[AdmSmith]

A powerful tropical volcanic eruption around 266 CE, which in the following year brought a below-average flood of the Nile, presumably also played a role. Major eruptions are known from sulfuric acid deposits in ice cores from Greenland and Antarctica, and can be dated to within three years. Particles hurled up into the stratosphere lead to a cooling of the climate, disrupting the local monsoon system.(your ref)

Followed by the 535 eruption of Krakatoa. Summer temperatures in 536 fell by as much as 2.5 degrees Celsius (4.5 degrees Fahrenheit) below normal in Europe.

https://en.wikipedia.org/wiki/Volcanic_winter_of_536

[SunkenCiv]

I was constrained by the word count, also, I don't have much use for volcanological "explanations" for climate. That said, climate is 100 percent natural 100 percent of the time.