Modelling future changes in climate, ozone-depleting substances and ozone precursor emissions using the whole-atmosphere UM-UKCA model

Using the recently upgraded whole-atmosphere UM-UKCA chemistry-climate model, we investigate the atmospheric response to future changes in a) greenhouse gases under the RCP4.5 and 8.5 scenarios for climate change, b) ozone-depleting substances (ODS) and a recovery of the ozone layer and c) ozone precursor emissions and tropospheric oxidising capacity. In addition, we combine theses scenarios in order to explore the interactions between individual perturbations. Within this framework, the coupled stratosphere-troposphere system and whole-atmosphere chemistry allows us to study the impacts of changes in composition of the stratosphere on the troposphere and vice versa. Under a scenario for moderate climate change (RCP4.5), we find that by the year 2100: 1) the stratosphere significantly impacts the troposphere via changes in stratosphere-troposphere exchange (STE) but the chemical changes induced in the troposphere do not impact the stratosphere, 2) perturbations are linearly additive with regard to the total ozone column and tropospheric odd oxygen budget, 3) while the Brewer-Dobson circulation strengthens under climate change (with an increase in the tropical upward mass flux at 70hPa of 17%), this strengthening is offset by ozone recovery (which on its own leads to a decrease in the mass flux of 9%) and 4) the tropospheric ozone burden decreases by 10% given mitigation of its precursor emissions but this is offset by climate change and stratospheric ozone recovery (9% and 6% increases in the burden respectively).