One of the longest-lived ozone holes on record is expected to close this Wednesday after several weeks of exposing wildlife and people in Antarctica to very high levels of ultraviolet radiation.听
The Montreal Protocol鈥檚 ban on gases, including CFCs, causing the destruction of the ozone layer have . But the swing this year is a reminder of how much the ozone layer can vary annually depending on polar conditions.
The hole emerges each year above Antarctica between August and October, and in September this year was larger than the continent itself. If it closes on Wednesday, as forecast by the Copernicus Atmosphere Monitoring Service (CAMS), it will be the second longest-lasting hole in more than 40 years, and just five days shorter-lived than the longest, in 2020. By comparison, 2019 had an unusually short-lived hole.
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鈥淚t is striking because it illustrates how important interannual variability is in addition to the slow, long-term recovery of the ozone layer thanks to the Montreal Protocol,鈥� says at the European Centre for Medium-Range Weather Forecasts.
The big drivers on a year-by-year basis are the stratospheric temperature and the strength of the winds at this altitude, known as the polar vortex. 2021 and 2020 have been characterised by very cold and strong polar vortices, resulting in strong ozone depletion, explains Inness.听
Smoke from Australia鈥檚 record-breaking bushfires reaching the stratosphere may also have contributed to 2020鈥檚 ozone hole, .
While this year鈥檚 hole has been long-lived, its maximum extent was only the ninth largest since 1979, at 22.75 million square kilometres. The largest was in 1998, at 24.32 million square kilometres.听
The high UV levels won鈥檛 have affected many people given Antarctica鈥檚 isolation. But if this year鈥檚 hole had extended over part of South America or Australia it would have affected many more people. 鈥淭his is not what we are seeing now, but it has happened in the past,鈥� says Inness.
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