Ozone is toxic to humans if inhaled, but high up in the atmosphere, it shields us from harmful solar radiation. Chemical compounds called chlorofluorocarbons ("CFCs," for short) break down ozone. CFCs were used widely as propellants in aersol cans starting in the 1930s. But by the 1980s, it became clear these chemicals were contributing to an increasingly thin ozone layer over the Antarctic. In 1987, the Montreal Protocol, an international agreement to combat ozone depletion, was agreed to by a large coalition of nations, and CFC use was phased out all over the globe. The protocol has since been ratified by every U.N. member nation.
If there was no international action to reduce the use of ozone-eating chemicals, NASA has estimated the Earth would have lost 67 percent of its ozone layer by 2065 (compared with 1970s levels). At those low-ozone levels, "the intensity of U.V. radiation at Earth's surface doubles," NASA's Earth Observatory explains. "Skin cancer rates would soar."
NASA illustrates how the Antarctic ozone hole formed in the animation above. CFCs are released into the atmosphere at all latitudes, and atmospheric winds push those chemicals down to the South Pole, where they become trapped in polar-vortex winds. Stuck over the South Pole, CFCs began eating away at the ozone layer there.