Pinatubo, the Philippines: A.D. 1991
The 1991 blast at Mount Pinatubo in the Philippines killed 800 people, which actually makes it one of the least deadly human-era eruptions on this list. However, the eruption also left 100,000 people became homeless, and caused a half a billion dollars in damage.
Pinatubo also threw 20 million tons of sulfur dioxide into the air, which scientists say was a result of volcanic rock soaking up excess sulfur and other elements underground prior to the actual eruption. Once released, the aerosols obscured part of the incoming sunlight, and caused a global cooling effect that dropped worldwide temperatures by a degree Fahrenheit.