Half the world's population could face a climate-induced food crisis by 2100, a new report by US scientists warns. Rapid warming is likely to reduce crop yields in the tropics and subtropics, according to Prof David Battisti of the University of Washington, Seattle. The most extreme summers of the last century will become the norm, he calculates, using 23 climate models. We must urgently create crops tolerant to heat and drought if we are to adapt in time, he writes in Science journal.