Volcanoes and climate

Historical evidence supports the premise that volcanic eruptions cool the earth. Between 1812 and 1817 there were three major volcanic eruptions. Soufrier on St. Vincent Island erupted in 1812; Mayon in the Philippines in 1812; Tambora in Sumbawa Indonesia in April 1815. Tambora was by far the largest and preceded the disastrous famines of 1816-1817. These abnormal cool temperatures of 1816-1817 were accompanied by wetter than normal weather in many areas.

Debris from Mt. Tambora (8°S latitude, 118°E longitude) took one year to spread globally. The following year is known as the year without a summer. While extensive meteorological observations did not exist at this time, people's diaries and weather journals documented the cold weather of the summer of 1816. In New England snow fell in June and frost occurred in July and August. Late frost killed a large number of crops; however, the entire summer was not below freezing. Indeed, on June 5, the day before the snowfall, the temperatures in Vermont were in the low 30's°C (upper 80's°F)! After the early June cold spell in New England, farmers, hoping for a good crop, replanted their crops as temperatures returned to normal. Another cold spell hit in early July bringing freezing temperatures to the area. Harvests were bad that year and resulted in severe food shortages in parts of New England. The poor harvest had an economic impact throughout the United States. The price of a bushel of corn in Philadelphia in May 1817 was double the price it was in April 1816.

Weather in Europe and other regions of the globe were also abnormal in 1816. In Europe, the cold and wet weather contributed to a disastrous harvest as crops rotted in the field. Famine, food riots, grain hoarding, and government embargoes resulted. These cold, moist weather patterns may have contributed to the typhus epidemic of 1816-1819 in Europe that killed approximately 200,000 people and the cholera outbreak of 1816-1817 originated in Bengal and spread throughout the world.

Bad weather during this time also resulted in positive things. Rather than going outside in the cold damp weather, Mary and Percy Bysshe Shelly passed their summer vacation indoors telling ghost stories with Lord Byron. In 1818 Mary Shelly's ghost story was published, giving birth to a monster that gave me nightmares--Frankenstein.

Not all volcanoes result in a cooling of the earth. Here we will compare three recent volcanic eruptions: Mt. St. Helens, El Chichón, and Mt. Pinatubo. The amount of cooling due to a volcanic eruption is determined by:

  • the force of the eruption: For a global impact, the debris from the volcanoes must be injected into the stratosphere where it can remain for months.
  • the amount of sulfur dioxide (SO2) in the volcanic plume: In the stratosphere, SO2 combines with water vapor to make tiny particles of sulfuric acid. The particles reflect solar radiation back to space, reducing the amount of solar energy at the surface.
  • latitude and winds in the stratosphere: For global effect on weather, the sulfuric acid particles have to spread over the globe. Stratospheric winds at the time of the eruption and the latitude of the volcano determine the spreading the volcanic plume.

The eruption of Mt. St. Helens in the state of Washington in May of 1980 produced little, if any, effect on global temperatures. While a violent eruption, most the force of the eruption was horizontal, resulting in relatively little debris being injected into the stratosphere. The emissions from Mt. St. Helens primarily stayed in the troposphere and the ash and dust settled quickly to the ground.

El Chichón, Mexico erupted in 1982. El Chichón was a much less violent eruption than Mt. St. Helens; however, debris was injected into the stratosphere. The global spread of El Chichón's stratospheric debris was primarily limited to between 5° N and 40° N latitude. Estimates of the global cooling due to the eruption of El Chichón are approximately 0.3 to 0.5 °C. El Chichón also had much more sulfur dioxide in its plume than Mount St. Helens. The cooling effects of the El Chichón eruption may have also been hidden by the warming of another natural phenomenon -- El Niño.

Mt. Pinatubo was this century's most violent eruption, injecting over 25 million tons of sulfur dioxide into the stratosphere. Once in the stratosphere, tiny sulfuric acid particles formed and rapidly spread all over the globe. These tiny particles reflected solar energy back to space and resulted in a cooling of the globally averaged surface temperature by approximately 0.6°C (1°F). The NASA ERBE program measured the effect of the Mt. Pinatubo's stratospheric aerosol on the radiation balance of the planet and for the first time provided firm evidence that volcanic eruptions tend to cool the Earth.

The Verner E. Suomi Virtual Museum development funded in part by the National Science Foundation Grant #EAR9809458.  Material presented is Copyrighted (C) 1999 by Steve Ackerman and Tom Whittaker.  If you have questions or comments, please let us know!