The raw numbers make for daunting reading. One in 10 people out of the current global population of 7.4 billion already goes hungry. Crop yields that soared in the decades after the second world war are flatlining, and the UN predicts there will be 2.3 billion more mouths to feed by 2050. So how to keep people fed without trashing the planet? Some estimates put the contribution of the global food system to manmade greenhouse…