While they will suffer serious casualties, the longer term effect of the radiation and dust cloud released will influence agriculture all over the world for some years after. Estimates of up to 1 billion dying world wide.
Doesn't a good sized volcanic eruption send an equal (or greater) volume of dust/ash into the atmosphere? We've had a number of those in the past few decades and while the weather was disrupted in some areas, there were no widespread crop failures. Is this another one of those alarmist predictions?