Division of Energy
Global Climate Change: Volcanoes and Climate
The eruption of Mount Pinatubo in the Phillippines on June 15, 1991 was one of the largest explosive eruptions of this century. The eruption spewed huge amounts of fine volcanic ash and more than 19 million tons of sulfur dioxide gas into the earth's atmosphere. From comparison with previous volcanic eruptions, it was estimated that the eruption of Pinatubo would reduce the earth's average surface temperature by about 1 degree Fahrenheit for the following 3-4 years.
Large explosive volcanic eruptions have long been known to have the effect of cooling the earth's atmosphere. The eruption of Tamboro in 1815 and Krakatoa in 1883 were each followed by several years of dramatically cooler weather. Following the eruption of Tamboro, world temperature fell nearly 2 degrees Fahrenheit, and 1816 became known as "the year without a summer".
Volcanoes affect the earth's climate in several ways. Explosive volcanic eruptions spew large clouds of volcanic dust and gases that form aerosols (gaseous suspension of fine solid or liquid particles) in the earth's atmosphere. The clouds of volcanic dust eventually disperse to form a thin dust shield around the globe. The dust cools the earth by increasing the earth's albedo (ability to reflect radiation), allowing less of the sun's energy to reach the earth's surface. Aerosols of erupted gases reach the stratosphere and absorb solar radiation. Following the eruption of Krakatoa, incoming solar radiation decreased 25 percent and remained 10 percent below normal for about three years.
Volcanoes produce large volumes of carbon dioxide, water vapor, carbon monoxide, nitrogen and sulfur dioxide, and lesser volumes of other gases. In fact, most of the gases of our atmosphere and the water of the hydrosphere were contributed by volcanoes over the life span of the earth. Fumes emitted by individual volcanoes for decades can contribute more gases to the atmosphere than all of the coal burning power plants of a metropolitan area. However, the overall fraction of gases emitted is less than industrial contributions.
The cooling effects of volcanic eruptions are short term, however, and seldom lasting for more than a decade. In fact, long-term cooling effects are negligible because large amounts of carbon dioxide are added to the atmosphere by volcanoes, and carbon dioxide is the major contributor to the greenhouse effect. For instance, the Miocene Epoch, about 26 million years ago, was a period of intense vulcanism, yet it was noticeably warmer than at present.
Understanding how volcanic eruptions can influence climate is important when trying to determine whether global climate change is occurring. The climatic effect of volcanoes can temporarily override and confuse long-term temperature increase trends.