Projections of climate change rely on an adequate representation of UTLS processes and their feedbacks in climate models. In the Collaborative Research Centre TPChange this will be addressed by a combination of field measurements, laboratory studies, theoretical approaches, and multiscale numerical modelling. Based on an improved understanding of relevant processes at different scales, we will develop parameterisations to improve state-of-the-art climate models. Our goal is to specify the impact of UTLS processes on composition, dynamics and ultimately on future climate and climate variability.