Long chemistry–climate runs are used to investigate the changes that sudden stratospheric warmings (extreme and fast disruptions of the wintertime stratospheric polar vortex) induce on Arctic ozone. Ozone increases rapidly during the onset of the events, driven by deep changes in the stratospheric transport circulation. These anomalies decay slowly, particularly in the lower stratosphere where they can last up to 2 months. Irreversible mixing makes an important contribution to this behavior.