A geological event such as massive flood basalt , volcanism , or the eruption of a supervolcano could lead to a so-called volcanic winter , similar to a nuclear winter . One such event , the Toba eruption , occurred in Indonesia about 71,500 years ago . According to the Toba catastrophe theory , the event may have reduced human populations to only a few tens of thousands of individuals . Yellowstone Caldera is another such supervolcano , having undergone 142 or more caldera-forming eruptions in the past 17 million years . A massive volcano eruption would eject extraordinary volumes of volcanic dust , toxic and greenhouse gases into the atmosphere with serious effects on global climate ( towards extreme global cooling : volcanic winter if short-term , and ice age if long-term ) or global warming ( if greenhouse gases were to prevail )
Toba catastrophe theory
Toba catastrophe theory
Global catastrophic risk