The geographical limits of countries are not barriers to either dispersal of gases in layers of atmosphere or depletion of gases. The causes for depletion may arise in any country. The effects in terms of depletion may arise in any other country. The effects in terms of ozone depletion need not be exactly above the country causing the depletion. It is now established that chloroflouro carbon CFC chemicals evolved from various refrigerants, coolants and propellants are the primary reasons for depletion of ozone.
CFC are a group of chlorine bearing gases of low specific gravity. They rise to stratosphere and mesosphere. A simplified description of the process involving CFCs is as follows:. The fact that most of the ozone depletion happens over Antarctica also requires some explanation. CFCs and other ozone depleting gases may come from anywhere, but it is in the south polar stratosphere where the conditions become most favourable for ozone destruction. The key factor is the presence of stratospheric clouds and the lack of atmospheric mixing between the south polar latitudes and air from elsewhere during the austral winter and early spring.
Normally there are no clouds in the stratosphere because there is so little water vapour present. As long as it remains dark, nothing happens; but when spring arrives, UV radiation from the Sun reaches the Antarctic Circle and starts the process of chlorine release and ozone destruction. This continues until the stratospheric clouds disappear due to warming of the south polar atmosphere as summer approaches.
By summertime, stratospheric air from lower latitudes is able to penetrate the polar latitudes, and thereby replenish the ozone layer above Antarctica. Hence, there is a seasonal cycle to the ozone hole over Antarctica with the lowest ozone levels recorded in late September and early October. The ozone layer protects life from harmful UV-B radiation which can cause cancer and stunt the growth of plants.
As UV radiation can penetrate into the surface of the ocean, marine organisms especially phytoplankton can also be damaged. If there was no ozone layer at all, photosynthesis by plants would be impaired and ecosystems could not function as they do today — so it is clearly in our interest to make sure we do not damage the ozone layer.
In an historic international agreement was signed the Montreal Protocol which came into force in and set deadlines for reducing and eliminating the production and use of ozone depleting substances. It also promotes research and development into finding ozone safe substitute chemicals for the uses to which CFCs, etc. It has since been ratified by countries, has been revised several times, and has been described as one of the most successful international treaties.
Through its various mechanisms, the treaty has brought down worldwide emissions of CFCs and other ozone depleting chemicals sharply. However, due to the long residence time of many of these gases in the atmosphere for example CFC resides in the atmosphere for approximately years , the ozone layer will not fully recover until around Use the text above, and information from any of the links listed, to write your own summary of the ozone hole.
Address the following questions in your summary document:. Suggest some reasons why annual CFC emission is not the only factor affecting October ozone levels. Using the information in both this section and Climate change: past and future , as well as any of the suggested links, write an essay answering this question: Why does tackling the problem of global warming present a bigger challenge to the international community than the problem of the ozone hole?
Skip to content Menu. Sizing up Antarctica The world turned upside down? Measuring the ice Going back in time Antarctica: The frozen continent Oceans, atmosphere, landscape A changing climate Seasonal change The climate today The climate of the past The climate of the future Rising seas Making waves Glaciation So you think you know about glaciers? What are glaciers? Temperatures decrease with altitude in the troposphere.
As warm air rises, it cools, falling back to Earth. This process, known as convection, means there are huge air movements that mix the troposphere very efficiently. The stratosphere, the next higher layer, extends about 6 to 31 miles or 10 to 50 kilometers above the Earth's surface. Learn more about the ozone layer. Stratospheric ozone is a naturally occurring gas that filters the sun's ultraviolet UV UV Ultraviolet radiation is a portion of the electromagnetic spectrum with wavelengths shorter than visible light.
UVA is not absorbed by ozone. UVB is mostly absorbed by ozone, although some reaches the Earth. UVC is completely absorbed by ozone and normal oxygen.
A diminished ozone layer allows more UV radiation to reach the Earth's surface. For people, overexposure to UV rays can lead to skin cancer, cataracts, and weakened immune systems. Increased UV can also lead to reduced crop yield and disruptions in the marine food chain.
Learn about the health and environmental effects of ozone layer depletion. Ozone molecules in the stratosphere are constantly being produced and destroyed by different types of UV radiation from the sun. Normally, the production and destruction is balanced, so the amount of ozone in the stratosphere at any given time is stable. However, scientists have discovered that certain chemicals react with UV radiation in the stratosphere, which causes them to break apart and release chlorine or bromine atoms.
These atoms, in turn, destroy ozone molecules. ODS include chlorofluorocarbons CFCs , hydrochlorofluorocarbons HCFCs , halons, methyl bromide, carbon tetrachloride, hydrobromofluorocarbons, chlorobromomethane, and methyl chloroform. ODS are generally very stable in the troposphere and only degrade under intense ultraviolet light in the stratosphere.
When they break down, they release chlorine or bromine atoms, which then deplete ozone. Since they are not destroyed in the lower atmosphere, CFCs drift into the upper atmosphere where, given suitable conditions, they break down ozone. Plants, animals, and all forms of life developed under a sky that shielded them from damaging and mutating radiation. Whether the molecule is helpful or harmful has nothing to do with the chemical makeup and everything to do with location.
This ozone is created by chemical reactions between air pollutants from vehicle exhaust, gasoline vapors, and other emissions. At ground level, high concentrations of ozone are toxic to people and plants. Aura MLS observations of unprecedented Arctic ozone loss.
Destruction of Arctic Ozone during the Winter.
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