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This year, the ozone hole over Antarctica reminds us of what could have been.

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In 1987, the world’s nations agreed to the Montreal Protocol, banning the use of chemicals that destroy ozone.

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The ozone layer began to recover.

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The ozone hole reaches an annual maximum size at the end of each southern winter.

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In recent years, these maximums have been getting slightly smaller.

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The ozone hole fluctuates with temperature – chemical destruction of ozone is enhanced when it’s colder.

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This year, the South Pole region was relatively cold, so the hole grew larger than in the previous two years.

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Scientists were able to compare this year’s ozone layer to models of what the ozone layer might have looked like without the Montreal Protocol.

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In spite of the colder temperatures, the ozone hole was still much smaller

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than it would have been, evidence of ongoing scientific success.