How did a treaty agreed in 1987 and eventually ratified by every nation shrink a hole in the atmosphere the size of North America back toward 1980 levels?

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The latest complete Antarctic season, in 2025, produced the fifth-smallest average ozone hole since 1992, while a return to 1980 ozone levels over Antarctica is projected for around 2066 if current policies remain in place. During the dark polar winter, extremely cold air is trapped inside the polar vortex and polar stratospheric clouds form. That is why the Antarctic ozone hole still opens each southern spring. NASA and NOAA reported that, from September 7 to October 13, the average area of the 2025 Antarctic ozone hole was 18.71 million square kilometres, the fifth-smallest average since 1992. The 2026 Antarctic ozone-hole season is only beginning as this article is written, so 2025 remains the latest complete season for comparison.