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The year 1980 has often been used as a benchmark for the returnof Antarctic ozone to conditions assumed to be unaffected by emissions ofozone-depleting substances (ODSs), implying that anthropogenic ozonedepletion in Antarctica started around 1980. Here, the extent ofanthropogenically driven Antarctic ozone depletion prior to 1980 is examinedusing output from transient chemistry–climate model (CCM) simulations from 1960 to 2000 with prescribed changes of ozone-depleting substanceconcentrations in conjunction with observations. A regression model is usedto attribute CCM modelled and observed changes in Antarctic total columnozone to halogen-driven chemistry prior to 1980. Wintertime Antarctic ozoneis strongly affected by dynamical processes that vary in amplitude from yearto year and from model to model. However, when the dynamical and chemicalimpacts on ozone are separated, all models consistently show a long-term,halogen-induced negative trend in Antarctic ozone from 1960 to 1980. Theanthropogenically driven ozone loss from 1960 to 1980 ranges between26.4 ± 3.4 and 49.8 ± 6.2 % of the total anthropogenic ozonedepletion from 1960 to 2000. An even stronger ozone decline of 56.4 ± 6.8 %was estimated from ozone observations. This analysis of theobservations and simulations from 17 CCMs clarifies that while the return ofAntarctic ozone to 1980 values remains a valid milestone, achieving thatmilestone is not indicative of full recovery of the Antarctic ozone layerfrom the effects of ODSs

Antarctic ozone depletion between 1960 and 1980 in observations and chemistry–climate model simulations