text: Data accessibility. This article has no additional data. 
  Competing interests. We declare we have no competing interests. 
  Funding. This research received funding from the European Union Seventh Framework Programme FP7/2007– 
  2013 under grant agreement no. 603864 (HELIX: 
  ‘High-End cLimate Impacts and eXtremes’; www. 
  helixclimate.eu). The work of R.A.B., C.B., J.C., L.G., K.L. and K.R. was additionally supported by the Joint 
  UK BEIS/Defra Met Ofﬁce Hadley Centre Climate Programme (GA01101). 
  Acknowledgements. The authors thank Ed Pope, Jason Lowe and Dann Mitchell for advice and discussion, 
  Alissa Haward and Maria Pearce for project management and administration of HELIX, and two anonymous 
  reviewers whose comments substantially improved the paper. 