The ozone hole over the Antarctic region, about which we heard so much in the news in the 1980s, is alive and well. In fact, on September 7, 1996, the hole reached its largest size on record, extending over 10 million square miles (see first image above). In comparison, the North American continent has an area of 9.4 million square miles.
The size of the ozone hole above Antarctica is not constant. It varies from day to day and season to season. Compare, for instance, the October 7 image above with the September 7 image and note the change during a one-month period. In most years, the hole begins to form in August, reaches its greatest extent in September, and then shrinks. The ozone hole usually disappears by early December.
At any given time of the year, the ozone level varies significantly from location to location all over the globe, as illustrated by the third image above. Data from the TOMS spacecraft indicate that worldwide ozone in the upper atmosphere is gradually being depleted. Scientists expect ozone to reach a minimum in the next few years and to slowly recover over the next fifty years (see the discussion below on international efforts to limit the emission of ozone-destroying chemicals).
Ozone refers to oxygen molecules that consist of three oxygen atoms. Most of the oxygen in our atmosphere consists of two oxygen atoms. Ozone is relatively rare in our atmosphere. It is found at two different levels:
If all of the ozone in the Earth's upper atmosphere were brought down to sea level, spread out evenly over the entire Earth, and kept at a temperature of 32 degrees Fahrenheit, it would make a layer just three millimeters thick (about the thickness of three dimes stacked upon each other). Scientists say this layer of ozone is 300 Dobson units thick. The unit is named after George Dobson, an English scientist who began to systematically measure ozone from the ground in the 1920s.
In the above images, the Antarctic ozone hole is indicated by ozone values of 225 Dobson units or less, namely the areas shaded gray, pink, violet, and dark blue.
Scientists and policy makers in many countries are concerned about the destruction of ozone in the Earth's upper atmosphere and the potential damaging effects on life. Since the early 1970s, convincing evidence has been gathered to indicate that the major cause of this destruction is the release of industrial chemicals into the atmosphere, in particular the release of chlorine-containing chemicals such as chlorofluorocarbons, or CFCs. Chlorofluorocarbons are used in refrigeration, electronics, and insulating materials.
If humans stop releasing CFCs and other ozone-destroying chemicals, the ozone layer will repair itself. Eliminating the release of these chemicals requires that alternative technologies be developed and that these technologies be adopted by all nations. Much progress has been made in this regard. Furthermore, through the leadership of the United Nations, twenty-four states adopted the Montreal Protocol in 1987, according to which CFC production was to be cut to half of the 1986 levels by the year 1999. This protocol has been amended twice, and most ozone-destroying substances were to have been eliminated by 1996. Furthermore, the industrialized nations are to extend financial support to the developing nations to aid them in acquiring technologies that replace the use of ozone-destroying chemicals.
Check out other observations in the Observation of the Week Archive.