There's a certain group of people that take the absolute worst predictions of climate science and just runs with it. Granted, there's a far larger group of people that think we'll be ok with business as usual. Neither is true.
I'm using BAU loosely here. I'm not referring to RCP 8.5. I have my own issues with the IPCC's estimates relying to much on direct air capture, but I don't think 5-6c is likely unless there's an unforseen feedback loop we haven't factored in.
I'd almost bet money on the eventual use of stratospheric sulfide injection to cool the planet. It's cheap enough that even a third world country could conceivably pay for it. We have no idea what the side effects will be, but it may well be worth the risk to avoid 3-4c of warming.
I work with climatologists in the development of AI models that improve over the climatology.
The amount of arable land that will be lost in the tropics is going to dramatically impact all countries around the Equator. Some areas simply will not support human life without air conditioning with a 2 degree increase in wet bulb temperature and +3C increase in extreme weather events.
Crop failures are linked to many historically extreme events. A 15%-30% in staple foods has _massive_ impacts in the poorest 20% of the population. In poor democracies it leads to people voting for demagogues and autocrats; in other places it's much worse.
The cascade of these events with ever increasing temperature is exponential.