Carbon Cycle

Source:http://www.esd.ornl.gov/iab/iab2-2.htm
The carbon cycle is a complex series of processes through which all of the carbon atoms on earth rotate. In one part of the cycle, plants absorb carbon dioxide (CO2) from the atmosphere and through photosynthesis incorporate the associated carbon atoms into sugars and other molecules necessary for growth. Plants use some of these sugars to generate energy in a process called respiration, which returns carbon atoms back to the atmosphere in the form of CO2. However, much of the carbon absorbed remains "locked up" in the plants' biomass until decomposition or fire releases it back to the atmosphere. As the graphic illustrates, carbon atoms are constantly being cycled through the earth's atmosphere by a number of physical, natural and industrial processes.
Although natural transfers of carbon dioxide are approximately 20 times greater than those due to human activity, they are in near balance, with the magnitude of carbon sources closely matching those of the sinks. The additional carbon resulting from human activity is the cause of the rise in atmospheric carbon dioxide concentration over the last 150 years.

For a video explanation of this cycle and how it can increase the greenhouse effect and contribute to global warming please go to the following link: http://video.search.yahoo.com/video/play?p=carbon+cycle&n=21&ei=utf-8&js=1&fr=yfp-t-501&tnr=20&vid=1073840370