The largest threat of future rapid sea level rise is from the collapse of ice sheets due to instability and runaway ice loss. It could lead to more than 1 m of sea level rise by 2100, submerging land currently home to 100 million people and causing further destruction in higher-elevation coastal regions through enhanced storm and flood risk. Predicting the future possibility of such instabilities and the resulting plausible 'worst case' sea level change is critical for adequately planning coastal defences and long term infrastructures (e.g. 150 years planning horizon), especially those for which a rare event could have devastating consequences (e.g. nuclear power plants, the Thames barrier, transport networks). Yet, this is extremely challenging, because ice sheet instabilities have not occurred since we started observing ice sheets (the record is too short and ice sheets have been stable in the recent past) and they depend on poorly understood mechanisms (e.g. sliding of ice) that occur in inaccessible areas, such as under kilometres of ice. There is a solution: ice sheet instabilities have occurred in the geological past, for example in North America, 14,500 years ago (the time of mammoths and modern humans), producing ~7 m sea level rise in 340 years. Ancient ice sheets have left fingerprints of their activity and retreat on the landscape, which have been reconstructed in great detail in places such as the UK, Northern Europe and North America. These records of past ice sheet evolution provide an untapped goldmine of data that could be used to test and improve numerical models, informing future projections. This concept was demonstrated by DeConto and Pollard (2016), who projected Antarctic melting resulting in 15 m of sea level rise by 2500 based on constraints from 3 million years ago (the last time levels of atmospheric carbon dioxide were as high as today). However, there is an important missing piece to this work. In order to reliably translate knowledge from the past into confident future projections, the most important and complex source of uncertainty in modelling past ice sheets needs to be accounted for: the climate. This requires new statistical methods and a person with a unique combination of expertise in statistics, climate and ice sheet instabilities to lead their development. The ambition for this fellowship, is to make that person me . I will lead an interdisciplinary team of researchers to develop and apply new statistical and physically-based tools to accurately quantify uncertainties in past, present and future climate and ice sheet evolution, thus unlocking the key potential of geological records to constrain future ice sheet instability. This will produce the first robust projection of future ice sheet instability and the resulting sea level change. It will unite and grow the three leading strands of my research: mechanisms of ice sheet instability, climate change, and uncertainty quantification, establishing me as a world leader in using geological data to constrain ice sheet behaviour and future sea level change.