Karen Harpp, an assistant professor of geology at Colgate University, provides this explanation:

Image: ¿PHOTODISC VOLCANIC ERUPTIONS inject ash and aerosol clouds into the atmosphere and produce more than 100 million tons of carbon dioxide each year.

In 1784, Benjamin Franklin made what may have been the first connection between volcanoes and global climate while stationed in Paris as the first diplomatic representative of the United States of America. He observed that during the summer of 1783, the climate was abnormally cold, both in Europe and back in the U.S. The ground froze early, the first snow stayed on the ground without melting, the winter was more severe than usual, and there seemed to be "a constant fog over all Europe, and [a] great part of North America."

What Benjamin Franklin observed was indeed the result of volcanic activity. An enormous eruption of the Laki fissure system (a chain of volcanoes in which the lava erupts through a crack in the ground instead of from a single point) in Iceland caused the disruptions. The Laki eruptions produced about 14 cubic kilometers of basalt (thin, black, fluid lava) during more than eight months of activity. More importantly in terms of global climate, however, the Laki event also produced an ash cloud that may have reached up into the stratosphere. This cloud caused a dense haze across Europe that dimmed the sun, perhaps as far west as Siberia. In addition to ash, the eruptive cloud consisted primarily of vast quantities of sulfur dioxide (SO₂), hydrogen chloride (HCl), and hydrogen fluoride gases (HF). The gases combined with water in the atmosphere to produce acid rain, destroying crops and killing livestock. The effects, of course, were most severe in Iceland; ultimately, more than 75 percent of Iceland¿s livestock and 25 percent of its human population died from famine or the toxic impact of the Laki eruption clouds. Consequences were also felt far beyond Iceland. Temperature data from the U.S. indicate that record lows occurred during the winter of 1783-1784. In fact, the temperature decreased about one degree Celsius in the Northern Hemisphere overall. That may not sound like much, but it had enormous effects in terms of food supplies and the survival of people across the Northern Hemisphere. For comparison, the global temperature of the most recent Ice Age was only about five degrees C below the current average.

There are many reasons that large volcanic eruptions have such far-reaching effects on global climate. First, volcanic eruptions produce major quantities of carbon dioxide (CO₂), a gas known to contribute to the greenhouse effect. Such greenhouse gases trap heat radiated off of the surface of the earth forming a type of insulation around the planet. The greenhouse effect is essential for our survival because it maintains the temperature of our planet within a habitable range. Nevertheless, there is growing concern that our production of gases such as CO₂ from the burning of fossil fuels may be pushing the system a little too far, resulting in excessive warming on a global scale. There is no doubt that volcanic eruptions add CO₂ to the atmosphere, but compared to the quantity produced by human activities, their impact is virtually trivial: volcanic eruptions produce about 110 million tons of CO₂ each year, whereas human activities contribute almost 10,000 times that quantity.

By far the more substantive climatic effect from volcanoes results from the production of atmospheric haze. Large eruption columns inject ash particles and sulfur-rich gases into the troposphere and stratosphere and these clouds can circle the globe within weeks of the volcanic activity. The small ash particles decrease the amount of sunlight reaching the surface of the earth and lower average global temperatures. The sulfurous gases combine with water in the atmosphere to form acidic aerosols that also absorb incoming solar radiation and scatter it back out into space.

5 Comments

1. 1. berrysweet12 05:59 AM 5/5/09

   i love this

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2. 2. nottellinyou 02:55 AM 2/3/10

   According to the US Geological Survey, http://volcanoes.usgs.gov/hazards/gas/index.php
   
   "Scientists have calculated that volcanoes emit between about 130-230 million tonnes (145-255 million tons) of CO2 into the atmosphere every year (Gerlach, 1991)"
   
   while humans...
   
   "Emissions of CO2 by human activities, including fossil fuel burning, cement production, and gas flaring, amount to about 27 billion tonnes per year (30 billion tons) [ ( Marland, et al., 2006)"
   
   to which they (USGS) estimate "Human activities release more than 130 times the amount of CO2 emitted by volcanoes"
   
   However you guys, Scientific American, state: "volcanic eruptions produce about 110 million tons of CO2 each year, whereas human activities contribute almost 10,000 times that quantity."
   
   130 time vs 10,000 times seems like a huge difference. Am I missing something or is someone lying?

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3. 3. Elmira Blossom 11:16 PM 4/19/10

   So- is this current Iceland volcano producing dangerous amts of SO2? I'm enjoying watching this volcano via webcams, but maybe I'd better spend my time planting a bigger garden and getting ready to can everything I can manage to grow.

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4. 4. mehri1335@yahoo.com 12:18 AM 4/21/10

   ONE OF THE MOST INTERESTING ARTICLES I HAVE EVER HAD READ. THE HEALING POWER OF OUR PLANET EARTH IS JUST FACINATING. DO NOT WE HAVE STILL MANY MANY THINGS TO LEARN??????????

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5. 5. scotland baba 07:07 AM 6/30/10

   i would like more information on the actually effect that volcanic eruptions have on the earths atmosphere for my geography project which has to be in for today and it must be the physical effects ....
   
   thatnk you very muchf rom stacEY forsyth....... scotland xxx

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