Ozone depletion is the thinning of Earth's ozone layer. It is caused by human-made chemicals, mainly chlorofluorocarbons and halons. These compounds rise to the stratosphere, where ultraviolet radiation breaks them apart and releases chlorine and bromine atoms. A single chlorine atom can destroy thousands of ozone molecules before it leaves the stratosphere.

The result is more ultraviolet radiation reaching the surface. That increases skin cancer, cataracts, and immune suppression in humans. It harms crops, marine phytoplankton, and other organisms. The Antarctic ozone hole, discovered in 1985, shocked the world. At its worst, it covered an area larger than Antarctica.

The response was swift and effective. The 1987 Montreal Protocol phased out ozone-depleting chemicals. It is one of the most successful environmental treaties in history. The ozone layer is slowly recovering. Full recovery is expected by the 2060s. The lesson is that coordinated global action can solve environmental problems when the science is clear and the alternatives exist.

Main culprits

• Chlorofluorocarbons
• Halons
• Carbon tetrachloride
• Methyl chloroform
• Hydrochlorofluorocarbons