Eh? There absolutely are plausible scenarios. For example, the Permian-Triassic extinction event was probably the result of runaway warming, perhaps as a result

Eh? There absolutely are plausible scenarios. For example, the Permian-Triassic extinction event was probably the result of runaway warming, perhaps as a result of the "clathrate gun": https://en.m.wikipedia.org/wiki/Clathrate_gun_hypothesis https://en.m.wikipedia.org/wiki/Clathrate_gun_hypothesis This event resulted in 96% of marine species dying and 70% of land animals dying. I don't think anyone thinks such an event is certain or likely, but it is surely a "remote possibility".