Ozone Hole
Loss of ozone high up in the atmosphere occurs when there is more ozone being destroyed by CFCs than there is being created naturally. Scientists believed that ozone levels were quite stable until the late 1970s. Since then, a general decline in ozone levels has been seen. However, every year during September and October (the Southern Hemisphere spring), ozone loss is much greater over Antarctica, where an ozone hole forms.
The hole forms because the air above Antarctica is cut off from the rest of the world by a natural circulation of wind called the Polar Vortex. This prevents mixing in the atmosphere and so any ozone depletion is concentrated here. In addition, the very cold temperatures in the air high above Antarctica speed up the destruction of ozone. In summer (December and January), the ozone hole repairs itself, but forms again the following spring.
Recently, an ozone hole has been seen forming above the Arctic during the Northern Hemisphere springtime. Fortunately, this ozone hole is not as big as the one that forms over Antarctica, but more people live in the Northern Hemisphere who could be affected by it.
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