produces more CO2 than the atmosphere and oceans have historically been able to absorb. Human contribution is enough to throw the cycle off balance and anthropogenic emissions have increased the carbon content in the cycle by about 0.7 percent over the past 150 years.


Learn about carbon dioxide’s role in the Earth’s atmosphere.