In what is likely to be several such posts...
This weekend, a friend said that volcanoes produce far more CO2 emissions than mankind ever has. While I knew this statement to be wrong, I didn't have any facts to back it up, just general sciencey stuff that wasn't going to do much to alter the argument.
Basically, the type of pollutants put into the air by volcanoes tend to have a general cooling effect on the atmosphere, so the argument that volcanoes are a larger source of global warming is false. Global warming continues regardless of recent volcanic activity.
This is not to say that volcanoes don't pump out CO2. They do. It is estimated that volcanoes will produce anywhere from 65-319 million metric tonnes of CO2 any given year. Of course, large volcanic events can definitely jack up that number. However, humans produce 29 billion tonnes of CO2 as a direct result of burning fossil fuels. So, volcanoes are in the millions, humans are in the billions. The argument doesn't hold up to facts.
It has been recognized by some climate scientists that a lack of volcanic activity in the early to middle part of the 20th Century may have contributed to warming back then, but the activity has picked up in the last 50 years or so. Again, the reason being is that volcanoes pump out sulfur pollutants (which reflect sunlight back into space before getting to Earth) in far larger quantities than CO2. The Pinatubo eruption back in the early 1990s did have a global cooling effect for several years. Typical cooling effects tended to last a decade or more in ancient times, so the human effects of global warming quickly erased any cooling effects from Pinatubo.