Volcanic Aerosols Likely Limited Warming Between 2000 and 2010, World Would Have Warmed Even More Otherwise

Volcanic aerosols likely offset some of the warming that would have otherwise occurred over the years of 2000-2010, according to research from the University of Colorado Boulder. Nine of the ten warmest years since global temperature records began were between 2000-2010, and the trend has been continuing.


Previous research has implicated the industrial sulfur dioxide emissions released by countries such as India and China as having a dampening effect on the general warming trend. Those two countries increased their total sulfur dioxide emissions by around 60% from 2000-2010. But this new research argues that more of the dampening effect was from volcanic emissions rather than industrial. The new work was done through the use of computer models, and without a necessarily accurate representation of the factors involved. It will be interesting to see if this research holds up, or if it is contradicted by further research.

The effect in question works thusly; small quantities of sulfur dioxide are released from the Earth’s surface (volcanos or industry) and eventually makes their way up to about “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.” This effect has a very limited duration that wears off after only a few years, as opposed to gases that have a longer term effect on the climate, such as many, but not all, greenhouse gases. So they can account for short term drops in average temperatures but not for longer term trends.

Current estimates are that recent increases in the levels of stratospheric aerosols since 2000 have counterbalanced as much as 25% of the warming that would have otherwise occurred. With how much global average temperatures have already increased within the past 13 years, that’s an interesting thought to consider. Without the dampening effect that aerosols provide, how high would the temperatures have been?

But there is still some contention about the exact source of these aerosols. And the new research puts forward the argument that it is primarily from volcanic 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 researcher on the study.

“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 key to the new results was the combined use 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.”

According to the researchers, the “10-year climate data sets like the one gathered for the new study are not long enough to determine climate change trends.”

The overall warming trend has been continuing in recent years, regardless of the limited dampening effect that aerosols provide, and is set to become much worse in the coming decades. While the rising temperatures and seas are the effects that first come to mind, the real effects of climate change will be the damage done to the agricultural system, the spread of infectious disease carriers, increasing political instability and war, and desertification.

The new research was just published online in the journal Geophysical Research Letters.

Source: University of Colorado at Boulder

Image Credits: U.S. Geological Survey

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