DIMSUM: Drivers and impacts of North Atlantic heat and freshwater fluxes unsettling modern-day climate

气候变化带来的最致命的社会风险之一是气候临界点的跨越，从而导致突然的、可能不可逆转的气候变化。来自古气候记录、已确立的理论和模式的观测表明，由冰川和海冰融化释放的淡水所驱动的北大西洋环流变化可能引发这一风险。最近的研究已经表明，北大西洋的淡水过剩与北半球高纬度地区冬季的暴风雨天气和欧洲夏季更干燥、更温暖的天气有关。反过来，冰融化和相关的淡水通量对北极和北大西洋海洋和大气环流的热量分布高度敏感。因此，预测北极和北大西洋的热量和淡水分布的变化需要对冰、海洋和大气之间的反馈有详细的了解。不幸的是，目前的许多气候模式没有充分捕捉到这些反馈，因此可能潜在地低估了气候快速变化的风险。考虑到北极目前正在变暖和融冰的速度，迫切需要评估由此导致的北大西洋海洋变化及其大规模气候后果。DIMSUM通过独特的观测、新模式产品和工具组合，填补了我们在北极和北大西洋地区冰-海-大气反馈方面的知识空白。利用横跨北大西洋的OSNAP和RAPID系泊阵列的长期现场观测，NC CANARI项目中产生的高分辨率模拟和最先进的北极亚极地环流状态估计（ASTE），我们将首先表征北极和北大西洋地区的热量和淡水变化。我们将进一步利用ASTE模型的特殊伴随能力进行敏感性和归因研究。这些研究将帮助我们评估驱动热量和淡水分布变化的机制。此外，我们将通过应用统计技术对ASTE、遥感观测、大气再分析数据和新的、大集合、高分辨率CANARI模拟来评估气候反馈和影响。通过最终将结果整合到一个新的概念模型分析中，我们将为北大西洋地区的气候临界点提供改进的阈值估计。

Among the most fatal, societal risks of the changing climate is the crossing of climate tipping points, leading to an abrupt and potentially irreversible climate change. Observations from paleoclimate records, established theory, and models suggest that changes in North Atlantic ocean circulation, driven by freshwater discharges from melting glaciers and sea ice, may trigger this risk. Already, recent research has shown that excess freshwater in the North Atlantic is linked to stormier weather in the high northern latitudes in winter and drier, warmer European summers. The ice melt and the associated freshwater fluxes are, in turn, highly sensitive to the distribution of heat by the ocean and atmospheric circulations of the Arctic and North Atlantic. Thus, predicting changes in the distribution of heat and freshwater in the Arctic and the North Atlantic requires a detailed understanding of the feedbacks between the ice, the ocean, and the atmosphere. Unfortunately, many current climate models do not adequately capture these feedbacks and may hence, potentially, underestimate the risk of rapid climate change. Considering the rate at which the Arctic is currently warming and losing ice, there is an urgent need to assess the resulting ocean changes in the North Atlantic and their large-scale climatic consequences. DIMSUM approaches the gap in our knowledge around ice-ocean-atmosphere feedbacks in the Arctic and North Atlantic region with a unique combination of observations, new model products, and tools. Taking advantage of the long-term field observations from the OSNAP and RAPID mooring arrays across the North Atlantic, high resolution simulations produced within the NC CANARI project and the state-of-the-art Arctic Subpolar gyre sTate Estimate (ASTE), we will first characterise heat and freshwater changes in the Arctic and North Atlantic regions. We will further use the special adjoint capability of the ASTE model to carry out sensitivity and attributions studies. These studies will help us assess mechanisms that drive changes in the heat and freshwater distribution. In addition, we will evaluate climate feedbacks and impacts by applying statistical techniques to ASTE, remote sensing observations, atmospheric reanalysis data, and the new, large ensemble, high resolution CANARI simulations. By finally integrating the results into a new, conceptual model analysis, we will provide improved threshold estimates for climate tipping points in the North Atlantic sector.