The other fairly plausible GCR that is discussed is biological. Black death likely killed 20% of the population (excluding the Americas, but not China or Africa, which we affected) in the middle ages. Many think that bioengineered pathogens or other threats could plausibly have similar effects now. Supervolcanos and asteroids are also on the list of potential GCRs, but we have better ideas about their frequency / probability.
The other fairly plausible GCR that is discussed is biological. Black death likely killed 20% of the population (excluding the Americas, but not China or Africa, which we affected) in the middle ages. Many think that bioengineered pathogens or other threats could plausibly have similar effects now. Supervolcanos and asteroids are also on the list of potential GCRs, but we have better ideas about their frequency / probability.
Of course, Toby’s book will discuss all of this—and it’s coming out soon!