Do humans add more gases to the atmosphere or do volcanoes? It's a simple question with a complicated answer. Reaching a good estimate is important in guiding global policy for standards to reduce emissions from man-made sources of gases.

Carbon Dioxide


Present-day carbon dioxide (CO2) emissions from subaerial and submarine volcanoes are uncertain at the present time. Gerlach (1991) estimated a total global release of 3-4 x 10E12 mol/yr from volcanoes. While this is a conservative estimate, man-made (anthropogenic) CO2 emissions overwhelm this estimate by at least 150 times.

Sulfur Emissions


Andres and Kasgnoc (1997) estimated the time-averaged inventory of subaerial volcanic sulfur emissions. There inventory was based upon the 25 year history of making sulfur measurements, primarily sulfur dioxide (SO2), at volcanoes. Actual measurements of subaerial volcanic sulfur dioxide emissions indicate a time-averaged flux of 13 Tg/yr sulfur dioxide from early 1970 to 1997. [Note: a Tg is equal to 10E12 grams]. About 4 Tg come from explosive eruptions and 9 Tg is released by passivedegassing, in an average year. When considering the other sulfur species also present in volcanic emissions, a time-averaged inventory of subaerial volcanic sulfur emissions is 10.4 Tg/yr sulfur.

Volcanoes and other natural processes release approximately 24 Tg of sulfur to the atmosphere each year. Thus, volcanoes are responsible for 43% of the total natural S flux each year. Man's activities add about 79 Tg sulfur to the atmosphere each year. In an average year, volcanoes release only 13% of the sulfur added to the atmosphere compared to anthropogenic sources. Andres and Kasgnoc (1997) noted that the bulk of the anthropogenic flux is located in the northern hemisphere while volcanic fluxes occur in much more focused belts around the world.

Gases from Kilauea provides a comparison of a man-made sulfur dioxide gas leaked at a refinery to the gas released by a volcano.


Annual Average Global Emissions of HCl, HF, and HBr, in Tg














Coal combustion




Petroleum combustion




Natural gas combustion



Data compiled by Cadle (1980). Most of the gases emitted by the ocean return to the oceans.

Heavy Metals

Volcanoes also release heavy metal elements as particulate matter. Buat-Menard and Arnold (1978) looked at heavy metals released by Etna. Compared to anthropogenic (man-made) sources, the amount of lead released by Etna is insignificant, the amounts of cadmium, mercury, copper, and zinc are comparable; and the amount of selenium is greater than other sources in the Mediterranean atmospheric environment.


Sources of Information:


Andreae M.O., 1990, Ocean-atmosphere interaction in the global biogeochemical sulfur cycle: Marine Chemistry, v. 30: 1-29.

Andres, R.J., and Kasgnoc, A.D., Global Emissions Inventory Activity, 1997, Global Emissions Inventory Activity: Time-Averaged Inventory of Volcanic Sulfur Emissions.

Barnes, Ivan, Irwin, W.P., and White, D.E., 1978, Global distribution of carbon dioxide discrages, and major zones of seismicity: U.S. Geological Survey Water Resources Investigation 78-79, Open-File Report, 12 p.

Bates, T.S., Lamb, B.K., Guenther, A., Dignon, J., Stoiber, R.E., 1992, Sulfur emissions to the atmosphere from natural sources. Journal of Atmospheric Chemistry 14:315-337.

Buat-Menard, P., and Arnold, M., 1978, The heavy metal chemistry of atmospheric particulate matter emitted by Mount Etna volcano: Geophysical Research Letters, v. 5, p. 245.

Cadle, R.D., 1980, A comparison of volcanic with other fluxes of atmospheric trace gas constituents: Reviews of Geophysics and Space Physics, v. 18, p. 746-752.

Tamar Elias, written communication, , 28 May 1997.

Gerlach, T.M., 1991, Present-day CO2 emissions from volcanoes: Transactions of the American Geophysical Union (EOS), v. 72, p. 249, and 254-255.

Gerlach, T.M., 1991, Etna's Greenhouse Pump: Nature, 351, p. 352-353.

Gerlach, T.M., 1990, Natural Sources of Greenhouse gases: CO2 emissions from volcanoes. Geothermal Resources Council Transactions, vol. 14, part I, pp. 639-641,