It is important that we understand how carbon cycles through the ecosystem for two reasons. The first of these reasons is that all organic material contains carbon. From the smallest vitamin molecule all the way up to the long polymer chains of proteins and DNA, carbon provides the basis of all organic compounds. The slide show on the next page will provide more information about the element carbon, including what types of structures and materials it creates in living (organic) things, and why it is able to do so.

The second reason why we need to understand the carbon cycle is because of its effect on the physical environment. Carbon, in the form of carbon dioxide, is released as a waste product of oxidation. This means that it is released during the combustion of fossil fuels, as well as the respiration of organisms. As we will see later, this can have a tremendous effect on our climate, since carbon dioxide is a greenhouse gas.

Carbon has two phases in the carbon cycle: gaseous and solid. Its gaseous phase is mostly in the form of carbon dioxide, but it can also be found in compounds like methane and carbon monoxide. Carbon dioxide can be taken out of the atmosphere by photosynthesis in plants, which convert the carbon into a solid form (sugars) that can be stored or put back into the air during respiration. It can also be removed from the atmosphere by being absorbed by water, where it becomes available to water plants for photosynthesis as well as being available to form compounds such as calcium carbonate (chalk) or to be put back into the atmosphere when the water gets warmer.

As we can see, the carbon cycle has reservoirs where it is stored as a solid. The diagram below shows some of these. In a cycle that has reached equilibrium, the rate at which carbon is removed from storage is equal to the amount that is being taken out of the atmosphere. The reason why many people are concerned about the carbon cycle is because mankind's intervention has caused this system to go grossly out of equilibrium. By burning fossil fuels, mankind has upset the balance of the cycle and greatly increased the rate at which carbon is returning to the gaseous phase. Is this a problem? In order to understand why it might be a problem, we need to understand more about the properties of carbon dioxide.


Source: Environmental Science Activities for the 21st Century. Trees and Carbon. Retrieved from http://esa21.kennesaw.edu/activities/trees-carbon/trees-carbon.pdf on October 20, 2010.