How much did the worst volcanic eruption in human history affect global temperature? 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?
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.