Speaker
Description
Lower stratospheric ozone between 60S and 60N has continued to decline since 1998, in spite of the reduction of ozone-depleting substances as a result of the Montreal Protocol. Previous studies have shown that Chemistry Climate Models are not able to reproduce these negative trends in mid-latitudes, but the underlying reason for this discrepancy between models and observations remains unknown.
In this work, we reassess recent trends in lower stratospheric ozone using the new simulations from the Chemistry Climate Model Initiative 2022 (CCMI-2022). Historical simulations with observed sea surface temperatures (SSTs) and nudged QBO (ref-D1), and fully-coupled atmosphere-ocean simulations (ref-D2) are available spanning up to 2018, which allows a better analysis of the role of natural variability in recent ozone trends compared to previous studies.
CCMI-2022 models present a slight improvement in capturing lower stratospheric ozone trends in mid-latitudes compared to previous studies that used CCMI-1 and CCMVal models. The observational trend now lies inside the 90% confidence interval of the models’ trend distribution. However, the majority of the models are still not able to reproduce the observed pattern of negative trends in the tropics extending into mid-latitudes. The spread in the trends is dominated by intermodel differences, while natural variability from SSTs and QBO is not decisive in explaining the negative mid-latitude trends. The role of the different ozone transport representations is also explored.
