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Old 04 June 2008, 06:47 PM
MEMcNeil
 
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Flame A single volcano emits more greenhouse gases than all mankind has throughout history

One sees the foregoing urban legend frequently being promulgated by many folk ideologically opposed to the idea that global warming may be occurring or starting to occur as a result of anthropogenic (human-caused) emissions of heat-retaining “greenhouse gases”; however, it's quite incorrect. In actuality, humans presently annually vent into the atmosphere something like four hundred times as much carbon dioxide in particular as all the (surface) volcanoes of the world combined.

Getting into the nitty-gritty of comparative numerology, according to this research report [1; see also 2], “subaerial” [surficial] volcanoes on Earth annually produce an average of 34 × 10^12 grams of carbon dioxide from “passive degassing,” together with 31 × 10^12 grams per year resulting from active eruptions, for a total volcanic emission rate of 6.5 × 10^7 or 65 million metric tons of CO2 per year. That sounds like a lot, but per the indicated piece that amounts to a mere 0.22% of present levels of human-caused emissions of carbon dioxide — which anthropogenic contributions may therefore be calculated to lie in the vicinity of 29 or 30 gigatons of CO2 annually.

Another sourced value for anthropogenic CO2 emissions may be found here [3]: “Fossil fuels account for most of the 6.5 billion tons [gigatons] of carbon — the amount present in 25 gigatons of CO2 — that people around the world vent into the air every year.” Twenty-five gigatons is 2.5 × 10^10 metric tons of carbon dioxide released every year as a result of human activities, indicating via this route that volcanoes produce a mere 0.26% of the CO2 that mankind vents into the Earth’s atmosphere.

According to either source we see that modern-day anthropogenic activities exhaust into the Earth’s air around 400 times as much CO2 as all the surficial volcanoes of the planet put together.

(Undersea volcanoes also contribute somewhat to total planetary volcanic emissions, but that isn’t likely to significantly affect the vast disparity between volcanic and anthropogenic CO2 emissions, not to speak of the large likelihood that the great bulk of carbon dioxide exhaled by volcanoes into the (deeper) oceans, remains dissolved in the oceans.)


References:

[1] Stanley N. Williams, Stephen J. Schaefer, Marta Lucia Calvache V., and Dina Lopez, “Global carbon dioxide emission to the atmosphere by volcanoes,” Geochimica et Cosmochimica Acta (Journal of The Geochemical Society and The Meteoritical Society); Vol. 56, Issue No. 4 (April 1992 [1992-04]), pp. 1765-1770.

[2] Richard E. Stoiber, “Volcanic Gases From Subaerial Volcanoes on Earth” (pdf), Global Earth Physics: A Handbook of Physical Constants, AGU Reference Shelf 1, American Geophysical Union, 1995; Table 1, p. 310 [pdf: 3].

[3] Robert F. Service, “The Carbon Conundrum,” Science (journal of the American Association for the Advancement of Science); Vol. 305, Issue No. 5686 (13 August 2004 [2004-08-13]) (“Toward a Hydrogen Economy” special issue), pp. 962-963.
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