Although they spew tons of heat-trapping carbon dioxide into the air, volcanic eruptions may have slowed global warming during the past two decades, as volcanic gases form mirror-like particles in the air. Recent research is improving climate models by accurately incorporating the effects of these eruptions.

Along with CO2, volcanoes churn out sulfur dioxide gas. That gas turns into tiny droplets of sulfuric acid in the upper atmosphere. Those acid particles act like tiny mirrors to reflect sunlight back into space. For example, after the massive eruption of Mount Pinatubo on June 15, 1991, surface temperatures cooled by as much as 1.3 degrees Fahrenheit (.72 C), according to the U.S. Geological Survey.

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A recent paper published in Nature Geoscience presented evidence that those mirror-like droplets from early 21st century volcanic eruptions may have reduced the rate of climate change. Some previous climate models didn’t accurately represent the droplets’ effects, say the authors of the study.

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By incorporating the reflective particles into simulations, new models reduced the difference between forecasts and actually observed warming by as much as 15 percent.

“In the last decade, the amount of volcanic aerosol in the stratosphere has increased, so more sunlight is being reflected back into space,” said lead author Benjamin Santer, climate scientist at Laurence Livermore National Laboratory, in a press release. “This has created a natural cooling of the planet and has partly offset the increase in surface and atmospheric temperatures due to human influence.”

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Since 1998, the rate of surface temperature warming has plateaued, increasing less than it should have considering the ever-increasing amount of greenhouse gas in the atmosphere. Another recent study suggested that faster trade winds may have been submerging the heat in the waters of the tropical Pacific Ocean. Along with volcanoes and winds, other factors may be deterring climate change.

“The recent slow-down in observed surface and tropospheric warming is a fascinating detective story,” Santer said. “There is not a single culprit, as some scientists have claimed.” Santer pointed to a number of other possible factors including “an uptick in Chinese emissions of sulfur dioxide.”

The question remains: What happens when the trade winds slow, volcanic activity reduces, the sun increases its output or other factor cease to mask the greenhouse effect? A rapid increase in global temperatures could result and cause even more havoc than steadier, slower paced warming would have.

Photo: An aerial view shows a volcanic ash cloud from the Eyjafjallajokull Volcano in Iceland. Credit: Arctic-Images/Corbis