The initial, Nobel Prize winning discovery that ozone depleting chemicals called chlorofluorocarbons (CFCs) — carried in refrigerants, spray cans, foams and other substances — could damage the stratospheric layer that protects us from ultraviolet solar radiation (and thus, skin cancer) came in 1974. But it wasn’t until the sudden discovery of a vast seasonal ozone “hole” over Antarctica in 1985 that the world was shocked into action.

The so-called “hole” refers to a region of the stratosphere over Antarctica, between about 10 and 25 kilometers in altitude, where “the ozone gets destroyed completely,” explains Solomon, who conducted the new research with scientists from the National Center for Atmospheric Research and the University of Leeds in the UK. However, some ozone remains above and below this region, amounting to a 40 or 50 percent loss of atmospheric ozone overall in a very large area of air.

Ozone has been depleted in the stratosphere all across the globe, to be sure. But Antarctica in the spring (which is autumn in the northern hemisphere) presents uniquely conducive conditions for it to happen, as extremely cold polar stratospheric clouds provide a surface that enables the chemical reactions in which destructive forms of chlorine are created.