More Words, Deeper Hole

So an additional hundreds of millions of people somewhere between malnutrition and starvation in the next twenty years.

That reads to me like you think that's no big deal? I'm assuming I'm wrong. Either way, that would reverse the trends of the last 20 years where we've actually been, generally speaking, getting better at getting people out of malnutrition and starvation (although thirst and water born diseases on a 19th century scale might be worse)...

But to your other point. That is exactly what worries me about the potential situation in Western South America the most. The glaciers, at least in that part of the world, are continuing to shrink. The fresh water supply is largely dependent on that particular cycle, and having millions of previously 'well off' urban dwellers hitting problems that you normally see in less developed parts of the world isn't a good thing.

I'm not saying that there aren't technological fixes to problems like having your drinking water disappearing, just that we've not really had to deal with issues of this scale for advanced technological urban societies before. Historically, the climate removing your water supply has led to some amazing archaeological sites. I'm not sure that's an option today is it?