Stratospheric cOmposition in a changing CLIMate: drivers and mechanisms

Progress towards more useful and accurate weather and climate predictions requires identifying predictability sources, as well as constraining the circulation response to climate change. While the stratosphere plays a key role in these aspects, efforts have largely focused on dynamical aspects, disregarding its chemical composition. Ozone and water vapour largely determine the stratospheric chemical composition, but also protect the biosphere from harmful UV radiation and contribute to the Greenhouse Effect. Despite advances in understanding the effects of Antarctic ozone depletion and recovery, impacts in Arctic and global stratosphere are not understood.This is due to limited understanding of the complex interactions between stratospheric composition and circulation and their poor representation in models. The SOCLIM project will provide new understanding of the role of stratospheric ozone and water vapour as (1) source of predictability on sub-seasonal to seasonal (S2S) time-scales, (2) drivers of atmospheric circulation and (3) radiative effects on global climate by using theory, observations and models. We will develop, for the first time, a chemistry-weather predictionsystem to assess impacts on predictability. Then, we will use two independent chemistry-climate and other IPCC models to quantify impacts on climate change, via the influence of stratospheric composition on the atmospheric circulation response. Lastly, we will determine its contribution to global warming in a range of scenarios from unabated emissions to mitigation via geo-engineering. SOCLIM will provide new process-based understanding of stratospheric composition feedbacks on regional and global climate for a range of timescales never explored before. If successful, it will contribute towards reducing uncertainty in weather and climate predictions, providing better constraints on the climatic impacts of anthropogenic emissions and delivering crucial information for future emission policies.