Arguments
Do volcanoes emit more CO2 than humans?
What the science says...
| Select a level... |
Basic
|
Intermediate
| |||
|
Humans emit 100 times more CO2 than volcanoes. |
|||||
Climate Myth...
Volcanoes emit more CO2 than humans
"Human additions of CO2 to the atmosphere must be taken into perspective.
Over the past 250 years, humans have added just one part of CO2 in 10,000 to the atmosphere. One volcanic cough can do this in a day." (Ian Plimer)
At a glance
The false claim that volcanoes emit more CO2 than humans keeps resurfacing every so often. This is despite debunkings from bodies like the United States Geological Survey (USGS). Such claims may be easy to make, but they fall apart once a little scientific scrutiny is applied. So, to settle this once and for all, let's venture out into the fascinating world of geology, plate tectonics and volcanism.
According to the USGS, there are 1,350 active volcanoes on Earth at the moment. An active volcano is one that can erupt, even if it's decades since it last did so. As of June 2023, 48 volcanoes were in continuous eruption, meaning activity occurs every few weeks. Out of those, around 20 will be erupting on any particular day. Several of those will have erupted by the time you have finished reading this.
People are familiar with a typical volcano, an elevated area with one or more craters or fissures from which lava periodically erupts. But there are also the submarine volcanoes such as those along the mid-oceanic ridges. These vast undersea mountain ranges are a key component of Earth's Plate Tectonics system. The basalts they continually erupt solidify into the oceanic crust making up the flooring of the deep oceans. Oceanic crust is constantly moving away from any mid-ocean ridge in the process known as 'sea-floor spreading'.
Oceanic crust is chemically reactive. It reacts with seawater, allowing the formation of huge quantities of minerals including those carrying carbon in the form of carbonate. But oceanic crust is geologically young. That is because it is also being consumed at subduction zones - the deep ocean 'trenches' where it is forced down into Earth's mantle.
When oceanic crust is forced down into the mantle at subduction zones, it heats up and begins to melt into magma. Carbonate minerals in that crust lose their carbon - it is literally cooked out of them. Magmas then transport the CO2 and other gases up through Earth's crust and if they reach the surface, volcanic eruptions occur and the CO2 and other gases leave the magma for the atmosphere.
So here you can see a long-term cycle in which carbon gets trapped in the sea-floor, subducted into the mantle, liberated into new magma and erupted again. It's a key part of Earth's Slow Carbon Cycle.
Volcanoes are also dangerous. That's why we have studied them for centuries. We have hundreds of years of observations of all sorts of eruptions, at Earth's surface and beneath the oceans. Those observations include millions of geochemical analyses of both lavas and gases.
Because of all of that data collected over so many years, we have a very good idea of the amount of CO2 released to the atmosphere by volcanic activity. According to the USGS, it is between 180 and 440 million tons a year.
In 2019, according to the IPCC's Sixth Assessment Report (2022), human CO2 emissions were:
44.25 thousand million tons.
That's at least a hundred times the amount emitted by volcanoes. Case dismissed.
Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!
Further details
Beneath the surface of the Earth, in the various rocks making up the crust and the mantle, is a huge quantity of carbon, far more than is present in the atmosphere or oceans. As well as fossil fuels (those still left in the ground) and limestones (made of calcium carbonate), there are many other compounds of carbon in combination with other chemical elements, making up a range of minerals. According to the respected mineralogy reference website mindat, there are 258 different valid carbonate minerals alone!
Some of this carbon is released in the form of carbon dioxide, through vents at volcanoes and hot springs. Volcanic emissions are an important part of the global Slow Carbon Cycle, involving the movement of carbon from rocks to the atmosphere and back on geological timescales. In this part of the Slow Carbon Cycle (fig. 1), carbonate minerals such as calcite form through the chemical reaction of sea water with the basalt making up oceanic crust. Almost all oceanic crust ends up getting subducted, whereupon it starts to melt deep in the heat of the mantle. Hydrous minerals lose their water which acts as a flux in the melting process. Carbonates get their carbon driven off by the heating. The result is copious amounts of volatile-rich magma.
Magma is buoyant relative to the dense rocks deep inside the Earth. It rises up into the crust and heads towards the surface. Some magma is trapped underground where it slowly cools and solidifies to form intrusions. Some magma reaches the surface to be erupted from volcanoes. Thus a significant amount of carbon is transferred from ocean water to ocean floor, then to the mantle, then to magma and finally to the atmosphere through volcanic degassing.
Fig. 1: An endless cycle of carbon entrapment and release: plate tectonics in cartoon form. Graphic: jg.
Estimates of the amount of CO2 emitted by volcanic activity vary but are all in the low hundreds of millions of tons per annum. That's a fraction of human emissions (Fischer & Aiuppa 2020 and references therein; open access). There have been counter-claims that volcanoes, especially submarine volcanoes, produce vastly greater amounts of CO2 than these estimates. But they are not supported by any papers published by the scientists who study the subject. The USGS and other organisations have debunked such claims repeatedly, for example here and here. To continue to make the claims is tiresome.
The burning of fossil fuels and changes in land use results in the emission into the atmosphere of approximately 44.25 billion tonnes of carbon dioxide per year worldwide (2019 figures, taken from IPCC AR6, WG III Technical Summary 2022). Human emissions numbers are in the region of two orders of magnitude greater than estimated volcanic CO2 fluxes.
Our knowledge of volcanic CO2 discharges would have to be shown to be very mistaken before volcanic CO2 discharges could be considered anything but a bit player in the current picture. They have done nothing to contribute to the recent changes observed in the concentration of CO2 in the Earth's atmosphere. In the Slow Carbon cycle, volcanic outgassing is only part of the picture. There are also the ways in which CO2 is removed from the atmosphere and oceans. If fossil fuel burning was not happening, the Slow Carbon Cycle would be in balance. Instead we've chucked a great big wrench into its gears.
Some people like classic graphs, others prefer alternative ways of illustrating a point. Here's the graph (fig. 2):
Fig. 2: Since the start of the Industrial Revolution, human emissions of carbon dioxide from fossil fuels and cement production (green line) have risen to more than 35 billion metric tons per year, while volcanoes (purple line) produce less than 1 billion metric tons annually. NOAA Climate.gov graph, based on data from the Carbon Dioxide Information Analysis Center (CDIAC) at the DOE's Oak Ridge National Laboratory and Burton et al. (2013).
And here's a cartoon version (fig. 3):
Fig. 3: Another way of expressing the difference between current volcanic and human annual CO2 emissions (as of 2022). Graphic: jg.
Volcanoes can - and do - influence the global climate over time periods of a few years. This is occasionally achieved through the injection of sulfate aerosols into the high reaches of the atmosphere during the very large volcanic eruptions that occur sporadically each century. When such eruptions occur, such as the 1991 example of Mount Pinatubu, a short-lived cooling may be expected and did indeed happen. The aerosols are a cooling agent. So occasional volcanic climate forcing mostly has the opposite sign to global warming.
An exception to this general rule, however, was the cataclysmic January 2022 eruption of the undersea volcano Hunga Tonga–Hunga Ha'apai. The explosion, destroying most of an island, was caused by the sudden interaction of a magma chamber with a vast amount of seawater. It was detected worldwide and the eruption plume shot higher into the atmosphere than any other recorded. The chemistry of the plume was unusual in that water vapour was far more abundant than sulfate. Loading the regional stratosphere with around 150 million tons of water vapour, the eruption is considered to be a rare example of a volcano causing short-term warming, although the amount represents a small addition to the much greater warming caused by human emissions (e.g. Sellitto et al. 2022).
Over geological time, even more intense volcanism has occurred - sometimes on a vast scale compared to anything humans have ever witnessed. Such 'Large Igneous Province' eruptions have even been linked to mass-extinctions, such as that at the end of the Permian period 250 million years ago. So in the absence of humans and their fossil fuel burning, volcanic activity and its carbon emissions have certainly had a hand in driving climate fluctuations on Earth. At times such events have proved disastrous. It's just that today is not one such time. This time, it's mostly down to us.
Last updated on 10 September 2023 by John Mason. View Archives
Thanks for that Logan. I see that this study includes outgassing from volcanic lakes which were missing from earlier estimates. However, as the paper notes, the emissions are still insignificant compared to anthropogenic sources.
The article could be updated because "Humans emit 100 times more CO2 than volcanoes" no longer reflects current best estimates. Human emission is about 50 times more than volcanic.
Here's a recent article by a volcanologist, summarizing latest developments in volcanic CO2 emission research, and the significant uncertainties in the field:
Long Invisible, Research Shows Volcanic CO2 Levels Are Staggering
Logan, the link to the Italian study mentioned in the Op-ed you cite does not lead anywhere, can you reference it otherwise?
PhilippeChantreau @254.
It was linked @250. Burton et al (2013) Deep Carbon Emissions from Volcanoes.
Logan, I agree that the article should be updated to include the recent figures. Those figures indicate 637 Mt per year of CO2 from volcanic sources (including volcanic lakes), and 300 Mt per year from non-volcanic sources (ie, metamorphism), the later derived from Morner and Etiope (2002). In Burton et al (2013), the 937 Mt CO2 per annum from geophysical sources is compared to 35,000 Mt CO2 per annum as calculated by Friedlingstein et al (2010). That estimate was for 2010. A more recent estimate (for 2012), by Le Quere et al (2013), indicates total anthropogenic emissions of CO2 of 38,867 +/- 2,600 Mt CO2 per annum (10.6 +/- 0.71 PgC). Consequently CO2 from geophysical sources represents 2.4% of anthropogenic CO2.
The Burton et al estimate is likely to be too high rather than too low, in that it is significantly greater than recent estimates of in gassing of CO2.
While important to update the figures in the interests of accuracy, it remains clear that geophysically sourced CO2 is emitted far to slow to have been responsible for the recent rapid rise in CO2, which is entirely of anthropogenic origin.
That's also confirmed by carbon isotope measurements as well. So, we have two methods that converge on the same answer.
The Robin Wylie article is bizarrely over-the-top with regards to rhetoric, with the title stating that volcanic CO2 levels are "staggering." And, of course, when you google the article title you see that it's been reposted numerous times throughout the denial blogosphere.
Logan, the article has been noted as needing update but it will sit in the queue with many others. As Tom points out, a good literature review of both volcanic and anthropogenic estimate papers is needed for such an update. Note though that while it is good to put emissions in a context, it is worth noting that no revision of estimates is going get humans off the hook. As Rob points out, FF and volcanoes have different isotopic signitures. Almost all of the increase in CO2 since pre-industrial is of human origin.
CO2 degassing rate by volcanoes does have implications on our understanding of long-tail of antropogenic CO2 slug (i.e. the rate of CO2 sequestration by silicate thermostat or rock weathering).
For example GEOCAB model from UChicago has default parameters of co2 degassing (both Spinup & Simulation) as 7.5E12 mol/y, which is 0.1GtC/y - 1/100 of human emmisions. With such assumption, the GEOCARB simulation of the 1000GtC initial slug ver 10ky, yields the final pCO2 as 319ppm, which is 1.17 times the initial value of 272ppm before Spinup. In other words, 17% of the original C slug remains in the atmosphere after 10ky according to GEOCARB.
Now, if you keep everything the same but increase the CO2 degassing (both Spinup & Simulation), say twice to 15E12 mol/y closer to the latest figures discussed herein, then the final pCO2 value reported by GEOCARB will be 1.07 times the initial value, i.e. only 7% of the original C slug would remain in the atmosphere after 10ky.
So, we can see that increased natural degessing rate would signifficantly shorten the 'long tail' of CO2, now commonly tought to be 'at least 100ky', to something less, say 50ky. Which is good news for the possibility of earth's recovery, maybe the sixth mass exctinction will be avoided. But within human timescale, such correction is irrelevant because 50ky as 100ky, is still "essencially forever".
chriskoz @259, I am not sure what you did with the online model. I increased the volcanic degassing to 27.5 terra moles per annum (the value arrived at in Burton et al), and increased land area by the same factor (3.67) to set the default ingassing level to the same value. Doing so I arrived at the same result that you did. I noticed, however, that after 1000 years, the CO2 level was still 338 ppmv (24% increase; 1.15 W/m^2 forcing), and that it was 412 ppmv (51% increas; 2.2 W/m^2 forcing) afer 400 years. At a time scale where long term feedbacks are starting to be significant, these are still significant forcings. Further, the 1000 Gtc slug used here is the trillion tonnes of carbon target that is commonly accepted to maintain temperature increases below 2 C. That is, it is the policy target we are very far from achieving. Increasing the slug to 2000 Gtc increases the CO2 concentration to 554 ppmv (100% increase; 3.7 W/m^2 forcing) in 400 years, to 417 ppmv in 1000 years (53% increase; 2.3 W/m^2 forcing), and 322 ppmv in 10,000 years (18% increase; 0.9 W/m^2 forcing). Clearly if we overshoot the 1000 Gtc mark, this salvation comes to late and to slowly to be of much use.
Further, this estimate of geophysical outgassing is significantly greater than current estimates of ingassing. It may be that those estimates will also be revised upwards in future; but it is as likely that future estimates of geophysical outgassing will be revised down towards the current ingassing estimates of 403 to 515 Mt CO2 per annum (the two figures cited by Burton et al). That would still represent a substantial increase over over previous estimates of geophysical outgassing, but just half of the Burton et al estimate.
It may, of course, be that both the ingassing and outgassing estimates are accurate, and that there is an imbalance between the two. That, however, would be bad news in the long term as it would indicate the current high outgassing levels to be an aberration, not likely to last long, and likely to permanently raise CO2 levels if they do. It is the presumed increase in ingassing that is the good news, not the increased rate of degassing. And even that is only good news in the very long term, humanly speaking. (I am certain you are aware of these nuances, but think they are worth clariffying for others.)
Tom@260,
Indeed i ran the GEOCARB model just like your did, except I increased the Degas rate just twice (15E12 mol/y) as my own experiment (Burton et al value maybe an overestimate). I also increased land area twice so that degassing and ingassing (shown as "WeatS") be in balanace which was my implicit assumption that I forgot to state in my previous comment (sorry). Then I compared the pCO2 output with the default run.
Hint for those who play with this model online: in between two runs, you can hit "save model run in background" button and all your graphs will be duplicated (the other run values will be displayed as "pCO2 alt", "WeatS alt" etc.), and you can compare the two runs superimposed.
So comparing the pCO2 of my two runs, in say 500y timeframe, the difference is 413 (default) vs. 401 (mine), i.e. 12ppm only. In 1000y the difference is 372 vs. 356, therefore more. In 10ky, it is 319 vs. 307 which is still more in terms of climate forcing. As expected, the stronger degassing/ingassing exchange has signifficant influence on atmospheric carbon carbon slug decline in long term (>1000y) only.
This sentence doesn't seem to make any sense:
''In fact, the rate of change of CO2 levels actually drops slightly after a volcanic eruption, possibly due to the cooling effect of aerosols.''
Shouldn't that read ''...the rate of temperature increase actually drops slightly after a volcanic eruption, possibly due to the cooling effect of aerosols.''?
LuisC @262, cooler water absorbs more CO2 than warmer water. That is why soft drinks give of CO2 as they warm. The volcanic cooling due to aerosols sufficiently cools the surface ocean that the oceans absorb more CO2 than the volcanoes emit. Consequently the statement you quote is typically true. (Coincidence of a strong El Nino with a volcano can cancel this effect.)
While the statement is true and does emphasize the small amount of total volcanic emissions, not to much should be read into it. In particular, as the ocean warms with the passing of the volcanic aerosols, the excess CO2 emited by the volcano will be outgassed by the warming oceans (or at least, 55% of it will, as with human emissions). Therefore the volcanic cooling has no long term effect. The volcanic emissions, particularly those of a single volcano remain small in annual terms relative to anthropogenic emissions.
I would like to see more about what would have to occur in order for volcanic activity to make humans decreasing carbon emissions not effective. I also want know how much if any volcanic activity has on global warming and compared to humans effects.
Clapper, large volcanoes in this era mostly cool the earth temporarily thanks to aerosols which persist for a few years. In the distant past, gigantic volcanic eruptions sustained for a long time (Large Igneous Provences) are associated with mass extinctions. See here (and the other part) for more detail. Short answer is that you need volcanic activity like hasnt been experienced for 100s of million years to get something comparable to human FF emission rates.
"Counter claims that volcanoes, especially submarine volcanoes, produce vastly greater amounts of CO2 than these estimates are not supported by any papers published by the scientists who study the subject" ... this statement inferes that the scientists who study the subject know everything there is to know about the subject. The inconvenient truth is that the ocean occupies two thirds of the planet and the ocean floor isn't mapped as nicely as the streets of Manhattan. Just recently a vast area of underwater vents emmitting CO2 like a glass of champagne were accidentally found near sea coral off New Guninea. Science is not based on consensus, it is based on fact. Before we can determine cause and effect as it pertains to global warming we must identify all of the CO2 emmitting sources then measure their variance against the change in global temperature. We are a long way from knowing how many CO2 emmitting sources are under the sea.
Ybnvs @266, it is ironic that somebody trumpeting that "science is based on fact" provides no evidence if the CO2 vents "just recently" found of New Guinea - something I can find no evidence of either by searching google, or google scholar.
However, science is not founded on 'fact' as you put it, but on fact and reasoning. It follows that if you are to criticize a scientific finding, you must be at least aware of the scientific reasoning behind the result. In this case, the total volcanic CO2 flux is determined not just be adding up sources, but by detecting atmospheric (or sea water) concentration of tracer gases from volcanoes, such as H3 - determining the total flux from that concentration, and from that and knowledge of the ratio of CO2 to the tracer gas from volcanic emissions, determining the total CO2 flux.
A third approach is to determine the rate at which CO2 is naturally sequestered. Given that CO2 concentrations have been stable for 10 thousand years, and (once temperature fluctuations are accounted for, over millions of years), the total geological flux of CO2 must be very close to the rate at which CO2 is sequestered - given a third method of determining the total geological CO2 flux.
As the rate of geological CO2 flux has been determined by two methods in addition to the simple inventory method you assume, we have good reason to think that changes in that inventory will not substantially revise the current estimates, and certainly not by two orders of magnitude required for geological flux to equal anthropogenic flux. That is particularly the case given that your uncited new source consists of a CO2 vent, ie, a type with a much lower overall flux than is typical of direct volcanic sources.
Well Tom that's a long winded way of saying that we're still not sure of exactly what's occuring. Occum's razor has it's place in discussions such as this and we have to be careful not to get caught up in the lure of excessive and obscure data, after all... figures can lie and liars can figure. Sometimes it's not as difficult to find meaningful information as we tend to make it, and learning of the CO2 emitting vents near New Guinea can be as easy as watching a documentary on Nova. In regard to climate change one thing that has remained constant is change. The planet isn't as it was and won't be as it is. My interest in this topic came from hearing environmentalists voice the absurd notion that mankind is responsible for climate change. Decades ago I noticed that the hockey stick graph actually showed temperature increasing before CO2 increased, but it was only recently that I heard someone else point that out, I wonder why it took so long. Anyway... I don't know anyone who wants dirty air or water and I'm suspicious of demagogues whose solution to a perceived problem is monetary. I understand that my thoughts will be criticised as simple (Occums razor) but my assertion that we can't establish cause and effect is rock solid. Time is the best underwriter and in time I'm sure I will be vindicated. Peace.
Ybnvs says "that's a long winded way of saying that we're still not sure of exactly what's occuring." I do not see how Tom's post can possibly be interpreted this way. In fact, it is exactly the opposite. The atmospheric carbon budget is a well understood part of the climate and there are numerous ways to address it. Newly discovered vents would have to spew out amounts of gas ata rate that would defy the laws of physics to make a significant difference.
The isotopic signatures of volcanic vs organic fossil carbon are well studied. The physics of radiative transfer are also well understood. Occam's razor does not cut the way you seem to think it does in this case. Everything that is well known and easily verifiable about Earth climate indicates that the climate should be changing because of anthropogenic CO2; it would be very strange if observations did not match that expectation. Fortunately, they do.
I tried to locate a recent NOVA documentary on deep sea vents off New Guinea. I located several short segments intended for teachers, the most recent dated from 2005, 11 years ago. Other ranged between 1977 and 1999. If you are to contribute anything here, you should link the specific new information that you think invalidates some really well established knowledge. Extraordinary claims require extraordinary evidence.
The most recent I could find is a National Geographic story about a hydrothermal field 1300 ft long located 150 miles East of La Paz, Mexico. Not quite a game changer.
Ybnvs @268:
1) It is not simple reasoning (except in a perjorative sense) to take William of Ockham's principle that we should not multiply entities beyond necessity and conclude that volcanic seeps and subsurface volcanism exist far in excess of, not just what has been observed, but what would be expected from surveys of the ocean floor. Rather, it invokes a principle as justification of doing the reverse of what the principle dictates by mulitiplying our estimate of the number of seeps and subsurface volcanoes beyond any necessity justified by the data. (Note it is Ockham in the English spelling, or Occam from the anglicized latin spelling - not Occum.)
2) That a NOVA documentary features a volcanic seep near New Guinea (of which several are known) in no way proves the seep to be newly discovered, or extensive enough to alter in any way estimates of subsurface CO2 emissions. And FYI, there are smaller seeps than those listed at the link above such as those in Milne bay, but again these are well known. It remains the case that you have yet to present any evidence for your claims.
3) While the uncertainty about volcanic emissions is sufficiently large that they may be up to double current estimates, we would need to be underestimating volcanic emissions by a factor of 50 for volcanic emissions to represent even 50% of anthropogenic emissions. That scale of error is simply not on the cards, and for you to be certain that the error in current estimates is even greater than that, as it would need to be for volcanic emissions to be the primary cause of the increased CO2 levels, without having become even superficially familiar with the relevant scientific papers shows that your certainty the the scientists who have dedicated their career to studying this issue (and hence who are well familliar with the facts, as you are not; and well familliar with the relevant arguments, as you are not) represents a breath taking arrogance. The style of reasoning you evidence even has a formal name - invincible ignorance.
4) As PhillipeChantreau alludes to, while there is significant uncertainty as to the actual value of volcanic emissions, regardless, other evidence makes as certain as it is possible to be in science that anthropogenic emissions are the cause of the rapid rise in CO2 levels in the twentieth century.
5) CO2 emissions and concentrations started rising around 1750, and rose rapidly after 1850:
In contrast, temperatures did not start rising significantly until 1910:
Again, whatever your argument with regard to temperatures, it is based on a very selective misinterpretation of the evidence.
Ybnvs
Just a reaction to several things you have said:
"My interest in this topic came from hearing environmentalists voice the absurd notion that mankind is responsible for climate change."
Why absurd? This sounds like an 'Argument from Incredulity'. Surely whether humans are responsible for climate change depends on two factors, both ultimately quantitaive.
Both these questions can be explored through measurement, observation and quantification. Just using the label 'absurd' is a cop out.
"Decades ago I noticed that the hockey stick graph actually showed temperature increasing before CO2 increased, but it was only recently that I heard someone else point that out"
Then you need to check your sources. The 'temperature increased before CO2' argument applies to the ice cores that cover time scales 10 to 80 times longer than the 'hockey stick'. The 'hockey stick' does not reference CO2 levels at all. And the ice core ecord is more complex than that. Different ice cores show different raltionships.
'and I'm suspicious of demagogues whose solution to a perceived problem is monetary. '
So what does this have to do with the science? If the science says that we need to reduce CO2 emissions, that is not as as such a monetary question. Implementing it might be but it is a logical fallacy to say that 'Problem A requires a solution that looks like B and since I don't like B, A is not real'.
"I understand that my thoughts will be criticised as simple (Occums razor) but my assertion that we can't establish cause and effect is rock solid."
Sorry, this is illogical. If your assertion is rock solid then you are claiming that you have established an alternative cause and effect relationship. Also there is a fundamental distinction between saying we 'haven't' established a cause and effect relationship and saying we 'can't'. Finally, if you think a cause and effect relationship hasn't yet been established, you need to back that up.
Gavin over at RealClimate has a good post up on the "Volcano Gambit" — a look at the twisted history of misinformation on volcanoes over the last few decades.
Hi John C, you might want to use this quote from the United States Geological Survey as regards the amount of CO2 released by volcanoes compared to human emmissions:
This might be a more digestible reference for a basic level audience compared to a quote from two scientific papers.
earthquake tragedy in china was on 2008. there is volcanoes and earthquake zone in ring of fire. see on information of earthquake prone zones.