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In 2017, the ozone hole's annual maximum set a record -- the smallest it's been since 1988

This year, the ozone hole's annual maximum set a record -- the smallest it's been since 1988. The hole in the ozone layer is caused each year as ozone molecules react with chlorofluorocarbons (CFCs) in the atmosphere. The reactions occur at cold temperatures, so the hole reaches a maximum size each year at the end of southern winter, and then heals during the warmer summer months.