Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon is referred to as the ozone hole.
The Earth's ozone layer protects all life from the sun's harmful radiation, but human activities have damaged this shield. Less protection from ultraviolet light will, over time, lead to higher skin cancer and cataract rates and crop damage.
Hydrofluorocarbons (HFCs), which have been used in recent years in increasing quantities as substitutes for CFCs, are also climatically very active and many are also extremely long-lived. In the journal Science an international team of researchers recommends that the most potent of these gases also be regulated. This could save the positive "side effect" of the Montreal Protocol for the global climate.
The Vienna Convention for the Protection of the Ozone Layer and its Montreal Protocol on Substances that Deplete the Ozone Layer are dedicated to the protection of the earth's ozone layer. With 196 parties, they are the most widely ratified treaties in United Nations history, and have, to date, enabled reductions of over 97% of all global consumption of controlled ozone depleting substances (measured in ODP tonnes).
In 1995, the United Nations named September 16 the International Day for the Protection of the Ozone Layer Exit EPA Disclaimer. To celebrate the success of the last 20 years, countries gathered in Montreal, Canada, from September 16-21, 2007, to recognize the broad coalition of governments, scientific researchers, and others who have developed smart, flexible, and innovative approaches to protecting human health and the global environment.
President Bush announced yesterday that the United States will eliminate most chemicals that damage the earth's ozone layer by the end of 1995 rather than by the year 2000.
The action was taken after a report last week that the risk of ozone depletion is much greater than previously recognized over much of the Northern Hemisphere, including Europe, Canada and New England.
In 1985 a team of British researchers first reported unusually low ozone levels over Halley Bay, Antarctica, which were caused by chemical reactions with chlorine and nitrogen compounds. Research was initiated that found CFCs to be largely responsible for the anomalously low levels during the polar springtime. This polar ozone depletion at lower stratospheric altitudes is what has been termed the "ozone hole."
Natural variations in ozone do occur, but recent levels of ozone loss over the poles and lower latitudes cannot be explained by natural variability alone. Manmade CFC compounds were developed in the early 1930s for a variety of industrial and commercial applications, but it was not until the 1970s that these and other chlorine-containing substances were suspected of having the potential to destroy atmospheric ozone.
Although ozone is found in small amounts at all altitudes in the atmosphere, due to chemical, dynamical, and radiative processes it is not evenly distributed. Approximately 90 percent of all ozone is contained in the region of the atmosphere known as the stratosphere, which lies between 15 and 50 km above the Earth's surface.
Stratospheric ozone depletion has been a major environmental issue of the last two decades--first as an interesting hypothesis following publication of the seminal paper by Molina and Rowland (1974), and then as a matter of urgency and intergovernmental action following the discovery of the ozone 'hole' in the Antarctic stratosphere in 1984 (Farman et al., 1985). The primary concern regarding ozone depletion is that a decrease in the total column content of ozone leads to an increase in the amount of UV-B radiation reaching the Earth's surface, with adverse effects on human health and ecosystems
The stratosphere, or "good" ozone layer extends upward from about 6 to 30 miles and protects life on Earth from the sun's harmful ultraviolet (UV) rays. This natural shield has been gradually depleted by man-made chemicals like chlorofluorocarbons (CFCs). A depleted ozone shield allows more UV radiation to reach the ground, leading to more cases of skin cancer, cataracts, and other health and environmental problems.