GENEVA, Switzerland, Oct. 29 (UPI) -- Scientists have spotted a near-record hole in the Antarctic ozone layer.
On Thursday, the World Meteorological Organization, the UN's weather agency, blamed the larger than usual hole on "colder than usual high-altitude (stratospheric) meteorological conditions."
Earlier this month, the hole measured 28.2 million square kilometers, or just over 10.9 million square miles, in size. It's the third largest ozone hole in history, after record-breaking holes in 2000 and 2006.
Despite the hole's expanded size, researchers say the ozone's continued recovery is not in jeopardy.
"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," said Geir Braathen, a senior scientist with WMO's Atmospheric and Environment Research Division.
Prior to the 1987 Montreal Protocol, ozone-destroying chemicals, chiefly chlorofluorocarbons (CFCs), were unregulated and widely used as a refrigerant and in aerosol cans. In the decades since, the ozone has slowly regenerated. But CFCs and other pollutants that are converted to ozone-eating chlorine at high altitudes can remain in the atmosphere for decades. Scientists say it may be another four or five decades before chlorine levels in the stratosphere return to normal levels.
The ozone is a thick belt of trioxygen, or O3, a highly reactive oxygen molecule helps protects the Earth from ultraviolet solar radiation. Some scientists believe it was key in enabling the development of life, as ultraviolet radiation damages DNA. O3 exposure can cause skin cancer in humans and is disruptive to single-celled organisms like phytoplankton, also known as microalgae.
Ozone depletion is typically most dramatic in the spring, when the stratosphere is coldest and the sun hits the polar region more directly, freeing chlorine radicals that eat away at the ozone.