Peter Ward’s new book “Flooded Earth” gives some scenarios. He tries to not be too pessimistic. The mass extinction chapter does not include our own.
We, as a species, are as tough as cockroaches. We can live at damned near any altitude, so we can escape some really bad air. We can live at damned near any latitude, in damned near any temperature.
We will probably pull through as a species, however bad it gets. That’s the good news. The bad news is, no birds make it. Too much sulfur fumes in the air, and their lungs suck it up. Our livestock doesn’t make it either, for the most part. Perhaps goats. They’re survivors too.
His optimistic scenario includes considerable efforts, from now going forward, at emissions reductions. But it also assumes a certain amount of geoengineering.
We can put particulate sulfur into the stratosphere, a megaton a year. On the scale of the earth, it’s not that much. The earth has on the order of 10^8 square miles surface area, so we’re looking at 10 kg per square mile per year fallout from that. It might be bearable, at least as a stopgap until we could get something better in place.
We can raise crops and char the waste foliage instead of just leaving it to rot and oxidize. If the charcoal thus generated is buried, plowed under, then that much CO2 has been removed from circulation. This can go on for quite a while before the soil becomes too much like coal to till.
His mid-range scenario has us ducking the sulfur-fuming ocean but taking all the other hits. Poor Holland—-3 million dead in one night, after record winter rains [not snow!] flood down the Rhine, only to collide with a winter storm surge pushing already higher seas inland.
Bangladesh has its own troubles, in the story. As land becomes ever scarcer, Bangladesh tries its luck with invading an India that has problems of its own, including nothing much to spare for conventional military forces. Nuclear weapons will stop any invasion.
This is the mid-range! This is what a “C” for today’s politicans, grading on the curve, brings.
Even an “A’ means that our daytime skies are always murky, washed out whitish no-fun, like Beijing is now.
The world we enjoy today is not going to be there for our descendants. The only remaining question is the scale of the tragedy we have brought down on ourselves. It’s a big question; there is a world of difference, literally, between losing this and that city, losing this and that nation, and losing civilization and being thrown back to multi-millennium epochs of subsistence agriculture in a world that is being poison gassed by sulfur-metabolizing bacteria.