The thinning of the ozone layer in the stratosphere, caused mainly by man-made chemicals, which reduces the Earth's shield against harmful ultraviolet radiation.
- The ozone layer lies in the stratosphere (roughly 15 to 35 km up) and absorbs most of the Sun's harmful ultraviolet-B radiation.
- The main culprits are chlorofluorocarbons (CFCs), used in refrigerants, aerosols, and foams; their chlorine atoms break ozone molecules.
- The "ozone hole" is a seasonal severe thinning over Antarctica, first reported in the mid-1980s.
- Increased ultraviolet exposure raises rates of skin cancer, cataracts, and damage to crops and marine life.
- The Montreal Protocol (1987) phases out ozone-depleting substances and is regarded as the most successful environmental treaty; the Kigali Amendment (2016) adds phasedown of hydrofluorocarbons (HFCs), which are also potent greenhouse gases.
Ozone depletion, CFCs, the Montreal Protocol, and the distinction from global warming are standard environment facts that recur in statement-based questions.
Ozone depletion (stratospheric, caused by CFCs, allows harmful UV in) is distinct from the greenhouse effect (heat trapping, caused by CO2 and methane). Stratospheric ozone shields life; ground-level ozone is a pollutant.
CFCs thin the stratospheric ozone layer, letting in harmful UV; addressed by the Montreal Protocol (1987).