Any damage to the ozone layer allows more ultra-violet radiation (UV-B) from the sun to reach the earth’s surface. During the 1970s and 1980s scientists first detected an increasing depletion of the ozone layer. It was subsequently discovered that it this depletion was accompanied by an increase in UV-B radiation reaching the earth’s surface. It was also discovered that the levels of UV-B radiation were even higher at the poles, particularly the Antarctic region in the southern hemisphere. Some countries in the temperate climate regions that are exposed to this ozone layer damage include: Australia, New Zealand, South Africa, Argentina and Chile.

In the Antarctic region the ozone levels in the stratosphere were discovered to have dropped to as low as 33% of their pre-1975 values. This reduction in the ozone levels was termed a ‘hole’ in the ozone layer. It occurs primarily during the Antarctic spring, from September to early December, during which time a strong westerly wind circulates around the continent and creates an ‘atmospheric container’ in which over 50% of the stratospheric ozone is destroyed.

The effect of the Antarctic hole on global ozone levels is relatively small. However, it has generated great interest for the following reasons:

• In the 1980s, the likely decrease in ozone levels was predicted to be about 7% over a sixty year period. Yet the disappearance of 50% of the ozone in the Antarctic happened very rapidly and many scientists were worried that ozone holes might start to appear in other parts of the globe. However, to date the only other 'significant’ localized ozone depletion is a much smaller one observed during the Arctic spring over the north pole.
  
• The Arctic hole is a warning that if global conditions become more Antarctic (cooler stratospheric temperatures, more stratospheric clouds, more active chlorine) – then global ozone depletion will decrease at a much greater pace. Some of the more popular scenarios of global warming predict that these changes could occur in larger portions of the stratosphere.
  
• When the Antarctic ozone hole breaks up – the ozone depleted air drifts out to nearby areas. In New Zealand for example, decreases of up to 10% in ozone levels have been detected in the months following the break-up of the Antarctic hole.
  
  For more information on ozone layer depletion and the hole in the ozone layer follow the links below:
  UNEP ozone Secretariat
  World Meteorological Organisation Ozone Home Page
  US Environmental Protection Agency Ozone page
  Grid Arendal Ozone page
  Environment Canada Ozone Page