This is a manuscript for submission to Science, in its policy forum. Led by CCAFS but with a very large cast of co-authors (I'm just somewhere amongst the list: Authors: E. Wollenberg1,20*, M. Richards1,20, P. Smith17, 18†, P. Havlík9†, M. Obersteiner9†, F.N. Tubiello7†, M. Herold22†, P. Gerber7,22†, S. Carter22†, A. Reisinger14, D. van Vuuren15†, A. Dickie2†, H. Neufeldt8†, B.O. Sander13†, R. Wassmann13†, R. Sommer3†, J.E. Amonette16†, A. Falcucci7†, M. Herrero6†, C. Opio7†, R. Roman-Cuesta4,22†, E. Stehfest15, H. Westhoek15, I. Ortiz-Monasterio5†, T. Sapkota5†, M.C. Rufino4†, P.K. Thornton1,10, L. Verchot4†, P.C. West12†, J.-F. Soussana11, T. Baedeker21, M. Sadler21, S. Vermeulen1,19, B.M. Campbell1,3). Hence possibility for any changes to the manuscript at this stage are close to zero.