The Carbon Cycle

Carbon is a chemical element essential to all life on earth. The major stores or reservoirs of carbon include rock and marine sediment, the oceans, soils, the atmosphere and land plants.  The systems of movement of carbon between these stores is called the carbon cycle.

Carbon dioxide is one the most important parts of the carbon cycle and has a number of sources and sinks. Firstly, terrestrial organisms release carbon dioxide into the atmosphere by respiration, and also draw it from the atmosphere through photosynthesis, with the balance of these processes varying with the seasons (more photosynthesis in summer due to more leaf coverage). Secondly, oceans are the largest active reservoir in the cycle. Dissolved carbon dioxide is taken deep into the ocean by sinking cold water and takes 1000s of years to return to the surface. Lastly, human activity is also a source of carbon dioxide that has been increasing since the industrial revolution. This is due to an intensification of processes such as the burning of fossil fuels and land use change for agriculture.

This increase in the contribution of carbon dioxide from humans has led to an estimated rise in global temperature of 0.85°C between 1850-2012.

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Key Terms:

Reservoirs – A store of material that is separate from other stores either in physical location or chemical nature

Terrestrial – Relating to the land

Respiration – Process of transferring  energy in an organism into forms it can use. Usually involving the intake of oxygen and release of carbon dioxide.

Photosynthesis – The process of plants using energy from sunlight to break down water and carbon dioxide producing oxygen as a by-product.

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