Huh, my first thought is that there also have been extinction events in the past. The Permian-Triassic (known as the great dying because, well, almost everything died) was largely caused by methanogenic bacteria (algae? I’m rusty), so yes, biologically induced climate change.
In our case, we have industry to help us along, so we did in decades what a sea full of microbes took millenia. Still, they killed nearly everything.