Volcanic Gases and Climate Change Overview
Volcanoes can impact climate change. During major explosive eruptions huge amounts of volcanic gas, aerosol droplets, and ash are injected into the stratosphere. Injected ash falls rapidly from the stratosphere -- most of it is removed within several days to weeks -- and has little impact on climate change. But volcanic gases like sulfur dioxide can cause global cooling, while volcanic carbon dioxide, a greenhouse gas, has the potential to promote global warming.
The most significant climate impacts from volcanic injections into the stratosphere come from the conversion of sulfur dioxide to sulfuric acid, which condenses rapidly in the stratosphere to form fine sulfate aerosols. The aerosols increase the reflection of radiation from the Sun back into space, cooling the Earth's lower atmosphere or troposphere. Several eruptions during the past century have caused a decline in the average temperature at the Earth's surface of up to half a degree (Fahrenheit scale) for periods of one to three years. The climactic eruption of Mount Pinatubo on June 15, 1991, was one of the largest eruptions of the twentieth century and injected a 20-million ton (metric scale) sulfur dioxide cloud into the stratosphere at an altitude of more than 20 miles. The Pinatubo cloud was the largest sulfur dioxide cloud ever observed in the stratosphere since the beginning of such observations by satellites in 1978. It caused what is believed to be the largest aerosol disturbance of the stratosphere in the twentieth century, though probably smaller than the disturbances from eruptions of Krakatau in 1883 and Tambora in 1815. Consequently, it was a standout in its climate impact and cooled the Earth's surface for three years following the eruption, by as much as 1.3 degrees at the height of the impact. Sulfur dioxide from the large 1783-1784 Laki fissure eruption in Iceland caused regional cooling of Europe and North America by similar amounts for similar periods of time.
For more information about sulfur in the atmosphere, please see Volcanic Sulfur Aerosols Affect Climate and the Earth's Ozone Layer.
While sulfur dioxide released in contemporary volcanic eruptions has occasionally caused detectable global cooling of the lower atmosphere, the carbon dioxide released in contemporary volcanic eruptions has never caused detectable global warming of the atmosphere. This is probably because the amounts of carbon dioxide released in contemporary volcanism have not been of sufficient magnitude to produce detectable global warming. For example, all studies to date of global volcanic carbon dioxide emissions indicate that present-day subaerial and submarine volcanoes release less than a percent of the carbon dioxide released currently by human activities. While it has been proposed that intense volcanic release of carbon dioxide in the deep geologic past did cause global warming, and possibly some mass extinctions, this is a topic of scientific debate at present.
Volcanic versus anthropogenic CO2 emissions
Do the Earths volcanoes emit more CO2 than human activities? Research findings indicate that the answer to this frequently asked question is a clear and unequivocal, No. Human activities, responsible for a projected 35 billion metric tons (gigatons) of CO2 emissions in 2010 (Friedlingstein et al., 2010), release an amount of CO2 that dwarfs the annual CO2 emissions of all the world’s degassing subaerial and submarine volcanoes (Gerlach, 2011).
The published estimates of the global CO2 emission rate for all degassing subaerial (on land) and submarine volcanoes lie in a range from 0.13 gigaton to 0.44 gigaton per year (Gerlach, 1991; Varekamp et al., 1992; Allard, 1992; Sano and Williams, 1996; Marty and Tolstikhin, 1998). The preferred global estimates of the authors of these studies range from about 0.15 to 0.26 gigaton per year. The 35-gigaton projected anthropogenic CO2 emission for 2010 is about 80 to 270 times larger than the respective maximum and minimum annual global volcanic CO2 emission estimates. It is 135 times larger than the highest preferred global volcanic CO2 estimate of 0.26 gigaton per year (Marty and Tolstikhin, 1998).
In recent times, about 70 volcanoes are normally active each year on the Earth’s subaerial terrain. One of these is Kīlauea volcano in Hawaii, which has an annual baseline CO2 output of about 0.0031 gigatons per year [Gerlach et al., 2002]. It would take a huge addition of volcanoes to the subaerial landscape—the equivalent of an extra 11,200 Kīlauea volcanoes—to scale up the global volcanic CO2 emission rate to the anthropogenic CO2 emission rate. Similarly, scaling up the volcanic rate to the current anthropogenic rate by adding more submarine volcanoes would require an addition of about 360 more mid-ocean ridge systems to the sea floor, based on mid-ocean ridge CO2 estimates of Marty and Tolstikhin (1998).
There continues to be efforts to reduce uncertainties and improve estimates of present-day global volcanic CO2 emissions, but there is little doubt among volcanic gas scientists that the anthropogenic CO2 emissions dwarf global volcanic CO2 emissions.
For additional information about this subject, please read the American Geophysical Union's Eos article "Volcanic Versus Anthropogenic Carbon Dioxide" written by USGS scientist Terrence M. Gerlach.
Yearly CO2 emitters
||Billion metric tons per year (Gt/y)|
|Global volcanic emissions (highest preferred estimate)||0.26|
|Anthropogenic CO2 in 2010 (projected)||35.0|
|Light-duty vehicles (cars/trucks)||3.0|
|Approximately 24 1000-megawatt coal-fired power stations *||0.22|
|Saudi Arabia||  0.44|
CO2 emission events
|Mount St. Helens, 18 May 1980||0.01 Gt|
|Mount Pinatubo, 15 June 1991||0.05 Gt|
|Number of Pinatubo-equivalent eruptions equal to annual anthropogenic CO2||700|
|Number of Mount St. Helens-equivalent eruptions equal to annual anthropogenic CO2||3500|
2010 anthropogenic CO2 multiplier (ACM)**
|Number of days for anthropogenic CO2 to equal a year's worth of global volcanism||2.7|
* Equal to 2% of the world's coal-fired electricity-generating capacity.
**Ratio of annual anthropogenic CO2 (35 Gt) to maximum preferred estimate for annual volcanic CO2.
- Volcanic gases in the atmosphere: Volcanic Gases and Their Effects
- Effects of Volcanic Sulfur Aerosols.
- Volcanic Gas Pollution in Hawaii.
- Information about Eyjafjallajökull, Iceland.
Allard, P., 1992, Global emissions of helium-3 by subaerial volcanism: Geophysical Research Letters, v. 19, n. 14, p. 1479-1481.
Friedlingstein, P., Houghton, R. A., Marland, G., Hackler, J., Boden, T. A., Conway, T. J., Canadell, J. G., Raupach, M. R., Ciais, P., and Le Quéré, C., 2010, Update on CO2 emissions, Nat. Geosci., v. 3, n. 12, p. 811–812, doi:10.1038/ngeo1022.
Gerlach, T.M., 2011, Volcanic versus anthropogenic carbon dioxide: Eos Trans. AGU, v. 92, n. 24, p. 201-202.
Gerlach, T.M., 1991, Present-day CO2 emissions from volcanoes: Eos Trans. AGU, v. 72, n. 23, p. 249 and 254-255.
Gerlach, T.M., McGee, K.A., Elias, T., Sutton, A.J., and Doukas, M.P., 2002, Carbon dioxide emission rate of Kīlauea Volcano: Implications for primary magma and the summit reservoir: Journal of Geophysical Research, v. 107, n. B9, p. ECV3-1 – ECV3-15, 2189, doi: 10.1029/2001JB000407.
Marty, B., and I.N. Tolstikhin, 1998, CO2 fluxes from mid-ocean ridges, arcs and plumes: Chemical Geology, v. 145, p. 233-248.
Sano, Y. and Williams, S.N., 1996, Fluxes of mantle and subducted carbon along convergent plate boundaries: Geophysical Research Letters, v. 23, n. 20, p. 2749-2752.
Varekamp, J.C.R., Kreulen, R., Poorter, R.P.E., and Van Bergen, M.J., 1992, Carbon sources and arc volcanism, with implications for the carbon cycle: Terra Nova, v. 4, p. 363-373.