[JVIDEL]

OP makes a number of mistakes about the past.

For starters it wasn't Portuguese conquistadores who descended on South America 500 years ago but the Spanish. The Portuguese had more important operations in Asia at the time. It wasn't until the 17th that the Portuguese really started to exploit part of what today is known as Brazil, part because a chunk of Brazil used to be part of the Spanish Empire, not the Portuguese.

Of course we are not going back to hunter-gatherers, that's stupid on the face of it. Even after a massive collapse the first thing survivors will do is try to salvage whatever machinery they can find and start anew, first with crops and eventually industry. The "dark ages" weren't really dark, the north of the Roman Empire had always been underdeveloped which is why after the fall it continued to be a number of backwater kingdoms while Venice remained as a center of scientific and cultural development.

Also I don't get why OP comes with all these amazing sometimes insane technologies but rules out any attempts at geoengineering which rely on technology which we already have (but we don't deploy because the costs are still too high and the political motivation too low to support it).

And his understanding of the roots of racism is egregious, he completely ignores the vast political and economical reasons for recent and still enduring racism in many parts of the world. For example the Rwandan genocide background lies on which tribe had the upper hand during the colonial age and was thus wealthier and more powerful. It had next to nothing to do with religion or patriarchy.

[Gravityloss]

One problem with geoengineering is that it doesn't neatly negate effects of increased CO2 - it's hard to predict exactly what will happen. If we triple CO2 and install space glasses that refract sunlight so that it misses the earth, what will happen? Maybe the refraction and CO2's radiative forcing will cancel itself at some latitudes on some days. But in many other places and climate conditions, they won't.

For relative climate stability, by far the technically simplest and most straightforward way would be just to stop burning coal and stop projects like tar sands and oil shale.