Energy > Climate Change
Are volcanic eruptions warming the earth?
This article is part of our series focused on the causes and consequences of a warming planet
How do we know the carbon dioxide emissions that are driving the greenhouse effect are coming from the burning fossil fuels and not some natural source?
During major volcanic eruptions, huge amounts of volcanic gas, aerosol droplets and ash are pumped into the atmosphere. Much of the volcanic gas is carbon dioxide. Although it has been proposed by some that volcanic emissions of carbon dioxide are large enough to play a significant role in the warming of the earth, scientific studies do not support this claim.
According to the US Geological Survey, the world’s volcanoes generate about 200 million tons of carbon dioxide annually. While this is a large amount of carbon dioxide, it is only about 1% of the amount emitted by human activities. Volcanos emit millions of tons per year, humans emit billions of tons per year. It is not volcanoes that are bringing massive amounts of fossilized carbon to the surface of the Earth. Instead, it is oil wells and coal mines.
For example, in 1980, Mount St. Helens in the state of Washington erupted releasing millions of tons of carbon dioxide into the atmosphere in nine hours. While this is a massive release of carbon dioxide, it did not exceed the amount of carbon dioxide released from human activities during the same nine-hour period. In addition, human emissions are on-going, day-after-day and month-after-month while volcanic eruptions the size of Mount St. Helens are infrequent.
Another impact of volcanic eruptions is a cooling effect. In addition to large amounts of carbon dioxide, large amounts of sulfur dioxide are also released into the atmosphere. The sulfur dioxide converts to sulfuric acid which forms sulfate particles (aerosols). These aerosols reflect sunlight back into space, cooling the earth’s lower atmosphere. Although these sulfate aerosols can cause a considerable amount of cooling, they stay in the atmosphere for only a couple of years before being washed out by precipitation. By comparison, carbon dioxide stays in the atmosphere for over a hundred years.
Several eruptions over the past century have caused a cooling effect for one or more years. Probably the biggest emitter of sulfur dioxide was the Laki fissure eruption in Iceland which erupted violently over an eight-month period between June 1783 and February 1784. It emitted an estimated 120 million tons of sulfur dioxide. The cooling caused crop failures in Europe.
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Don Hofstrand, retired extension agricultural business specialist, email@example.com
Reviewed by Dr. Eugene Takle, retired professor emeritus Iowa State University