Tropospherc Ozone Budgets: Past, present and future understanding.

The Tropospheric Ozone Assessment Report (TOAR) brings together experts from across the globe in an effort to provide the research community with an up-to-date scientific assessment of tropospheric ozone's global distribution and trends from the surface to the tropopause. In TOAR Budgets we have reviewed the scientific basis for our understanding of the physical and chemical controls on tropospheric ozone and it's evolution over the recent past and coming decades. In this presentation, we will present the key findings from TOAR Budgets. Analysis and evaluation of historic chemistry climate model simulations and recent model simulations from the CCMI MIP highlight that there exists large (±40 %) inter-model uncertainty on the role of stratospheric ozone on the tropospheric ozone budget, with particular disagreement at the regional scale (± 200 %) and on the magnitude of STE over time. These and other findings provide new challenges for using models to understand the processes controlling ozone and present a case for (i) new observational analyses to constrain current and near-future projections of the evolution of tropospheric ozone (ii) new coordinated modelling studies, which in doing so will help reduce uncertainty in our understanding of the processes that control this multifarious molecule.