The winter atmosphere above Antarctica is very cold. The cold temperatures result in a temperature gradient between the South Pole and the Southern Hemisphere middle latitudes.
These temperature gradients lead to a belt of strong westerly stratospheric winds that encircle the South Pole region. These strong winds prevent the transport of warm equatorial air to the polar latitudes.
The extremely cold temperatures confined inside the ring of strong winds help to form unique types of clouds called Polar Stratospheric Clouds, or PSC. In the southern hemisphere winter, chemical reactions on the particles composing PSCs remove the chlorine from atmospheric compounds such as man-made CFCs. When the sun returns to the Antarctic stratosphere in the spring, sunlight splits the chlorine molecules into highly reactive chlorine atoms and ozone is rapidly depleted. Destruction is so rapid over the South Pole region in the Southern Hemisphere springtime that it has been termed a “hole in the ozone layer,” and it is seen every October.
Ozone depletion now is widespread over Antarctica. The Antarctic ozone hole varies in size each year. Current measurements indicate the size of the ozone hole is about five times the size of California. This is anomalously large in comparison to recent years.
Representatives from 23 nations met in 1987 in Montreal to address concerns of ozone depletion by CFCs. The resulting Montreal Protocol, and subsequent international agreements have limited usage and production of CFCs. Although the use of these chemicals has declined, their concentrations in the atmosphere have not responded as quickly. This is because CFCs are very stable molecules and will stay in the atmosphere for nearly 100 years after their release before they decompose. Despite this waiting period, the Montreal Protocol successfully put a stop to the rapid ozone loss that was occurring and has set the stage for recovery of this important chemical.