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What is the source for the amount of CO2 put in the air by volcanoes? It seems to be hotly debated, but I can't find the evidence one way of the other.
John Jones, Exeter
Professor Mitchell: Human activities produce about 150 times as much CO2 as volcanism. Emissions from volcanoes are estimated to be 20 to 50 million tonnes of carbon each year. Human emissions for the period 2000-2005 have been estimated at over 7,000 million of carbon per year (The sources of these numbers can be found within the IPCC WG1 reports). The major eruption of Pinatubo in 1991 was estimated to produce between 10 and 60 millions tonnes of carbon which was not large enough to be detected in the global CO2 record.
