The Antarctic ozone hole, which yawns wide every spring in the Southern Hemisphere, reached its annual peak on September 12, 2011. It stretched to 10.05 million square miles, the ninth largest ozone hole on record, according to data from NASA and the National Oceanic and Atmospheric Administration (NOAA).
Above the South Pole, the ozone hole reached its deepest point of the season on October 9, tying this year for the 10th lowest in this 26-year record.
NASA and the NOAA use balloon-borne instruments, ground-based instruments and satellites to monitor the annual Antarctic ozone hole, global levels of ozone in the stratosphere and the human-made chemicals that contribute to ozone depletion.
Paul Newman, chief scientist for atmospheres at NASA’s Goddard Space Flight Center, said:
The colder than average temperatures in the stratosphere this year caused a larger than average ozone hole. 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 NASA video below describes how cold temperatures in the stratosphere — along with high levels of chlorine, bromine and a little sunlight — deplete ozone. Researchers predict the hole will return to 1980 levels by the year 2070, though the effects of climate change on the hole are uncertain.
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 causing other harmful effects.
James Butler, director of NOAA’s Global Monitoring Division, said:
The manmade chemicals known to destroy ozone are slowly declining because of international action, but there are still large amounts of these chemicals doing damage.
In the Antarctic spring (August and September) the sun begins rising again after several months of darkness, and polar-circling winds keep cold air trapped above the continent. Sunlight-sparked reactions involving ice clouds and human-made chemicals begin eating away at the ozone. Most years, the conditions for ozone depletion ease before early December when the seasonal hole closes.
Levels of most ozone-depleting chemicals in the atmosphere have been gradually declining as the result of the 1987 Montreal Protocol, an international treaty to protect the ozone layer. That international treaty caused the phase-out of ozone-depleting chemicals, which had been used widely in refrigeration, as solvents and in aerosol spray cans.
However, most of those chemicals remain in the atmosphere for decades. Global atmospheric computer models predict that stratospheric ozone could recover by midcentury, but the ozone hole in the Antarctic will likely persist one to two decades longer.
On October 28, NASA will launch a satellite carrying a new ozone-monitoring instrument that will provide more detailed daily, global ozone measurements than ever before to continue observing the ozone layer’s gradual recovery.
It will take a few years of averaging yearly lows in Antarctic ozone to see evidence of recovery in ozone levels because seasonal cycles and other variable natural factors — from the temperature of the atmosphere to the stability of atmospheric layers — can make ozone levels dip and soar from day to day and year to year.
Bottom line: According to data from NASA and the National Oceanic and Atmospheric Administration (NOAA), The Antarctic ozone hole reached its annual peak on September 12, 2011, stretching to 10.05 million square miles, the ninth largest ozone hole on record. Above the South Pole, the ozone hole reached its deepest point of the season on October 9, tying this year for the 10th lowest in this 26-year record.