March 3rd, 2013 by James Ayre
New research is suggesting that volcanic aerosol emissions may have had a dampening effect on the warming trend observed from 2000-2010. Without the increase in volcanic emissions the warming trend would have been even more pronounced. The years 2000 through 2010 featured 9 of the 10 warmest years since average global temperature record keeping began. Previously high sulfur dioxide emissions from industrializing countries such as China and India had been implicated in a dampening effect on the overall warming trend that is observed. But the new research, done using computer models, suggests that the dampening effect was more a result of volcanic emissions during this time than from aerosol pollution. It’s worth keeping in complex computer models like the one used in this research have limitations to them, and the research that comes from them is often amended or corrected. It will be interesting to see how this research holds up after further research from other scientists.
As a result of rapid industrialization, India and China both increased their total sulfur dioxide emissions by about from urging the years of 2000 through 2010. And these sulfur dioxide emissions once within the atmosphere interact with other chemicals and function somewhat like a reflective surface in the high-atmospher. Reflecting slightly more solar radiation back to space than previously, for a couple of years. The effect is a short-term one as opposed to the effects of most greenhouse gases, which remain in the atmosphere for longer.
“12 to 20 miles into the stratospheric aerosol layer of the atmosphere, where chemical reactions create sulfuric acid and water particles that reflect sunlight back to space, cooling the planet.”
“Stratospheric aerosols since 2000 have counterbalanced as much as 25 percent of the warming scientists blame on human greenhouse gas emissions. This new study indicates it is emissions from small to moderate volcanoes that have been slowing the warming of the planet,” said Ryan Neely, the lead author of the new paper based on the research.
“The new project was undertaken in part to resolve conflicting results of two recent studies on the origins of the sulfur dioxide in the stratosphere, including a 2009 study led by the late David Hoffman of NOAA indicating aerosol increases in the stratosphere may have come from rising emissions of sulfur dioxide from India and China. In contrast, a 2011 study led by Vernier — who also provided essential observation data for the new GRL study — showed moderate volcanic eruptions play a role in increasing particulates in the stratosphere,” Neely said.
“The new GRL study also builds on a 2011 study led by Solomon showing stratospheric aerosols offset about a quarter of the greenhouse effect warming on Earth during the past decade,” said Neely.
“The new study relies on long-term measurements of changes in the stratospheric aerosol layer’s ‘optical depth,’ which is a measure of transparency,” said Neely. “Since 2000, the optical depth in the stratospheric aerosol layer has increased by about 4 to 7 percent, meaning it is slightly more opaque now than in previous years.”
“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 Toon of CU-Boulder’s Department of Atmospheric and Oceanic Sciences. “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 new research was done using a new combination “of two sophisticated computer models, including the Whole Atmosphere Community Climate Model, or WACCM, Version 3, developed by NCAR and which is widely used around the world by scientists to study the atmosphere. The team coupled WACCM with a second model, the Community Aerosol and Radiation Model for Atmosphere, or CARMA, which allows researchers to calculate properties of specific aerosols and which has been under development by a team led by Toon for the past several decades.”
“Neely said the team used the Janus supercomputer on campus to conduct seven computer ‘runs,’ each simulating 10 years of atmospheric activity tied to both coal-burning activities in Asia and to emissions by volcanoes around the world. Each run took about a week of computer time using 192 processors, allowing the team to separate coal-burning pollution in Asia from aerosol contributions from moderate, global volcanic eruptions. The project would have taken a single computer processor roughly 25 years to complete, said Neely.”
Given that this is all in effect “theoretical”, and based on models, there is still a reasonable argument about how much of the dampening effect is coming from volcanic emissions as opposed to from industrial emissions. Further research is needed for a more clear picture to emerge.
Even with volcanic emissions and industrial aerosol pollution, the warming trend has been continuing. Without these short-term cooling effects, the warming trend would have been more pronounced. The effects of aerosol emission, and where they are originating from, are worth considering because they may be masking a significant amount of the warming caused by greenhouse gases.
As it stands, with greenhouse gas emissions continuing to rise every year the future effects of climate change are set to be severe, causing widespread loss of agricultural productivity, political instability and war, pandemics, and desertification.
The new research was just published online in the journal Geophysical Research Letters.
Image Credits: U.S. Geological Survey; Aerosols India via Wikimedia Commons
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