Volcanoes - molten hot, or chilling?

One of my friends from home posted a question about the role of volcanoes in climate change. It took me a while to gather my thoughts and to research this question. I figured it was important to consider because I have heard this question bandied about in the news, and in conversation about climate change. First, Let me put B's comment below:

"Emily, I personally think you missed one important thing the debate should be about. Yes, no doubt there is global warming. However, are we humans really that big of an influence or is this just a normal, cyclical change in our environment? Sure, we burn carbon based fuels but does anyone really believe that the CO2 output of what we are doing comes anywhere close to what the hundreds of volcanoes around the world spew out every day? There are numerous sources of research to indicate that about every 10000 years or so the earth's climate has changed drastically - I do believe we may be in that cycle of reversal right now. I also believe that it is awfully presumptuous to conclude, based on a little over a hundred years of climate data, that this is an issue that we know ANYTHING about. I'm all for cleaning up the environment and lower emissions but let's keep it real."

The question is interesting because, in my mind, it gets at some of the underlying morality questions of climate change. Is the earth a system impervious to human-induced change, or is it highly sensitive to our every motion? The models that the IPCC relies on to make predictions use at least 5 levels of "climate sensitivity" - because the truth is that we don't really know how sensitive the climate actually is. Some of us are inclined to believe that the climate has reacted immediately to the release of greenhouse gases, others believe that the earth can withstand many more violent fluctuations. I think the answer is probably somewhere in the middle. In my opinion, an extreme assumption either way is more of a moral judgement regarding the relationship between earth and mankind than a scientific one.

In terms of volcanoes and climate change - I did a little research because I didn't know anything about about the topic. What I found is somewhat surprising. I had assumed that volcanoes added carbon and heat to the atmosphere. However, the opposite is true - volcanoes add mostly aerosols and large particulate matter to the atmosphere. The large particulates fall out pretty soon, and have few long term effects on climate. However, the aerosols remain in the atmosphere for years and have a cooling forcing effect on climate. For example, scientists carefully followed the recent explosion of Mount Pinatubo and found that it was correlated to a global cooling period.

Of course, this does not get at the heart of the question, which is whether we truly know anything about our climate - enough to even know whether our activities are causing climate change. My opinion is that we do know that human activities are causing climate change - we have climate data dating back thousands of years (ice cores, dust loggers, tree rings). However, I think that beyond that our suppositions are riddled with uncertainty. The hard part is making decisions in a situation where the uncertainty is so so huge (environmentalists downplay the large gaps in our knowledge) and where the risks may also be big. (Of course, I feel that we should spend more time thinking about what the actual risks are).