This may not sound like much, but it can be devastating to agriculture. In Europe and North America, 1816 was known as the "year without a summer" because of global cooling caused by the 1815 eruption of Tambora, in Indonesia. A large number of crops failed as a result of the cooling due to the eruption. The more recent 1991 eruption of Pinatubo, in the Philippines, also caused global cooling, perhaps by an average of about 1 degree during the following year.

Huge volcanic eruptions like the most recent big Yellowstone explosion, which occurred 631,000 years ago, are about 10 times bigger than that of Tambora in 1815, and perhaps 100 times bigger than Pinatubo's 1991 blast. So it's easy to see that such huge eruptions probably have a significant impact on global climate that might last for years. But will this lead to the extinction of humanity?

No. We can be confident of this because there have been two massive explosions while humans were present on Earth, and both of these were actually larger than Yellowstone's most recent cataclysmic eruption. These eruptions were from Toba, Indonesia, about 74,000 years ago and from Taupo, New Zealand, about 26,500 years ago.