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Volcanic Eruptions and the Role of Sulfur Dioxide in Climate Change

In March and April of this year, a series of severe volcanic eruptions shook Alaska's Mount Redoubt.¹  To date, the largest of the eruptions produced an ash plume that reached 50,000 feet above sea level and released a significant amount of sulfur dioxide (CAS Registry Number 7446-09-5) into the earth's atmosphere.  According to the Alaska Volcano Observatory, "The main concerns for human health in volcanic haze consist of ash, sulfur dioxide gas (SO₂), and sulfuric acid droplets (H₂SO₄), which forms when volcanic SO₂ oxidizes in the atmosphere."¹

While there is obvious reason for alarm among local populations, sulfur dioxide from the Mount Redoubt eruption could also have more widespread impacts, particularly on the climate.  According to a 1997 article published in the Journal of Geology, "The mechanism by which large eruptions affect climate is generally accepted: injection of sulfur into the stratosphere and conversion to sulfate aerosol, which in turn reduces the solar energy reaching the earth's surface."²

In the years following a volcanic eruption, sulfate aerosol that remains in the atmosphere is thought to cause surface cooling by reflecting the sun's energy back into space.  In fact, sulfate aerosol from the massive eruption of Indonesia's Mount Tambora in 1815 is blamed, at least in part, for the "year without a summer" reported in Europe and North America in 1816:

• "Daily temperatures (especially the daily minimums) were in many cases abnormally low from late spring through early fall; frequent northwest winds brought snow and frost to northern New England and Canada, and heavy rains fell in western Europe.  Many crops failed to ripen, and the poor harvests led to famine, disease, and social distress..."³

Supporting this claim, sulfate aerosol-related climate changes were also reported after the 1991 eruption of Mount Pinatubo in the Philippines.⁴  An article published in Science in 2002 summarizes a decade's worth of research on Pinatubo's effects on the global climate, highlighting impacts far more widespread and complex than previously thought:

• Robock, A. Pinatubo Eruption: The Climatic Aftermath. Science 2002, 295, 1242-1244.

You can use SciFinder or STN to search the CAS databases for additional information about sulfur dioxide from volcanic eruptions.  If your organization is enabled to use the web version of SciFinder, you can click the links in this article to directly access details of the substances and references.

Contributed by
Peter S. Carlton, Ph.D.
CAS Communications

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References

1. Alaska Volcano Observatory. http://www.avo.alaska.edu/ (accessed April 15, 2009).
2. Bluth, G.J.S.; Rose, W.J.; Sprod, I.E.; Krueger, A.J. Stratospheric Loading of Sulfur from Explosive Volcanic Eruptions. J. Geol. 1997, 105, 671-683.
3. Stothers, R.B. The Great Tambora Eruption in 1815 and Its Aftermath. Science 1984, 224, 1191-1198.
4. Parker, D.E.; Wilson, H.; Jones, P.D.; Christy, J.R.; Folland, C.K. The Impact of Mount Pinatubo on World-Wide Temperatures. Int. J. Clim. 1998, 16, 487-497.

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