Ozone occurs about 18 miles above the surface. Ozone is both caused by and provides protection from damaging ultraviolet energy emitted by the sun. The development of an atmospheric “ozone layer” allowed life to move out of the oceans and onto land.
The ozone hole occurs high over the continent of Antarctica. It is not actually a hole, but rather the appearance of very low values of ozone in the stratosphere. Typically, the Antarctic ozone hole has its largest area in early September and lowest values in late September to early October.
The Antarctic ozone hole varies in size each year, from nearly zero in 1980 to an area larger than North America in 2000. The amount of ozone in the atmosphere is now routinely measured from instruments flying on satellites.
The size of this year’s ozone hole reached a maximum size in September of about 7 million square miles. It is about the same size as the ozone hole in 2011 and 2012.
The ozone hole forms through the destruction of ozone over Antarctica. The winter atmosphere above that continent is very cold. The cold temperatures result in a temperature gradient between the South Pole and the Southern Hemisphere middle latitudes, which results in strong westerly stratospheric winds that encircle the South Pole region.
These strong winds prevent warm air from the equator from reaching these polar latitudes. These extremely cold temperatures inside the strong winds help to form unique types of clouds called polar stratospheric clouds, or PSCs.
PSCs begin to form during June, which is winter time at the South Pole. Chemicals on the surface of the particles composing PSCs result in chemical reactions that remove the chlorine from the atmospheric compounds. When the sun returns to the Antarctic stratosphere in the spring (our fall), sunlight splits the chlorine molecules into highly reactive chlorine atoms which rapidly deplete ozone. The depletion is so rapid that it has been termed a “hole in the ozone layer.”
Thanks to the Montreal Protocol’s phased global ban on chlorofluorocarbon (CFC) use and the natural decay of these chlorine compounds, the stratosphere will be CFC-free near the end of the 21st century. In their absence, the ozone layer will repair itself naturally.
The good news is that the size of this ozone hole is showing signs of shrinking. This recovery is a prime example of the power of employing science research in the shaping of public policy.
We would be wise to learn from this example to inform our collective approach to climate change.