Climate catastrophe isn't so certain

[Anomalocaris]

That's because the volcanic activity that caused the Permian and Cretaceous extinctions covered the size of a continent.

Which continent? Neither the Ermensan nor the Siberian flood basalt eruptions near the end of Permean covered an entire continent.

The Deccan flood basalt eruption near the end of the cretaceous is not though to have been responsible for the end of cretaceous, nor did it cover an entire continent. An asteroid laid a layer of iridium right at the termination of cretaceous, and its impact is generally accepted to have caused the K-T extinction event that killed the dinosaurs.

The biggest known flood basalt eruption on earth in the last 500 million years in fact happened in the middle of cretaceous near Java. It was bigger than either Siberian trap or the Deccan trap, and it didn't cause a global extinction event.

The columbia rover flood basalt eruption was not as big as deccan trap, but it was certainly the size of a small continent, and it didn't cause any major extinction event.

So out of 4 big flood basalt events, only one is a strong candidate for having caused a global extinction.

Also you take one incident and you will get relatively negibile atmospheric change, but you have the volcanic activity you mentioned in a relatively short amount of time geologically speaking and there will be much more dramatic (say one to two degree C change) in the atmosphere.

Edit: also the millions of years was that Iceland volcanic system.

What is your evidence Iceland volcanic system is now more active than in millions of years? The icelandic volcanic system has probably been steadily active more or less at the same spot since when North America and Europe first separated about a hundred million years before end of cretaceous. Since end of cretaceous, the hawaiian hot spot probably erupted a good deal more lava than iceland, the total volume of Lava in the entire Hawaiian - Emperor sea mount chain considerably exceeds the volume of Iceland.

The columbia river flood basalt group seems to have emplaced a a amount of Lava comparable to the entire volume of Iceland in just a few enormous eruptions within 1 million years, and Icleand may have taken up to 150 million years to reach present size.