Living on a river delta is indeed precarious and the probable results of climate change would progressively add to the effect of wind and current as the sea level start to flood the delta, presently home to 100 million people, a mass migration into central Asia could trigger all sorts of events.
How long until this occurs?
According to ClimateHotMap.org it is only about 3mm per annum.
It depends on what melts. Sea ice does not matter so much but if Greenland were to lose its 2km icesheet, sea levels could cover much of this map.
Population growth is the core disturbing trend that can only get more intense and unsolvable as religious belief and economic priorities define our politics.
Our brains quiver at the figures presented in the EU and the USA of debt mountains that appear increasingly insurmountable. We forget that we are barking at the moon, criticising the figures but ignoring what they are measuring. We care more about our economic scorecard, consider political alignment a sign of sanity, and criticise green thinkers and the Left as a form of irrationality.
Chinese economic growth and its growing domination on the economic stage say two things. One is that huge populations bestow economic muscle, and the other is that exploitation of need allows an export economy to outpace consumption. The problem that the West is threatened by is consumers believe their largess is a birth right. The wars of religious beliefs have been an expression of fear in our DNA, we have evolved a need for huge explosions in population and thus require economic growth to sustain consumption. The deterioration on our environments is more of a political issue than a scientific one. And for the fundamentalists who control much of the political thinking in America large families and environmental destruction are seen as religious duty.
These are all forces that could contribute to our eventual demise, and the sixth mass extinction. Humans are so many and so greedy. Nobody wants to surrender luxury in favour of their grandchildren. Nobody wants to give up on greed.
As our population keeps edging up and up, we seem unable to restrain ourselves.
Contraception is not the only solution required. It is a new economics and religious philosophy that allows all life to continue ad infinitum that is required. It is realising that our thinking has brought us to where we are, for example: threatened fish stocks and climate change will suddenly and drastically reduce populations and then our intellectual infrastructure is undone. War, famine and plagues do not save us from ourselves, we are but a blip on the geological time scale, but a blip that has changed the nature of nature and the meaning of survival.
Our inability to manage the relatively simple calculus of economics does not bode well for the more complex management required to prevent ecological doom. A nation may be able to default on sovereign debt, but we can not hide from extinctions of vital parts of the food chain.
A population constriction, when the population is forcibly reduced by war, disease or policy requires a different set of release valves than a growing economy. Instead of inflation vs interest rates, it is deflation sets in because decreasing numbers of people create demand, in other words nobody is there to buy things. It is hard enough to sell your products into a niche in competition, but when your customer base erodes, there is a sense of that being economically troubling.