The earth didn't warm as much expected from 2000 to 2010, and scientists at the University of Colorado Boulder say they may have identified the reason: sulfur dioxide emissions from volcanoes.
When volcanoes emit sulfur dioxide, says CU, it rises into the stratospheric aerosol layer, and a series of chemical reactions then reflects rays from the sun back into space, cooling the planet.
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Some geoengineering projects suggest that global warming could be counteracted using human technology if we could figure out a way to inject sulfur dioxide into the stratosphere, as this Wired article highlights — a massive project that no one has quite figured out how to make work yet.
Volcanoes, on the other hand, appear to be cooling the planet for us, according to a Colorado University Boulder paper entitled "Recent anthropogenic increases in SO2 from Asia have minimal impact on stratospheric aerosol," thereby removing some of the blame from India and China — who rely largely on coal burning and have increased their sulfur dioxide emissions by a hefty 60 percent since the year 2000.
There's historical precedent for this phenomenon: after the massive 1883 eruption of the Krakatoa volcano in Indonesia, the world experienced a remarkably chilly "year without a summer" — and a cooling of the ocean that may have helped to quell both ocean warming and the rise of the sea level for generations, according to a Nature.com paper.
“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 Brian Toon of Colorado University Boulder's Department of Atmospheric and Oceanic Sciences, on the university website.
“But overall these eruptions are not going to counter the greenhouse effect," warned Toon.
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"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.”
Scientists used supercomputers to simulate 10 years of atmospheric activity linked to both Asian coal-burning and volcanic emissions, conducting 7 "runs" that used a week of computer time and 192 processors, says CU.
The CU scientists stressed that these 10-year-long climate data sets aren't extensive enough to determine true climate change trends, although they noted that the paper "addresses a question of immediate relevance to our understanding of the human impact on climate."