Levels of global catastrophes: from mild to extinction
It is important to make a bridge between existential risks and other possible risks. If we say that existential risks are infinitely more important than other risks, we put them out of scope of policymakers (as they can’t work with infinities). We could reach them if we show x-risks as extreme cases of smaller risks. It could be done for most risks (with AI and accelerator's catastrophes are notable exceptions).
Smaller catastrophes play complex role in estimating probability of x-risks. A chain of smaller catastrophes may result in extinction, but one small catastrophe could postpone bigger risks (but it is not good solution). The following table presents different levels of global catastrophes depending of their size. Numbers are mostly arbitrary and are more like placeholders for future updates.
http://immortality-roadmap.com/degradlev.pdf
Most of the planet being uninhabitable means that there are still part of it that are habitable.
May be it will be highest mountains after 7000 meters, which will turn from - 50 to +30 C. Wiki said that threshold for water runway warming is 47 C (at 10 per cent high solar luminosity) and if it reached, the temperature will reach 900 C in new stable state. https://en.wikipedia.org/wiki/Future_of_the_Earth#Loss_of_oceans It means that very hot earth where small highlands will still be habitable - is still in unstable condition and could have much higher global warming.