How do volcanic eruptions affect the climate?

Sulfur dioxide gets into the upper atmosphere and can filter out sunlight, so the planet cools. After Tambora in Indonesia blew in the early 1800's there followed the year without any summer...crop failures all around the world, starvation, economic collapse. Krakatoa blew in 1883 (?) it cooled the world too but because it was MUCH smaller than Tambora the world economy, and agriculture, did not collapse. When Pinatubo blew in the early 1990's the world got pink sunsets for about a year.