I know that I might be walking into Kent territory here, but this recently came up on Stross blog... If find it fascinatingly and frighteningly real, so here goes:

"The Bay of Bengal is becoming anoxic, depleted of oxygen in the surface waters to the point where fish cannot survive.

Bangladesh's population are totally dependent for dietary protein on the catch from their local fisheries. About 85% of the population live along the coast.

That's nearly 165 million people who are going to be facing a permanent famine state within the next couple of years. 1-2 orders of magnitude more than the number who were caught up in those war-induced North African famines a decade or two ago that you might remember?

Now. What are the implications for a refugee crisis if the numbers on the move rise from ~10 million (population of Syrian/Libyan/Iraqi war zones) to ~100 million (because Bangladesh just imploded)?

Hint: when WS/CD uses the term "gigacide", she's not being overly alarmist.

Second hint: some of the nastier right-wing shitbags now clogging up the White House would like to solve the global sustainability problem by "allowing" maybe 1-3 billion people to die off. The scale is so large that gas chambers and death camps won't work: instead, they're thinking in terms of building walls around entire subcontinents, policed by killer drones, and letting heat emergencies and starvation do the job, sort of like the Ukraine famines of the 1920s/1930s only on a vastly larger scale."