Antarctic Ice Sheet tipping in the last 800,000 years warns of future ice loss

Ice loss from the Antarctic Ice Sheet could threaten coastal communities and the global economy if ice volume decreases by just a few percent. Observed changes in ice volume are limited to a few decades, and hard to interpret in the context of an ice sheet with response timescales reaching centuries to millennia. To gain a much longer-term perspective, we combine transient and equilibrium simulations of the Antarctic Ice Sheet response to glacial-interglacial warming and cooling cycles over the last 800,000 years. We find hysteresis between ice volume and climate forcing, caused by the crossing of tipping points as well as the long response time. Notably, West Antarctic Ice Sheet collapse contributes over 4 m sea level rise in equilibrium ice sheet states with little (0.25°C) or even no ocean warming above present. Given that climate projections indicate continued Southern Ocean warming, we will likely cross the threshold for West Antarctic Ice Sheet tipping in the coming decades (if not already). This supports other recent studies warning of substantial irreversible ice loss with little or no further climate warming.