I'm just doing some reading to prove/disprove my current opinions on this topic, and while reading, I found the following article:
<quote>
Anything else that could shield us from global warming?
Yes, volcanoes. When Mount Pinatubo erupted in June 1991, it threw a huge amount of debris into the stratosphere that partially shielded the surface of the Earth from incoming solar energy. Sulphate particles ejected from the volcano were particularly effective at scattering the sunlight. Computer models successfully predicted that in the short term, the debris would temporarily cool the Earth's atmosphere. The models also predicted that as the volcanic debris cleared in 1992 and 1993, average temperatures would swiftly return first to the level of the 1980s, and then, by the middle of the 1990s, to the slightly higher levels that would be expected with the ongoing build-up of greenhouse gases.
</quote>