A volcanic eruption by itself can trigger some cooling by reflecting a bunch of sunlight off the dust/gas that's in the volcano emissions. Those cooling periods last a couple years.

In terms of having a longer cooling period with volcanoes, what happened historically was you had several volcanic eruptions in a row that caused something else to happen entirely -- sea ice restoration which caused a feedback loop. Generally, more sea ice begets more sea ice (Effectively, you're trading black ocean surface that absorbs light/heat for white ice that reflects light/heat. And so you get this feedback loop, more ice, cooler temps, even more ice) Anyway, The More You Know Star about some climate history stuff. (One issue with global warming is we're nearing the opposite end of that feedback loop, where less sea ice begets less sea ice and everything melts super fast. For shorthand, you can say that the temperature of Earth is likely rising as slowly as it will during the rest of our lifetimes. The ice is melting as slowly as it will for the rest of our lifetime. The sea level is rising as slowly as it will for the rest of our lifetime. etc)

The other thing to point out here is that volcanic emissions just mask warming caused by greenhouse gasses (ignoring the ability to start feedback loops). At the extreme end, for example, human IQ starts to suffer around 1,000 parts per million of carbon dioxide, so no matter what the temperature is in that scenario it's likely a decent idea to deal with carbon dioxide.