This is fascinating. Reading in Slate about the eruption of Eyjafjallajokull, I came across the following paragraph:
How will the Icelandic eruption affect the climate?Let us see. If I barbecue a hamburger in my backyard, use the air conditioner or drive a car I am contributing to global warming. Tons of sulfur dioxide and and ash will not. Got to love those leftist scientist with degrees in women studies and political science when they discuss climatology.
Probably not significantly, but it's too early to say. The ash and sulfur dioxide ejected in a volcanic eruption can block the sun's rays from reaching the earth. The most important predictors of how much an eruption will impact the weather are ash volume, column height, and duration. These three factors help determine where an eruption falls on the Volcanic Explosivity Index, which runs from 0 ("non-explosive") to 8 ("mega-colossal"). We don't know how the Icelandic eruption will score, but volcanoes in the area rarely clear a 1 ("gentle").