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

在南半球，在人为臭氧消耗的背景下，对平流层臭氧对对流层气候的影响进行了广泛的评估，但其对北方半球的影响仍存在很大的不确定性。北极臭氧的长期趋势不大，但年际变化很大。北半球的平流层臭氧通常被视为一种被动成分，对气象条件作出反应。这一观点受到了最近研究的挑战，这些研究表明，北半球高纬度地区的臭氧反馈到环流中，从而影响地表气候，尽管对于臭氧-环流关系的因果关系方向仍存在争议。平流层臭氧的影响也可能延伸到更长的时间尺度。预计在21世纪，北极臭氧丰度将超过历史水平。这一长期趋势可能通过动力和辐射过程影响未来的气候预测。此外，最近的研究表明，在气候变化模拟中纳入相互作用的臭氧化学可以减少（高达20%）预计的全球变暖：这主要是由于涉及平流层水蒸气的反馈。然而，这种反馈是依赖于模型的，这种不确定性的原因尚不清楚。总之，由于臭氧、环流和气候之间的复杂耦合，臭氧变异性和趋势对气候的影响存在很大的不确定性，而大多数气候模型都没有体现这一点。该项目旨在通过结合新的观测结果和气候模型，评估臭氧层在形成气候变异性和变化方面的作用，特别是北半球，来回答这些问题。首先，通过在两个气候模型中使用交互式或规定的臭氧，该项目将评估对平流层环流和地面气候的影响，包括其作为北大西洋涛动可预测性来源的作用，北大西洋涛动是欧洲气候变异的主要模式。第二，它将量化臭氧数十年趋势对环流的影响。第三，它将探讨臭氧在确定全球气候对温室气体和太阳辐照度等强迫因素的反应方面的作用。该项目将通过对不同时间尺度上臭氧-气候反馈的过程性理解，为臭氧在地球系统中的作用提供新的见解。它将评估准确表示臭氧化学对季节性到数十年期预测的好处，同时提出如何在未来一代模型中改进这种耦合的表示。该项目的成果将有助于指导未来的环境政策，从而有助于实现Emmy-Noether项目的使命，即为社会利益提供有影响力的研究。

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.