According to many Skeptics, volcanoes release more Carbon Dioxide than humans, therefore, any human release of the gas is trivial and does not contribute to Global Warming. However, according to the United States Geologic Service, we have released 100 times more CO2 than volcanoes. The United States Geological Survey (USGS) states:
All studies to date of global volcanic carbon dioxide emissions indicate that present-day subaerial and submarine volcanoes release less than a percent of the carbon dioxide released currently by human activities.
Figure 1: The proportion of volcanic emissions of CO2 (small illustration) compared to human emissions (large illustration).
Also, in a detailed scientific paper by the American Geophysical Union, we read:
Which emits more carbon dioxide (CO2): Earth’s volcanoes or human activities? Research findings indicate unequivocally that the answer to this frequently asked question is human activities. However, most people, including some Earth scientists working in fields outside volcanology, are surprised by this answer. The climate change debate has revived and reinforced the belief, widespread among climate skeptics, that volcanoes emit more CO2 than human activities [Gerlach, 2010; Plimer, 2009]. – EOS, Transactions, American Geophysical Union, Volume 92, Number 24, June 14, 2011 Pages 201-208