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 Athe year without a summer.
Volcanoes affect the earth's climate in several ways.
The clouds of volcanic dust eventually disperse to form a thin dust shield around the globe. 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.