Life at the surface of the Earth is protected from the harmful ultraviolet (UV) radiation of the Sun by the stratospheric ozone layer. Over the last several decades, synthetic chemical compounds, such as chlorofluorocarbons (CFCs) and halons, were developed to provide a new generation of refrigerants, insulating foams, fire retardants, and other products. Unfortunately, after extensive use of these compounds, it was discovered that they remain inert in the atmosphere until they reach the stratosphere, where they break down into an active form that destroys ozone. One chlorine atom originating from a CFC molecule can destroy thousands of protective ozone molecules.
Satellite and ground-based observations confirm that losses of ozone are occurring seasonally, particularly in the springtime polar vortex of the Antarctic stratosphere, leading to what is known as the ozone "hole." Also of concern is the more moderate ozone depletion observed in mid-latitudes, where a large portion of the Earth's population resides. In the absence of changes in clouds or pollution, decreases in atmospheric ozone will increase ground-level UV radiation.
Analyses of data related to human health, Antarctic marine phytoplankton production, and careful field and laboratory experiments on the impacts of elevated UV exposure, indicate that increased UV radiation at the surface could have substantial negative impacts on human health, fish populations, and many terrestrial and marine ecosystems. In humans and other animals, impacts include immune system suppression, increased incidence of serious sunburn, cataracts and epidermal lesions, reduced vitamin D synthesis, and cancer. In plants, exposure to enhanced UV radiation can inhibit the essential process of photosynthesis. Increased UV radiation can also influence agricultural productivity and cause deterioration of synthetic materials such as plastics.
Due to global recognition of the implications of ozone depletion, emissions of many CFCs and halons are to be phased out over the next few years. Global observations of CFC concentrations in the atmosphere indicate that actions taken in response to the Montreal Protocol and its amendments are having the desired effect. Atmospheric measurements of trichloroethane, a short-lived ozone-depleting substance, indicate that its concentrations are actually declining.