Small Volcanic Eruptions Can Cool Global Climate

By Chelsea Whyte on July 6, 2012 9:26 PM EDT

volcano eruption
Even small volcanic eruptions can emit enough aerosols to affect the global climate, according to new research from the University of Saskatchewan. (Photo: Creative Commons: coolinsights)

Large volcanic eruptions release aerosols into the atmosphere that can help cool the planet, and new research shows that even smaller volcanoes can have the same effect.

An international research team led by the University of Saskatchewan has discovered that aerosols from relatively small volcanic eruptions can be lifted into the high atmosphere by weather systems such as monsoons, where they can affect global temperatures.

"If an aerosol is in the lower atmosphere, it's affected by the weather and it precipitates back down right away," said lead researcher Adam Bourassa. "Once it reaches the stratosphere, it can persist for years, and with that kind of a sustained lifetime, it can really have a lasting effect."

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When aerosols hang out in the stratosphere, the droplets scatter incoming sunlight, a phenomenon that researchers say can potentially cool the Earth's surface.

The team looked at the June 2011 eruption of the Nabro volcano in Eritrea in northeast Africa. The volcano gas and aerosol, made up of small drops of sulfuric acid, was carried on the wind into the path of the annual Asian summer monsoon. The heavy dust particles from the eruption settled back down to the Earth, but the monsoon lifted the volcanic gas and lighter liquid droplets into the stratosphere.

It was previously thought that storms could not penetrate the stratosphere's high layers, which are over 6 miles up at the poles and about 10.5 miles high at the equator. Using the Canadian Space Agency's OSIRIS instrument aboard the Swedish satellite Odin, the team was able to detect the ejected gasses in the stratosphere.

Not only that, the Nabro volcano caused the largest stratospheric aerosol load ever recorded by OSIRIS in its more than 10 years of flight.

The effect of the monsoon was unexpected. Rain and wind usually clear gasses away before they have a chance to rise as far as the stratosphere. But the hot air of the monsoon gave the aerosols a boost.

"We've shown for the first time that volcanoes don't have to have enough power to pump the gases into the stratosphere directly during the eruption," said study co-author Alan Robock, according to The Christian Science Monitor. But this wouldn't necessarily be the case for every small eruption; it would take something of a "perfect storm" combination of weather patterns meeting an eruption.

"It has to be at the right time at the right place," Robock said.

Still, the research shows upends the notion that only large volcanoes can have eruptions that affect the global climate.

"We used to think that a volcano had to have enough energy that it would put its aerosol and gas directly into the stratosphere in order for it to have a climate effect," Bourassa told Canada.com. "But what we see now is that it can be a low altitude as long as it's say next to the Asian summer monsoon and then we can get a climate effect."

"This is the first time that we've ever observed volcanic aerosol reaching the stratosphere via some other pathway," he said. 

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