Volcanic eruptions are inconsequential. A large one might have a small effect for a short time. A very large one for a couple of years. Only those very few of biblical proportions that the Planet has experienced on a few occasions have the power to affect climate for long enough to be noted in the geological record.
I don't use any scale except in that answer to a non question. In genral, the thirthy year record is what has been used to say that there is a trend in Global warming. And the temperature increases in this trend are very different. They are not from any natural variable like volcanic outpourings would be. They are entirely from the carbon that we are putting out.
The "dirty thirties" were a short lived anomaly. Their cause were of natural variablity - just larger than are experienced quite regularly and that are removed from calculations that establish this trend.
Volcanic eruptions
Volcanoes and Climate Change : Feature Articles
Large-scale volcanic activity may last only a few days, but the massive outpouring of gases and ash can influence climate patterns for years. Sulfuric gases convert to sulfate aerosols, sub-micron droplets containing about 75 percent sulfuric acid. Following eruptions, these aerosol particles can linger as long as three to four years in the stratosphere.
Major eruptions alter the Earth's radiative balance because volcanic aerosol clouds absorb terrestrial radiation, and scatter a significant amount of the incoming solar radiation, an effect known as "radiative forcing" that can last from two to three years following a volcanic eruption.
How Volcanoes Work - volcano climate effects
Krakatoa - Wikipedia, the free encyclopedia
The accompanying Editors’ Summary of the 2006 Nature article by Gleckler et al. provides the gist:
The 1883 eruption of the volcano Krakatoa in Indonesia has echoed down the centuries in art and in legend. Now an analysis of a suite of 12 climate models shows that Krakatoa also made its presence felt well into the twentieth century in the form of reduced ocean warming and sea-level rise. The changes lasted much longer than was previously suspected and were sufficient to offset much of the ocean warming and sea-level rise caused by more recent human activities.
The eruption of Krakatoa, August 27, 1883
t has been suggested that an eruption of Krakatoa may have been responsible for the global climate changes of 535-536. Additionally, in recent times, it has been argued that it was this eruption which created the islands of Verlaten and Lang (remnants of the original) and the beginnings of Rakata - all indicators of that early Krakatoa's caldera size, and not the long-believed eruption of c. 416, for which conclusive evidence does not exist.
