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.
Caveat: preprint, not yet peer reviewed.
I think when/if this get peer review, we hold some big sad party about how fk’d we are