Apologies to those who are sick of this stuff but this one is important to the current "argument" of the deniers. "Volcanic eruptions, even small and moderate ones, might counter some of the effects of global warming, new research suggests. The planet didn't heat up as much as scientists expected it to from 2000 to 2010 (though it was still the warmest decade on record), and a new study finds that chemical compounds spewed during modest eruptions around the globe could be behind the trend. When sulfur dioxide emitted by a volcano rises up to the stratospheric aerosol layer of the atmosphere, it undergoes chemical reactions, forming particles that reflect sunlight back into space instead of letting it get to the surface of the planet. This has a cooling effect on Earth that can help mitigate the impacts of heat-trapping greenhouse gasses. Scientists observed an increase in these sun-scattering aerosols in the atmosphere from 2000 to 2010. Some studies suggested that emissions from rapidly developing countries in Asia could be largely to blame â India and China, for example, are thought to have ramped up their sulfur dioxide output by about 60 percent over the decade through coal burning. But other studies pointed to volcanoes, which are also an important source of sulfur dioxide." http://news.yahoo.com/even-modest-volcanic-eruptions-may-mask-global-warming-210120341.html
So basically one volcano is about the same amount of sulfur dioxide as eight villages and one hospital in Pakistan.