The eruption of the Toba supervolcano , 70,000 to 75,000 years ago reduced the average global temperature by 5 degrees Celsius for several years and may have triggered an ice age . It has been postulated that this created a bottleneck in human evolution . A much smaller but similar effect occurred after the eruption of Krakatoa in 1883 , when global temperatures fell for about 5 years in a row
Toba supervolcano
Toba catastrophe theory
Historical climatology