The Carbon Cycle

Carbon is an element necessary for life on Earth. The carbon cycle is the exchange of carbon and three major carbon stores, or “sinks” in nature (UDSA Forest Service 2009):

  • The oceans
  • The atmosphere
  • The terrestrial system

Global Atmospheric Carbon Cycle

This image shows the transfer of carbon between land, water and air.

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Terrestrial Carbon Cycle

Let us examine the basic concepts of the carbon cycle in plants.  Carbon Dioxide and sunlight is used during photosynthesis to produce carbohydrates (C), and Oxygen (O2) is released as a byproduct. 

Carbohydrates are then stored (or sequestered) in their biomass (leaves, stems, roots, etc.) as plants live and grow. Stored carbohydrates can be used as energy.  To use the energy, carbohydrates need to be broken down in respiration and the cycle’s end result is carbon being released back in to the air (USDA 2009).

The terrestrial system includes geological forms such as fossil fuel stores, which take hundreds of years to form, but also soils, plants and forests, which can store CO2 on a much quicker scale (CO2Logic).

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Basic facts about Carbon Dioxide (CO2):

We need a certain amount of CO2 in the atmosphere to breathe (0.04%)

We breathe out CO2

Plants absorb and store CO2 in their biomass

Plants and animals release CO2 when they expire

CO2 is released into our atmosphere when carbon-containing fossil fuels are burned (such as coal, oil, or natural gas)

Some unresolved issues about CO2 are that:

CO2 levels are rising exponentially due to human activities

CO2 serves as a greenhouse gas

Rise of CO2 levels can lead to melting of ice caps and glaciers which cause sea levels to rise as well

Temperatures are rising globally due to climate change caused by increased greenhouse gases

That restoring degraded land (Forest Preservation), replacing old forests with new, young-growth forests (Reforestation), and planting forest plantations (Afforestation) are good approaches to offset human CO2 emissions.


Carbon Sinks and Sources


Anthropogenic Carbon Cycle