Erupting volcanoes offset recent Earth warming,according to a team led by the University of Colorado at Boulder. Researchers arrived at this conclusion after searching for clues about why Earth did not warm as much as climatologists expected between 2000 and 2010.
Lead study author Ryan Neely said that the study’s findings take some of the pressure off of India and China, two countries that are believed to have increased their industrial sulfur dioxide emissions by approximately 60 percent from 2000 to 2010 through coal burning.
According to the United States Environmental Protection Agency, the biggest sources of sulfur dioxide emissions are from fossil fuel combustion at power plants (73 percent) and other industrial facilities (20 percent). Smaller sources of sulfur dioxide emissions include trains, large ships and some industrial processes. Sulfur dioxide emissions are associated with a number of negative effects on the respiratory system.
According to Neely, tiny amounts of sulfur dioxide emissions from Earth’s surface eventually rise 12 to 20 miles into the stratospheric aerosol layer of the atmosphere, where chemical reactions generate sulfuric acid and water particles that reflect sunlight away from the Earth and back to space.
The study’s findings reveal that it is emissions from small to moderate volcanoes that have been offsetting recent Earth warming, according to Neely, a researcher at the Cooperative Institute for Research in Environmental Sciences.
According to the U.S. Geological Survey, the effects of sulfur dioxide emissions on the environment depend on several factors, including the amount of gas a volcano emits into the atmosphere, whether the gas travels into the troposphere or stratosphere and the regional or global wind and weather pattern that moves the gas.
The motivation for the study was a desire to resolve conflicting results of two recent studies on the origins of the sulfur dioxide in the stratosphere. One study showed that aerosol increases in the stratosphere may have come from India and China’s rising sulfur dioxide emissions, while the other study revealed that moderate volcanic eruptions were to blame.
The new study looks at long-term measurements of changes in the stratospheric aerosol layer’s “optical depth,” which is a measure of transparency, according to Neely. Since 2000, the optical depth in the stratospheric aerosol layer has increased by approximately four to seven percent.
Study co-author Brian Toon of the University of Colorado at Boulder said that scientists must spend more time examining the impact of small and moderate volcanic eruptions when attempting to learn about changes in the Earth’s climate. He added that “overall” these eruptions will not counter the greenhouse effect. While the emissions of volcanic gases increase and decrease, greenhouse gas emissions due to human activity are rising.
The researchers combined the Whole Atmosphere Community Climate Model with a second model, the Community Aerosol and Radiation Model for Atmosphere. The combined use of these two computer models produced the new results from which the researchers drew their conclusions.
According to Neely, the researchers used a supercomputer on campus to process 10 years of atmospheric activity linked to both coal-burning activities in Asia and to emissions by volcanoes around the world. They ran this simulation several times. The team was able to separate coal-burning pollution in Asia from aerosol contributions from moderate volcanic eruptions. According to Neely, each computer “run” took approximately a week to complete.
The researchers warn that the 10-year climate data sets collected by this study are not extensive enough to identify climate change trends. Neely added that the study provides valuable information for those looking into the “sources of decadal climate variability,” in addition to the global impact of local pollution and the role of volcanoes.
According to Toon, larger volcanoes can have an even bigger effect than small and moderate volcanoes. He noted that when Mount Pinatubo erupted in 1991, it sent millions of tons of sulfur dioxide into the atmosphere, cooling the planet for the next several years.
The study’s findings were recently described in the journal Geophysical Research Letters.