Chlorofluorocarbons are man-made chemicals that contain the elements chlorine, fluorine and carbon. They normally exist as liquids or gases, and when in the liquid state, they tend to be volatile. CFCs offer a number of benefits to human beings, but these are outweighed by the damage they do to the environment. Besides being greenhouse gases, and trapping heat in the atmosphere, they deplete ozone in the upper stratosphere, exposing humans to ultraviolet solar radiation.

In the early part of the 20th century, refrigerator manufacturers used such toxic chemicals as ammonia, methyl chloride and sulfur dioxide as refrigerants. Several fatal accidents prompted people to keep their refrigerators outside and manufacturers to search for a better refrigerant. They found one in 1928, when Thomas Midgley, Jr. and Charles Franklin Kettering invented Freon, which was the Dupont Co.'s trade name for chemicals otherwise known as chlorofluorocarbons. As a nontoxic and nonflammable alternative to the chemicals that were in use, Freon was considered a miracle compound up until the 1970s, when scientists discovered its effect on Earth's ozone layer.

The Montreal Protocol, which is a 1987 international agreement phasing out the use of CFCs, lists five applications for the compounds. Besides being effective refrigerants, CFCs make superior propellants for aerosol products and fire extinguishers. They are also useful as solvents for such applications as metal-working, dry cleaning and the manufacture of electronic equipment. Adding CFCs to ethylene oxide provides a safer sterilization product for hospitals and medical equipment manufacturers than ethylene oxide does by itself. Finally, CFCs are an important component of plastic foam products used in the building trades and for insulation of electric appliances.

Because they are such inert compounds, CFCs can persist in the atmosphere for 20 to 100 years. This gives them ample time to migrate up to the upper stratosphere, where the energetic sunlight at that altitude breaks them down and releases free chlorine. Chlorine isn't usually available in the atmosphere, and it acts as a catalyst to convert ozone, a compound with three oxygen atoms, to molecular oxygen. This reaction thins Earth's ozone layer and creates a seasonal "hole" over the Antarctic. Besides this, CFCs also contribute to the greenhouse effect, which results in the steady warming of the surface of the planet.

Although CFCs are benign in low concentrations, high concentrations can affect the heart, central nervous system, liver, kidneys and lungs, and extremely high levels can kill. Of more concern, however, are the possible consequences of ozone depletion and global warming. If the Antarctic ozone hole -- or the more recently discovered Arctic one -- expand over populated areas, people could experience increased instances of skin cancer and cataracts. Moreover, elevated levels of UVB radiation could affect the food supply. Global warming can lead to severe weather phenomena, such as storms, tornadoes, drought and unusually heavy precipitation, all of which have the potential to cause loss of life and property.