On the size of the Antarctic ozone hole

A primary estimate of the severity of the Antarctic ozone hole is its size. The size is calculated from the area contained by total column ozone values less than 220 Dobson Units (DU) during September–October. The 220‐DU value is used because it is lower than pre‐1980 observed ozone values, and because it is in the strong ozone gradient region. We quantitatively show that the ozone hole size is primarily sensitive to effective stratospheric chlorine trends, and secondarily to the year‐to‐year variations in temperatures near the edge of the polar vortex. Temperatures are in turn sensitive to variations in tropospheric planetary wave forcing of the Southern Hemisphere stratosphere. Currently the average hole size reaches approximately 25 million km2 each spring. Slow decreases of ozone depleting substances will only result in a decrease of about 1 million km2 by 2015. This slow size decrease will be obscured by large dynamically forced year‐to‐year variations of 4 million km2 (1σ), and possibly delayed by greenhouse gas cooling of the Antarctic stratosphere.