A new JGR article by M. Chipperfield and co-authors highlights some of the modelling work that was done as part of the SPARC ‘Lifetimes of stratospheric ozone-depleting substances, their replacements, and related species’ Report (SPARC report no. 6). They diagnosed the lifetimes of long-lived source gases removed in the stratosphere using six 3D and one 2D model, which all used the same standard photochemical data. They investigate the effect of different lifetime definitions and find that different methods agree very well within the same model. Larger differences in lifetimes are calculated by different models, the main causes of which are variation in the simulated rates of ascent and horizontal mixing in the tropical mid-lower stratosphere. For 2100 conditions, the model circulation speeds generally increase, but a thicker ozone layer due to recovery and climate change reduces photolysis rates. These effects compensate so the net impact on modelled lifetimes is small. The abstract can be found here.