On the Role of Stratospheric Ozone in shaping climate variability and change

• Applicant: Gabriel Chiodo, Ph.D.
• Subject Area: Atmospheric Science
• Term: from 2019 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 418516150

While the influence of stratospheric ozone on tropospheric climate has been extensively assessed in the Southern Hemisphere (SH) in the context of human-induced ozone depletion, large uncertainties remain for its effects in the Northern Hemisphere (NH). Arctic ozone exhibits small long-term trends, but large inter-annual variability. Stratospheric ozone in the NH has been commonly viewed as a passive constituent that responds to meteorological conditions. This view has been challenged by recent studies, which suggest that ozone in the NH high latitudes feeds back into the circulation, thereby affecting surface climate, although there is still controversy about the direction of causality in the ozone-circulation relationship. Stratospheric ozone influences may also extend to longer time-scales. Over the 21st century, Arctic ozone abundances are projected to exceed historical levels. This long-term trend may affect future climate projections through dynamical and radiative processes. Moreover, recent studies have documented that the inclusion of interactive ozone chemistry in climate change simulations can reduce (by up to 20%) the projected global warming: this is largely due to a feedback involving stratospheric water vapor. However, this feedback is model-dependent, and the reason for this uncertainty is unclear. In summary, the impact of ozone variability and trends on climate is subject to large uncertainties due to complex coupling between ozone, circulation and climate, which is not represented in the majority of climate models. This project aims to answer these questions by combining new observations and climate models, and assessing the role of the ozone layer in shaping climate variability and change, with emphasis on the NH. First, by using either interactive or prescribed ozone in two climate models, this project will assess the influence on the stratospheric circulation and surface climate, including its role as a source of predictability in the North Atlantic Oscillation (NAO), the dominant mode of climate variability in Europe. Second, it will quantify the impact of multi-decadal trends in ozone on the circulation. Third, it will explore the role of ozone in determining the global climate response to forcing agents, such as greenhouse-gases and solar irradiance. This project will provide novel insights into the role of ozone in the Earth System, through a process-based understanding of ozone-climate feedbacks on various timescales. It will assess the benefit of an accurate representation of ozone chemistry for seasonal to multi-decadal predictions, whilst proposing ways to improve the representation of this coupling in the future generation of models. Output from this project will help guiding future environmental policies, thus contributing to the Emmy-Noether program's mission to provide impactful research for the benefit of the society.

• DFG Programme: Independent Junior Research Groups
• International Connection: Switzerland, USA
• Cooperation Partners: Dr. William T. Ball (†); Professorin Dr. Daniela Domeisen; Dr. Jaga Richter; Professor Dr. Darryn W. Waugh