Ozone layer depletion occurs mainly as a result of overuse of the chemicals, chlorofluorocarbons, or CFCs.  These were used for a variety of purposes, including air-conditioning fluids and fire suppressants, for the better part of the twentieth-century.  It was eventually discovered, though, that CFCs are largely responsible for the progress of stratospheric ozone depletion.

Because of this revelation, the international community established the Montreal Protocol in 1987.  This was a plan to phase out the use of ozone-depleting substances.  By this treaty, developed countries were to end production of such chemicals by 1996.  Developing countries could actually increase production until 1999, when they were to begin phasing them out.  This process was to be completed by 2010.  Even with this plan, the ozone layer is not expected to return to its normal state until the end of the 21st century.

With the depletion of the ozone layer comes more and more exposure to solar ultraviolet radiation, specifically UV-B rays.  Such exposure could dangerously increase ground-level radiation as well.  Increased radiation would greatly increase the risk of skin cancer.  Although it is still uncertain, it is estimated that a ten to fifteen percent ozone depletion would result in a fifteen to twenty percent increase in the occurrence of skin cancer, especially in fair skinned individuals.  This would mean 250,000 more cases per year.  However, this figure could be altered drastically due to a number of variables, including personal behavior such as sunscreen use.

Besides skin cancer, UV light causes cataracts.  Although not as drastically, the incidence of cataracts would rise with depletion. Finally, UV-B has been shown to exhibit immunosuppressive effects.  By creating a weakened immune system, and making it difficult to ward off disease, UV rays could possibly pose the greatest threat to humans.

The Ozone Hole Tour

Video from the EPA on the ozone