Recovery and regression
Antarctic ozone hole should start healing, while Arctic hole getting worse
Posted October 14, 2011
Researchers at the National Oceanic and Atmospheric Administration (NOAA) announced late last month that the ozone hole that appears over Antarctica every spring in the Southern Hemisphere may start showing signs of recovery in the next decade.
That estimate is based on a new analysis of 25 years of data collected by NOAA scientists and colleagues at the Atmospheric Research Observatory (ARO) at the South Pole Station , which is managed by the National Science Foundation (NSF) .
The research team — led by Birgit Hassler of NOAA’s Earth System Research Laboratory and the Cooperative Institute for Research in Environmental Sciences in Boulder, Colo. — calculated that between 2017 and 2021 measurements should show that ozone is not being lost as quickly during the austral spring when the hole forms. The findings were published online in the Journal of Geophysical Research on Sept. 29.
The ozone layer in the Earth’s stratosphere, between about 10 and 30 kilometers above the ground, helps shield the planet from harmful ultraviolet radiation. Human-produced compounds known as chlorofluorocarbons, or CFCs, release ozone-destroying chemicals into the atmosphere that are responsible for the depletion.
Photo Credit: NASA
NASA images show the Arctic in 2010, at left, along with the severe ozone depletion, on right, in 2011.
Extreme cold, ice cloud formation in the stratosphere, and a pattern of rapidly circulating air, called the polar vortex, make the ozone layer over Antarctica much more vulnerable to CFC-destruction than almost anywhere else on the planet.
Scientists first discovered the hole in 1985. An international treaty, known as the Montreal Protocol , went into effect in 1989, banning many of the substances believed to be responsible for ozone depletion. Scientists predict the ozone hole will recover by the end of the century, as the chemicals finally dissipate.
NOAA scientists at ARO launch balloons to measure ozone vertically at least once a week year-round at the South Pole, and more frequently in the austral spring when the polar vortex forms. [See previous article: Fresh air.]
“This is not a total recovery. This will just be the first time that we can see the effects [of the ban],” Hassler told Boulder’s The Daily Camera newspaper in an interview.
But all is not good news for ozone recovery in the Earth’s atmosphere.
A NASA-led study published only three days later in the journal Nature on Oct. 2 has documented an unprecedented depletion of ozone above the Arctic last winter and spring, caused by an unusually prolonged period of extremely low temperatures in the stratosphere.
The amount of ozone destroyed in the Arctic in 2011 was comparable to that seen in some years in the Antarctic, according to the Nature paper. The process of ozone loss is similar in the polar regions, though warmer stratospheric conditions in the Arctic generally limit the extent of ozone depletion.
Although the total amount of Arctic ozone measured was much more than twice that typically seen in an Antarctic spring, the amount destroyed was comparable to that in some previous Antarctic ozone holes, according to a press release from NASA. This is because ozone levels at the beginning of Arctic winter are typically much greater than ozone values at the beginning of Antarctic winter.