This work was carried out in the framework of the British Antarctic Survey GEACEP (Greenhouse to ice-house: Evolution of the Antarctic Cryosphere and Palaeoenvironment) programme. D.J.L. is funded by BAS and RCUK fellowships. G.L.F. is funded by a NERC research fellowship. E.J.S. is funded by a NERC studentship.

Author Contributions D.J.L. carried out the GCM and ice-sheet model simulations, except for the permanent El Niño GCM simulation, which was provided by P. Valdes at the University of Bristol, UK. A.M.H. contributed to setting up the Pliocene control and permanent El Niño GCM simulations. D.J.L., G.L.F. and A.M.H. were involved in the study design. E.J.S. devised parts of the ice-sheet model driver and experimental set-up. All authors discussed the results and commented on the manuscript.