The United Nations' weather organisation says the "ozone hole" has formed again over the Antarctic and is showing signs of growing toward record size.
The so-called "hole," actually a thinner-than-normal area in the protective layer high up in the earth's atmosphere, has been reforming at the end of Antarctic winter every year since the mid-1980s.
"The ozone hole is developing quite rapidly this year, in a very similar manner to the record-breaking year 2000," said Ms Carine Richard-van Maele, spokeswoman of the World Meteorological Organisation.
The ozone hole now appears to be 10 per cent below the record size recorded in mid-September 2000.
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US scientists have said the hole briefly approached 11.5 million square miles in 2000.