Climate catastrophe isn't so certain

[Polaris]

Atmospheric changes have a long-lasting affect. Krakatoa was the last but was actually almost a century past the worst of the volcanic eruption cycle. The worst is believed to have come from Iceland, the worst eruptions seen in several million years. These were not your typical volcanic eruptions you think about, but created mass magma fields which were much more devastating to the climate (it's these that are also believed to have lead to the end of the Cretaceous.

They ended near the beginning of the early 19th century...I had always assumed that the Industrial Revolution with its CO2 emissions had curtailed the affect of the SO2 until it was revealed in new data that there was a rebound effect from volcanic activity of this magnitude. Venus is the best example of this. It just does not end when you cut off the switch...that's why it's called a runaway greenhouse effect.

I think you really need to familarize yourself with some concrete numbers regarding volcanic eruption before sprouting off figures like "worst in several million years". Lakagígar eruption in Iceland in 1783 is a very modest eruption by the standards of what is seen on earth on a time scale of just several hundred years, much less millions of years. It eruption about 5 cubic miles of lava. It was beaten within 30 years in both volume of magma involved in eruption and SO2 emission by Tambora eruption in Indonesia. An earlier eruption off the coast of Eastern Australia iaround 1450 emitted 3-4 times more SO2 than the Lakagígar.

For a large resurgent caldera eruption of the sort that happen once every roughly 100,000 years or so, you will be looking at about 200 times more lava and SO2 than Lakagígar. Last eruption of this magnitude happened about 80,000 years. At least 3 more of them happened just within the borders of the lower 48 states within the last 1.3 million years.

For a truly large eruption like the sort that form large basalt igneous provinces, you will be looking at single eruptions spewing out about 20,000 times more lava and SO2 than Lakagígar. You find this type of eruption about 15 million years ago in Oregon.

The key is even the columbia river basalt province that featured multiple eruptions that may have individually been been up to 20,000 times the size of Lakagígar eruption in 1783 did not seem to cause a global extinction event.

So hardly can we blame a mere sliver of a volcano in Iceland for major climate change with fairly severe extinction implications.

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

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.