Agriculture faces its biggest challenge since Neolithic days in the way it adapts – or fails to adapt – to climate change. Africa and southeast Asia will be worst affected. In 20 years' time, their climate will be quite different from their climate today: crop varieties used now will yield dramatically less in the changed conditions. Famine and higher food prices will follow. To avert this disaster, we need to develop worldwide seed banks with detailed catalogues showing the traits of each variety and the resistance they have to heat, soil saturation or drought. Farmers can then begin to trial crops and prepare for the future. Seed banks are not the only answer to impending famine but they are an achievable first step.