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Global warming might be even worse were it not for the impact of a rash of smaller volcanic eruptions around the globe, a new study suggests.
Those eruptions are blasting more of an atmosphere-cooling gas into the lower stratosphere than scientists previously thought, according to the study, which has been accepted for publication in Geophysical Research Letters. The additional sulfur dioxide may at least partially explain the slowdown in global warming over the last 15 years, an international team of researchers reported.
Scientists have long known that the gases that bigger volcanoes spew out can cool the atmosphere, but they had assumed that smaller eruptions didn’t have the explosive power to reach the stratosphere, said the study’s lead author, David A. Ridley.
“We were looking at medium-sized eruptions like the one in Sarychev Peak in Russia,” Ridley said. “They turned out to be more powerful than we previously thought. And they’re getting stuff into the bottom of the stratosphere.”
Once there, the sulfur dioxide combines with oxygen and forms droplets of sulfuric acid that can remain in the air for many months, reflecting sunlight away from the Earth and lowering temperatures.
Earlier studies missed the effects of the smaller volcanoes because they were based on readings from satellites that don’t see down to the lower part of the stratosphere. Ridley and his colleagues examined data from a NASA network that is based on the Earth and can look up to the bottom of the stratosphere.
Over the last 15 years there have been far more eruptions of moderate-sized volcanoes compared to the previous two decades, Ridley said. And that can at least partly explain why global warming has slowed over the last decade and a half.
By the researchers’ calculations, the moderate-sized eruptions have led to a decrease of about 0.22 degrees Fahrenheit (0.12 Celsius) in global temperatures. But the effect won’t be lasting.
“This is just a brief intermission,” Ridley said. “You can be pretty sure we’ll return to the predicted trend.”