“no past event perfectly parallels” what is happening right now, owing to “the unprecedented rapidity of CO2 release currently taking place.” It turns out there just aren’t many ways to inject billions of tons of carbon into the air very quickly. The best explanation anyone has come up with for the end-Permian extinction is a massive burst of vulcanism in what’s now Siberia. But even this spectacular event, which created the formation known as the Siberian Traps, probably released, on an annual basis, less carbon than our cars and factories and power plants.
