Increased sensitivity of the Antarctic Ice Sheet to decreasing CO2 across the Mid-Pleistocene Transition

Abstract

Ice sheet model simulations show that continued warming due to rising greenhouse gas concentrations could lead to a rapid decline of the Antarctic Ice Sheet volume, resulting in increased global sea-level rise and coastal flooding. It has been challenging to test such models against palaeoclimate records owing to the lack of spatially continuous global climate forcing needed to drive transient (time-evolving) simulations. Here we use the Penn State University bihemispheric ice sheet–ice shelf model and realistic climate fields from the Community Earth System Model to simulate the evolution of global ice sheets over the past 3 million years. Our study identifies a nonlinear regime shift in the Antarctic Ice Sheet during the Mid-Pleistocene Transition, marked by an increased sensitivity of the ice sheet to declining atmospheric CO2 levels below ~240 ppmv. Additional experiments reveal that decreases in Antarctic temperatures and sea level after the Mid-Pleistocene Transition, combined with bedrock dynamics and changes in ice mass balance, accelerated Antarctic Ice Sheet growth during cold glacial intervals. Our discovery of past threshold behaviour in the Antarctic Ice Sheet highlights the potential for nonlinear responses of the ice sheet to future climate forcing and their implication for global sea-level change.