Volcanic Emissions & Global Cooling

The effect of volcanic emissions on global climate has been a hotly debated topic over the past few decades.  Below, we will take a look at the current arguments and science relating to volcanic emissions and global cooling.

Table of Contents

  I. Volcanic Emissions                               

 II. Carbon Dioxide              
III. Sulfur Dioxide
IV. Examples of Global Cooling                                                
V.  Monitoring the Effects of Volcanoes
VI. Conclusion
VII.Sources Cited

Volcanic Emissions

As volcanoes erupt, they blast huge clouds into the atmosphere. These clouds are made up of particles and gases that were previously trapped in the geosphere, including sulfur dioxide, carbon dioxide, chlorine, argon, carbon monoxide, and water vapor.  Millions of tons of harmful sulfur dioxide and carbon dioxide gas can reach the stratosphere from a major volcano.   While all these gases play a small part in volcanic-induced climate change, carbon dioxide and sulfur dioxide are by far the largest contributors to global cooling.

Carbon Dioxide
    Carbon dioxide emissions from volcanoes total around 110 million tons per year, but this number is extremely small if compared to the 10 billion tons put into the atmosphere by human activities.  Despite being a greenhouse gas that is known for its global warming potential, carbon dioxide, combined with volcanic ash, actually act as short-term coolants in the atmosphere by acting as a “blanket” that absorbs the sun’s radiation in the stratosphere before it can reach the earth’s surface.  There are those who argue that volcanic carbon dioxide emissions result in long-term global warming, but the amounts released by volcanoes have not proven to be substantial enough to significantly affect the global temperature in the long run.

Sulfur Dioxide
    Sulfur dioxide has the most adverse effect on the atmosphere of any of the volcanic gases.  Sulfur dioxide is converted to sulfuric acid within months of the eruption.  Winds then spread these newly formed aerosols over the majority of the globe, where they stay in the atmosphere for upwards of two years.  Not only do these aerosols cool the earth’s surface by reflecting sunlight back into space, but the sulfuric acid also plays a role in the increased depletion of ozone (http://oea.larc.nasa.gov/PAIS/Aerosols.html).  Ozone is a natural absorbant of solar radiation, so when it is replaced by reflective aerosols the total radiative energy in the atmosphere decreases, resulting in global cooling. The following diagrams illustrate this transformation of sulfur dioxide into the aerosols that destroy ozone:

Examples of Global Cooling

One of the greatest examples of the global cooling caused by volcanic eruptions occurred in 1816, known as “The Year without a Summer” (http://itg1.meteor.wisc.edu/wxwise/museum/a5/a5volcan.html). One year after Mount Tambora erupted in Indonesia its effects were already being felt globally.  In New England snow fell in July of 1816, with temperatures reaching the 30’s.  Both Europe and America faced economic hardships as a result of premature frosts destroying large amounts of crops.  Some scientist also believe that the eruption of Mt. Toba in Sumatra 73,500 years ago may have cooled the planet by 3-5 degrees Celsius, resulting in a 'volcanic winter'.
        The eruption of Mt. Pinatubo in the Philippines in 1991 was one of the largest volcanic eruptions in the past century.  The injection of between 14-26 million tons of sulfur into the stratosphere resulted in a global surface cooling of 0.5 degrees Celsius one year after the eruption.  The short-term climatic impact of this eruption was greater than El Nino or human-induced greenhouse gas changes between 1991 and 1993.

 The images below illustrate the spreading of volcanic gases during the June 15, 1991 eruption of Mt. Pinatubo. These satellite observations demonstrate the enormous amounts of gas and ash emitted, as well as details such as differences in peak concentrations and geographic extent.  The one on the left shows sulfur dioxide concentrations, while the one on the right illustrates aerosol and volcanic dust concentrations.

        In most cases, however, volcanic eruptions do not have such an extreme effect on the atmosphere.  Eruptions of the magnitude of Pinatubo only happen around once every 100 years.  The overall impact of a volcanic eruption on the atmosphere is dependent on the size of the volcano, its overall emissions, and the height of the volcano.  No substantial climate change due to a volcano, however, has ever been witnessed for more than 10 years after the initial eruption. 

Monitoring the Effects of Volcanoes

    Measurements of the quantities of gases released by volcanoes is still an educated guess at best.  Human-led expedititions are nearly impossible due to the dangerous nature of volcanic eruptions.  Even research planes can't collect accurate samples because they can't fly high enough and it is simply too dangerous.  Space observations from NASA's Total Ozone Mapping Spectrometer (TOMS) instrument have contributed significantly to our knowledge of the total amount of greenhouse gases emitted into the atmosphere in the course of major volcanic eruptions.  Following the eruption of Mount Pinatubo, TOMS images (above) showed sulfer-dioxide spreading across the Pacific Ocean, and eventually covering the globe.  To date TOMS has been used to observe and record data on over 100 volcanic events.  (http://www.nasa.gov)


       The magnitude of eruptions differ tremendously; they are unpredictable; they differ in size; and ash and gases vary in composition.  All of these factors make it difficult for scientists to seperate volcanic effects from other influences on  the global climate.  While there is a definite short-term global cooling process brought about by volcanic eruptions, there have been no noticeable long-term effects, other than the depletion of ozone due to the release of aerosols.  The relatively small amount of harm done to the atmosphere by volcanoes cannot even compare to the extensive damage done by man.

Sources Cited

1. "Atmospheric Aersols: What are they, and why are they so important?"  http://oea.larc.nasa.gov/PAIS/Aerosols.html

2. "Volcanoes and Climate." 

3. "Recent volcanic eruption data."  http://skye.gsfc.nasa.gov

"The Science of Climate Change: The Aerosol Effect."  http://www.panda.org/resources/publications

"The Effects of Volcanic Eruptions on Earth's Climate."  http://www.geo.mtu.edu

6.  "Volcanoes and global cooling."  http://www.nasa.gov