01/07/2011 16:48

 Colossal, mind-bogglingly hot and capable of spewing billowing clouds of flight-grounding smoke and searing, molten lava, volcanoes are spectacular displays of the massive forces at work inside our planet. Yet they are dwarfed by humans in at least one respect: their carbon dioxide emissions.



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"The question of whether or not volcanoes emit more CO2 than human activity is one I get more than any question in my email from the general public.' said Terrence Gerlach, a retired volcanologist, formerly with the Cascades Volcano Observatory, part of the US Geological Survey in Vancouver, Wash. Even earth scientists who work in other areas often pose him the question, he said.



"A lot of climate skeptics claim that volcanoes emit more CO2 than humans do," Gerlach said. "They never give any numbers, but the fact is you will never be able to find the volcanic gas scientist that will agree to that," he said.

One example of these skeptic's claims is the 2009 book, "Heaven and Earth: Global Warming, the Missing Science" by Ian Plimer of the University of Adelaide, who did not respond to Discovery News' requests for comment.

"However, these spectacular volcanic explosions that are so stunning on TV last only a few hours," he added. "They are ephemeral. In contrast, the sources of anthropogenic CO2 (smokestacks, exhaust pipes, etc) are comparatively unspectacular, commonplace, and familiar, and in addition they are ubiquitous, ceaseless, and relentless. They emit CO2 24/7."

"The main reason, I think, that this myth persists," Gerlach said: "First of all, the emissions are extremely spectacular. When people see volcanic eruptions on television and it's awesome, and it's very easy for people to imagine that huge amounts of CO2 are being emitted to the atmosphere."

While there is uncertainty in the measurements--researchers estimate between 0.13 and 0.44 billion metric tons per year, with their best estimates between 0.15 and 0.26 billion tons--even the highest end of the range is dwarfed by anthropogenic emissions of 35 billion metric tons in 2010.

Gerlach noted that human land-use changes alone, which include deforestation, release 3.5 billion metric tons per year. Cars and light-duty trucks produce 2 billion metric tons; even cement production produces 1.5 billion tons. Any of these by itself is still several times higher than the annual emissions of all of the world's volcanoes .

Pakistan or Kazakhstan each produce about the amount of CO2 as volcanoes do each year, Gerlach noted in the article.

In yet another comparison, Gerlach reported that in order for volcanic emissions to match those made by humans, the May 18, 1980, Mount St. Helens eruption would need to happen every 2.5 hours. The June 15, 1991, Mount Pinatubo eruption would need to occur every 12.5 hours.

"There is no way you can escape the fact that volcanoes are releasing a tiny amount of emissions right now," said Bernard Marty of the Centre de Recherches Petrographiques et Geochimiques in Nancy, France. "There is no doubt about this."


Marie Edmonds, a volcanologist at Cambridge University agreed. While volcanoes are the most important natural source of atmospheric CO2, she noted, "The results show clearly that the amount is 100-150 times less than anthropogenic amounts."


-Discovery News-

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