The ozone hole over the Antarctic this year is smaller than last year's but is still colossal. At 26 million square kilometres, it is about the size of North America.
The US National Oceanic and Atmospheric Administration said this week that observations suggested that the size of the annual hole, which forms over the Antarctic during its spring, has levelled off and will slowly decline in the coming years.
Researchers in New Zealand have warned, however, that the 2001 hole will probably persist longer. This, they say, will allow more ultraviolet (UV) radiation to reach the earth in the southern hemisphere.
Too much UV disturbs the growth of plant life. It increases the risk of cataracts and skin cancer in humans.
The hole is caused after the release over many years of chlorine compounds that drifted into the upper atmosphere. There, they react with sunlight over the Antarctic and Arctic to destroy ozone, a gas which absorbs UV radiation coming from the sun.
Last year's hole reached a record 30 million square kilometres.
Repeated depletions over the years have reduced the total ozone overhead by about 15 per cent in temperate parts of the southern hemisphere.
