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This year, the ozone hole over Antarctica

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was far smaller than expected. In fact,

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it was the smallest since the ozone hole was discovered,

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the result of unusual weather patterns in the stratosphere over the South Pole.

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The ozone hole is caused by interactions between chlorine from chemicals called chlorofluorocarbons, or CFCs,

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and ozone. Although CFCs were banned

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by the Montreal Protocol in 1987, they last a long time in the atmosphere.

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Ozone depletion is enhanced when temperatures are colder.

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So the ozone hole fluctuates with the season, appearing during the colder,

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austral winter months and disappearing by summer.

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It reaches an annual maximum size in early southern spring, usually in October.

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This year, the polar vortex, a spiraling wind pattern over the South Pole,

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was unusually wonky. This warmed the stratosphere –

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the part of the atmosphere with the ozone layer – which significantly slowed down ozone depletion.

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Although the small ozone hole this year was caused by weather patterns,

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the ozone layer has shown overall signs of improvement as a result of the Montreal Protocol.

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NASA and NOAA have worked together to study

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study the ozone hole since its discovery.

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