RELATIONSHIP OF TREES TO ENERGY AND POLLUTION: During photosynthesis, trees remove carbon dioxide from the atmosphere and store it away in the tree's wood. This process is known as sequestration, and it reduces levels of carbon dioxide in the air. Trees also provide shade and lower air temperatures, reducing the amount of energy that buildings use and, therefore, the amount of work required -- and carbon dioxide released -- by power plants. Trees with denser wood, such as hawthorn trees, are most effective at removing carbon dioxide from the air. Other trees emit volatile organic compounds, which contribute to the formation of ozone. Ozone in the upper levels of Earth's atmosphere can have a protective effect, but particles of ozone in the air we breathe are considered pollutants.
THE CARBON CYCLE: The carbon cycle describes the movement of carbon, in its many forms, between the earth, atmosphere, oceans, and the animals, plants and bacteria that live there. For example, much of the carbon stored in trees and soils is released into the atmosphere when forests are cleared and cultivated. Sometimes this release happens very quickly, like when a forest fire burns. Sometimes it happens slowly, as dead plants decompose. When forests return to previously cleared land, trees draw carbon from the atmosphere and store it again in the plants and soil. If the global totals for photosynthesis (plants taking carbon dioxide from the air and using it for energy, giving off oxygen) and respiration (animals taking in oxygen and using it to make energy, giving off carbon dioxide) are not equal, carbon accumulates, either on land or in the atmosphere. The rates of photosynthesis and respiration are not known, and they're not measured well enough, but there does appear to be an imbalance, known as the "missing sink" of carbon. Yet the carbon cycle must be a closed system, which means there is a fixed amount of carbon; we just don't know where the missing carbon is yet. Understanding why there is an imbalance, and where it occurs, is critical to combating the threat of global warming.
The American Geophysical Union and the Institute for Operations Research and the Management Sciences contributed to the information contained in the TV portion of this report.