An interesting article in this week's New Scientist ('The ice age that never was', 16th December, p46-47) points out that a crucial turning point of the Second World War, Hitler's failure to take Moscow, was caused by the vicious European winter of 1941-42, and this, in turn, was part of a global cooling trend which lasted until the 1970s. This global cooling trend was caused by a set of volcanic eruptions, which pumped sulphate aerosols into the upper atmosphere, and reflected a sufficient proportion of the Sun's radiation to cause a temporary reduction in global temperatures. Perhaps, then, Hitler was ultimately defeated by the movement of tectonic plates.
The New Scientist article also raises the intriguing possibility that we might want to deliberately inject sulphate aerosols into the upper atmosphere today as an anthropogenic means of controlling global warming. (Some similar suggestions are mentioned in Bryan Appleyard's excellent Sunday Times survey of the various possible responses to global warming: http://www.timesonline.co.uk/article/0,,2099-2208385_1,00.html).
Volcanism, in fact, may be far more beneficial for the environment than often thought. The 'Naked Scientist', Chris Smith, has spotted an excellent idea from Pete McGrail of the Pacific North-West National Laboratory: volcanic basalt may provide an excellent means of sequestrating carbon dioxide, (http://seattletimes.nwsource.com/html/localnews/2003445393_carbonstorage24m.html). When carbon dioxide forms a very strong solution in water (to form carbolic acid), and is then pumped into the sponge-like structure of basalt, the result is solid calcium carbonate, a comparatively safe form in which to store carbon.