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

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.