A quick google will find you many links but for a couple <a href="http://en.wikipedia.org/wiki/Supervolcano">http://en.wikipedia.org/wiki/Supervolcano</a> (many rightly do not like wiki ???but you gave me one so you obviously do place some faith in them. <a href="http://advance.uri.edu/pacer/march2004/story23.htm">http://advance.uri.edu/pacer/march2004/story23.htm</a> You also tell me that everything is a balance between solar, greenhouse, land surface and aerosol.