[beat]

That's assuming there are mass migrations due to lack of food. Why can't they just adjust crops? We keep imagining agriculture as some sort of on-off switch - "We have crops, and then the global warming happens, and suddenly we no longer have crops". It doesn't work that way. We'll see production declines, maybe, but not sudden elimination of entire food supplies. And production declines can be dealt with intelligently - switching crops, altering harvest cycles, etc. Again, in the past century, humanity has handled a quadrupling of the population and wound up with more food surplus and lower food costs than at any point in history. And that's without whatever future the introduction of genetic engineering, internet-of-things, and other modern technologies bring to the table.