Global Warming Stemmed by Volcanic Aerosols: Eruptions Keep it Cool

Volcanoes may have helped stem the tide of global warming, according to a new study. A team led by the University of Colorado Boulder has found that the reason why the Earth did not warm as much between 2000 and 2010 could be due to the dozens of volcanoes spewing sulfur dioxide into our atmosphere.

The study, published online in the journal Geophysical Research Letters, was conducted in part to resolve the conflicting results of two recent studies on the origin of sulfur dioxide in the atmosphere. One, conducted in 2009, indicated that aerosol increases in the stratosphere may have come from rising emissions of sulfur dioxide from both India in China. This contrasted sharply against a 2011 study which found that moderate volcanic eruptions played a role in increasing particulates in the atmosphere.

Researchers used long-term measurements of changes in the stratospheric aerosol layer's "optical depth" in order to find out the truth. The optical depth is a measure of transparency of the aerosol layer, and has increased by about four to seven percent since the year 2000. In other words, it's slightly more opaque now than in previous years. This data was then used in two sophisticated computer models, including the Whole Community Climate Model (WACCM) and the Community Aerosol and Radiation Model for Atmosphere (CARMA). This allowed researchers to both examine the atmosphere and calculate the properties of specific aerosols.

After simulating 10 years of atmospheric activity during seven computer "runs," the researchers had their results. They discovered that small and moderate volcanoes could mask some of the human-caused warming of the planet as they spew sulfur dioxide into the atmosphere. Larger volcanoes could potentially have a much larger effect as they emit millions of tons of the same material.

"The biggest implication here is that scientists need to pay more attention to small and moderate volcanic eruptions when trying to understand changes in Earth's climate," said Brian Toon, one of the researchers, in a press release.

While volcanoes certainly have a stake in Earth's temperatures, they're not going to halt global warming. Toon continued, "But overall these eruptions are not going to counter the greenhouse effect. Emissions of volcanic gases go up and down, helping to cool or heat the planet, while greenhouse gas emissions from human activity just continue to go up."

The findings could have implications for how climatologists create models that predict temperature over the years. It also helps provide a reason for why cooling event occur for the next several years after a major volcanic eruption.