The biggest spike in the Phanerozoic was at the Permian extinction event 251m years ago and was caused by huge volcanic eruptions in Siberia that burned off coa

The biggest spike in the Phanerozoic was at the Permian extinction event 251m years ago and was caused by huge volcanic eruptions in Siberia that burned off coal deposits created in the Carboniferous era. See Figure 7 in this publication. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2007GB002985 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200...