However, the United States National Oceanic and Atmospheric Administration differed in its interpretation of the depth, saying that at the hole's deepest on a single day it stopped short of a record in 1993. Satellite images recorded by NASA show the hole stretching over towns of South America and less depleted air, outside its rim, brushing southern Tasmania. On September 10, as it spun slowly around the South Pole, the satellite images show levels of ozone normally seen over Australia in mid-summer. Scientists had predicted that the hole would reach its maximum at the turn of the century as CFCs and other ozone-depleting substances floated into the atmosphere. But they have warned that key developing countries are still to agree to forgo ozone-depleting substances and the greenhouse effect is also likely to lengthen the period of ozone damage.
Ozone depletion allows harmful ultraviolet radiation through the earth's atmosphere.
This layer protects people, animals and plants from excessive doses of UV, which can cause skin cancer. Since September 12, scientists have watched as the hole deepened and the ozone levels declined further. It is now beginning to subside, but analysts are pondering whether its scale this year was due to a normal annual variation of the weather, or linked to global warming. Dr Lehmann said that this year the colder air in the upper atmosphere had encouraged the polar vortex to form earlier and last longer than ever before. The possibility that greenhouse gases may also be devouring the ozone layer is likely to become an issue when environmental ministers meet in The Hague in November to discuss progress on implementing a UN framework convention on climate change.