Are scenario projections overly optimistic about future yield progress?

Willem-Jan van Zeist^*, Elke Stehfest, Jonathan C. Doelman, Hugo Valin, Katherine Calvin, Shinichiro Fujimori, Tomoko Hasegawa, Petr Havlik, Florian Humpenöder, Page Kyle, Hermann Lotze-Campen, Daniel Mason-D'Croz, Hans van Meijl, Alexander Popp, Timothy B. Sulser, Andrzej Tabeau, Willem Verhagen, Keith Wiebe