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How much ozone thinning has been measured in the Arctic during especially cold years?
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Ozone depletion
The Antarctic ozone hole reaches its maximum extent in October of each year. On October 7, 2021, when this image was captured, the Antarctic ozone hole spanned 24.8 million square km (9.6 million square miles).
In the Arctic, ozone thinning of as much as 40 percent has been measured during years when lower-stratospheric temperatures within the polar vortex are sufficiently low to trigger ozone-destruction processes similar to those observed in the Antarctic.1
While a polar winter vortex forms in the Northern Hemisphere, it is generally neither as strong nor as cold as the one that develops over the Antarctic. Consequently, although polar stratospheric clouds can form in the Arctic, they rarely persist long enough to cause the extensive, recurring ozone depletion seen in the Southern Hemisphere.1