This factors in some feedback loops which most sudies to date have ignored. Note, that it excludes extra warming caused by all the additional water vapour in the air.
For context, studies suggest that the largest extinction event in Earth’s history (so far), the Late Permian Extinction Event, saw temperature rises of around 8°C.
I hope this paper gets peer reviewed - I want to believe it so bad as I agree with the general ideas (people ignoring feedback loops and other factors which impact the climate as well). Though I do wonder sometimes if there are any remaining negative feedback loops which we aren’t aware of, and might help as CO2 levels worsen. It certainly seems like we’re already aware of all negative loops (the ocean, plant life, rocks?, etc), so we’re really only missing the positive loops