Posted by Rocky Rex
The United States Geological Survey must get asked about this a lot, as they have several web pages on this. Here is one:
On average, human activities put out in just three to five days, the equivalent amount of carbon dioxide that volcanoes produce globally each year.
present-day global volcanic CO2 emissions that give a range of results from a minimum of about one tenth of a billion, to a maximum of about half a billion metric tons of CO2 per year
The published projected anthropogenic CO2 emission rate for 2010 is about 35 billion metric tons per year.
So annually human CO2 production is AT LEAST 70 times that of all volcanoes.
present-day annual anthropogenic CO2 emissions may exceed the CO2 output of one or more supereruptions per year.
Supereruptions are extremely rare with recurrence intervals of 100,000-200,000 years; none have occurred historically