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Climate Hustle

Global climate impacts of a potential volcanic eruption of Mount Agung

Posted on 4 October 2017 by Guest Author

Guest post by: 

Flavio Lehner ( and John Fasullo

National Center for Atmospheric Research, Boulder, CO, USA

An example of a stratovolcano eruption (note: not Mt. Agung). On July 13, 2015, the Operational Land Imager (OLI) on Landsat 8 took a close up of Mount Raung's summit caldera (on the Indonesian island of Java). Visible is afternoon cloud cover and an eruption plume. Image courtesy of NASA.

Recent weeks have seen an increase in the number of earthquakes happening below Mount Agung, a 9,944ft (3,031m) high volcano in eastern Bali, Indonesia. Authorities have evacuated nearly 50,000 people in the vicinity of the volcano in light of a potential eruption. In addition to concern for people’s lives and infrastructure, the tourism industry fears the potential for disrupted flight plans.

Mount Agung erupted last in 1963, killing over 1,000 people. As is common with large explosive eruptions, it also injected significant amounts of sulfur dioxide into the stratosphere (at least 16-18km above the surface). There, sulfur dioxide combined with water to form sulfuric acid aerosols. These aerosols reflect incoming solar radiation, causing cooling of the Earth’s climate. In fact, volcanic eruptions have been the most important external driver of interannual to decadal variability in global mean surface temperature for at least the past millennium1.

The cooling of global mean temperature from the 1963 eruption amounted to about 0.2 to 0.3°C, although it is difficult to precisely quantify from the noisy observational record where temperature variations unrelated to the volcanic eruption can occur simultaneously2. After such eruptions, global temperature eventually recovers to pre-eruption levels, but both the peak cooling and the recovery time depend on the magnitude and evolution of the eruption; that is, the amount of sulfur dioxide that is emitted and the duration of the eruption.

The second half of the 20th century has seen only two other large eruptions of comparable magnitude: El Chichón in 1982, and Pinatubo in 1991. As with the 1963 Agung eruption, all left significant imprints on climate, most prominently in global temperature but also in global ocean heat content and sea level3, the carbon cycle4, precipitation and streamflow5.

Scientists have been analyzing the precious data that emerged from these rare events for decades. For example, these eruptions serve as test beds for climate models and their ability to simulate the response to energy balance perturbations such as those arising from the reduced incoming solar radiation after volcanic eruptions6. However, it has been over 26 years since the last large eruption and the observing systems in place at that time were relatively primitive. Now, there are a number of new observing systems in place (most notably satellites such as the NASA A-Train and ARGO floats that measure ocean conditions at depth) that have never been tested during such an eruption. These systems could provide critical new measurements to improve our understanding of volcanic impacts on climate and the Earth system, which in turn will serve as an important test of climate models.

Coincidently, the three major eruptions since 1950 were contemporaneous with the warm phase of the El Niño-Southern Oscillation (ENSO), called El Niño events. During these natural events, large amounts of energy are redistributed from the tropical Pacific Ocean around the world, typically leading to a bump in global temperature of about +0.1 to 0.2°C.

While it remains debated whether volcanic eruptions themselves are able to trigger El Niño events, scientists recognized the tendency for volcanic cooling to be balanced by a warming El Niño event in the last about 60 years. Using climate models, such confounding effects have been estimated and removed7,8, revealing that when such effects are taken into account, climate models are significantly better at simulating the global temperature response to eruptions than was previously thought8.

So what should we expect global temperature to do if Mount Agung erupts again within the coming months? While the general forecasting of volcanic eruptions has improved greatly over recent decades – saving many lives like on Bali today – we still cannot predict when exactly an eruption will occur, what its strength will be, and how long it will last. These are all critical factors that determine the response of temperature and other climate aspects to a potential eruption and thus we cannot currently make reliable climate forecasts associated with it. We can think through possible scenarios, though.

The NOAA Climate Prediction Center in its latest ENSO forecast advisory (2nd October 2017) gave a 55-60% chance for the development of a La Niña during this coming winter. La Niña is the counterpart to El Niño and typically causes global mean temperature to be lower than it would be if ENSO conditions were neutral.

One scenario to think through could thus be a major eruption occurring during a La Niña this coming winter. Using the Community Earth System Model Large Ensemble9 (CESM) we can estimate, at least with a climate model, how much the volcanic cooling might be amplified through the coincidental occurrence of a La Niña. The CESM simulations consist of 40 historical simulations, all of which include a representation of the three volcanic eruptions as they occurred in 1963, 1982, and 1991. While imperfect, the CESM does a decent job of simulating the global mean temperature response to recent volcanic eruptions8. We then subsample the 40 historical simulations of the CESM according to whether the eruptions occurred during an El Niño or a La Niña.

Here we use the model information from all three late 20th Century eruptions even though Pinatubo and El Chichón are obviously located in different parts of the world, and erupted with somewhat different strength than Agung. However, they are all located in the tropics close to the Equator, which allows the sulfur dioxide injected into the stratosphere to spread easily across the hemisphere, thus maximizing its impact on global climate. Research has shown that the location and season of an eruption can also influence the characteristics of its climate impact, although decisively less than the eruption strength and duration10,11.

As expected, the CESM suggests that an eruption comparable in magnitude to the 1963 Mount Agung eruption occurring during a La Niña would lead to significantly more cooling than if ENSO neutral conditions coincided with it (Figure 1). Similarly, such an eruption would cool significantly less if it happened during an El Niño. The CESM on average suggests almost 0.3°C cooling for an eruption during a La Niña and less than 0.1°C during an El Niño.

The model also suggests that for an eruption of this strength, global temperature should return to pre-eruption levels within about 5 years, irrespective of which ENSO state prevails during the eruption (Figure 1).


Figure 1: (Left) Composite global mean surface temperature anomaly from the Community Earth System Model Large Ensemble (CESM) during the three volcanic eruptions Agung 1963, El Chichón 1982, and Pinatubo 1991. Anomalies are relative to the 5-year mean preceding the eruption. The CESM simulations have 40 members, yielding 120 simulations of the 3 eruptions. Once the 120 simulations are subsampled according to ENSO state during the eruption, they reveal how El Niños dampen and La Niñas exacerbate the volcanic cooling. Time series are filtered with a 1-2-1 filter, the shading shows 5-95% uncertainty range, the lines are the ensemble mean, and the blue and red bars indicate when the ‘El Niño’ and ‘La Niña’ cases differ significantly from the ‘All’ cases. (Right) Scenarios of annual mean global temperature evolution if an Agung­-like eruption occurred in 2017, constructed by adding the ensemble of temperature anomalies from the left panel to random ensemble members from CESM in 2017. Observations are from the Berkley Earth Surface Temperature (BEST) dataset.

These cooling estimates need to be kept in mind when we turn to other comparisons of climate models with reality. For example, in the heated debate over whether climate models are overestimating the global warming response to increased greenhouse gas concentrations, such nuances become important. CMIP5 and the last IPCC assessment were based on simulations that were forced, among other things, with observed volcanic eruptions up until 2005. At the time, that was all that was available and climate models did not therefore include volcanic eruptions after 2005. In reality, however, a number of smaller eruptions did occur after 2005 and thus caused some expected discrepancy with the model simulations12.

To address this issue, scientists are now producing climate projections that include hypothetical future volcanic eruptions, which enables us to answer more quantitatively the question of whether we should expect the effect of volcanic eruptions on climate to be different in a warmer future compared to the past13,14.

Current forecasts, whether statistical or dynamical, as to how warm the years 2017 and 2018 will be, would clearly be affected by a new eruption of Mount Agung (at least if it is similar in strength and duration to the three largest late 20th century eruptions). As illustrated in Figure 1, global temperatures within the next two years could easily drop as low as what they were in 2012 at the end of the infamous "global warming slowdown". Further, given the recovery time of global temperature after an eruption, some discrepancies with CMIP5 model projections until the beginning of the 2020s might also be expected.

This example also shows that global temperature, albeit popular, is not the most robust quantity to measure changes in Earth’s climate. Even absent a strong external forcing, global temperature can vary substantially from year to year, making it difficult to separate the signal from the noise in case of a volcanic eruption or increasing greenhouse gas concentrations. Instead, scientists propose to look at quantities such as global sea level or ocean heat content to take the pulse of our planet15. Those quantities integrate the response of the climate system over very large volumes, thus beating down the noise relative to the signal.


1. Schurer, A. P., Hegerl, G. C., Mann, M. E., Tett, S. F. B. & Phipps, S. J. Separating forced from chaotic climate variability over the past millennium. J. Clim. 26, 6954–6973 (2013).

2. Thompson, D. W. J., Wallace, J. M., Jones, P. D. & Kennedy, J. J. Identifying signatures of natural climate variability in time series of global-mean surface temperature: Methodology and insights. J. Clim. 22, 6120–6141 (2009).

3. Fasullo, J. T., Nerem, R. S. & Hamlington, B. Is the detection of accelerated sea level rise imminent? Sci. Rep. 6, 31245 (2016).

4. Frölicher, T. L., Joos, F., Raible, C. C. & Sarmiento, J. L. Atmospheric CO2 response to volcanic eruptions: The role of ENSO, season, and variability. Global Biogeochem. Cycles 27, 239–251 (2013).

5. Iles, C. E. & Hegerl, G. C. Systematic change in global patterns of streamflow following volcanic eruptions. Nat. Geosci. 8, 838–842 (2015).

6. Hansen, J., Wang, W. & Lacis, A. Mount Agung Eruption Provides Test of a Global Climatic Perturbation. Science 199, 1065–1068 (1978).

7. Kirchner, I. & Graf, H.-F. Volcanos and El Niño: signal separation in Northern Hemisphere winter. Climate Dynamics 11, 341–358 (1995).

8. Lehner, F., Schurer, A. P., Hegerl, G. C., Deser, C. & Frölicher, T. L. The importance of ENSO phase during volcanic eruptions for detection and attribution. Geophysical Research Letters (2016). doi:10.1002/2016GL067935

9. Kay, J. E. et al. The Community Earth System Model (CESM) Large Ensemble Project: A Community Resource for Studying Climate Change in the Presence of Internal Climate Variability. Bull. Am. Meteorol. Soc. 141119125353005 (2014). doi:10.1175/BAMS-D-13-00255.1

10. Colose, C. M., LeGrande, A. N. & Vuille, M. Hemispherically asymmetric volcanic forcing of tropical hydroclimate during the last millennium. Earth Syst. Dyn. 7, 681–696 (2016).

11. Stevenson, S., Fasullo, J. T., Otto-Bliesner, B. L., Tomas, R. A. & Gao, C. Role of eruption season in reconciling model and proxy responses to tropical volcanism. Proc. Natl. Acad. Sci. 114, 201612505 (2017).

12. Santer, B. D. et al. Volcanic contribution to decadal changes in tropospheric temperature. Nat. Geosci. 7, 185–189 (2014).

13. Bethke, I. et al. Potential volcanic impacts on future climate variability. Nat. Clim. Chang. (2017). doi:10.1038/nclimate3394

14. Fasullo, J. T. et al. The Amplifying Influence of Increased Ocean Stratification on A Future Year Without A Summer. Nat. Commun. (2017).

15. Cheng, L. et al. Taking the pulse of the planet. Eos (Washington. DC). 98, (2017).


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Comments 1 to 50 out of 51:

  1. So in other words we could get a combination of a volcanic eruption, and a la nina, thus two or three years of quite low temperatues, and the climate sceptics will start chanting "global warming has stopped" and "liberal scam" and "greenhouse effect falsified" all over again. It's enough to make you weep.

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  2. I had exactly the same thoughts, nigelj.

    Just wait.... and the press will lap it up.

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  3. A respite from warming is good news. Really. However, if emissions continue unabated there will be even more GHG when the aerosols abate and we will rapidly warm again. One can hope that time will be used wisely rather than listening to idiots who are going to deny no matter what.

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  4. This is a timely and useful article. If Mt. Agung erupts and there is temporary cooling, the denialista will regard any such explanations as "making up excuses after the fact". The fact that this very same volcano has been studied in the past shows that pre-bunked argument for what it is.

    I remember Mt. Agung being discussed in climatology classes back in the 1970s and 1980s, when I was at university. One of the references listed here is from 1978, fer christ's sake.

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  5. @Nigelj 

    They will do that regardless. A political position does not change based on physical evidence. 

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  6. @Nigelj - 2 

    If it's any comfort, the majority of the world already acknowledges AGW. Even US-based oil companies all do so privately, and some publicly (which is against their own interests).  The biggest players are the likes of Saudi Aramco and Venezula, which both own the oil and oil production companies.  It would be interesting to find their official statments on the matter. 

    I believe (mmm, can't remember where I saw the figures) that a majority of the US population considers AGW to be real. Most also have other things on their mind, such as why their school will not discipline the two kids who disrupt every class, etc.  We may know that it is on track to be a huge problem somewhere in the future, but people don't live somewhere in the future.  There are now 7.5 billion humans, and outside of a relative handful they all want more:  more meat, refrigerators, cars, houses, wives.

    Them's the breaks.

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  7. ' more meat, refrigerators, cars, houses, wives.'

    LOL. I'm pretty sure that around half of that 7.5 billion don't want wives, more or otherwise. :-)

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  8. Driving by @5

    "They will do that regardless. A political position does not change based on physical evidence."

    This is so true with a lot of people. Political tribalism is strong and people hold beliefs passionately, even when the evidence against is overwhelming, and you also have the pluralistic ignorance effect somebody mentioned. Sigh.

    But thats no excuse. People need to work a bit harder at being less "political". I'm one of those swing voters and  I just refuse point blank to be too partisan. 

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  9. "One scenario to think through could thus be a major eruption occurring during a La Niña this coming winter." Should probably be "...coming north hemisphere winter."

    And "global temperature" near the beginning of the last paragraph should probably be "global atmospheric temperature" since this is later contrasted with global ocean temperature.

    Those interested in the possibility that large volcanic eruptions may be able to actually trigger El Nino conditions might be interested in the physorg article linked here:

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  10. Direct link to Bethke et al: LINK

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    Moderator Response:

    [TD] Replaced link because it was breaking page format.

  11. Thanks for the comments and feedback.

    Indeed, with "global temperature" we mean "global surface air temperature" throughout the article, which refers to an estimate of the air temperature 2 meters (~6.5 ft) above ground. Also, we should have clarified that we mean Northern Hemisphere/boreal winter.

    @DrivingBy: you might be thinking about the Yale climate opinion maps:

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  12. During all volcano eruptions so called greenhouse gases (H2O, CO2, SO2,etc.) are emitted in great amounts. May be, any supporter of the greenhouse effect theory can explain why all eruptions caused cooling of the Earth's climate. The effect of sulfuric acid aerosols and other solid particles (volcanic ash, soot) is, of course, important, but why we don't see the vidence of greenhouse effect in this case? As this is your first post, Skeptical Science respectfully reminds you to  comments policy. Thank You!

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  13. Aleks @12

    Just briefly the sort of volcanic eruptions we typically see decade to decade dont emit enough CO2 and other greenhouse gases to make much difference as below from an article on this website:

    "Published reviews (on volcanoes) of the scientific literature by Mörner and Etiope (2002) and Kerrick (2001) report a range of emission of 65 to 319 million tonnes of CO2 per year. "

    The burning of fossil fuels and changes in land use results in the emission into the atmosphere of approximately 34 billion tonnes of carbon dioxide per year worldwide, according to the U.S. Energy Information Administration (EIA)

    They do emit enough aerosols to cool the climate dor a year or two.

    Some massive volcanic explosions like Krakatoa have emitted enough CO2 to get really significant, but they are infrequent. In fact theres evidence that a massive and frequent series of volcanic eruptions millions of years ago in Asia caused a period of global warming, but the modern world is very unlikely to experince something like that, because geological conditions are now very different.

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  14. nigellj@13

    From the cited data is evident  only that all greenhouse gases emitted during volcano eruption (including H2O and SO2) plus annual additional 34 billion tonnes of CO2 can not overcome the cooling effect of volcano aerosols and solid particles. It's impossible to say what factor is more significant because the greenhouse effect theory does not have math model to determine relation between amount of gas absorbing IR-radiattoin and temperature. 

    The absence of such model can be explained. Absorption of infrared radiation by the gas molecule changes the rotational and vibrational energy of the gas molecule, so the the molecule gains more potential energy. However, temperature is related to kinetic energy, that's why it's impossible to calculate the contribution of different gases absorbing IR-radiation to the atmosphere temperature on the base of thie IR-spectra.

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  15. Wrong. Pseudoscience. Empty assertions. Made up twaddle. 

    Go read a textbook.

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    Moderator Response:

    [PS] Over the line as well. A definitive citation is preferred.

  16. nigelj@15

    Rudeness does not replace the arguments

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    Moderator Response:

    [DB] You were given a citation refuting your claims.  Simply saying, in effect, "nuh-uh" is an insufficient response on your part.  First read the linked citation given.  If you still feel otherwise, stake your claims there, on that thread.  But it is also incumbent upon you to provide a link citation to a credible source that supports your claims.

  17. Quick note for aleks. SO2 isn't a greenhouse gas.

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  18. Rob Honeycutt @17

    According to greenhouse effect theory, the ability of a gas to absorb IR-radiation determines its behavior as greenhouse gas. (Th.L.Brown, H.E.LeMay a.o. Chemisty. The Central Science/ Pearson. Prentice Hall. 4th Ed. 2009, p.780-781). SOabsorbs IR-radiation in the region 3.5-19 micron.

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    Moderator Response:

    [DB] "SOabsorbs IR-radiation in the region 3.5-19 micron"

    Link citation required for this. 

  19. Addition to #18: sulfur dioxide infrared spectra

    Link to Google search

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    Moderator Response:

    (BW) Embedded link as it was breaking the page format. Please make sure to embed links properly via the "Insert" tab.

  20. sulfur dioxide infrared spectrum

    Link to Google search

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    Moderator Response:

    (BW) embedded link

  21. aleks @14 and 18

    "The greenhouse effect theory does not have math model to determine relation between amount of gas absorbing IR-radiattoin and temperature. "

    I disagree. Im no expert on all this, but the effects of CO2 on temperature are very settled and quantified science. This is why I said read a textbook, because perhaps you have missed something. Alternatively read the original research paper by Arrhenius below which still stands as solid science today.

    "Absorption of infrared radiation by the gas molecule changes the rotational and vibrational energy of the gas molecule, so the the molecule gains more potential energy. However, temperature is related to kinetic energy,"

    This doesnt make sense to me as vibrational energy is kinetic energy, and the molecule emits photons that stike other molecules, so theres kinetic energy. However Im telling you Im not going to debate this and go down some crazy rabbit hole over it.

    "SO2 absorbs IR-radiation in the region 3.5-19 micron.

    I will accept this, but SO2 has a very weak greenhouse gas effect. This is why its not listed in the entry in wikipedia on greenhouses gases mentioned above. However SO2 can combine with water to form sulphuric acid which can have a strong cooling effect by reflecting solar energy - and this is what dominates.

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    Moderator Response:

    [PS] "not have math model". I think aleks needs to clarify what he/she means since Ramanathan and Coakley 1978 sure looks like that model to me via the radiative transfer Equations. Modtran and Hitran are modern versions that do this to exquisite precision.

  22. Aleks @12 and later :

    possibly some confusion is arising over (A) sulfur dioxide as gas , and its conversion in the stratosphere to sulfuric acid aerosols [which conversion takes place over a matter of weeks, according to the NASA website — with the aerosols then acting as a reflectant of solar radiation over a year or two]

    ~ and also (B) the relative "potency" of IR re-radiation versus the reflection of visible light [visible light flux being far greater than IR flux].


    Aleks , you might enjoy seeing a 5-minute youtube presentation by Andy Skuce [his Denial101 talk on "Human CO2 emissions trump volcanoes"] . It is brief but clearly stated — in Skuce's pleasantly dry calm manner.

    I think you will find it interesting, regarding the various components of volcanic CO2.   Certainly, the main thrust of his talk is the debunking of the myth that volcanic CO2 (as opposed to "human" CO2) could be the origin of recent rapid global warming — but of course you would already be very aware of that scientific fact.

    However: regarding the points you make in this thread, Andy Skuce's comments discuss how it is the continuous venting of volcanic CO2 from volcanic lakes & inactive volcanoes which matches or exceeds the CO2 emission from active volcanoes. (From my own laziness, I had not previously appreciated how the "non-eruptive" CO2 exceeds the contribution from the spectacular explosions & plumes of the intermittently active volcanoes.)   Indirectly, that answers your question about the relative importance of reflective sulfur-type aerosols from eruptions.

    Skuce's short lecture also surprised me, in that the large number of submarine volcanoes contributed little or nothing to our atmospheric CO2 level.  Again, showing up my previous ignorance on the subject !

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  23. My apologies :

    I should have supplied link to Skuce —

    Hope that works!

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  24. Aleks @14,

    When you say - "From the cited data is evident ... the greenhouse effect theory does not have math model to determine relation between amount of gas absorbing IR-radiattoin and temperature." - it is not clear what "data" you are citing.

    That said, may I be presumptious and reply to your comment.

    Your explanation for the absence of this "model" of IR-absorption & temperature appears in error. (Note your use of the terms "potential energy" and "kinetic energy" are a poor choice. The waggling of a CO2 molecule when excited by a photon may displace the molecules atomic positions but as this is into a dynamic process it would not be termed "potential energy". Note that were the photons involved not IR but more powerful, they could shift the orbit of electrons and that could be termed "potential energy".)

    What your point appears to be addressing is the difference between the molecular waggling of gas molecules and the aggregate motion of a gas molecule within the gas. The latter is described by the ideal gas law PV=μRT but this law does not account for (and does not need to account for)  waggling (or for spinning) of the molecules. The waggling/spinning is thus not considered as defining the temperature of the gas for which it is not a significant factor. The spinning and waggling is a significant factor in calculating the Specific Heat Capacity with spinning more than doubling its value. The waggle (present within poliatomic gases) adds perhaps 10 percent. Do note that overwhelmingly the waggle is induced/dissipated by gas collisions (which is how absorbed/emitted IR is converted into temperature and thus how IR is a significant factor in warming/cooling a gas).

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  25. I think one point of confusion here is terminological - spectroscopists and climate scientists may use the term 'greenhouse gas' differently.

    As far as I can tell, SO2 has the molecular properties of being a greenhouse gas (i.e. absorbing infrared radiation). But unfortunately I can't find any estimates of the resulting radiative forcing.

    There is probably a reason for this - to estimate the radiative forcing, you have to put it in a real atmosphere. But in its gaseous form it is so short lived that it has no appreciable effect - hence concentrations 100,000 times lower than CO2. So it generally isn't even worth modelling, hence for climatic questions it is not a greenhouse gas.

    MODTRAN looks as though it might be capable of estimating the radiative forcing impact of instantaneously dumping a large concentration of SO2 into the atmosphere and measuring the effect before it can convert to aerosol, but I don't have a license.

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  26. nigelj@21

    Thanks for link to S.Arrhenius original article. For this discussion I believe the most important the S.Arrhenius idea that "... one should arrange experiments on the absorption of heat from a body at 15o by means of appropriate quantities of both gases (CO2 and H2O)". However, S.Arrhenius could not perfom such experiments himself because "...they would require very expensive apparatus beyond that at my disposal". Apparently his followers did not accomplish this idea during the past 120 years. Only this year P.L.Ward published the article where the results of experimental checking of greenhouse effect were reported.

    If these results are reliable, it means that greenhouse effect of carbon dioxide was not confirmed by experiment.  

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  27. nigelj@21 (continued)

    "SO2 has a very weak greenhouse gas effect". I don't know what is the quantitative measure of greenhouse effect. For example, water-vapor is considered as stronger greenhouse gas than CO2, because its molecules have more bands in IR-spectrum (see ref. in #18). May be, intensity of bands also matters.

    "SO2 can combine with water to form sulphuric acid which can have a strong cooling effect..." More exactly, SO2 with H2O forms sulfurous acid H2SO3. However, the ratio H2O/SO2 at the altitude where aerosols are forming is unknown, so it's impossible to estimate the amounts of 'free' SO2 and aerosols, and, hence, their relative contributions to heat balance.

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  28. Aleks @26 ,

    "thehill" article, by Peter Langdon Ward, is unmitigated garbage.

    Unmitigated.  Looney-tunes stuff.  Bat excrement crazy.

    Aleks, the good Mr Ward spouts so much garbage, that a rebuttal of his nonsense would take 20 very long paragraphs.  Better, Aleks, if you start reading some of the Climate Myths (look on the top left part of the Home page here at SkS).

    Education will soon show you how the word "reliable" and the name "P.L.Ward" cannot seriously be used in the same sentence.

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  29. Moderator comment to #21

    Thanks for link to Ramanathan article.

    This work is an attempt to make a math model of global climate change, and many factors (cloud amounts, surface albedo, relative humidity, etc.) are considered as far as some unpredictable factors (volcanoes eruptions, ocean currents changes, and, especially, solar constant change) are not considered. However, speaking about "math model of greenhouse effect" I have meant not a global climate model, but a quantitative relationship between amount of greenhouse gas and temperature, at least for laboratory conditions when other factors are excluded.

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  30. Aleks @27, as mentioned earlier in this thread, volcanic SO2 in the stratosphere has a very short life indeed, even despite the rather low levels of H2O at that altitude.  Similarly with human-caused SO2 in the lower atmosphere (where a vast amount of H2O is available to react with it).

    End result : SO2 has negligible greenhouse effect, because it exists in negligible quantities.

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  31. Aleks

    Regarding SO2.

    Basically there are tables of the IR absorption coefficients of various greenhouse gases ranking them in strength easily googled. None of these tables even mention SO2 so it must be a very weak greenhouse gas. All google searches just say SO2 has no direct greenhouse gas effects. All three atom gases have some greenhouse properties but they do actually vary a lot. 

    As eclectic points out theres just not enough SO2 to be significant anyway. Its all academic.

    Now regarding cooling aerosol effects SO2 converts to SO3 and thus to H2SO4 which has acid rain and cooling properties as below

    Regarding the effects of a given specific quantity of CO2 on temperatures. Im not a climate scientist, just an interested observer, but I gather people like Arrhenius and later E O Hulbert and others calculated this working backwards from atmospheric concentrations and knowledge of the different IR coefficients of various gases and atmospheric temperatures, and that the results are very accurate something like 99%, and are accepted science. They have never been over turned in the science literature. Thats good enough for me.

    Tests have been done on jars of CO2 in the laboratory under light etc and clearly demonstrated different concentrations of CO2 causing different temperatures. But Im not sure this would be as definitive as the above mentioned derivations by Hulbert etc because you cant duplicate the full complexity of the atmosphere of the planet in a jar.

    Basically none of the climate sceptics like Spencer and Pielke etc dispute any of the findings on what a specific quantity of CO2 does. Its settled science. Only cranks go over all this. There is debate on feedbacks of course but even this area of knowledge is constantly improving.

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  32. Aleks @29.

    You say:-

    "However, speaking about "math model of greenhouse effect" I have meant not a global climate model, but a quantitative relationship between amount of greenhouse gas and temperature, at least for laboratory conditions when other factors are excluded."

    Echoing nigelj @31, there are simplistic demonstrations that show that CO2 does absorb IR. This LINK shows a series of short YouTube videos of such experiments. The science which provides the detail of CO2's IR absorption is old and the literature listed HERE although much of it is sadly available publicly on-line only in abstract.

    The mechanisms which result in  increased CO2 raising global temperature are complex and cannot be reproduced within a laboratory. Indeed, it took science many decades to start to understand how CO2 effects global temperatures. (See this SkS POST describing an important part of the mechanism.) It would be akin to asking for a lab experiment to demonstrate specifically that the moon is responsible for the tidal effects witnessed in the English Channel. The proof would require either a full-sized experiment (which won't fit in a laboratory) or has to be calculated mathematically from data obtained in laboratory experiments.

    And having been calculated mathematically, the big grown-up model that is then passed across to climatologists for use in their global climate models is HITRAN. (You would have noted mention of its little brother MODTRAN up-thread). It is HITRAN which allows calculation of global temperatures for different levels of the greenhouse gases.

    And to again echo nigelj @31, no serious scientists and indeed no serious climate skeptic have issues with HITRAN. Those that do by acting as though HITRAN doesn't exist (like the Peter Ward you mention @26) are away with the faries and can be ignored.

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  33. When I look at a chart of upwelling absorption and compare that to the narrow spectral band of SO2, it looks to me like one of two things is going on. Either the SO2 is there and it's swamped out in that spectral range by H2O, or it's not there acting as a radiative forcing on the climate system. 

    It's a (mildly) interesting tidbit of information.

    Also, aleks stated that, "SO2 absorbs IR-radiation in the region 3.5-19 micron." But that doesn't sound right to me. I find this which shows a much narrower absorption range:

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  34. According to (the Line List Browser & Atmosphere Browser) CO2 is a much stronger GHG than SO2 but most important, it's at least 1 million times more abundant in the atmosphere, so I think it's safe to say that SO2 as a GHG can be ignored here on Earth.

    CO2 vs SO2

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  35. Our discussion turned out of topic of the article: effect of volcanoes eruptions on the environment. We speak about the physical essence of greenhouse effect theory, and evidently the consensus in this problem is impossible now.

    However, other aspect of this topic is also important. Sulfur dioxide forms aerosols with water, and these aerosols eventually fall into sea, lakes, rivers. In this case, water pH depends on oxidation state of sulfur: strong acid H2SOis more dangerous than weak H2SO3. That's why is inreresting what oxidizing agent could convert SO2 to SO3. If SO2 during eruption reaches ozone layer in the stratosphere (O3 oxidizes SO2 to SO3), then volcanoes eruptions could be an important cause of ozone layer depletion. It seems, this problem also deserves attention.

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  36. aleks:

    I don't know where you are getting your information, but it is way, way out of date. The myth that "volcanoes eruptions could be an important cause of ozone layer depletion" was doing the rounds over 20 years ago. Before the World Wide Web was popular, there was Usenet and news groups. The FAQ on ozone myths was produced way back then.

    Look at part II. It's 20 years old (last update), but the debunking of your myth is probably older than some of the people reading this web site.

    Please try to catch up.

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    Moderator Response:

    [PS] watch tone please.

  37. Eclectic @28

    I did not know before about Mr.Ward scientific activity. But in any case it seems to me impossible to speak bad about the person who does not take part in our discussion. I was not sure about the reliability P.L.Ward's data because the cited article did not contain a detailed description of the experiment and estimation of the data precision. Nevertheless, the experiment can be refuted only by other experiment. So, I will be very grateful for link containing description of such or similar experiment. 

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    Moderator Response:

    [DB] "the experiment can be refuted only by other experiment"

    An opinion piece like Ward's is not a peer-reviewed piece published in a credible scientific journal, thus it needs no scientific refutation via published research study.  The existing research stands unchallenged by such.

  38. aleks @35.

    When you say "the consensus in this problem is impossible now," I will assume you are saying that you remain unconvinced by any of the scientific evidence. This may be your personal position but it is not a scientific one.

    However, there is one loose end in all this. You stated @18 "SO2 absorbs IR-radiation in the region 3.5-19 micron."  The basis for your statement remains unclear. I will assume it would not lie within the chemistry text book you cite (although the reasons for your citation are not entirely clear). And there is no sign of a "region 3.5-19 micron" in the Google Image Search page you linked to up-thread.

    Up-thread there are graphs of the SO2 IR absorption spectrum. More precisely the SO2 absorption peaks could be described as spanning 4μm to 18μm. Or the absorbtion bands could be described as spanning 3.9μm to 20μm. (I note the graph @34 shows a 200μm absorption peak which perhaps has more chance of interferring with a radio than interferring with climate.) But I am unable to make sense of describing the range 3.5μm to 19μm.

    So can you set out the basis for your statement "SO2 absorbs IR-radiation in the region 3.5-19 micron" ?

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  39. The OP does appear to take for ganted that there is a good chance of an La Nina developing in the next few months and also that Mount Agung is soon to erupt. I would suggest there is some significant doubt on both assumptions.

    Concerning the La Nina, this is a long way from a certain outcome, even a weak La Nina. The predictions (eg here) have been remarkably changeable over the last couple of months with an El Nino being predicited as much more likely as recently as July. And even as recent as September the continued ENSO Neutral condition was predicted as the most likely outcome over the winter.

    Also the seismic activity generated by Mount Agung is being taken as the sign of a forthcoming major eruption. Yet (and this a hostage to fortune - a major eruption is entirely possible), the BBC report the following in their Mount Agung story:-

    "According to the volcanologists monitoring Mount Agung, this situation could continue for weeks, maybe even months. An eruption may not even happen, they simply don't know. At the government observation base, senior seismologist Devy Kamil remains patient - despite the long queue of journalists who have been knocking on his door all week, hoping for some news. "There are some examples where you have swarms of activity for as long as six years," he explains, "and it is not always ended by an eruption."

    So an eruption is not guaranteed and the seismic activity may last years. (The further point is made elsewhere that today's instrumentation was not available back in 1963 so comparisons with that eruption are not possible.)

    And the idea that any new eruption will be a repeat of 1963 is not supported by the historical evidence. The eruption previous to 1963 was 1843 and that does not apper to feature in the volcanic ejection record in polar ice cores (eg Jiang et al 2012) (although Osipov et al (2014) show no 1836 Cosigüina eruption but instead an eruption dated to 1840 and labelled 'unknown' - this indicative of the reliability of the dating of ice core data).
    Certainly nothing giving such a mark as the 1963 eruption appears on the appropriate portion of the 19th century ice core record.
    Indeed, there is little enough information about Mt Agung prior to 1963. Zen & Hadikusumo (1964) set out the reports from 1843 thus:-

    " «After having been dormant for a long time, this year the mountain began to be alive again. In the first days of the activity earthquake shocks were felt after which followed the emission of ash, sand and stones.» These are the only words which described the eruption of 1843. "

    And prior to 1843, the record of Mt Agung eruptions is entirely sparce. There is mention of the first recorded eruption being a 1808 eruption that dragged on to 1821, or mention elsewhere that 1821 was a seperate eruption. Today the standard press quotes seems to be a repeat of a 20th Sept UPI item "There was an eruption of similar intensity in 1843, and several in the 16th to 18th centuries," a quote that beyond 1843 is not based on evidence, or none that I can see.

    So we may or may not have a weak La Nina in the offing. And we may or may not have Mt Agung erupt and if it does it may or may not be as climatically significant as 1963.

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  40. Aleks @37 ,

    why do you say it would be "impossible" to speak about the ideas put forward by a person (such as Mr Ward) who is not engaging in the discussion here?   We are able to discuss the ideas of Newton and Einstein, despite the absence of those two gentlemen.   Likewise, we are able to discuss (and disparage) the ideas put forward by members of the Flat Earth Society, despite the absence of those members.

    The Flat-Earthers put forward many ideas to support their Flat Earth hypothesis — and their many ideas are garbage.  Crazy unscientific garbage.  Completely unreliable!

    It is a waste of your (and everyone's) time to go into a detailed discussion of the Flat-Earther crazy ideas.   Likewise it is a waste of time going into a detailed discussion of the many points of unmitigated garbage put forward by P.L.Ward .

    Aleks, for your sake I beg of you — don't waste your valuable time on P.L.Ward .    Much better instead, for you to educate yourself with genuine scientific knowledge.

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  41. Eclectic@30

    "As mentioned above in this thread, volcanic SO2 in the stratosphere has a very short life". I did not find any mention about short life of SO2 both in  the discussed article and comments. Conversely, the authors of this article say that "sulfur dioxide injected into the stratosphere spreads easily along the hemisphere". So, when you told about short life of SO2, what do you mean: formation of aerosols with water (depends on ratio SO2/H2O and temperature), oxidation or reduction (by what agents?), or photochemical destruction by UV-radiation?

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  42. Aleks @41 ,

    the article (above) by Lehner & Fasullo is not a complete description of every aspect of climate science — and thus it is necessary for you to "add to it" with knowledge of other aspects [if not from your own prior scientific knowledge, then from your further reading from other threads & other sources].

    As mentioned earlier, the NASA website can give you information.  In this case, NASA describes the relatively rapid reaction of SO2 with atmospheric H2O, to alter the radiative & reflective properties associated with the volcanic-origin sulfur.

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  43. Aleks @37

    You appear to remain doubtful about the precise effect of C02 on temperature (your maths model thing) . It has already been explained that no experiment in a jar can achieve this accurately or even moderately accurately, because it cannot duplicate the atmosphere. Nobody has to prove Wards experiment wrong with another experiment, given his basic assumptions are wrong.

    You need to read the research done on inferring the maths of the effect of CO2 on temperature starting with Arrhenius and Hulbert and moving on from there to more modern work. You then need to prove them wrong through normal scientific channels, if you feel you see fault in their work. Just ignoring what they say, and expressing a preference for some other approach in a jar, is just the talk of a naive layperson. Their results are reasonably accurate, enough to be useful.

    The best test of a theory such as quantification of effects of CO2 is predictive ability. Look at the graphs of climate models in the article "How well have climate models predicted global warming" on this website a couple of days ago. The models have done reasonably well. They would not be able to do this is the basic "maths model" of CO2 was wildly innacurate. End of story.

    What's more we know the reason these models are not as yet perfect is because of the difficulties of dealing with natural variation and warming feedback effects, not doubt about the basic maths model of how a molecule of CO2 affects temperature. So all Im saying is step back and take a wider view of everything and it becomes clearer.

    Dont waste time over SO2. Ample evidence has been shown that its a weak greenhouse gas, and quantities in the atmosphere are vastly less than CO2. Therefore further discussion on detailed aspects is irrelevant to climate change and this website, and leads me to conclude you are deliberately muddying the waters.

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  44. aleks @41.
    The comment by Eclectic @30 you are referring to evidently concerned the greenhouse properties of SO2 (specifically in the stratosphere). Thus it would concern the lifetime of SO2 in the stratosphere alone. This stratospheric SO2 lifetime is significantly longer than the tropospheric SO2 lifetime, a few weeks rather than a few days. And, as set out up-thread by Eclectic @22 (which you apparently "did not find"), the aerosols resulting from stratospheric SO2 persist for much longer, many weeks, a few months or potentially a couple of years or so, this being dependent on the aerosol size, height and location. See for instance Kleinschmitt et al (2017).

    In your citing (& your misquoting) of the OP, the OP noted that the geographical location of the volcanic eruption is a factor, the volcanoes discussed being "all located in the tropics close to the Equator, which allows the sulfur dioxide injected into the stratosphere to spread easily across the hemisphere." This is not the case for volcanoes further from the equator (eg. like the 1980 Mt St Helens eruption).

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  45. Comments about SO2
    SO2 converts in the stratosphere to sulfuric acid aerosols (Eclectic@22, nigelj@31). For this process is necessary: a) mole concentration of H2O should be not less than of SO2, b) SO2 must be oxidized to SO3. Reliable data about H2O/SO2 ratio are unknown. Because of low temperatures in upper troposphere and stratosphere water converts to ice so aerosols of sulfurous acid will form in “lower atmosphere” (Eclectic@30). Oxidation of SO2 to SO3 in not an easy process: in chemical technology it requires high temperatures and special catalyst, in the atmosphere it catalyzed by hydroxyl radicals (J.J.Margitan. J.Phys. Chem., 88, 3914 (1984) ).
    So, I can't agree that “ SO2 in its gaseous form is short lived” (Kevin C @25). These facts are also important for estimation of possible effect of SO2 on ozone layer: Bob Loblaw @36 refutes it. The ozone is only one available oxidizing agent in the stratosphere that can oxidize SO2 without catalyst, and SO2 during eruption emitted close enough to ozone layer. Additionally, please pay attention to the lower graph in HK@34 post: altitude vs. SO2 amount. There is an interesting minimum of SO2 concentration between 20 and 40 km (what is ozone layer altitude?).
    Rob Honeycutt@17. “SO2 isn't a greenhouse gas”. At first, sorry for inaccurate link to region of IR-absorption. In this case, it is important that SO2 does absorb IR-radiation. It does not include into IPCC list, but such generally recognized greenhouse gas as water-vapor also absent there.

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  46. Aleks @45 , as you rightly say: the conversion of [infra-red] "absorbent" gasseous SO2 into [visible-light] reflectant sulfate aerosols is a somewhat complex process — the process rate is important, and is accelerated by ozone and H2O.

    D.J.Eatough et al., 1994 , states conversion rates of 1% - 10% per hour in warm tropospheric conditions : such rates implying a stratospheric rate being up to about 100 times slower — which rate fits well with the description you will find on the NASA website.

    Observations by NASA, NOAA, JMA and other meteorological organizations, all indicate that volcanic eruptions (sufficient to reach the stratosphere) cause global cooling for a year or two.  And this is the evidence that demonstrates the relative [lack of] importance of duration & effect of gasseous SO2.

    That being so, I do not see the point you are trying to lead to.  Please explain yourself more clearly.

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  47. alecks... Straight from the IPCC (AR4):

    Long-lived greenhouse gases (LLGHGs), for example, CO2, methane (CH4) and nitrous oxide (N2O), are chemically stable and persist in the atmosphere over time scales of a decade to centuries or longer, so that their emission has a long-term influence on climate. Because these gases are long lived, they become well mixed throughout the atmosphere much faster than they are removed and their global concentrations can be accurately estimated from data at a few locations. Carbon dioxide does not have a specific lifetime because it is continuously cycled between the atmosphere, oceans and land biosphere and its net removal from the atmosphere involves a range of processes with different time scales.

    Short-lived gases (e.g., sulphur dioxide and carbon monoxide) are chemically reactive and generally removed by natural oxidation processes in the atmosphere, by removal at the surface or by washout in precipitation; their concentrations are hence highly variable. Ozone is a significant greenhouse gas that is formed and destroyed by chemical reactions involving other species in the atmosphere. In the troposphere, the human influence on ozone occurs primarily through changes in precursor gases that lead to its formation, whereas in the stratosphere, the human influence has been primarily through changes in ozone removal rates caused by chlorofluorocarbons (CFCs) and other ozone-depleting substances.

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  48. It should also be pointed out that satellite measurements of stratospheric SO2 directly and conclusively demonstrate the drop in SO2 levels following the volcanic inputs. The literature is unequivocal (for instance - Carn et al (2009), Pumphrey et al 2015). The chemical theorising of aleks is uncalled for and flat wrong.

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  49. Eclectic @46

    I fully agree with you on the issue of sulfite aerosols formation "at warm troposphere conditions", but I'm not sure that it applies to stratosphere: reaction may be fully stopped because of liquid water absence at low temperatures. 

    I see also that you mark ozone participation in the processes associated with SO2 in the stratosphere. I would just like to clarify: ozone is not an accelerator of a process, it directly reacts with SO2 forming SO3.

    Rob Honeycutt@47

    We discuss not about long-lived and short-lived gases in all, but the behavior of the gaseous SO2 ejected by a volcano to the height 16-18 km.  Because of absence OH-radicals catalyzing SO2 oxidation by O2 in these conditions, the reaction of stratospheric ozone with SO2 is much more probable than with CFCs.

    MA Rodger@48

    When it comes to chemical problems (in this case SO2 oxidation), it's indispensable without the knowledge of chemistry. Sorry for "chemical theorising". The drop of SO2 levels is a fact, but it does not mean that oxidation of SO2 by oxygen is a reason for it. We may think about SO2 oxidation by ozone or just about lowering relatively heavy molecules of SO2 from the stratosphere to the troposphere where they react with water/ 

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  50. Aleks @49 and prior :

    your suggestion (or explanation?) does not accord with reality.

    The levels of H2O, OH, CH4 etc in the stratosphere are low but not zero.  Which is [part of] why the "degradation" rate of SO2 is two orders of magnitude slower than in the troposphere.

    Aleks, you are oversimplifying the situation.  Worse, you appear to be ignoring the reality — that gasseous SO2 (and any IR properties it may have) does relatively quickly "degrade" into radiation-reflective particles which produce a global cooling effect for up to two years or so.

    Your suggestions seem confused.  Please clarify whatever point it is that you are seeking to make.

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