[Svartalfiar]

reveals that concomitant volcanic activity and the associated climate and environmental changes were significant contributing factors in four of the five major mass extinctions in Earth history.

Wait.. So they're contradicting themselves here. If climate change on an extinction level was cause by volcanoes, and volcanoes like Iceland, Mt. St. Helens, Krakatoa, etc. all spew more CO2 each than humans have in our entire history, then how are human CO2 emissions causing climate change?

[JimSEA]

My reservation as to AGW are supported by the extreme conditions preceding mass extinctions and the historically higher CO2 levels experienced for most of earths history. One super volcano eruption could change everything for earth climates. Climates constantly change both in regional changes and worldwide variations. Geologic history is full of such variations. Look at the climatic variations that have been shown to affect human evolution.

[X Fretensis]

The volcanic activity they talk about at the end of the Cretaceous are not single volcanos like St Helens, Krakatoa,
or even Yellowstone size eruptions. They are talking about the outpouring of the Deccan Traps in Western India. These flood basalts covered 193000 square miles to a depth of 5660 feet or about 123000 cubic miles of basalt lava. The largest outpouring lasted about 30,000 years. The same is true at the end of the Permian. The Siberia Traps eruptions lasted less than 1 million years but poured 720000 cubic miles of lava onto Northern Siberia.