We here ask support for a visiting researcher grant for Dr. Claire Waelbroeck, LSCE/CNRS, France for a 6 month stay at the University of Bergen, Dep. of Earth Science and Bjerknes Centre for Climate Research. The purpose is to build research collaborations based on key outcomes from two recently executed and successful ERC grants (Advanced Grant ACCLIMATE to Waelbroeck and Synergy Grant ice2ice to Jansen and Nisancioglu). Through close contact we have realised that key results already achieved can be further developed by being brought together and that we can bring the state-of-the- art in our knowledge of rapid climate change to an even higher level through such a collaboration, achievable through a half-year research stay in Norway. This collaborative model-data integration project has the potential to yield the answer to the question forming the title of the project. The forward proxy-modeling approach will enable us to use the climate model in an optimal way to simulate dynamically consistent Atlantic circulation regimes in best agreement with the paleoceanographic data.