evidence: As with all volcanoes, the magma inside Etna holds gas bubbles, such as carbon dioxide, sulfur dioxide and water. Etna is one of the gassiest volcanoes on Earth, pumping out more carbon dioxide than any other volcano, said Keith Putirka, an igneous petrologist at California State University, Fresno, who has studied Etna's deep magma system. "Even though Etna isn't a massive volcano, it puts out massive amounts of carbon dioxide," Putirka told LiveScience's OurAmazingPlanet. "If you threw several more Mount Etnas onto the planet, you could really drive climate change in a serious way."