The "ozone hole" over Antarctica this year has matched the record size of 11.4 million square miles, the U.N. weather agency said Friday.
The area of the so-called hole — a thinning in the ozone layer during the South Pole winter — is the same as in the record year of 2000, according to measurements by NASA, said Geir Braathen, ozone specialist at the Geneva-based World Meteorological Organization.
But Braathen said of greater concern is that the amount of ozone gas particles remaining in the hole is even lower than in 2000, a measurement called "the mass deficit."
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According to the European Space Agency, the loss has been 39.8 megatons, he said.
"In a way, this mass deficit is a better measure of how much ozone is depleted ... because it counts how many tons of ozone are lacking," Braathen told The Associated Press.
The thinner layer this year "will lead to more ultraviolet radiation on the ground," Braathen said.
Too much ultraviolet radiation can cause skin cancer and destroy tiny plants at the base of the food chain.
Thinning in the ozone layer — largely due to the chemical compounds chlorofluorocarbons, or CFCs, leaked from refrigerators, air conditioners and other devices — exposes Earth to harmful solar rays.
Under a 1997 international treaty, most countries have agreed to reduce use of the ozone-depleting chemicals, and scientists are predicting the ozone layer will eventually recover.
The hole has been forming in the extremely low temperatures that mark the end of Antarctic winter every year since the mid-1980s. Generally, the hole is biggest around late September.
This year's Antarctic winter has been very cold, the weather agency said earlier this month, which has led to greater ozone depletion.
Although there has been a decrease in ozone-depleting substances over the last few years, the atmosphere is still saturated with them, it said.
According to the agency, it will take until 2065 for the ozone layer to recover and the hole over the Antarctic to close. That estimate is 15 years longer than previous predictions by the agency.