Reevaluation of Total‐Column Ozone Trends and of the Effective Radiative Forcing of Ozone‐Depleting Substances

Abstract

AbstractWe evaluate total‐column ozone trends using a piecewise linear regression approach and maximizing usage of five gridded total‐column ozone data sets. The new approach yields more consistent estimates of observed ozone loss during 1979–2000, when halocarbon concentrations were increasing, and consequently, using CMIP6 simulations, an increased effective radiative forcing estimate of ozone‐depleting substances with a substantially reduced uncertainty range versus an earlier evaluation. At more than 84% confidence, it is now larger than zero and compares more favorably with three previous evaluations. We furthermore find significant positive post‐1997 global‐ and Southern‐Hemisphere‐mean trends, respectively, in these five data sets. For the extrapolar region (S–N) and for the Northern Hemisphere, the assessment whether there is a positive trend is inconclusive and depends on which observational data set is included in the calculation.