Often you will hear the really gullible climate-change deniers state that compared to human emissions of the greenhouse gas, carbon dioxide, the amount coming out of volcanoes is vastly larger. This, like most stuff put about by climate change deniers, is a lie.
It is true that there are significant emissions of carbon dioxide either from volcanoes1, geysers2, hot springs3 or fumaroles4. These emissions are a small but are an important part of the global carbon cycle5.
Published reviews of the scientific literature by Mörner & Etiope (2002) and Kerrick (2001) have reported a range of emissions of Carbon Dioxide of between 65 million tonnes to 319 million tonnes of carbon dioxide per annum. Climate change deniers will often claim that submarine volcanoes produce vastly greater amounts of carbon dioxide. This is not so6. More recent estimates are that volcanoes (including submarine volcanoes) emit, in total, between 150 million tonnes and 270 million tonnes per annum. These are “utterly dwarfed” by carbon emissions from fossil fuel burning, cement production, gas flaring and land use changes which is estimated to be 36,300 million tonnes per annum, some 130 times greater than emissions from the earth7.
As lies go, that is a pretty big one.