Here's the shape of a 21st century I don't want to see. Unfortunately it looks like it's the one we're going to get, unless we're very lucky.
Shorter version is: there will be much dying: even more so than during the worst conflicts of the 20th century. But rather than conventional wars ("nation vs nation") it'll be "us vs them", where "us" and "them" will be defined by whichever dehumanized enemy your network filter bubble points you at—Orwell was ahead of the game with the Two Minute Hate, something with which all of us who use social media are now uncomfortably, intimately, familiar.
People will be die in large numbers, but it will happen out of sight. It'll be "soft genocide" or "malign neglect", and the victims will be the climate change refugees who are kept out of sight by virtual walls. On land there may be fences and minefields and debatable ground dominated by gangs, and at sea there may be drone-patrolled waters where refugees can be encouraged to sink and drown out of sight of the denizens of their destination countries. This much we already see. But the exterminatory policies will continue at home in the destination zones as well, and that's the new innovation that is gradually coming online. There will be no death camps in this shiny new extermination system. Rather, death by starvation and exposure will be inflicted by the operation of deliberately broken social security systems (see also universal credit), deportation of anyone who can be portrayed as an un-citizen (the Windrush scandal is an early prototype of this mechanism), and removal of the right to use money (via electronic fund transfers, once cash is phased out) from those deemed undesirable by an extrapolation of today's Hostile Environment Policy and its equivalents.
You don't need to build concentration camps with barbed wire fences and guards if you can turn your entire society into a machine-mediated panopticon with automated penalties for non-compliance.
The Nazis had to leave their offices in order to round people up and brutalize or murder them. They had to travel to the Wannsee Conference to hammer out how to implement Generalplan Ost. Tomorrow's genocides will be decentralized and algorithmically tweaked, quite possibly executed without human intervention.
The people who buy into the idea of eugenics and racial supremacy—the alt-right and their fellow travellers—will sooner or later have to come to terms with the inevitability of anthropogenic climate change. Right now climate denialism is a touchstone of the American right, but the evidence is almost impossible to argue against right now and it's increasingly obvious that many of the people who espouse disbelief are faking it—virtue signalling on the hard right. Sooner or later they'll flip. When they do so, they will inevitably come to the sincere, deeply held belief that culling the bottom 50% to 90% of the planetary population will give them a shot at survival in the post-greenhouse world. (That's the "bottom 50-90%" as defined by white supremacists and neo-Nazis.) They'll justify their cull using the values we're seeing field-tested today racism, religious and anti-religious bigotry, nationalism, sexism, xenophobia, white supremacism. These are values with tested, proven appeal to [petty authoritarians](https://theauthoritarians.org who feel that their way of life is under threat.
Of course there will, as time goes on, be fewer and fewer members of the murdering class, as climate insecurity causes periodic crop collapses, automation reduces the need for human labour is required to keep things running, and capital accumulation outstrips labour value accumulmation (leading to increased wealth concentration and societal stratification and rigidity).
Who are the murderers? I'll give you a clue: they're the current ruling class and their descendants. A while ago Bruce Sterling described the 21st century as "old people, living in cities, who are afraid of the sky". I'm calling it "wealthy white people, living in cities, who are afraid of the rising seas (and the refugees they'll bring)".
As for what this soft genocide will look, right here at home in Brexitland ...
Forget barbed wire, concentration camps, gas chambers and gallows, and Hugo Boss uniforms. That's the 20th century pattern of centralized, industrialized genocide. In the 21st century deep-learning mediated AI era, we have the tools to inflict agile, decentralized genocide as a cloud service on our victims.
Think in terms of old age homes where robots curate the isolated elderlies (no low-paid immigrant workers needed) and fail to identify their terminal medical conditions until they're too advanced to treat. People fed by vertical farms where solar/battery powered robots attend to the individual plants (thank you, Elon Musk's younger brother), food delivered by self-driving vehicles from lights-out warehouses, an end to high street shopping and restaurants and a phasing out of cash money.
Think in terms of a great and terrible simplification of our society that cleans out all the niches the underclass (which by then will include the struggling middle class) survive within.
Think in terms of policing by ubiquitous surveillance and social scoring and behavior monitoring. Think in terms of punishment by "community service"—picking up litter on starvation wages (and I mean, wages calculated to induce death through slow starvation), where if you fail to comply your ability to purchase the essentials of life using e-cash will simply stop working. Prisons where extensively drug-resistant TB runs rife as a discipline on the community service peons (as in: if you receive the sanction of an actual prison sentence, they won't need to execute you: 50% will be dead within 6 months).
There's no state censor in this regime. Just a filter bubble imposed through your social media and email contacts that downranks anything remotely subversive and gently punishes you if you express an unconvenient opinion or show signs of noticing what's missing—the way you don't see people with dark skins or foreign accents any more, for example. The corporate social media will of course comply with state requirements for a safe and secure internet—if they want to stay in business, that is.
We're getting a glimpse of the way this future is shaped, thanks to Trump and Brexit and, to a lesser extent, China today. Trump has discovered that in times of insecurity, the spectacle of cruelty provides a shared common focus for his supporters. This is nothing new: the Romans were there millennia ago with their festivities at the Coliseum.
What's new is the speed and specificity with which the cruelty can be applied, and the ability to redirect it in a matter of hours—increasing the sense of insecurity, which in turn drives social conservativism and support for violent self-defense.
There is a feedback loop in play. It may already be established globally. And it's going to kill billions of us.