GENEVA -- The ozone hole over the Antarctic is the deepest on record since scientists began measuring the seasonal phenomenon 15 years ago, United Nations experts said on Friday.
The World Meteorological Organization (WMO) said "near total destruction" of the ozone in some layers of the stratosphere had been observed since the middle of September, much earlier than in previous years.
More than 50-percent thinning, as compared against the norms set decades ago before the ozone hole was detected, is currently being recorded throughout most of the shifting Antarctic ozone hole, the Geneva-based agency said in a statement.
"The most important parameter is how deep the ozone hole is, how much has been lost. This is the deepest ever seen. There is a large area with more than 50-percent depletion," Dr Michael Proffitt, WMO's senior scientific officer, told Reuters.
"It's a record. This is the first time we have seen an ozone hole this large in terms of depth," the American added. "It has gone further than the previous record in 1998."
The Earth's protective layer shields the planet and humans from harmful ultraviolet radiation which can cause skin cancer and destroy tiny plants at the beginning of the food chain.
Two weeks ago, the hole was over the Argentinian city of Ushuaia, as well as Punta Arenas, Chile to the north of Ushuaia -- exposing populations to the ultraviolet radiation.
Chemicals -- including chlorine compounds used in refrigerants, aerosol sprays and solvents and bromine compounds used in firefighting halogens -- are blamed for causing depletion. Extremely low temperatures in the stratosphere during the Southern Hemisphere's winter set off the chemical processes.
From year to year, the intensity of the ozone hole varies in both area and depth, or variation from pre-ozone-hole norms set in the 1964-76 period.
"The size is not unusual now, it is the depth. The extent or area is now very near to normal values," Proffitt said.
Instruments carried by balloons have recorded near total destruction of the ozone layer over a limited altitude range for a number of years.
"Presently, ozone is more than 50 percent below the 1964-76 pre-ozone-hole norms throughout most of the ozone hole," the WMO said.
Since mid September, a network of 12 stations ringing the Antarctic have observed these "very low values" in a layer from 10 to 12.5 miles (15 to 20 kilometers), it said.
"In some cases, the loss appears to be total over this entire range. The near total destruction has occurred earlier than in previous years," it said.
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