Volcanoes are very cool. Here’s a money quote: Present-day carbon dioxide (CO2) emissions from subaerial and submarine volcanoes are uncertain at the present time. Gerlach (1991) estimated a total global release of 3-4 x 10E12 mol/yr from volcanoes. While this is a conservative estimate, man-made (anthropogenic) CO2 emissions overwhelm this estimate by at least 150 times. How sure about that are they, and how can those claims be made when they don’t know? Not that everything has to be 100% sure, but the scientific community concerned with AGW is circling the wagons. Me thinks they doth protest too much.

http://volcano.oregonstate.edu/education/gases/man.html

They, them, those who we look to don’t know, and try not to let on that they know they don’t know until we know they don’t know. This is that moment. Everyone, to a person, likes to know about what they do with some degree of certainty. It’s human nature. It’s territorial to not allow anyone to see your code, or your sources. That is not higher order thinking, being territorial. That brings much into question, does it not?
Several ways to look at this multiplicity of chemicals released in unknown quantities. Particulate matter blocks or reflects the Sun’s rays, leading to lower temperatures. It’s not just CO2. This is also interesting:

http://www.geology.sdsu.edu/how_volcanoes_work/Volcanic_gases.html
And this:
http://volcanoes.usgs.gov/hazards/gas/index.php

A virtual firehose of information out there.