This paper was accepted for publication in the journal Nature and the definitive published version is available at http://dx.doi.org/10.1038/nature16542
S.I.S. acknowledges the European Research Council (ERC) ‘DROUGHT-HEAT’ project funded by the European Community’s Seventh
Framework Programme (grant agreement FP7-IDEAS-ERC-617518). A.J.P. and M.G.D. were supported by the Australian Research Council (ARC) Centre of Excellence for Climate System Science (grant number CE110001028). M.G.D. was also supported by the ARC (grant number DE1501004).