Carbon Cycle

Take a bite of dinner, a breath, or a drive in a car — you are part of the carbon cycle.

Most of Earth’s carbon is stored in rocks and sediments, while the rest is located in the ocean, atmosphere, and in living organisms. These are the reservoirs through which carbon cycles.

Coastal salt marshes, mangroves, and seagrass beds are incredibly efficient at absorbing and storing large quantities of the greenhouse gas carbon dioxide from the atmosphere.
Coastal blue carbon
Coastal salt marshes, mangroves, and seagrass beds are incredibly efficient at absorbing and storing large quantities of the greenhouse gas carbon dioxide...

Carbon storage and exchange

Carbon moves from one storage reservoir to another through a variety of mechanisms. One example is the movement of carbon through the food chain. Plants move carbon from the atmosphere into the biosphere through photosynthesis: they take in carbon dioxide and use energy from the sun to chemically combine it with hydrogen and oxygen to create sugar molecules. Animals that eat the plant can digest the sugar molecules to get energy for their bodies. Respiration, excretion, and decomposition release the carbon back into the atmosphere or soil continuing the cycle.

The ocean plays a critical role in the storage of carbon, as it holds about 50 times more carbon than the atmosphere. Two-way carbon exchange can occur quickly between the ocean’s surface waters and the atmosphere, but carbon may also be stored for centuries at the deepest ocean depths.

Rocks such as limestone and fossil fuels such as coal and oil are storage reservoirs that contain carbon from plants and animals that lived millions of years ago. When these organisms died, slow geologic processes trapped their carbon and transformed it into these natural resources. Processes such as erosion release this carbon back into the atmosphere very slowly while volcanic activity can release it very quickly. Burning of fossil fuels in cars or power plants is another way this carbon can be released into the atmospheric reservoir quickly.

Scientists at NOAA’s Earth Systems Research Laboratory created CarbonTracker: a carbon dioxide measuring and modeling system that tracks sources and sinks around the globe.
Tracking carbon dioxide across the globe
Between burning fossil fuels and clearing forests, humans emit far more carbon dioxide than Earth’s natural physical and biological processes can remove...

Changes to the carbon cycle

The increasing human population and their activitiesoffsite link have a tremendous impact on the carbon cycle. Burning of fossil fuels, changes in land use, and the use of limestone to make concrete all transfer significant quantities of carbon into the atmosphere. As a result the amount of carbon dioxide (CO2) in the atmosphere is rapidly rising and is already significantly greater than at any time in the last 800,000 years. This increase of CO2 is affecting our ocean as it absorbs much of the CO2 that is released from burning fossil fuels. This extra CO2 is lowering the ocean’s pH, this process is called ocean acidification and interferes with the ability of marine organisms (such as corals) to build their shells and skeletons.

Change in the onset of spring in days per decade from 2001 - 2012.
Eastern forests inhaling more carbon dioxide than they're exhaling
New research indicates that in the eastern United States, increased carbon uptake has outpaced a simultaneous increase in carbon dioxide “exhaled” into...


All of our daily activities impact the carbon cycle. The resources in this collection provide real world examples of the changes occurring in the cycle. There is much to learn about this essential topic and some of the resources highlight exciting career opportunities in this field of study.

Introductory text compiled from resources provided by NOAA's Office of Oceanic and Atmospheric Research.

Last updated February 2011.