That is,the lower the ozone levels, the higher the solar UVR. Australia has high levels of solar UVR, due mainly to its geographical position. The southern hemisphere generally has higher levels of solar UVR than the northern hemisphere, because the Earth is approximately 1. The intensity of solar UVR is proportional to the square of the distance, so this means solar UVR levels are already 3.
Australians are predominantly descended from fair-skinned individuals used to European conditions, so exposure to these high levels of solar UVR has resulted in very high rates of skin cancer within the population.
Generally the higher the sun is in the sky, the shorter the path through the atmosphere and the higher the solar UVR levels. Although the CFC molecules are heavier than air, the air currents and mixing processes of the atmosphere carry them into the stratosphere. Once in the stratosphere, the CFC molecules are no longer shielded from ultraviolet radiation by the ozone layer.
Free chlorine atoms then react with ozone molecules, taking one oxygen atom to form chlorine monoxide and leaving an ordinary oxygen molecule. The destruction of ozone, also animated. If each chlorine atom released from a CFC molecule destroyed only one ozone molecule, CFCs would pose very little threat to the ozone layer. However, when a chlorine monoxide molecule encounters a free atom of oxygen, the oxygen atom breaks up the chlorine monoxide, stealing the oxygen atom and releasing the chlorine atom back into the stratosphere to destroy more ozone.
This reaction happens over and over again, allowing a single atom of chlorine to act as a catalyst, destroying many molecules of ozone. Fortunately, chlorine atoms do not remain in the stratosphere forever. When a free chlorine atom reacts with gases such as methane CH 4 , it is bound up into a molecule of hydrogen chloride HCl , which can be carried downward from the stratosphere into the troposphere, where it can be washed away by rain. Therefore, if humans stop putting CFCs and other ozone-destroying chemicals into the stratosphere, the ozone layer eventually may repair itself.
But what if the Montreal Protocol had not been successful? How would the major diseases have been affected by unchecked ozone depletion on this world-avoided? There are strong links between over-exposure to UV radiation and the development of the three most common forms of skin cancer malignant melanoma, basal cell carcinoma and squamous cell carcinoma. Even now, with the successful implementation of the Montreal Protocol, skin cancers are amongst the most common forms of cancer, especially in pale-skinned populations [WHO5].
Understanding how the prevalence of skin cancers would have increased with uncontrolled ozone depletion comes from computer models of the world avoided. These models combine our understanding of how ozone-depleting substances affect the ozone layer, of how changes in ozone affect UV radiation and of how UV radiation affects the incidence of skin cancers.
For example, one global model suggests that by the successful implementation of the Montreal Protocol will be preventing about two million skin cancers every year. A longer-term model focussed on health effects in people born in the USA between and This model estimates that protecting the ozone layer will have prevented a total of approximately million cases of skin cancers and 2. This includes million cases of malignant melanoma.
As yet there are no long-term world-avoided models for skin cancers globally. However, all the existing models lead to the same conclusion. Uncontrolled ozone depletion would have substantially increased the risk of skin cancers worldwide. Exposure to high levels of UV radiation leads to an increased risk of cataracts. Cataracts are responsible for around half of blindness world-wide, equivalent to about 20 million people in [WHO6]. At the moment a world-avoided model for cataracts is only available for the USA.
This model indicates that failure to control ozone depletion effectively would have led to almost 63 million additional cataract cases in people born in the USA between and As well as skin cancers and cataracts UV radiation can have other health effects.
These effects include the production of vitamin D in the skin that is beneficial to health. In the world we live in now, with effective protection of the ozone layer, there is a balance between the positive and negative effects of UV-B [WHO4].
Had we failed to protect the ozone layer that balance would have swung dramatically towards the negatives, above all the increased risks of skin cancer and cataracts.
By avoiding these negative consequences, the Montreal Protocol has made a major contribution to good health and well-being, one of the sustainable development goals adopted by all United Nations Member States in Over the course of evolution, animals, plants and microbes have developed mechanisms that allow them to cope with the variation in UV-B radiation that they experience in their normal environments, protected by the intact ozone layer.
This includes the plants and animals that we all rely on for our food. Crops need sunlight for photosynthesis, so cannot avoid exposure to UV-B. As with human health, there is a balance between the positive and negative effects of UVB on plants. Uncontrolled ozone depletion would have shifted this balance very much towards the negative.
Increased exposure to UV radiation can damage aquatic food chains and cause direct damage to crustaceans and fish eggs. As a result, uncontrolled ozone depletion would have threatened fisheries and other aquatic resources that make a significant contribution to global food supply.
These suggest that a 10 per cent reduction in stratospheric ozone might reduce plant production by about 6 per cent. If this relationship holds for the very severe ozone depletions expected in the world avoided then uncontrolled ozone depletion would have substantially reduced crop production globally.
Overall, while we cannot yet quantify the loss in food production, it is clear that without the Montreal Protocol ozone depletion would have made it progressively harder to deliver the sustainable development goal of zero hunger. Just as uncontrolled ozone depletion threatens food production, it also threatens plants, animals and microbes in natural ecosystems.
As with crops, wild plants are able to cope with current levels of UV-B radiation, but their growth can be reduced by large increases in UV-B. Most animals also seem to be able to avoid the damaging effects of current levels of UV-B radiation. If a media asset is downloadable, a download button appears in the corner of the media viewer.
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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. An element is a substance that cannot be broken down into a simpler format.
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The atmosphere protects life on earth by shielding it from incoming ultraviolet UV radiation, keeping the planet warm through insulation, and preventing extremes between day and night temperatures. The sun heats layers of the atmosphere causing it to convect driving air movement and weather patterns around the world.
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