What effect on climate might a large volcano cause?

Question

Certainly in mankind's wake, from car exhaust, and industry to atmospheric weapons tests, there cannot be found anything equaling the changes inflicted by nature. One super-volcanic eruption, a recurrent visitor--- albeit an infrequent one--- could decimate higher life forms in half the continent in which it spewed from. But what about merely large volcanoes? What effect do they have on global climate. Do they not cool the planet somewhat, if only regionally? Do you think nature would laugh at us if it were human, would it snicker at our naive vanity? Would she blow her top and be rid of us?

Answer 1

Large volcanic eruptions can and have had a substantial effect on world weather. Best known is the eruption of Krakatoa, which resulted in reduced insolation and a distinct cool year or two.

Answer 2

The effects of the Tambora eruption were not permanent, but the eruption of a supervolcano might cover a large enough area and last long enough to cause permanent changes.

Tambora erupted in 1815 with a rating of seven on the Volcanic Explosivity Index, making it the largest eruption since the Lake Taupo eruption in AD 181.  The explosion was heard on Sumatra island (more than 2,000 km or 1,200 mi away). Heavy volcanic ash falls were observed as far away as Borneo, Sulawesi, Java and Maluku islands. The death toll was at least 71,000 people (perhaps the most deadly eruption in history), of whom 11,000–12,000 were killed directly by the eruption;  the often-cited figure of 92,000 people killed is believed to be an overestimate.

The eruption created global climate anomalies; 1816 became known as the Year Without a Summer because of the effect on North American and European weather. Agricultural crops failed and livestock died in much of the Northern Hemisphere, resulting in the worst famine of the 19th century.