cteristics is consistent: from 1980 through the early 1990s, the hole rapidly grew in size and depth. Since the mid-1990s, area and depth have roughly stabilized (see the Ozone Hole Watch website for annual averages). Year-to-year variations in area and depth are caused by variations in stratospheric temperature and circulation. Colder conditions result in a larger area and lower ozone values in the center of the hole.
An uneven seam in the contours of the data marks the location of the international date line. Ozone data are measured by polar-orbiting satellites that collect observations in a series of swaths over the course of the day; the passes are generally separated by about 90 minutes. Stratospheric circulation slowly shifts the contours of the ozone hole over the course of the day (like winds shift the location of clouds). The contours move little from any one swath to the next, but by the end of the day, the cumulative movement is apparent at the date line.
The ozone hole opened the world’s eyes to the global effects of human activity on the atmosphere. It turned out that chlorofluorocarbons (CFCs)—long-lived chemicals that had been used in refrigerators and aerosols sprays since the 1930s—had a dark side. In the layer of the atmosphere closest to Earth (the troposphere), CFCs circulated for decades without degrading or reacting with other chemicals. When they reached the stratosphere, however, their behavior changed. In the upper stratosphere (beyond the protection of the ozone layer), ultraviolet light caused CFCs to break apart, releasing chlorine, a very reactive atom that repeatedly catalyzes ozone destruction.
The global recognition of CFCs’ destructive potential led to the 1989 Montreal Protocol banning the production of ozone-depleting chemicals. Scientists estimate that about 80 percent of the chlorine (and bromine, which has a similar ozone-depleting effect) in the stratosphere over Antarctica today is from human, not natural, sources. Models suggest that the concentration of chlorine and other ozone-depleting substances in the stratosphere will not return to pre-1980 levels until the middle decades of this century. These same models predict that the Antarctic ozone layer will recover around 2040. On the other hand, because of the impact of greenhouse gas warming, the ozone layer over the tropics and mid-southern latitudes may not recover for more than a century, and perhaps not ever.
- Carlowicz, M. (2009). The World We Avoided by Protecting the Ozone Layer. NASA’s Earth Observatory Website.
- Carlowicz, M. (2009). Climate Change and Atmospheric Circulation Will Make for Uneven Ozone Recovery. NASA Portal Website.
- NASA. Ozone Hole Watch Website.
Antarctic Ozone Hole
By Rebecca Lindsey
September 17, 1979
- Growing Deltas in Atchafalaya Bay
- Global Temperatures
- Columbia Glacier, Alaska
- Coastline Change
- Shrinking Aral Sea
- Antarctic Ozone Hole
- Water Level in Lake Powell
- Antarctic Sea Ice
- Arctic Sea Ice
- Amazon Deforestation
- Mountaintop Mining, West Virginia
- Recovery at Mt. St. Helens
- Fire in Etosha National Park
- Green Seasons of Maine
- Drought Cycles in Australia
- Athabasca Oil Sands
- Burn Recovery in Yellowstone
- Severe Storms
- Seasons of the Indus River
- Urbanization of Dubai
- Seasons of Lake Tahoe
- Solar Activity
- Larsen-B Ice Shelf
- Mesopotamia Marshes
- Yellow River Delta
- El Niño, La Niña, and Rainfall
- Global Biosphere