The atmospheric concentration of CO 2 is currently over 400 ppm and is projected to exceed 500 ppm in the coming decades. A climatic era with similar levels of CO 2 is the Miocene which showed evidence of large scale variability, speed-up, and retreat of the Antarctic ice sheet (AIS). The AIS is the largest potential contributor to sea-level rise, as it will increase the sea-level by more than 55 meters if it melts completely. Previous research focused mainly on how CO 2 and insolation variations regulate an equilibrated AIS but the contribution of ice shelves as a key element remained unexplored. Here I study the influence of ice shelves on the Miocene AIS variability, using the Parallel Ice Sheet Model forced by climate model output with different levels of CO 2 . The AIS is modeled with ice shelves and without ice shelves. Not allowing for the ice shelves to grow resulted in a total disintegration of the West AIS and some part of the East AIS. A huge difference between PI conditions and high CO 2 (600ppm) Miocene conditions was simulated, as the ice volume was 92.5% smaller (equivalent to 46 meter sea level rise) in the latter case. The observed ice speed shows that when the ice shelves were removed, the AIS flows faster than when the ice shelves are untouched as seen in the ice volume. All runs without the ice shelves equilibrate faster than the runs with the ice shelves. The implication of this research is that when the ice shelves are removed, there is a speed-up and retreat of the AIS.