Classifying the severity of the annual Antarctic ozone hole

Abstract Antarctic ozone hole summary metrics, such as area, have been long-established. However, such metrics must be examined alongside other years of observations to be meaningful: e.g. how severe is a 20 million km 2 ozone hole? Here, we address this gap by introducing a three-tiered ‘Minor’, ‘Moderate’, and ‘Major’ ozone hole classification system. Classifications are derived from existing metrics, tailored to unify varying datasets. The annual severity of the Antarctic ozone hole can now be summarised using a numerically-defined term, accessible to both scientific and general audiences. We use this system to demonstrate that Major ozone holes have recently become more frequent during the late spring, driving changes in circulation. When assessing CMIP6 simulations using this common framework, we find that Major and Moderate ozone holes will likely occur for several more decades. Minor ozone holes are unlikely to disappear before the year 2100, dependent on the future state of the climate.