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SASKATOON - An international team led by University of Saskatchewan researchers says small volcanic eruptions could cool the climate.
The team says aerosols — minute droplets of sulphuric acid — from relatively small volcanic bursts can be shot into the high atmosphere by weather systems such as monsoons.
Adam Bourassa, who is with the university's Institute of Space and Atmospheric Studies, said that until now it was thought that a massive eruption was needed to inject aerosols past the troposphere, the turbulent atmospheric layer closest to the Earth, into the stable layers of the stratosphere higher up.
"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 said in a phone interview from Saskatoon. "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."
Aerosols in the lower atmosphere usually rain back down to Earth right away.
But aerosols stratosphere can really have an impact on the climate, Bourassa said. Incoming sunlight hits the droplets and scatters, potentially cooling the Earth's surface.
Researchers noted that the massive eruption of Mount Pinatubo in the Philippines in 1991 temporarily dropped temperatures by half a degree Celsius worldwide.
The team, including scientists from Rutgers University in New Jersey, the National Center for Atmospheric Research in Colorado and the University of Wyoming, looked at the June 2011 eruption of the Nabro volcano in Eritrea in northeast Africa. The findings appear in Friday's issue of the journal Science.
The researchers found that wind carried the debris from the volcano into the path of the annual Asian summer monsoon.
Dust from the volcano, being slightly heavier, settled out. But the monsoon lofted volcanic gas and the lighter liquid droplets into the stratosphere where they were detected by the Canadian Space Agency's OSIRIS instrument aboard the Swedish satellite Odin.
The Nabro volcano caused the largest stratospheric aerosols load ever recorded by OSIRIS in its more than 10 years of flight.
Bourassa said the effect won't last forever.
"It's always temporary. You know what goes up must come down."
Researchers say they hope the findings will allow more accurate models of climate behaviour.
"I just want to caution people to know that what we found is an interesting mechanism," he said.
"It's one more piece in the big, complicated puzzle of understanding our Earth's climate. And this is certainly not something that we can ever hope for more volcanic eruptions say to cool off the Earth so we can keep doing whatever we want with greenhouse gases, lets say."
— By Jennifer Graham in Regina
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