Do volcanoes emit more carbon dioxide than human activities?
Carbon dioxide emitted by volcanoes to the atmosphere is one of the natural factors contributing to variations in the ancient climate. However, various studies have shown that, in the last century, the annual amount of carbon dioxide released by human activities far exceeded that released by terrestrial and submarine volcanoes. The estimated amount of anthropogenic (i.e. human-induced) carbon dioxide emission in 2010 is about 35 gigatons, which is more than 100 times the estimated global volcanic carbon dioxide emission (about 0.26 gigaton per year).
Reference:
U.S. Geological Survey, Volcanic Gases and Climate Change Overview.