Volcanoes and Global Cooling

It has been theorized that colossal volcanic eruptions throughout history have disrupted global climate and even caused the onset of glaciations.  Could the Yellowstone Supervolcano bring about the next ice age?

Mount Pinatubo, Philippines.  1991.

Mount Pinatubo, Philippines. 1991. Global temperatures dropped by about 0.9°F following the eruption

 

Yellowstone National Park, the oldest and one of the most renowned national parks in the world, lies atop a volcanic hotspot with a history of colossal eruptions (the most recent eruption occurred some 640,000 years ago).  There has been much speculation about the possibility of this supervolcano erupting again, as well as ponderings about its implications for humankind.

Volcanic eruptions are classified according to their magnitude, or explosivity.  This is known as  VEI, or “Volcanic Explosivity Index.”  Supervolcanoes are classified as VEI 8, with VEI 7 being the next most potent.  The most recent VEI 8 was the eruption of Toba in Indonesia some 74,000 years ago.  The most recent VEI 7, however, was the eruption of Mount Tambora, also in Indoneisa, in 1815.  It has been speculated that the eruption of Mt. Toba, which was about 3500 times greater than the Tambora eruption, contributed to the onset of the last glaciation, with one theory positing that it wiped out 60% of the human population.    What would happen if a colossal eruption occurred at Yellowstone in the near future?

Let’s first take a look at how volcanic eruptions can affect the climate.  When a volcano erupts, it ejects a plume into the atmosphere.  These plumes contain ash and sulfur-containing aerosol particles, which combine with water vapor in the stratosphere to form dense clouds of sulfuric acid droplets.  These droplets obscure the sun and increase Earth’s albedo, or reflectivity of solar radiation.  If enough of these particles get into the stratosphere, and effectively spread around the globe, worldwide cooling can result.

The most pronounced cooling phenomenon from a volcano within the last two centuries resulted from the eruption of Mount Tambora in 1815.  This eruption was responsible for what was known as the “Year Without a Summer.”  In the Spring and Summer of 1815 following the eruption, an ongoing dry fog was observed in the northeastern United States, often dimming and reddening the sunlight.  In 1816, many countries in the Northern Hemisphere experienced extreme weather conditions.  Average global temperatures fell 0.4° to 0.7°C (0.7° to 1.3°F), and significant agricultural losses were sustained worldwide. The 1883 eruption of Krakatoa, Indonesia (VEI 6) induced significant cooling as well, reducing average global temperatures about 1.2°C the year after the eruption, with erratic weather patterns persisting several years after.

In 1912, the Novarupta Volcano, located in Katmai National Park and Preserve in Alaska, erupted with a VEI of 6.  Although this was a huge eruption with the same VEI as that of Krakatoa, no significant global cooling occurred.  The reason why?

The location of the volcano.
 

Within the past two centuries, the six eruptions that affected global climate have all been located in the tropics:

  • Mount Pinatubo, Philippines. 1991 (15.13°N) VEI 6
  • El Chichón, Mexico. 1982 (17.36°N)  VEI 5
  • Mount Agung, Indonesia. 1963 (8.34°S) VEI 5
  • Santa María, Guatemala. 1902 (14.76°N) VEI 6
  • Krakatoa, Indonesia. 1883. (6.11°S) VEI 6
  • Mount Tambora, Indonesia.  1815 (8.14°S) VEI 7

Other eruptions of similar magnitude, occurring in mid to high latitudes, have not had a significant effect on global temperature:

  • Mount Hudson, Chile. 1991. (45.54°S) VEI 5
  • Mount St. Helens, Washington State. 1980. (46.11°N) VEI 5
  • Novarupta, Katmai, Alaska. 1912. (58.16°N) VEI 6
  • Askja, Iceland. 1875. (65.01°N) VEI 5
volcanoes

Within the past two centuries, all volcanic eruptions that affected global climate were located near the equator

 

A large volcanic explosion will eject its plume into the stratosphere (the second layer of the Earth’s atmosphere).  Above the equatorial latitudes, rising winds in the stratosphere’s circulation pull these aerosols high into the stratosphere.  In the upper levels of the stratosphere in equatorial zones,  winds flow poleward in both directions, and cause the sulfur aerosols from a volcanic plume to spread throughout both hemispheres. In mid to high latitudes on the other hand, when an eruption occurs, these aerosol particles will not spread as far, since the stratospheric circulation only flows poleward in one direction and contains sinking air.

 

Large volcanic eruptions occurring in equatorial regions transport aerosol particles throughout both hemispheres

Large volcanic eruptions occurring in equatorial regions transport aerosol particles throughout both hemispheres

 

One of the reasons that the eruption of Mt. Tambora was so catastrophic was due to its location near the equator.  The massive quantity of ejected aerosol particles spread into both hemispheres, and thus affected climate globally.   If a super eruption were to occur at Yellowstone (about 44.36°N)  in the future, it would most likely only spread aerosols throughout the northern hemisphere, with the most severe environmental effects concentrated in the northern hemisphere.  However, several other factors could come into play.

According to models by volcanologists, the chances of another super eruption occurring in the next 100 years is about .014%.  When it does occur, it most likely will not bring about the onset of the next ice age, however it will very likely cool global temperatures for several years and significantly reduce global rainfall for the first two years following the eruption.  It goes without saying it would have devastating effects on agriculture, let alone many other ecological functions.  But keep in mind, the planet has an uncanny way of self-regulating and returning to its natural state.

 

 

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