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In 1979
In 2003
What is it?
The antarctic ozone hole is an area of the antarctic stratosphere in which the recent (since about 1975) ozone levels have dropped to as low as 33% of their pre-1975 values. The ozone hole occurs during the antarctic spring, from September to early December, as strong westerly wind start to circulate around the continent and create an atmospheric container. In this container over 50% of the lower stratospheric ozone is destroyed.
Why is it important?
While the effective of the antarctic hole in decreasing the global ozone is relatively small, estimated at about 4% per decade, the hole has generated a great deal of interest because:
• The decrease in the ozone layer was predicted in the early 1980's to be roughly 7% over a sixty-year period. The sudden and, at that time unexplained, disappearance of over 50% of the ozone layer in a localized area of antarctica created quite a stir. Many were worried that ozone holes might start to appear over other areas of the globe but to date the only other significant, localized depletion is a much smaller ozone ''dimple''(R.Parson FAQ) ; observed during the arctic spring over the north pole.
• The antarctic hole is a warning that if conditions become more antarctic: cooler stratospheric temperatures, more stratospheric clouds, more active chlorine; then global ozone will decrease at a much greater pace. Some of the more popular senarios of global warming predict that these changes could occur in larger portions of the stratosphere.
• When the antarctic ozone hole does break-up, the ozone-depleted air drifts out into nearby areas. Decreases in the ozone level of up to 10% have been reported in New Zealand in the month following the break-up of the antarctic ozone hole [WMO 1991] [Atkinson et al.1989] [Roy et al. 1990]
What is so special about Antarctic conditions?
Polar regions get a much larger variation in sunlight than anywhere else, and during the 3 months of winter spend most of time in the dark without solar radiation. Temperatures hover around or below -80'C for much of the winter and the extremely low antarctic temperatures cause cloud formation in the relatively ''dry''stratosphere. These Polar Stratospheric Clouds (PSC's) are composed of ice crystals that provide the surface for a multitude of reactions, many of which speed the degredation of ozone molecules.

Source: Nasa