JMA-PSOS

1. Climate will worsen and billions will be displaced and famished as ocean major currents and melting polar caps severely alter the shorelines. The global economy will move in reverse, order will descend into chaos and most states will collapse into a new global dark age of privateers and lawlessness. Nuclear war and fallout will be very likely. A coup de grâce will be delivered by an extinction-level meteor or two.
2. Counter-intuitively, as humanity tech/medical progress advances, the gene pool will keep getting diluted with more knuckle-draggers and subsistent survivors per capita who will procreate unimpeded by their general stupidity or predictably boring lives and much faster than the dwindling creative minority. Population will quickly grow towards resource unsustainability and will collapse precipitously. Pandemics ought to untilt the imbalance somewhat, but most likely it won't be enough. Humanity will pollute and slowly kill Gaia from both ends: the psychopathic autocrats and theocrats at one end (e.g. China, Russia, Iran, Saudi Arabia) and the Dunning-Kruger populist "democracies" at the other (e.g. USA, UK, Canada, Oz, NZ first, and shortly after the increasingly more volatile Western democracies as they spiral toward self-destruction from over-exuberant and misguided fervour at both ends of the political spectrum).