Some critical remarks on trend analysis of total ozone data

Summary The 45-year series of total ozone observations at Arosa, Switzerland, is used, after being homogenized, to study the significance of the trend in atmospheric ozone content which seems to exist during the past decade. Much larger trends than during the 1960s were observed at Arosa during certain periods in the past. Trend values are decreasing with increasing period length. Even trends observed in a world-wide network must be considered with caution as long as the network is not dense enough and not equally distributed over the globe.