Sulfur dioxide being spewed into the stratosphere by coal-fired power plants and volcanic eruptions has blunted the impact of global warming over the past decade, offsetting roughly one third of the increased heat caused by greenhouse gas emissions, according to a new study. Researchers at the U.S. National Oceanic and Atmospheric Administration (NOAA) found that stratospheric aerosols formed by sulfur dioxide have nearly doubled in the past decade, and that those aerosols have been reflecting a significant amount of heat back into space. “Aerosols acted to keep warming from being as big as it would have been,” said NOAA atmospheric scientist John Daniel, a co-author of the study published online in Science. Much of the sulfur dioxide that rose into the stratosphere six miles above the Earth came from coal-fired power plants, the study said. The aerosol finding, along with a weaker sun due to the most recent solar cycle, may help explain why global warming has not accelerated as rapidly in the past decade as it did in the 1990s. But scientists say that if major polluters such as China add better scrubbing technology to their power plants, then aerosols in the stratosphere are likely to decrease, which could accelerate warming.