A popular myth among climate change skeptics is that volcanic emissions of carbon dioxide dwarf those generated by humans. But a new report in today's issue of Eos reveals precisely the opposite: In a mere 2 to 5 days, smokestacks, tailpipes, and other human sources of CO2 spew a year's worth of volcanic emissions of that greenhouse gas. According to the paper, five recent studies suggest that volcanoes worldwide (such as Alaska's Shishaldin, shown) emit, on average, between 130 million and 440 million metric tons of CO2 each year. But in 2010, anthropogenic emissions of the planet-warming gas were estimated to be a whopping 35 billion metric tons. Individual events—such as Mount Pinatubo, whose major eruption in 1991 lasted about 9 hours—can produce CO 2 at the same rate that humans do, but they do so only for short periods of time. It would take more than 700 Mount Pinatubo-sized eruptions over the course of a year to emit as much carbon dioxide as people do, the study notes.
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