What is the status of the ozone hole?

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What is the status of the ozone hole?
image of color-coded ozone hole on earth (as seen from space)
The South Pole from a NASA Ozone Mapping Spectrometer satellite. Blue and green colors indicate higher levels of ozone. Red and yellow colors show where there is less ozone (the ozone hole). Credit: NASA

The ozone hole is a region centered on the South Pole that is largely devoid of stratospheric ozone, a three-atom oxygen molecule that blocks harmful ultraviolet light from reaching the ground. The primary cause is man-made chlorofluorocarbons (CFCs), which were widely used as refrigerants for many years.

In the southern winter, the frigid conditions above Antarctica create a temperature gradient between the South Pole and the middle latitudes of the Southern Hemisphere. This gradient creates a belt of strong westerly stratospheric winds that encircle the polar region, preventing warm equatorial air from reaching it.

Extremely cold temperatures inside the strong winds help form unique clouds called Polar Stratospheric Clouds, or PSCs. In the southern winter, chemical reactions on the particles composing the PSCs remove the chlorine from compounds such as CFCs.

When the sun returns in the spring, its light splits the chlorine molecules into highly reactive chlorine atoms, which rapidly destroy ozone. Destruction is so extensive over the polar region in the southern spring — starting in October — that it is termed a “hole in the ozone layer.”
The size of the Antarctic ozone hole varies each year; in 2011, it was huge: about five times the size of California.

Representatives from 23 nations met in Montreal, Canada, in 1987 to address ozone depletion, which could be widely harmful to life. The Montreal Protocol and subsequent agreements have limited usage and production of CFCs, but their concentrations in the atmosphere have not fallen quickly. Because CFCs are extremely stable, they may remain in the atmosphere for nearly 100 years before decomposing.

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.