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转折点的交叉，导致突然的、可能不可逆转的气候变化。对古气候记录、已建立的理论和模型的观察表明，由融化的冰川和海冰的淡水排放所驱动的北大西洋环流的变化可能会触发这种风险。最近的研究已经表明，北大西洋淡水过剩与北部高纬度地区冬季的暴风雨天气和欧洲更干燥、更温暖的夏季有关。反过来，冰融化和相关的淡水通量对北极和北大西洋的海洋和大气环流的热量分配高度敏感。因此，要预测北极和北大西洋热量和淡水分布的变化，需要详细了解冰、海洋和大气之间的反馈。不幸的是，目前的许多气候模型没有充分地捕捉到这些反馈，因此可能低估了快速气候变化的风险。考虑到北极目前变暖和融冰的速度，迫切需要评估北大西洋由此产生的海洋变化及其大规模气候后果。点心通过独特的观测、新的模型产品和工具的组合，填补了我们对北极和北大西洋地区冰-海-气反馈知识的空白。利用OSNAP和横跨北大西洋的快速系泊阵列的长期现场观测、NC Canari项目产生的高分辨率模拟和最先进的北极亚极涡旋状态估计(ASTE)，我们将首先描述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来开展敏感性和归因研究。这些研究将帮助我们评估推动热量和淡水分布变化的机制。此外，我们将通过将统计技术应用于ASTE、遥感观测、大气再分析数据和新的、大型集合、高分辨率CANAI模拟来评估气候反馈和影响。通过最终将结果整合到新的概念性模型分析中，我们将提供改进的北大西洋地区气候临界点的门槛估计。

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.