The hole in the ozone layer over Antarctica will expand this year to its second-highest recorded level, the U.N. weather agency said Friday.
The ozone hole will reach at least a size of 27.9 million square kilometers (10.8 million square miles), as recorded in 2003, said Geir Braathen, ozone specialist at the World Meteorological Organization.
It will, however, fall short of the record set in 2000 of 28.5 million square kilometers (11 million square miles).
"It is very close if not equal to the ozone hole size of 2003," Braathen said, adding that its growth in coming days could see it surpass that level.
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.
Braathen said the Antarctic winter has been very cold this year, which has lead to stronger ozone depletion. The extremely low temperatures together with strong wind and sunshine around the South Pole make perfect conditions for the ozone layer's thinning, he said.
Braathen noted that although there has been a decrease in ozone-depleting substances, the atmosphere was still saturated with them.
"Even if chlorine and bromine are coming down, there is still for many years to come enough of these substances to deplete all the ozone in this height range," he said. "We will for the next couple of decades expect to see recurring ozone holes of the size that we see now."
WMO scientists said in August it would take until 2065 for the ozone layer to recover and the hole over the Antarctic to close. That estimate was 15 years longer than previous predictions by the agency.
Thinning in the ozone layer — largely due to the chemical compounds chlorofluorocarbons, or CFCs, leaked from refrigerators, air conditioners and other devices — exposes the Earth to harmful solar rays.
Too much ultraviolet radiation can cause skin cancer and destroy tiny plants at the beginning of the food chain. Less of these chemicals are used every year after 180 countries in 1997 committed to reducing CFCs under an international treaty.