Sea level rise due to instable ice sheets in Greenland and Antarctica: The future shape of our coasts will be characterised in the long term by rising sea levels due to global warming. Ice mass loss in Greenland and Antarctica is already responsible for around a third of the global average sea level rise of 4.0 cm per decade (Horwath et al. 2022).  And the contribution of the ice sheets is continuing to increase (Cazenave et al. 2018). This chapter addresses the following questions: What are the known instabilities of ice sheets in Antarctica and Greenland? What thresholds of global mean warming exist that, if exceeded, make the decline of the ice sheets irreversible? What is the probability that threshold values have already been exceeded with the global warming to date?