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According to this,

2018’s Biggest Volcanic Eruption of Sulfur Dioxide

In extreme cases, like the 1991 eruption of Mount Pinatubo in the Philippines, these tiny aerosol particles can scatter so much sunlight that they cool the Earth’s surface below. Mount Pinatubo’s violent eruption injected about 15 million tons of sulfur dioxide into the stratosphere. The resulting sulfuric acid aerosols remained in the stratosphere for about two years, and cooled the Earth’s surface by a range of 1 to 2 degrees Fahrenheit.

But according to this, Worst volcanic eruptions in human history

the worst volcanic eruption in human history injected 400 million tons of gas

(26,6 times more than Pinatubo's eruption) though I guess the composition of the gas could be different, and

the Earth began to cool and 1816 became known as "The Year Without Summer" because of the low temperatures, which killed crops and led to mass starvation.

Is it know what global temperature Earth had this year and how much in degrees celsius or fahrenheit temperature changed?

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    $\begingroup$ Those eruptions seem to be ranked as "worst" due to the human death toll, but some of them seem not to have been particularly notable for their sheer size. Also, how far back do you consider to be "history"? E.g. the Thera eruption en.wikipedia.org/wiki/Minoan_eruption or Mt. Mazama en.wikipedia.org/wiki/Mount_Mazama $\endgroup$ – jamesqf Sep 27 '19 at 3:41
  • $\begingroup$ Keep in mind eruptions have very little impact on the opposite hemisphere (unless they are very close to the equator) just due to how wind circulation works, and most of hte human population is in the northern hemisphere, so "worse" will always be somewhat relative. $\endgroup$ – John Sep 30 '19 at 14:23
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I'm not well studied in this field, but I suspect that global average temperature by proxy for a single year is difficult to measure accurately. The 1991 cooling from Mt. Pinatubo happened recently enough that accurate measurements were made, though cooling is still somewhat difficult to pin down exactly due to other variation factors, sunspots being a small variation and the Pacific current being a big variation.

1990, at the time, was the hottest year on record, driven in part by the El Nino that year. (El Nino warms the Earth and usually lasts for a year, maybe 18 months or 2 years sometimes).

The El Nino continued into 1991, though it weakened greatly by the end of 1991 (Peak El Nino being about 12 months is about right). And the Mt. Pinatubo eruption happened on June 15, so it didn't affect climate in 1991 until nearly half way through the year. 1991 might have been warmer than 1990 prior to the eruption (I looked for a source on the first half of 1991 but couldn't find it).

Overall, 1991 was colder than 1990 but only a little, and probably would have been warmer without Pinatubo. 1992 was considerably colder than 1993 and 1994 showed gradual warming and 1995 set a new hottest year on record at the time. The fall 1990 to 1991 was likely volcano driven but the bigger fall in 1992 was probably partially driven by the weakening El Nino.

Chart used as source if you scroll down

The article above - see quote says that Pinatubo lowered temperatures less than your source suggests.

in the year to follow, volcanic particles in the atmosphere would lower global temperatures by an average of 0.9 degrees Fahrenheit (0.5 degrees Celsius).

But, something to keep in mind about a 0.5 degree drop is that oceans are very slow to react, and unlike land, oceans don't warm up well under direct sunlight due to evaporation and the cooling effect of photon-generated evaporation. Because Earth is about 70% covered by ocean nearly all that 0.5 degree variation is over the land, land surface temperatures drop by nearly 1.5 degrees C and Oceans change very little.

Finally, and this is important, volcanic "winters" aren't just about temperature drop but also about sunlight blocking. Less sunlight means less crop growth and it only takes one frost at the wrong time to kill a lot of crops, so even if a 1 or 2 degree Celsius drop or, lets say 2-3 degree drop over land that might not sound devastating, but temperature drops like that can be associated with a considerably higher chance of frost and crop-death. The 1991 eruption wasn't associated with crop failures, but the 1883 and 1815 eruptions were. Sunlight blocking may have been as big or an even bigger factor as temperature drop, but late frosts may have played a key role as well. (I lack the knowledge to give precise data on this).

I realize I've not answered your question with a number like you asked. You can find estimates of temperature drop in various articles, usually about 1-2 degrees from big volcanic eruptions like the one in 1815, but neither the 1883 nor the 1815 were accurately measured. From what I gather (but I haven't found it said specifically), the 1883 cold spell lead to greater interest in global temperature, which is why many global average temperature charts begin in 1884, after Krakatoa. We may not have an accurate estimate on the temperature drop from a super-volcano. Narrowing down an accurate estimate based on geological evidence for one year, even supported with some local temperatures and historical records is tricky. I don't think anyone knows the specifics of temperature drop by super-volcano with accuracy. The numbers that get reported are probably somewhere between guesses and estimates.

Also, not all eruptions are alike. A higher SO2 content should create a longer cooling. Volcanoes vary in sulfur content.

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The largest volcanic eruption in human history was the Toba eruption on Sumatra about 75,000 years ago. There is still a huge lake, Lake Toba, in the crater. It dwarfed Thera, Krakatoa and Tambora. The Tambora eruption on the Indonesian island of Sumbawa occurred in 1815, and was the largest eruption in historical times, also dwarfing the other two. It caused bad weather and lower temperatures around the world, including Europe, for about a year. The much larger Toba eruption must have had even more drastic short term effects lasting for years, but strangely enough doesn't seem to have had any major effects on the human population of South East Asia. It may have emitted enough CO2 to have made a minute difference to the ppm figure had there been anyone around able to measure it.

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    $\begingroup$ Must is stretching it, the evidence could go either way, The evidence shows Toba may have had little effect on the climate. The composition of the eruption matters. $\endgroup$ – John Sep 30 '19 at 14:29
  • $\begingroup$ So, you don't think that Toba caused the human genetic "bottleneck" that happened about the same time? $\endgroup$ – Spencer Oct 6 '19 at 22:18
  • $\begingroup$ @spencer it may have but it would not need to have a huge impact on global climate to do that. Just having its ash fall land across the majority if human distribution would do that. and the evidence it had a large impact on the human population is circumstantial at best. $\endgroup$ – John Oct 7 '19 at 20:00
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I've found this information in this article Mount Tambora and year without summer

The eruption of Mount Tambora, cited in the first article posted in the question as the worst volcanic eruption of human history (debatable according to other answer in this thread) dropped global temperature 3 degrees celsius.

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