Decades of chemical pollution have damaged the ozone layer of the upper atmosphere that shields Earth from the harmful effects of the sun's ultraviolet rays, each summer eating a hole over the South Pole that expands to nearly the size of Antarctica.

But since 1996, when an international treaty banned the culprit chemical refrigerants and propellants (known as CFCs, or chlorofluorocarbons), the size of the seasonal tear has been shrinking—and scientists predict it may stop forming by the end of this century.

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