Updated analysis of data from Palmer Station, Antarctica (64° S), and San Diego, California (32° N), confirms large effect of the Antarctic ozone hole on UV radiation.

The status of the stratospheric ozone layer is assessed by a panel of experts every 4 years. Reports prepared by this panel include a section with common questions and answers (Q&A) about ozone depletion and related matters. Since 2002, this Q&A supplement has featured a plot comparing historical and current ultraviolet (UV) Index data from Palmer Station, Antarctica (64° S), with measurements at San Diego, California (32° N), and Barrow, Alaska (79° N). The assumptions in generating these plots are discussed and an updated version is presented. The revised plot uses additional data up to the year 2020 and the methods used to create it are better defined and substantiated compared to those used for the legacy plot. Differences between the old and new UV Index values are small (typically < 5%). Both versions illustrate that the ozone hole has led to a large increase in the UV Index at Palmer Station. Between mid-September and mid-November, the maximum UV Index at this site has more than doubled compared to the pre-ozone-hole era (i.e., prior to 1980). When Palmer Station was below the ozone hole in December 1998, an "extreme" UV Index of 14 was observed, exceeding the highest UV Index of 12 ever measured at San Diego despite the city's subtropical latitude. Increases in the UV Index at Barrow and San Diego remain below 40% and 3%, respectively.