Sulfur Dioxide from Volcanoes Keeping the Earth Cool

Volcanoes releasing sulfur dioxide in the atmosphere are the reason behind the temperature not rising as high as expected between years 2000 and 2010, according to a new study.

Ryan Neely, lead author of the study, said that sulfur dioxide emissions rise up to some 12 to 20 miles into the stratospheric aerosol layer of the atmosphere. Here, the gas reacts with other compounds in the aerosol and forms sulfuric acid and water, which later fall back to earth. These water particles reflect sunlight and cool the earth.

These aerosols have compensated for nearly 25 percent of greenhouse emissions, Neely said.

"This new study indicates it is emissions from small to moderate volcanoes that have been slowing the warming of the planet," said Neely, who is a researcher at the Cooperative Institute for Research in Environmental Sciences, according to a news release.

Till now, there were conflicting reports on rising sulfur dioxide emissions from India and China, and effects of the gas released by moderate volcanic eruptions in cooling the earth. Now Neely says that the present study absolves India and China of the change in global temperature by releasing huge amounts of sulfur dioxide in the atmosphere.

The study was based on data available on changing transparency of the stratospheric aerosol layer, which is measured in terms of optical depth. More particles in the aerosol layer make it more opaque. Since the beginning of the millennium, the optical depth of the aerosol layer in stratosphere has increased from 4 to 7 percent.

The study paper is published in the journal Geophysical Research Letters.

"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. 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," said Brian Toon of CU-Boulder's Department of Atmospheric and Oceanic Sciences.