NASA reports the hole in ozone layer above the Antarctic remains significantly large.
The Antarctic ozone hole, which spreads wide every spring in the Southern Hemisphere, reached its annual peak on Sept. 12. It stretched to 10.05 million square miles, making it the the ninth-largest ozone hole on record.
NASA and the National Oceanographic and Atmospheric Administration use balloon-borne instruments, ground instruments and satellites to monitor the ozone layer, which helps protect Earth's surface from harmful ultraviolet radiation.
"The colder than average temperatures in the stratosphere this year caused a larger than average ozone hole," said Paul Newman, chief scientist for atmospheres at NASA's Goddard Space Flight Center in Greenbelt, Md.
"Even though it was relatively large, the area of this year's ozone hole was within the range we'd expect given the levels of manmade ozone-depleting chemicals that continue to persist in the atmosphere."
"The upper part of the atmosphere over the South Pole was colder than average this season and that cold air is one of the key ingredients for ozone destruction," said James Butler, director of NOAA's Global Monitoring Division in Boulder, Colo.
The ozone layer helps protect the planet's surface from harmful ultraviolet radiation. Ozone depletion results in more incoming radiation that can hit the surface, elevating the risk of skin cancer and other harmful effects.
Seasonal cycles and other natural variables such as temperature of the atmosphere to the stability of atmospheric layers can cause ozone levels to rise and fall significantly, daily and annually.