Research > Carbon Cycle Science

Carbon Cycle Science

Global climate projections and regional climate forecasts depend on understanding the path of carbon through our environment.

Projecting climate into the future and forecasting regional impacts depends on our understanding of the exchange of carbon dioxide between the atmosphere, oceans and land ecosystems. NOAA is charged to provide the atmospheric measurements and analyses required to track the fate of carbon dioxide emissions caused by the burning of fossil fuels and biomass, and to reduce uncertainties in how the exchange of carbon responds to the variations and trends of climate and land use.

What is the Carbon Cycle?

Carbon is exchanged, or "cycled" among Earth's oceans, atmosphere, ecosystem, and geosphere. All living organisms are built of carbon compounds. It is the fundamental building block of life and an important component of many chemical processes. It is present in the atmosphere primarily as carbon dioxide (CO2), but also as other less abundant but climatically significant gases, such as methane (CH4).

Sources and Sinks

Because life processes are fueled by carbon compounds which are oxidized to CO2, the latter is exhaled by all animals and plants. Conversely, CO2 is assimilated by plants during photosynthesis to build new carbon compounds. CO2 is produced by the burning of fossil fuels, which derive from the preserved products of ancient photosynthesis. The atmophere exchanges CO2 continuously with the oceans. Regions or processes that predominately produce CO2 are called sources of atmospheric CO2, while those that absorb CO2 are called sinks.

Why is the Carbon Cycle important?

While CO2 is only a very small part of the atmosphere (0.04%), it plays a large role in the energy balance of the planet.

CO2 in the atmosphere acts like a blanket over the planet by trapping longwave radiation, which would otherwise radiate heat away from the planet. As the amount of CO2 increases, so will its warming effect. CO2 is the largest contributor (currently 63%) to this effect by long-lived gases and its role increases each year. The additional burden of CO2 in the atmosphere will remain for a very long time, of the order of thousands of years, if we have to rely on the natural mechanisms of erosion and sedimentation to process the added CO2.