Antarctic ozone hole expands to near-record size

The Antarctic ozone hole widened to one of its largest sizes on record earlier this month, the U.N.'s World Meteorological Organization (WMO) announced Thursday.

The hole's large size was due to unusually cold temperatures in the stratosphere, the level of the atmosphere where the ozone hole and ozone layer are located, the agency said.

"This shows us that the ozone hole problem is still with us and we need to remain vigilant. But there is no reason for undue alarm," Geir Braathen, a senior scientist in WMO's Atmospheric and Environment Research Division, said in a statement.

On Oct. 2, the hole reached its largest size of the year, some 10.9 million square miles, bigger than the size of Russia and Canada combined. The largest hole on record was in 2000, when it reached 11.1 million square miles, NASA said.

Located high up in the atmosphere, the ozone layer blocks potentially harmful ultraviolet energy from reaching the Earth's surface. If unblocked, this energy could lead to increased rates of skin cancer and other ailments in humans and animals.

The hole, discovered in the late 1970s, is a radical thinning of the ozone layer caused by the production of chlorofluorocarbons (CFCs), which at one time were used in refrigerators and aerosol sprays. The Montreal Protocol — an international treaty signed by 196 countries in the late 1980s — limited production of CFCs.

The hole fluctuates in size from year to year. It's typically at its largest after the cold of winter and smallest after summer. (The seasons are opposite in the Southern Hemisphere). The WMO stressed that temperatures in the Antarctic stratosphere vary each year, so some years the ozone hole is relatively small and other years relatively large.

The large size of the hole this year does not reverse the projected long-term recovery of the ozone layer in the coming decades. Full recovery of the ozone layer should occur by around 2070, according to the WMO.