How humans healed the ozone layer

IN 1985 SCIENTISTS discovered an area over Antarctica where the layer of stratospheric ozone, which protects Earth from ultraviolet radiation, had become dangerously thin. That chlorine from chlorofluorocarbons (CFCs), chemicals used in refrigeration and products such as hairspray, could break down ozone molecules had been known for some time. What the “hole” showed was that in the peculiar conditions of the Antarctic this breakdown happened at an unexpected rate. Two years later world leaders signed the Montreal Protocol, a deal to do away with CFCs. In 2003 Kofi Annan, then secretary-general of the United Nations, called it “perhaps the single most successful international treaty to date”.